Add another shader node demo

This one does stack-like transitions, using
some examples from gl-transitions.com.

demos/gtk-demo/demo.gresource.xml

@@ -133,6 +133,19 @@
     <file>cogs.glsl</file>
     <file>glowingstars.glsl</file>
   </gresource>
+  <gresource prefix="/glshader">
+    <file>fire.glsl</file>
+    <file>gtkshaderbin.h</file>
+    <file>gtkshaderbin.c</file>
+  </gresource>
+  <gresource prefix="/gltransition">
+    <file>gtkshaderstack.c</file>
+    <file>gtkshaderstack.h</file>
+    <file>transition1.glsl</file>
+    <file>transition2.glsl</file>
+    <file>transition3.glsl</file>
+    <file>transition4.glsl</file>
+  </gresource>
   <gresource prefix="/iconscroll">
     <file>iconscroll.ui</file>
   </gresource>
@@ -247,6 +260,8 @@
     <file>gears.c</file>
     <file>gestures.c</file>
     <file>glarea.c</file>
+    <file>glshader.c</file>
+    <file>gltransition.c</file>
     <file>headerbar.c</file>
     <file>hypertext.c</file>
     <file>iconscroll.c</file>

demos/gtk-demo/fire.glsl

@@ -0,0 +1,72 @@
+uniform float u_time;
+
+/* 2D -> [0..1] random number generator */
+float random(vec2 st) {
+  return fract(sin(dot(st.xy,
+                       vec2(12.9898,78.233))) *
+               43758.5453123);
+}
+
+/* Generate a smoothed 2d noise based on random() */
+float noise(vec2 v) {
+  /* Round point v to integer grid grid */
+  vec2 grid_point = floor(v);
+  /* Randomize in grid corners */
+  float corner1 = random(grid_point);
+  float corner2 = random(grid_point + vec2(1, 0));
+  float corner3 = random(grid_point + vec2(0, 1));
+  float corner4 = random(grid_point + vec2(1, 1));
+  /* Interpolate smoothly between grid points */
+  vec2 fraction = smoothstep(vec2(0.0), vec2(1.0), fract(v));
+  return mix(mix(corner1, corner2, fraction.x),
+             mix(corner3, corner4, fraction.x),
+             fraction.y);
+}
+
+/* fractal brownian motion noice, see https://www.iquilezles.org/www/articles/fbm/fbm.htm */
+float fbm(in vec2 x)
+{
+  const float octaveScale = 1.9;
+  const float G = 0.5;
+  float f = 1.0;
+  float a = 1.0;
+  float t = 0.0;
+  int numOctaves = 5;
+  for (int i = 0; i < numOctaves; i++) {
+    t += a*noise(f*x);
+    f *= octaveScale;
+    a *= G;
+  }
+
+  return t;
+}
+
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
+{
+  vec2 xy = fragCoord / resolution;
+
+  float zoom = 3.0 - sin(u_time*0.5)*0.3;
+
+  // Normalize coord to height of widget
+  vec2 p = (vec2 (-resolution.x/2 + fragCoord.x, resolution.y - fragCoord.y) / resolution.yy)* zoom;
+
+    // Use recursive incantations of fbm
+  float q1 = fbm(p - vec2(0.8, 0.3) * u_time);
+  float q2 = fbm(p - vec2(0.5, 1.3) * u_time);
+  float r = fbm(2.0*p + vec2(q1,q2) - vec2(0.0, 1.0)*u_time*10.0 *0.4);
+
+  // Compute intensity, mostly on the bottom
+  float w = 2 * r * p.y;
+
+  // Smooth out left/right side and fade in at start
+  w /= smoothstep(0.0,0.1, xy.x)* smoothstep(0.0,0.1, 1.0-xy.x) *  smoothstep(0.0,0.4, u_time);
+
+  // Compute colors
+  vec3 c = vec3(1.0,.2,.05);
+  vec3 color = 1.0 / (w*w/c + 1.0);
+
+  // Mix in widget
+  vec4 widget = texture(u_source,uv);
+  fragColor = mix(vec4(color,1), widget, 1.0-color.x);
+}

demos/gtk-demo/glshader.c

@@ -0,0 +1,85 @@
+/* OpenGL/GLShader
+ * #Keywords: OpenGL, shader
+ *
+ * Demonstrates using GskGLShaderNodes to integrate GLSL fragment shaders
+ * with the Gtk widget rendering.
+ */
+#include <math.h>
+#include <gtk/gtk.h>
+#include "gtkshaderbin.h"
+
+static GtkWidget *demo_window = NULL;
+
+static void
+close_window (GtkWidget *widget)
+{
+  /* Reset the state */
+  demo_window = NULL;
+}
+
+static GtkWidget *
+fire_bin_new (void)
+{
+  GtkWidget *bin = gtk_shader_bin_new ();
+  GBytes *shader_b;
+  GskGLShader *shader;
+
+  shader_b = g_resources_lookup_data ("/glshader/fire.glsl", 0, NULL);
+  shader = gsk_glshader_new ((const char *)g_bytes_get_data (shader_b, NULL));
+  gsk_glshader_add_uniform (shader, "u_time", GSK_GLUNIFORM_TYPE_FLOAT);
+  gtk_shader_bin_add_shader (GTK_SHADER_BIN (bin), shader, GTK_STATE_FLAG_PRELIGHT, GTK_STATE_FLAG_PRELIGHT);
+  g_bytes_unref (shader_b);
+  g_object_unref (shader);
+
+  return bin;
+}
+
+
+static GtkWidget *
+create_glshader_window (GtkWidget *do_widget)
+{
+  GtkWidget *window, *box, *button, *bin;
+
+  window = gtk_window_new ();
+  gtk_window_set_display (GTK_WINDOW (window),  gtk_widget_get_display (do_widget));
+  gtk_window_set_title (GTK_WINDOW (window), "glshader");
+  g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);
+
+  box = gtk_box_new (GTK_ORIENTATION_VERTICAL, FALSE);
+  gtk_widget_set_margin_start (box, 12);
+  gtk_widget_set_margin_end (box, 12);
+  gtk_widget_set_margin_top (box, 12);
+  gtk_widget_set_margin_bottom (box, 12);
+  gtk_box_set_spacing (GTK_BOX (box), 6);
+  gtk_window_set_child (GTK_WINDOW (window), box);
+
+  bin = fire_bin_new ();
+  gtk_box_append (GTK_BOX (box), bin);
+
+  button = gtk_button_new_with_label ("Click me");
+  gtk_widget_set_receives_default (button, TRUE);
+  gtk_shader_bin_set_child (GTK_SHADER_BIN (bin), button);
+
+  bin = fire_bin_new ();
+  gtk_box_append (GTK_BOX (box), bin);
+
+  button = gtk_button_new_with_label ("Or me!");
+  gtk_widget_set_receives_default (button, TRUE);
+  gtk_shader_bin_set_child (GTK_SHADER_BIN (bin), button);
+
+  return window;
+}
+
+GtkWidget *
+do_glshader (GtkWidget *do_widget)
+{
+  if (!demo_window)
+    demo_window = create_glshader_window (do_widget);
+
+  if (!gtk_widget_get_visible (demo_window))
+    gtk_widget_show (demo_window);
+  else
+    gtk_window_destroy (GTK_WINDOW (demo_window));
+
+  return demo_window;
+}

demos/gtk-demo/gltransition.c

@@ -0,0 +1,250 @@
+/* OpenGL/Transitions
+ * #Keywords: OpenGL, shader
+ *
+ * Create transitions between pages using a custom fragment shader.
+ * The examples here are taken from gl-transitions.com.
+ *
+ * Click to start a transition.
+ */
+
+#include <math.h>
+#include <gtk/gtk.h>
+#include "gtkshaderstack.h"
+
+static GtkWidget *demo_window = NULL;
+
+static void
+close_window (GtkWidget *widget)
+{
+  /* Reset the state */
+  demo_window = NULL;
+}
+
+static GskGLShader *
+gsk_shader_new_from_resource (const char *resource_path)
+{
+  GBytes *shader_b;
+  GskGLShader *shader;
+
+  shader_b = g_resources_lookup_data (resource_path, 0, NULL);
+  shader = gsk_glshader_new ((const char *)g_bytes_get_data (shader_b, NULL));
+  gsk_glshader_set_n_required_sources (shader, 2);
+  gsk_glshader_add_uniform (shader, "progress", GSK_GLUNIFORM_TYPE_FLOAT);
+  g_bytes_unref (shader_b);
+
+  return shader;
+}
+
+static void
+text_changed (GtkTextBuffer *buffer,
+              GtkWidget     *button)
+{
+  gtk_widget_show (button);
+}
+
+static void
+apply_text (GtkWidget     *button,
+            GtkTextBuffer *buffer)
+{
+  GtkWidget *stack;
+  GskGLShader *shader;
+  GtkTextIter start, end;
+  char *text;
+
+  stack = gtk_widget_get_ancestor (button, GTK_TYPE_SHADER_STACK);
+
+  gtk_text_buffer_get_bounds (buffer, &start, &end);
+  text = gtk_text_buffer_get_text (buffer, &start, &end, TRUE);
+
+  shader = gsk_glshader_new (text);
+  gsk_glshader_set_n_required_sources (shader, 2);
+  gsk_glshader_add_uniform (shader, "progress", GSK_GLUNIFORM_TYPE_FLOAT);
+
+  gtk_shader_stack_set_shader (GTK_SHADER_STACK (stack), shader);
+
+  g_object_unref (shader);
+  g_free (text);
+
+  gtk_widget_hide (button);
+}
+
+static void
+clicked_cb (GtkGestureClick *gesture,
+            guint            n_pressed,
+            double           x,
+            double           y,
+            gpointer         data)
+{
+  gtk_gesture_set_state (GTK_GESTURE (gesture), GTK_EVENT_SEQUENCE_CLAIMED);
+}
+
+static GtkWidget *
+make_shader_stack (const char *name,
+                   const char *resource_path,
+                   GtkWidget  *scale)
+{
+  GtkWidget *stack, *child, *widget;
+  GtkWidget *label, *button, *tv;
+  GskGLShader *shader;
+  GObjectClass *class;
+  GParamSpecFloat *pspec;
+  GtkAdjustment *adjustment;
+  GtkTextBuffer *buffer;
+  GBytes *bytes;
+  GtkEventController *controller;
+  GtkCssProvider *provider;
+
+  stack = gtk_shader_stack_new ();
+  shader = gsk_shader_new_from_resource (resource_path);
+  gtk_shader_stack_set_shader (GTK_SHADER_STACK (stack), shader);
+  g_object_unref (shader);
+
+  child = gtk_picture_new_for_resource ("/css_pixbufs/background.jpg");
+  gtk_picture_set_can_shrink (GTK_PICTURE (child), TRUE);
+  gtk_shader_stack_add_child (GTK_SHADER_STACK (stack), child);
+
+  child = gtk_picture_new_for_resource ("/transparent/portland-rose.jpg");
+  gtk_picture_set_can_shrink (GTK_PICTURE (child), TRUE);
+  gtk_shader_stack_add_child (GTK_SHADER_STACK (stack), child);
+
+  child = gtk_picture_new_for_resource ("/css_blendmodes/ducky.png");
+  gtk_picture_set_can_shrink (GTK_PICTURE (child), TRUE);
+  gtk_shader_stack_add_child (GTK_SHADER_STACK (stack), child);
+
+  child = gtk_box_new (GTK_ORIENTATION_VERTICAL, 6);
+
+  widget = gtk_center_box_new ();
+  label = gtk_label_new (name);
+  gtk_widget_add_css_class (label, "title-4");
+  gtk_widget_set_size_request (label, -1, 26);
+  gtk_center_box_set_center_widget (GTK_CENTER_BOX (widget), label);
+
+  button = gtk_button_new_from_icon_name ("view-refresh-symbolic");
+  provider = gtk_css_provider_new ();
+  gtk_css_provider_load_from_data (provider, "button.small { padding: 0; }", -1);
+  gtk_style_context_add_provider (gtk_widget_get_style_context (button),
+                                  GTK_STYLE_PROVIDER (provider),
+                                  GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+  g_object_unref (provider);
+  gtk_widget_set_halign (button, GTK_ALIGN_CENTER);
+  gtk_widget_set_valign (button, GTK_ALIGN_CENTER);
+  gtk_widget_add_css_class (button, "small");
+  gtk_widget_hide (button);
+  gtk_center_box_set_end_widget (GTK_CENTER_BOX (widget), button);
+
+  gtk_box_append (GTK_BOX (child), widget);
+
+  class = g_type_class_ref (GTK_TYPE_SHADER_STACK);
+  pspec = G_PARAM_SPEC_FLOAT (g_object_class_find_property (class, "duration"));
+
+  adjustment = gtk_range_get_adjustment (GTK_RANGE (scale));
+  if (gtk_adjustment_get_lower (adjustment) == 0.0 &&
+      gtk_adjustment_get_upper (adjustment) == 0.0)
+    {
+      gtk_adjustment_configure (adjustment,
+                                pspec->default_value,
+                                pspec->minimum,
+                                pspec->maximum,
+                                0.1, 0.5, 0);
+    }
+
+  g_type_class_unref (class);
+
+  g_object_bind_property (adjustment, "value",
+                          stack, "duration",
+                          G_BINDING_DEFAULT);
+
+  widget = gtk_scrolled_window_new ();
+  gtk_scrolled_window_set_has_frame (GTK_SCROLLED_WINDOW (widget), TRUE);
+  gtk_widget_set_hexpand (widget, TRUE);
+  gtk_widget_set_vexpand (widget, TRUE);
+
+  controller = GTK_EVENT_CONTROLLER (gtk_gesture_click_new ());
+  gtk_gesture_single_set_button (GTK_GESTURE_SINGLE (controller), 0);
+  g_signal_connect (controller, "released", G_CALLBACK (clicked_cb), NULL);
+  gtk_event_controller_set_propagation_phase (controller, GTK_PHASE_BUBBLE);
+  gtk_widget_add_controller (GTK_WIDGET (widget), controller);
+
+  tv = gtk_text_view_new ();
+  gtk_text_view_set_left_margin (GTK_TEXT_VIEW (tv), 4);
+  gtk_text_view_set_right_margin (GTK_TEXT_VIEW (tv), 4);
+  gtk_text_view_set_top_margin (GTK_TEXT_VIEW (tv), 4);
+  gtk_text_view_set_bottom_margin (GTK_TEXT_VIEW (tv), 4);
+  buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (tv));
+  bytes = g_resources_lookup_data (resource_path, 0, NULL);
+  gtk_text_buffer_set_text (buffer,
+                            (const char *)g_bytes_get_data (bytes, NULL),
+                            g_bytes_get_size (bytes));
+  g_bytes_unref (bytes);
+  gtk_scrolled_window_set_child (GTK_SCROLLED_WINDOW (widget), tv);
+
+  g_signal_connect (buffer, "changed", G_CALLBACK (text_changed), button);
+  g_signal_connect (button, "clicked", G_CALLBACK (apply_text), buffer);
+
+  gtk_box_append (GTK_BOX (child), widget);
+
+  gtk_shader_stack_add_child (GTK_SHADER_STACK (stack), child);
+
+  return stack;
+}
+
+static GtkWidget *
+create_gltransition_window (GtkWidget *do_widget)
+{
+  GtkWidget *window, *headerbar, *scale, *grid;
+
+  window = gtk_window_new ();
+  gtk_window_set_display (GTK_WINDOW (window),  gtk_widget_get_display (do_widget));
+  gtk_window_set_title (GTK_WINDOW (window), "Transitions");
+  headerbar = gtk_header_bar_new ();
+  scale = gtk_scale_new (GTK_ORIENTATION_HORIZONTAL, NULL);
+  gtk_scale_set_draw_value (GTK_SCALE (scale), FALSE);
+  gtk_widget_set_size_request (scale, 100, -1);
+  gtk_header_bar_pack_end (GTK_HEADER_BAR (headerbar), scale);
+  gtk_window_set_titlebar (GTK_WINDOW (window), headerbar);
+  gtk_window_set_default_size (GTK_WINDOW (window), 400, 400);
+  g_signal_connect (window, "destroy", G_CALLBACK (close_window), NULL);
+
+  grid = gtk_grid_new ();
+  gtk_window_set_child (GTK_WINDOW (window), grid);
+
+  gtk_widget_set_halign (grid, GTK_ALIGN_CENTER);
+  gtk_widget_set_valign (grid, GTK_ALIGN_CENTER);
+  gtk_widget_set_margin_start (grid, 12);
+  gtk_widget_set_margin_end (grid, 12);
+  gtk_widget_set_margin_top (grid, 12);
+  gtk_widget_set_margin_bottom (grid, 12);
+  gtk_grid_set_row_spacing (GTK_GRID (grid), 6);
+  gtk_grid_set_column_spacing (GTK_GRID (grid), 6);
+  gtk_grid_set_row_homogeneous (GTK_GRID (grid), TRUE);
+  gtk_grid_set_column_homogeneous (GTK_GRID (grid), TRUE);
+
+  gtk_grid_attach (GTK_GRID (grid),
+                   make_shader_stack ("Wind", "/gltransition/transition1.glsl", scale),
+                   0, 0, 1, 1);
+  gtk_grid_attach (GTK_GRID (grid),
+                   make_shader_stack ("Radial", "/gltransition/transition2.glsl", scale),
+                   1, 0, 1, 1);
+  gtk_grid_attach (GTK_GRID (grid),
+                   make_shader_stack ("Crosswarp", "/gltransition/transition3.glsl", scale),
+                   0, 1, 1, 1);
+  gtk_grid_attach (GTK_GRID (grid),
+                   make_shader_stack ("Kaleidoscope", "/gltransition/transition4.glsl", scale),
+                   1, 1, 1, 1);
+
+  return window;
+}
+
+GtkWidget *
+do_gltransition (GtkWidget *do_widget)
+{
+  if (!demo_window)
+    demo_window = create_gltransition_window (do_widget);
+
+  if (!gtk_widget_get_visible (demo_window))
+    gtk_widget_show (demo_window);
+  else
+    gtk_window_destroy (GTK_WINDOW (demo_window));
+
+  return demo_window;
+}

demos/gtk-demo/gtkshaderbin.c

@@ -0,0 +1,220 @@
+#include "gtkshaderbin.h"
+
+typedef struct {
+  GskGLShader *shader;
+  GtkStateFlags state;
+  GtkStateFlags state_mask;
+} ShaderInfo;
+
+struct _GtkShaderBin
+{
+  GtkWidget parent_instance;
+  GtkWidget *child;
+  GskGLShader *active_shader;
+  GPtrArray *shaders;
+  guint tick_id;
+  float time;
+  gint64 first_frame_time;
+};
+
+struct _GtkShaderBinClass
+{
+  GtkWidgetClass parent_class;
+};
+
+G_DEFINE_TYPE (GtkShaderBin, gtk_shader_bin, GTK_TYPE_WIDGET)
+
+static void
+shader_info_free (ShaderInfo *info)
+{
+  g_object_unref (info->shader);
+  g_free (info);
+}
+
+static void
+gtk_shader_bin_finalize (GObject *object)
+{
+  GtkShaderBin *self = GTK_SHADER_BIN (object);
+
+  g_ptr_array_free (self->shaders, TRUE);
+
+  G_OBJECT_CLASS (gtk_shader_bin_parent_class)->finalize (object);
+}
+
+static void
+gtk_shader_bin_dispose (GObject *object)
+{
+  GtkShaderBin *self = GTK_SHADER_BIN (object);
+
+  g_clear_pointer (&self->child, gtk_widget_unparent);
+
+  G_OBJECT_CLASS (gtk_shader_bin_parent_class)->dispose (object);
+}
+
+static gboolean
+gtk_shader_bin_tick (GtkWidget     *widget,
+                     GdkFrameClock *frame_clock,
+                     gpointer       unused)
+{
+  GtkShaderBin *self = GTK_SHADER_BIN (widget);
+  gint64 frame_time;
+
+  frame_time = gdk_frame_clock_get_frame_time (frame_clock);
+  if (self->first_frame_time == 0)
+    self->first_frame_time = frame_time;
+  self->time = (frame_time - self->first_frame_time) / (float)G_USEC_PER_SEC;
+
+  gtk_widget_queue_draw (widget);
+
+  return G_SOURCE_CONTINUE;
+}
+
+static void
+gtk_shader_bin_init (GtkShaderBin *self)
+{
+  self->shaders = g_ptr_array_new_with_free_func ((GDestroyNotify)shader_info_free);
+}
+
+void
+gtk_shader_bin_update_active_shader (GtkShaderBin *self)
+{
+  GtkStateFlags new_state = gtk_widget_get_state_flags (GTK_WIDGET (self));
+  GskGLShader *new_shader = NULL;
+
+  for (int i = 0; i < self->shaders->len; i++)
+    {
+      ShaderInfo *info = g_ptr_array_index (self->shaders, i);
+
+      if ((info->state_mask & new_state) == info->state)
+        {
+          new_shader = info->shader;
+          break;
+        }
+    }
+
+  if (self->active_shader == new_shader)
+    return;
+
+  self->active_shader = new_shader;
+  self->first_frame_time = 0;
+
+  if (self->active_shader)
+    {
+      if (self->tick_id == 0)
+        self->tick_id = gtk_widget_add_tick_callback (GTK_WIDGET (self),
+                                                      gtk_shader_bin_tick,
+                                                      NULL, NULL);
+    }
+  else
+    {
+      if (self->tick_id != 0)
+        {
+          gtk_widget_remove_tick_callback (GTK_WIDGET (self), self->tick_id);
+          self->tick_id = 0;
+        }
+    }
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+gtk_shader_bin_state_flags_changed (GtkWidget        *widget,
+                                    GtkStateFlags     previous_state_flags)
+{
+  GtkShaderBin *self = GTK_SHADER_BIN (widget);
+
+  gtk_shader_bin_update_active_shader (self);
+}
+
+void
+gtk_shader_bin_add_shader (GtkShaderBin *self,
+                           GskGLShader  *shader,
+                           GtkStateFlags state,
+                           GtkStateFlags state_mask)
+{
+  ShaderInfo *info = g_new0 (ShaderInfo, 1);
+  info->shader = g_object_ref (shader);
+  info->state = state;
+  info->state_mask = state_mask;
+
+  g_ptr_array_add (self->shaders, info);
+
+  gtk_shader_bin_update_active_shader (self);
+}
+
+void
+gtk_shader_bin_set_child (GtkShaderBin *self,
+                          GtkWidget    *child)
+{
+
+  if (self->child == child)
+    return;
+
+  g_clear_pointer (&self->child, gtk_widget_unparent);
+
+  if (child)
+    {
+      self->child = child;
+      gtk_widget_set_parent (child, GTK_WIDGET (self));
+    }
+}
+
+GtkWidget *
+gtk_shader_bin_get_child   (GtkShaderBin *self)
+{
+  return self->child;
+}
+
+static void
+gtk_shader_bin_snapshot (GtkWidget   *widget,
+                         GtkSnapshot *snapshot)
+{
+  GtkShaderBin *self = GTK_SHADER_BIN (widget);
+  int width, height;
+
+  width = gtk_widget_get_width (widget);
+  height = gtk_widget_get_height (widget);
+
+  if (self->active_shader)
+    {
+      gtk_snapshot_push_glshader (snapshot, self->active_shader,
+                                  &GRAPHENE_RECT_INIT(0, 0, width, height),
+                                  1,
+                                  "u_time", &self->time,
+                                  NULL
+                                  );
+      gtk_widget_snapshot_child (widget, self->child, snapshot);
+      gtk_snapshot_pop (snapshot); /* Fallback */
+      gtk_widget_snapshot_child (widget, self->child, snapshot);
+      gtk_snapshot_pop (snapshot); /* Shader node child 1 */
+    }
+  else
+    {
+      gtk_widget_snapshot_child (widget, self->child, snapshot);
+    }
+}
+
+static void
+gtk_shader_bin_class_init (GtkShaderBinClass *class)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  object_class->finalize = gtk_shader_bin_finalize;
+  object_class->dispose = gtk_shader_bin_dispose;
+
+  gtk_widget_class_set_layout_manager_type (widget_class, GTK_TYPE_BIN_LAYOUT);
+
+  widget_class->snapshot = gtk_shader_bin_snapshot;
+  widget_class->state_flags_changed = gtk_shader_bin_state_flags_changed;
+}
+
+GtkWidget *
+gtk_shader_bin_new (void)
+{
+  GtkShaderBin *self;
+
+  self = g_object_new (GTK_TYPE_SHADER_BIN, NULL);
+
+  return GTK_WIDGET (self);
+}

demos/gtk-demo/gtkshaderbin.h

@@ -0,0 +1,22 @@
+#ifndef __GTK_SHADER_BIN_H__
+#define __GTK_SHADER_BIN_H__
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_SHADER_BIN      (gtk_shader_bin_get_type ())
+G_DECLARE_FINAL_TYPE (GtkShaderBin, gtk_shader_bin, GTK, SHADER_BIN, GtkWidget)
+
+GtkWidget  *gtk_shader_bin_new        (void);
+void        gtk_shader_bin_add_shader (GtkShaderBin *self,
+                                       GskGLShader  *shader,
+                                       GtkStateFlags state,
+                                       GtkStateFlags state_mask);
+void       gtk_shader_bin_set_child   (GtkShaderBin *self,
+                                       GtkWidget    *child);
+GtkWidget *gtk_shader_bin_get_child   (GtkShaderBin *self);
+
+G_END_DECLS
+
+#endif /* __GTK_SHADER_BIN_H__ */

demos/gtk-demo/gtkshaderstack.c

@@ -0,0 +1,356 @@
+#include "gtkshaderstack.h"
+
+struct _GtkShaderStack
+{
+  GtkWidget parent_instance;
+
+  GskGLShader *shader;
+  GPtrArray *children;
+  int current;
+  int next;
+  gboolean backwards;
+
+  guint tick_id;
+  float time;
+  float duration;
+  gint64 start_time;
+};
+
+struct _GtkShaderStackClass
+{
+  GtkWidgetClass parent_class;
+};
+
+
+enum {
+  PROP_DURATION = 1,
+  NUM_PROPERTIES
+};
+
+static GParamSpec *properties[NUM_PROPERTIES] = { NULL };
+
+G_DEFINE_TYPE (GtkShaderStack, gtk_shader_stack, GTK_TYPE_WIDGET)
+
+static void
+gtk_shader_stack_finalize (GObject *object)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (object);
+
+  g_object_unref (self->shader);
+
+  G_OBJECT_CLASS (gtk_shader_stack_parent_class)->finalize (object);
+}
+
+static void
+update_child_visible (GtkShaderStack *self)
+{
+  int i;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      GtkWidget *child = g_ptr_array_index (self->children, i);
+
+      gtk_widget_set_child_visible (child,
+                                    i == self->current || i == self->next);
+    }
+}
+
+static gboolean
+transition_cb (GtkWidget     *widget,
+               GdkFrameClock *clock,
+               gpointer       unused)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (widget);
+  gint64 frame_time;
+
+  frame_time = gdk_frame_clock_get_frame_time (clock);
+
+  if (self->start_time == 0)
+    self->start_time = frame_time;
+
+  self->time = (frame_time - self->start_time) / (float)G_USEC_PER_SEC;
+
+  gtk_widget_queue_draw (widget);
+
+  if (self->time >= self->duration)
+    {
+      self->current = self->next;
+      self->next = -1;
+
+      update_child_visible (self);
+
+      return G_SOURCE_REMOVE;
+    }
+  else
+    return G_SOURCE_CONTINUE;
+}
+
+static void
+start_transition (GtkShaderStack *self)
+{
+  self->start_time = 0;
+  self->tick_id = gtk_widget_add_tick_callback (GTK_WIDGET (self),
+                                                transition_cb,
+                                                NULL, NULL);
+}
+
+static void
+stop_transition (GtkShaderStack *self)
+{
+  if (self->tick_id != 0)
+    {
+      gtk_widget_remove_tick_callback (GTK_WIDGET (self), self->tick_id);
+      self->tick_id = 0;
+    }
+
+  self->next = -1;
+
+  update_child_visible (self);
+}
+
+static void
+gtk_shader_stack_dispose (GObject *object)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (object);
+
+  stop_transition (self);
+
+  g_clear_pointer (&self->children, g_ptr_array_unref);
+
+  G_OBJECT_CLASS (gtk_shader_stack_parent_class)->dispose (object);
+}
+
+static void
+clicked_cb (GtkGestureClick *gesture,
+            guint            n_pressed,
+            double           x,
+            double           y,
+            gpointer         data)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (data);
+  guint button;
+
+  button = gtk_gesture_single_get_current_button (GTK_GESTURE_SINGLE (gesture));
+
+  stop_transition (self);
+
+  self->backwards = button == GDK_BUTTON_SECONDARY;
+  if (self->backwards)
+    self->next = (self->current + self->children->len - 1) % self->children->len;
+  else
+    self->next = (self->current + 1) % self->children->len;
+
+  update_child_visible (self);
+
+  start_transition (self);
+}
+
+static void
+gtk_shader_stack_init (GtkShaderStack *self)
+{
+  GtkEventController *controller;
+
+  self->children = g_ptr_array_new_with_free_func ((GDestroyNotify)gtk_widget_unparent);
+  self->current = -1;
+  self->next = -1;
+  self->backwards = FALSE;
+  self->duration = 1.0;
+
+  controller = GTK_EVENT_CONTROLLER (gtk_gesture_click_new ());
+  gtk_gesture_single_set_button (GTK_GESTURE_SINGLE (controller), 0);
+  g_signal_connect (controller, "released", G_CALLBACK (clicked_cb), self);
+  gtk_event_controller_set_propagation_phase (controller, GTK_PHASE_BUBBLE);
+  gtk_widget_add_controller (GTK_WIDGET (self), controller);
+}
+
+static void
+gtk_shader_stack_measure (GtkWidget      *widget,
+                          GtkOrientation  orientation,
+                          int             for_size,
+                          int            *minimum,
+                          int            *natural,
+                          int            *minimum_baseline,
+                          int            *natural_baseline)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (widget);
+  int i;
+
+  *minimum = 0;
+  *natural = 0;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      GtkWidget *child = g_ptr_array_index (self->children, i);
+      int child_min, child_nat;
+
+      if (gtk_widget_get_visible (child))
+        {
+          gtk_widget_measure (child, orientation, for_size, &child_min, &child_nat, NULL, NULL);
+
+          *minimum = MAX (*minimum, child_min);
+          *natural = MAX (*natural, child_nat);
+        }
+    }
+}
+
+static void
+gtk_shader_stack_size_allocate (GtkWidget *widget,
+                                int        width,
+                                int        height,
+                                int        baseline)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (widget);
+  GtkAllocation child_allocation;
+  GtkWidget *child;
+  int i;
+
+  child_allocation.x = 0;
+  child_allocation.y = 0;
+  child_allocation.width = width;
+  child_allocation.height = height;
+
+  for (i = 0; i < self->children->len; i++)
+    {
+      child = g_ptr_array_index (self->children, i);
+      if (gtk_widget_get_visible (child))
+        gtk_widget_size_allocate (child, &child_allocation, -1);
+    }
+}
+
+static void
+gtk_shader_stack_snapshot (GtkWidget   *widget,
+                           GtkSnapshot *snapshot)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (widget);
+  int width, height;
+  GtkWidget *current, *next;
+
+  width = gtk_widget_get_width (widget);
+  height = gtk_widget_get_height (widget);
+
+  current = g_ptr_array_index (self->children, self->current);
+
+  if (self->next == -1)
+    {
+      gtk_widget_snapshot_child (widget, current, snapshot);
+    }
+  else
+    {
+      float progress;
+
+      next = g_ptr_array_index (self->children, self->next);
+
+      progress = self->time / self->duration;
+
+      if (self->backwards)
+        {
+          GtkWidget *tmp = next;
+          next = current;
+          current = tmp;
+          progress = 1. - progress;
+        }
+
+      gtk_snapshot_push_glshader (snapshot,
+                                  self->shader,
+                                  &GRAPHENE_RECT_INIT(0, 0, width, height),
+                                  2,
+                                  "progress", &progress,
+                                  NULL);
+      gtk_widget_snapshot_child (widget, next, snapshot);
+      gtk_snapshot_pop (snapshot); /* Fallback */
+      gtk_widget_snapshot_child (widget, current, snapshot);
+      gtk_snapshot_pop (snapshot); /* current child */
+      gtk_widget_snapshot_child (widget, next, snapshot);
+      gtk_snapshot_pop (snapshot); /* next child */
+    }
+}
+
+static void
+gtk_shader_stack_get_property (GObject      *object,
+                               guint         prop_id,
+                               GValue       *value,
+                               GParamSpec   *pspec)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (object);
+
+  switch (prop_id)
+    {
+    case PROP_DURATION:
+      g_value_set_float (value, self->duration);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_shader_stack_set_property (GObject      *object,
+                               guint         prop_id,
+                               const GValue *value,
+                               GParamSpec   *pspec)
+{
+  GtkShaderStack *self = GTK_SHADER_STACK (object);
+
+  switch (prop_id)
+    {
+    case PROP_DURATION:
+      self->duration = g_value_get_float (value);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_shader_stack_class_init (GtkShaderStackClass *class)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (class);
+  GObjectClass *object_class = G_OBJECT_CLASS (class);
+
+  object_class->finalize = gtk_shader_stack_finalize;
+  object_class->dispose = gtk_shader_stack_dispose;
+  object_class->get_property = gtk_shader_stack_get_property;
+  object_class->set_property = gtk_shader_stack_set_property;
+
+  widget_class->snapshot = gtk_shader_stack_snapshot;
+  widget_class->measure = gtk_shader_stack_measure;
+  widget_class->size_allocate = gtk_shader_stack_size_allocate;
+
+  properties[PROP_DURATION] =
+      g_param_spec_float ("duration", "Duration", "Duration",
+                          0.1, 3.0, 1.0,
+                          G_PARAM_READWRITE);
+
+  g_object_class_install_properties (object_class, NUM_PROPERTIES, properties);
+}
+
+GtkWidget *
+gtk_shader_stack_new (void)
+{
+  return g_object_new (GTK_TYPE_SHADER_STACK, NULL);
+}
+
+void
+gtk_shader_stack_set_shader (GtkShaderStack *self,
+                             GskGLShader    *shader)
+{
+  g_set_object (&self->shader, shader);
+}
+
+void
+gtk_shader_stack_add_child (GtkShaderStack *self,
+                            GtkWidget      *child)
+{
+  g_ptr_array_add (self->children, child);
+  gtk_widget_set_parent (child, GTK_WIDGET (self));
+  gtk_widget_queue_resize (GTK_WIDGET (self));
+
+  if (self->current == -1)
+    self->current = 0;
+  else
+    gtk_widget_set_child_visible (child, FALSE);
+}

demos/gtk-demo/gtkshaderstack.h

@@ -0,0 +1,19 @@
+#ifndef __GTK_SHADER_STACK_H__
+#define __GTK_SHADER_STACK_H__
+
+#include <gtk/gtk.h>
+
+G_BEGIN_DECLS
+
+#define GTK_TYPE_SHADER_STACK     (gtk_shader_stack_get_type ())
+G_DECLARE_FINAL_TYPE (GtkShaderStack, gtk_shader_stack, GTK, SHADER_STACK, GtkWidget)
+
+GtkWidget * gtk_shader_stack_new          (void);
+void        gtk_shader_stack_set_shader   (GtkShaderStack *self,
+                                           GskGLShader    *shader);
+void        gtk_shader_stack_add_child    (GtkShaderStack *self,
+                                           GtkWidget      *child);
+
+G_END_DECLS
+
+#endif /* __GTK_SHADER_STACK_H__ */

demos/gtk-demo/meson.build

@@ -32,6 +32,8 @@ demos = files([
   'gears.c',
   'gestures.c',
   'glarea.c',
+  'glshader.c',
+  'gltransition.c',
   'headerbar.c',
   'hypertext.c',
   'iconscroll.c',
@@ -102,7 +104,9 @@ extra_demo_sources = files(['main.c',
                             'gtkfishbowl.c',
                             'fontplane.c',
                             'gtkgears.c',
+                            'gtkshaderbin.c',
                             'gtkshadertoy.c',
+                            'gtkshaderstack.c',
                             'puzzlepiece.c',
                             'bluroverlay.c',
                             'demoimage.c',

demos/gtk-demo/transition1.glsl

@@ -0,0 +1,32 @@
+uniform float progress;
+
+vec4 getFromColor(vec2 uv) {
+  return texture(u_source, uv);
+}
+
+vec4 getToColor(vec2 uv) {
+  return texture(u_source2, uv);
+}
+
+
+// Source: https://gl-transitions.com/editor/wind
+// Author: gre
+// License: MIT
+
+uniform float size = 0.2;
+
+float rand(vec2 co) {
+  return fract(sin(dot(co.xy ,vec2(12.9898,78.233))) * 43758.5453);
+}
+
+vec4 transition(vec2 p) {
+  float r = rand(vec2(0, p.y));
+  float m = smoothstep(0.0, -size, p.x*(1.0-size) + size*r - (progress * (1.0 + size)));
+  return mix(getFromColor(p), getToColor(p), m);
+}
+
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
+{
+  fragColor = transition(uv);
+}

demos/gtk-demo/transition2.glsl

@@ -0,0 +1,33 @@
+uniform float progress;
+
+vec4 getFromColor (vec2 uv) {
+  return texture(u_source, uv);
+}
+
+vec4 getToColor (vec2 uv) {
+  return texture(u_source2, uv);
+}
+
+
+// Source: https://gl-transitions.com/editor/Radial
+// License: MIT
+// Author: Xaychru
+
+uniform float smoothness = 1.0;
+
+const float PI = 3.141592653589;
+
+vec4 transition(vec2 p) {
+  vec2 rp = p*2.-1.;
+  return mix(
+    getToColor(p),
+    getFromColor(p),
+    smoothstep(0., smoothness, atan(rp.y,rp.x) - (progress-.5) * PI * 2.5)
+  );
+}
+
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
+{
+  fragColor = transition(uv);
+}

demos/gtk-demo/transition3.glsl

@@ -0,0 +1,26 @@
+uniform float progress;
+
+vec4 getFromColor (vec2 uv) {
+  return texture(u_source, uv);
+}
+
+vec4 getToColor (vec2 uv) {
+  return texture(u_source2, uv);
+}
+
+
+// Source: https://gl-transitions.com/editor/crosswarp
+// Author: Eke Péter <peterekepeter@gmail.com>
+// License: MIT
+
+vec4 transition(vec2 p) {
+  float x = progress;
+  x=smoothstep(.0,1.0,(x*2.0+p.x-1.0));
+  return mix(getFromColor((p-.5)*(1.-x)+.5), getToColor((p-.5)*x+.5), x);
+}
+
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
+{
+  fragColor = transition(uv);
+}

demos/gtk-demo/transition4.glsl

@@ -0,0 +1,40 @@
+uniform float progress;
+
+vec4 getFromColor (vec2 uv) {
+  return texture(u_source, uv);
+}
+
+vec4 getToColor (vec2 uv) {
+  return texture(u_source2, uv);
+}
+
+
+// Source: https://gl-transitions.com/editor/kaleidoscope
+// Author: nwoeanhinnogaehr
+// License: MIT
+
+uniform float speed = 1.0;
+uniform float angle = 1.0;
+uniform float power = 1.5;
+
+vec4 transition(vec2 uv) {
+  vec2 p = uv.xy / vec2(1.0).xy;
+  vec2 q = p;
+  float t = pow(progress, power)*speed;
+  p = p -0.5;
+  for (int i = 0; i < 7; i++) {
+    p = vec2(sin(t)*p.x + cos(t)*p.y, sin(t)*p.y - cos(t)*p.x);
+    t += angle;
+    p = abs(mod(p, 2.0) - 1.0);
+  }
+  abs(mod(p, 1.0));
+  return mix(
+    mix(getFromColor(q), getToColor(q), progress),
+    mix(getFromColor(p), getToColor(p), progress), 1.0 - 2.0*abs(progress - 0.5));
+}
+
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv)
+{
+  fragColor = transition(uv);
+}

gsk/broadway/gskbroadwayrenderer.c

@@ -272,6 +272,11 @@ collect_reused_child_nodes (GskRenderer *renderer,
 
       /* Bin nodes */
 
+    case GSK_GLSHADER_NODE:
+      collect_reused_node (renderer,
+                           gsk_glshader_node_get_fallback_child (node));
+      break;
+
     case GSK_SHADOW_NODE:
       collect_reused_node (renderer,
                            gsk_shadow_node_get_child (node));
@@ -792,6 +797,11 @@ gsk_broadway_renderer_add_node (GskRenderer *renderer,
         }
       return;
 
+    case GSK_GLSHADER_NODE:
+      gsk_broadway_renderer_add_node (renderer,
+                                      gsk_glshader_node_get_fallback_child (node), offset_x, offset_y, clip_bounds);
+      return;
+
       /* Generic nodes */
 
     case GSK_CONTAINER_NODE:

gsk/gl/gskglrenderer.c

@@ -19,6 +19,7 @@
 #include "gskglnodesampleprivate.h"
 #include "gsktransform.h"
 #include "glutilsprivate.h"
+#include "gskglshaderprivate.h"
 
 #include "gskprivate.h"
 
@@ -64,6 +65,11 @@
                               glGetUniformLocation(program_ptr->id, "u_" #uniform_basename);\
               }G_STMT_END
 
+static Program *gsk_gl_renderer_lookup_custom_program (GskGLRenderer  *self,
+                                                       GskGLShader *shader);
+static Program *gsk_gl_renderer_create_custom_program (GskGLRenderer  *self,
+                                                       GskGLShader *shader);
+
 typedef enum
 {
   FORCE_OFFSCREEN  = 1 << 0,
@@ -130,6 +136,13 @@ print_render_node_tree (GskRenderNode *root, int level)
         print_render_node_tree (gsk_shadow_node_get_child (root), level + 1);
         break;
 
+      case GSK_GLSHADER_NODE:
+        g_print ("%*s GLShader\n", level * INDENT, " ");
+        print_render_node_tree (gsk_glshader_node_get_fallback_child (root), level + 1);
+        for (i = 0; i < gsk_glshader_node_get_n_children (root); i++)
+          print_render_node_tree (gsk_glshader_node_get_child (root, i), level + 1);
+        break;
+
       case GSK_TEXTURE_NODE:
         g_print ("%*s Texture %p\n", level * INDENT, " ", gsk_texture_node_get_texture (root));
         break;
@@ -495,6 +508,40 @@ struct _GskGLRendererClass
 
 G_DEFINE_TYPE (GskGLRenderer, gsk_gl_renderer, GSK_TYPE_RENDERER)
 
+static void
+init_shader_builder (GskGLRenderer       *self,
+                     GskGLShaderBuilder  *shader_builder)
+{
+#ifdef G_ENABLE_DEBUG
+  if (GSK_RENDERER_DEBUG_CHECK (GSK_RENDERER (self), SHADERS))
+    shader_builder->debugging = TRUE;
+#endif
+
+  if (gdk_gl_context_get_use_es (self->gl_context))
+    {
+      gsk_gl_shader_builder_set_glsl_version (shader_builder, SHADER_VERSION_GLES);
+      shader_builder->gles = TRUE;
+    }
+  else if (gdk_gl_context_is_legacy (self->gl_context))
+    {
+      int maj, min;
+
+      gdk_gl_context_get_version (self->gl_context, &maj, &min);
+
+      if (maj == 3)
+        gsk_gl_shader_builder_set_glsl_version (shader_builder, SHADER_VERSION_GL3_LEGACY);
+      else
+        gsk_gl_shader_builder_set_glsl_version (shader_builder, SHADER_VERSION_GL2_LEGACY);
+
+      shader_builder->legacy = TRUE;
+        }
+  else
+    {
+      gsk_gl_shader_builder_set_glsl_version (shader_builder, SHADER_VERSION_GL3);
+      shader_builder->gl3 = TRUE;
+    }
+}
+
 static void G_GNUC_UNUSED
 add_rect_ops (RenderOpBuilder       *builder,
               const graphene_rect_t *r)
@@ -1006,6 +1053,128 @@ render_texture_node (GskGLRenderer       *self,
     }
 }
 
+static inline void
+render_glshader_node (GskGLRenderer       *self,
+                      GskRenderNode       *node,
+                      RenderOpBuilder     *builder)
+{
+  GskGLShader *shader = gsk_glshader_node_get_shader (node);
+  Program *program = gsk_gl_renderer_lookup_custom_program (self, shader);
+  GskRenderNode *fallback = gsk_glshader_node_get_fallback_child (node);
+  int n_children = gsk_glshader_node_get_n_children (node);
+
+  if (program == NULL)
+    {
+      GskGLShaderBuilder shader_builder;
+      const char *shader_source;
+      GError *error = NULL;
+      int n_uniforms;
+      const GskGLUniform *uniforms;
+      int n_required_sources = gsk_glshader_get_n_required_sources (shader);
+
+      /* We always create the program, so that any compiler warnings or other is only reported once */
+      program = gsk_gl_renderer_create_custom_program (self, shader);
+
+      shader_source = gsk_glshader_get_sourcecode (shader);
+      uniforms = gsk_glshader_get_uniforms (shader, &n_uniforms);
+
+      if (n_uniforms > G_N_ELEMENTS (program->glshader.args_locations))
+        {
+          g_set_error (&error, GDK_GL_ERROR, GDK_GL_ERROR_UNSUPPORTED_FORMAT,
+                       "GLShaderNode supports max %d custom uniforms", (int)G_N_ELEMENTS (program->glshader.args_locations));
+        }
+      else if (n_required_sources > 1 + G_N_ELEMENTS (program->glshader.extra_source_locations))
+        {
+          g_set_error (&error, GDK_GL_ERROR, GDK_GL_ERROR_UNSUPPORTED_FORMAT,
+                       "GLShaderNode supports max %d texture sources", (int)(1 + G_N_ELEMENTS (program->glshader.extra_source_locations)));
+        }
+      else
+        {
+          gsk_gl_shader_builder_init (&shader_builder,
+                                      "/org/gtk/libgsk/glsl/preamble.glsl",
+                                      "/org/gtk/libgsk/glsl/preamble.vs.glsl",
+                                      "/org/gtk/libgsk/glsl/preamble.fs.glsl");
+
+          init_shader_builder (self, &shader_builder);
+
+          program->id = gsk_gl_shader_builder_create_program (&shader_builder,
+                                                              "/org/gtk/libgsk/glsl/custom.glsl",
+                                                              shader_source,
+                                                              &error);
+          gsk_gl_shader_builder_finish (&shader_builder);
+
+          if (program->id >= 0)
+            {
+              INIT_COMMON_UNIFORM_LOCATION (program, alpha);
+              INIT_COMMON_UNIFORM_LOCATION (program, source);
+              INIT_COMMON_UNIFORM_LOCATION (program, clip_rect);
+              INIT_COMMON_UNIFORM_LOCATION (program, viewport);
+              INIT_COMMON_UNIFORM_LOCATION (program, projection);
+              INIT_COMMON_UNIFORM_LOCATION (program, modelview);
+              program->glshader.size_location = glGetUniformLocation(program->id, "u_size");
+              program->glshader.extra_source_locations[0] = glGetUniformLocation(program->id, "u_source2");
+              program->glshader.extra_source_locations[1] = glGetUniformLocation(program->id, "u_source3");
+              program->glshader.extra_source_locations[2] = glGetUniformLocation(program->id, "u_source4");
+              for (int i = 0; i < G_N_ELEMENTS (program->glshader.args_locations); i++)
+                {
+                  if (i < n_uniforms)
+                    {
+                      program->glshader.args_locations[i] = glGetUniformLocation(program->id, uniforms[i].name);
+                      if (program->glshader.args_locations[i] == -1)
+                        g_warning ("Expected uniform `%s` not found in shader", uniforms[i].name);
+                    }
+                  else
+                    program->glshader.args_locations[i] = -1;
+                }
+            }
+        }
+
+      if (program->id <= 0)
+        {
+          g_warning ("Failed to compile gl shader: %s\n", error->message);
+          g_error_free (error);
+        }
+    }
+
+  if (program->id >= 0 && n_children <= 4)
+    {
+      const guchar *uniform_data;
+      TextureRegion regions[4];
+      gboolean is_offscreen[4];
+
+      for (guint i = 0; i < n_children; i++)
+        {
+          GskRenderNode *child = gsk_glshader_node_get_child (node, i);
+          if (!add_offscreen_ops (self, builder,
+                                  &node->bounds,
+                                  child,
+                                  &regions[i], &is_offscreen[i],
+                                  FORCE_OFFSCREEN | RESET_CLIP | RESET_OPACITY))
+            {
+              if (fallback)
+                gsk_gl_renderer_add_render_ops (self, fallback, builder);
+              return;
+            }
+        }
+
+      uniform_data = gsk_glshader_node_get_uniform_data (node);
+      ops_set_program (builder, program);
+
+      ops_set_glshader_args (builder, shader, node->bounds.size.width, node->bounds.size.height, uniform_data);
+      if (n_children >= 0)
+        ops_set_texture (builder, regions[0].texture_id);
+      for (guint i = 1; i < n_children; i++)
+        ops_set_extra_texture (builder, regions[i].texture_id, i-1);
+
+      load_offscreen_vertex_data (ops_draw (builder, NULL), node, builder);
+    }
+  else
+    {
+      if (fallback)
+        gsk_gl_renderer_add_render_ops (self, fallback, builder);
+    }
+}
+
 /* Returns TRUE is applying transform to bounds
  * yields an axis-aligned rectangle
  */
@@ -2671,6 +2840,18 @@ apply_source_texture_op (const Program   *program,
   glBindTexture (GL_TEXTURE_2D, op->texture_id);
 }
 
+static inline void
+apply_source_extra_texture_op (const Program        *program,
+                               const OpExtraTexture *op)
+{
+  g_assert(op->texture_id != 0);
+  OP_PRINT (" -> New extra texture %d: %d", op->idx, op->texture_id);
+  /* Use texture unit 1 + op->idx for the source */
+  glUniform1i (program->glshader.extra_source_locations[op->idx], 1 + op->idx);
+  glActiveTexture (GL_TEXTURE0 + 1 + op->idx);
+  glBindTexture (GL_TEXTURE_2D, op->texture_id);
+}
+
 static inline void
 apply_color_matrix_op (const Program       *program,
                        const OpColorMatrix *op)
@@ -2815,6 +2996,51 @@ apply_border_op (const Program  *program,
   glUniform4fv (program->border.outline_rect_location, 3, (float *)&op->outline.bounds);
 }
 
+static inline void
+apply_glshader_args_op (const Program  *program,
+                        const OpGLShader *op)
+{
+  int n_uniforms, i;
+  const GskGLUniform *uniforms;
+
+  OP_PRINT (" -> GLShader Args");
+
+  glUniform2fv (program->glshader.size_location, 1, op->size);
+
+  uniforms = gsk_glshader_get_uniforms (op->shader, &n_uniforms);
+  for (i = 0; i < n_uniforms; i++)
+    {
+      const GskGLUniform *u = &uniforms[i];
+      const guchar *data = op->uniform_data + u->offset;
+
+      switch (u->type)
+        {
+        default:
+        case GSK_GLUNIFORM_TYPE_NONE:
+          break;
+        case GSK_GLUNIFORM_TYPE_FLOAT:
+          glUniform1fv (program->glshader.args_locations[i], 1, (const float *)data);
+          break;
+        case GSK_GLUNIFORM_TYPE_INT:
+          glUniform1iv (program->glshader.args_locations[i], 1, (const gint32 *)data);
+          break;
+        case GSK_GLUNIFORM_TYPE_UINT:
+        case GSK_GLUNIFORM_TYPE_BOOL:
+          glUniform1uiv (program->glshader.args_locations[i], 1, (const guint32 *) data);
+          break;
+        case GSK_GLUNIFORM_TYPE_VEC2:
+          glUniform2fv (program->glshader.args_locations[i], 1, (const float *)data);
+          break;
+        case GSK_GLUNIFORM_TYPE_VEC3:
+          glUniform3fv (program->glshader.args_locations[i], 1, (const float *)data);
+          break;
+        case GSK_GLUNIFORM_TYPE_VEC4:
+          glUniform4fv (program->glshader.args_locations[i], 1, (const float *)data);
+          break;
+        }
+    }
+}
+
 static inline void
 apply_border_width_op (const Program  *program,
                        const OpBorder *op)
@@ -2886,6 +3112,28 @@ gsk_gl_renderer_dispose (GObject *gobject)
   G_OBJECT_CLASS (gsk_gl_renderer_parent_class)->dispose (gobject);
 }
 
+static void
+program_init (Program *program)
+{
+  program->index = -1;
+  program->state.opacity = 1.0f;
+}
+
+static void
+program_finalize (Program *program)
+{
+  if (program->id > 0)
+    glDeleteProgram (program->id);
+  gsk_transform_unref (program->state.modelview);
+}
+
+static void
+program_free (Program *program)
+{
+  program_finalize (program);
+  g_free (program);
+}
+
 static GskGLRendererPrograms *
 gsk_gl_renderer_programs_new (void)
 {
@@ -2895,9 +3143,11 @@ gsk_gl_renderer_programs_new (void)
   programs = g_new0 (GskGLRendererPrograms, 1);
   programs->ref_count = 1;
   for (i = 0; i < GL_N_PROGRAMS; i ++)
-    {
-      programs->programs[i].state.opacity = 1.0f;
-    }
+    program_init (&programs->programs[i]);
+
+  /* We use direct hash for performance, not string hash on the source, because we assume each caller
+   * reuses a single GskGLShader for all uses and different callers will use different source content. */
+  programs->custom_programs = g_hash_table_new_full (g_direct_hash, g_direct_equal, (GDestroyNotify)g_object_unref, (GDestroyNotify)program_free);
 
   return programs;
 }
@@ -2918,15 +3168,33 @@ gsk_gl_renderer_programs_unref (GskGLRendererPrograms *programs)
   if (programs->ref_count == 0)
     {
       for (i = 0; i < GL_N_PROGRAMS; i ++)
-        {
-          if (programs->programs[i].id > 0)
-            glDeleteProgram (programs->programs[i].id);
-          gsk_transform_unref (programs->programs[i].state.modelview);
-        }
+        program_finalize (&programs->programs[i]);
+
+      g_hash_table_destroy (programs->custom_programs);
       g_free (programs);
     }
 }
 
+static Program *
+gsk_gl_renderer_lookup_custom_program (GskGLRenderer  *self,
+                                       GskGLShader *shader)
+{
+  return g_hash_table_lookup (self->programs->custom_programs, shader);
+}
+
+static Program *
+gsk_gl_renderer_create_custom_program (GskGLRenderer  *self,
+                                       GskGLShader *shader)
+{
+  Program *program = g_new0 (Program, 1);
+
+  program_init (program);
+
+  g_hash_table_insert (self->programs->custom_programs, g_object_ref (shader), program);
+
+  return program;
+}
+
 static GskGLRendererPrograms *
 gsk_gl_renderer_create_programs (GskGLRenderer  *self,
                                  GError        **error)
@@ -2961,35 +3229,7 @@ gsk_gl_renderer_create_programs (GskGLRenderer  *self,
 
   g_assert (G_N_ELEMENTS (program_definitions) == GL_N_PROGRAMS);
 
-#ifdef G_ENABLE_DEBUG
-  if (GSK_RENDERER_DEBUG_CHECK (GSK_RENDERER (self), SHADERS))
-    shader_builder.debugging = TRUE;
-#endif
-
-  if (gdk_gl_context_get_use_es (self->gl_context))
-    {
-
-      gsk_gl_shader_builder_set_glsl_version (&shader_builder, SHADER_VERSION_GLES);
-      shader_builder.gles = TRUE;
-    }
-  else if (gdk_gl_context_is_legacy (self->gl_context))
-    {
-      int maj, min;
-
-      gdk_gl_context_get_version (self->gl_context, &maj, &min);
-
-      if (maj == 3)
-        gsk_gl_shader_builder_set_glsl_version (&shader_builder, SHADER_VERSION_GL3_LEGACY);
-      else
-        gsk_gl_shader_builder_set_glsl_version (&shader_builder, SHADER_VERSION_GL2_LEGACY);
-
-      shader_builder.legacy = TRUE;
-    }
-  else
-    {
-      gsk_gl_shader_builder_set_glsl_version (&shader_builder, SHADER_VERSION_GL3);
-      shader_builder.gl3 = TRUE;
-    }
+  init_shader_builder (self, &shader_builder);
 
   programs = gsk_gl_renderer_programs_new ();
 
@@ -3000,7 +3240,7 @@ gsk_gl_renderer_create_programs (GskGLRenderer  *self,
       prog->index = i;
       prog->id = gsk_gl_shader_builder_create_program (&shader_builder,
                                                        program_definitions[i].resource_path,
-                                                       error);
+                                                       NULL, error);
       if (prog->id < 0)
         {
           g_clear_pointer (&programs, gsk_gl_renderer_programs_unref);
@@ -3445,6 +3685,10 @@ gsk_gl_renderer_add_render_ops (GskGLRenderer   *self,
       render_repeat_node (self, node, builder);
     break;
 
+    case GSK_GLSHADER_NODE:
+      render_glshader_node (self, node, builder);
+    break;
+
     case GSK_REPEATING_LINEAR_GRADIENT_NODE:
     case GSK_REPEATING_RADIAL_GRADIENT_NODE:
     case GSK_CAIRO_NODE:
@@ -3727,6 +3971,10 @@ gsk_gl_renderer_render_ops (GskGLRenderer *self)
           apply_source_texture_op (program, ptr);
           break;
 
+        case OP_CHANGE_EXTRA_SOURCE_TEXTURE:
+          apply_source_extra_texture_op (program, ptr);
+          break;
+
         case OP_CHANGE_CROSS_FADE:
           g_assert (program == &self->programs->cross_fade_program);
           apply_cross_fade_op (program, ptr);
@@ -3773,6 +4021,10 @@ gsk_gl_renderer_render_ops (GskGLRenderer *self)
           apply_repeat_op (program, ptr);
           break;
 
+        case OP_CHANGE_GLSHADER_ARGS:
+          apply_glshader_args_op (program, ptr);
+          break;
+
         case OP_DRAW:
           {
             const OpDraw *op = ptr;

gsk/gl/gskglrenderops.c

@@ -558,6 +558,18 @@ ops_set_texture (RenderOpBuilder *builder,
   builder->current_texture = texture_id;
 }
 
+void
+ops_set_extra_texture (RenderOpBuilder *builder,
+                       int              texture_id,
+                       int              idx)
+{
+  OpExtraTexture *op;
+
+  op = ops_begin (builder, OP_CHANGE_EXTRA_SOURCE_TEXTURE);
+  op->texture_id = texture_id;
+  op->idx = idx;
+}
+
 int
 ops_set_render_target (RenderOpBuilder *builder,
                        int              render_target_id)
@@ -621,6 +633,22 @@ ops_set_color (RenderOpBuilder *builder,
   op->rgba = color;
 }
 
+void
+ops_set_glshader_args (RenderOpBuilder       *builder,
+                       GskGLShader           *shader,
+                       float                  width,
+                       float                  height,
+                       const guchar          *uniform_data)
+{
+  OpGLShader *op;
+
+  op = ops_begin (builder, OP_CHANGE_GLSHADER_ARGS);
+  op->shader = shader;
+  op->size[0] = width;
+  op->size[1] = height;
+  op->uniform_data = uniform_data;
+}
+
 void
 ops_set_color_matrix (RenderOpBuilder         *builder,
                       const graphene_matrix_t *matrix,

gsk/gl/gskglrenderopsprivate.h

@@ -159,6 +159,11 @@ struct _Program
       int child_bounds_location;
       int texture_rect_location;
     } repeat;
+    struct {
+      int size_location;
+      int args_locations[8];
+      int extra_source_locations[3];
+    } glshader;
   };
 
   ProgramState state;
@@ -185,7 +190,7 @@ typedef struct {
       Program unblurred_outset_shadow_program;
     };
   };
-  ProgramState state[GL_N_PROGRAMS];
+  GHashTable *custom_programs; /* GskGLShader -> Program* */
 } GskGLRendererPrograms;
 
 typedef struct
@@ -257,6 +262,9 @@ graphene_rect_t   ops_set_viewport       (RenderOpBuilder         *builder,
 
 void              ops_set_texture        (RenderOpBuilder         *builder,
                                           int                      texture_id);
+void              ops_set_extra_texture  (RenderOpBuilder         *builder,
+                                          int                      texture_id,
+                                          int                      idx);
 
 int               ops_set_render_target  (RenderOpBuilder         *builder,
                                           int                      render_target_id);
@@ -283,6 +291,11 @@ void              ops_set_inset_shadow   (RenderOpBuilder         *self,
                                           const GdkRGBA           *color,
                                           float                    dx,
                                           float                    dy);
+void              ops_set_glshader_args  (RenderOpBuilder         *builder,
+                                          GskGLShader             *shader,
+                                          float                    width,
+                                          float                    height,
+                                          const guchar            *uniform_data);
 void              ops_set_unblurred_outset_shadow   (RenderOpBuilder         *self,
                                                      const GskRoundedRect     outline,
                                                      float                    spread,

gsk/gl/gskglshaderbuilder.c

@@ -96,6 +96,7 @@ check_shader_error (int     shader_id,
 int
 gsk_gl_shader_builder_create_program (GskGLShaderBuilder  *self,
                                       const char          *resource_path,
+                                      const char          *extra_fragment_snippet,
                                       GError             **error)
 {
 
@@ -156,7 +157,7 @@ gsk_gl_shader_builder_create_program (GskGLShaderBuilder  *self,
     }
 
   fragment_id = glCreateShader (GL_FRAGMENT_SHADER);
-  glShaderSource (fragment_id, 8,
+  glShaderSource (fragment_id, 9,
                   (const char *[]) {
                     version_buffer,
                     self->debugging ? "#define GSK_DEBUG 1\n" : "",
@@ -165,7 +166,8 @@ gsk_gl_shader_builder_create_program (GskGLShaderBuilder  *self,
                     self->gles ? "#define GSK_GLES 1\n" : "",
                     g_bytes_get_data (self->preamble, NULL),
                     g_bytes_get_data (self->fs_preamble, NULL),
-                    fragment_shader_start
+                    fragment_shader_start,
+                    extra_fragment_snippet ? extra_fragment_snippet : ""
                   },
                   (int[]) {
                     -1,
@@ -176,6 +178,7 @@ gsk_gl_shader_builder_create_program (GskGLShaderBuilder  *self,
                     -1,
                     -1,
                     -1,
+                    -1,
                   });
   glCompileShader (fragment_id);
 

gsk/gl/gskglshaderbuilderprivate.h

@@ -33,6 +33,7 @@ void   gsk_gl_shader_builder_set_glsl_version (GskGLShaderBuilder  *self,
 
 int    gsk_gl_shader_builder_create_program   (GskGLShaderBuilder  *self,
                                                const char          *resource_path,
+                                               const char          *extra_fragment_snippet,
                                                GError             **error);
 
 G_END_DECLS

gsk/gl/opbuffer.c

@@ -31,6 +31,8 @@ static guint op_sizes[OP_LAST] = {
   sizeof (OpDebugGroup),
   0,
   sizeof (OpBlend),
+  sizeof (OpGLShader),
+  sizeof (OpExtraTexture),
 };
 
 void

gsk/gl/opbuffer.h

@@ -39,6 +39,8 @@ typedef enum
   OP_PUSH_DEBUG_GROUP                  = 25,
   OP_POP_DEBUG_GROUP                   = 26,
   OP_CHANGE_BLEND                      = 27,
+  OP_CHANGE_GLSHADER_ARGS              = 28,
+  OP_CHANGE_EXTRA_SOURCE_TEXTURE       = 29,
   OP_LAST
 } OpKind;
 
@@ -124,6 +126,12 @@ typedef struct
   int texture_id;
 } OpTexture;
 
+typedef struct
+{
+  int texture_id;
+  int idx;
+} OpExtraTexture;
+
 typedef struct
 {
   gsize vao_offset;
@@ -198,6 +206,13 @@ typedef struct
   float texture_rect[4];
 } OpRepeat;
 
+typedef struct
+{
+  float size[2];
+  GskGLShader *shader;
+  const guchar *uniform_data;
+} OpGLShader;
+
 void     op_buffer_init            (OpBuffer *buffer);
 void     op_buffer_destroy         (OpBuffer *buffer);
 void     op_buffer_clear           (OpBuffer *buffer);

gsk/gskenums.h

@@ -75,7 +75,8 @@ typedef enum {
   GSK_CROSS_FADE_NODE,
   GSK_TEXT_NODE,
   GSK_BLUR_NODE,
-  GSK_DEBUG_NODE
+  GSK_DEBUG_NODE,
+  GSK_GLSHADER_NODE
 } GskRenderNodeType;
 
 /**
@@ -218,4 +219,32 @@ typedef enum
   GSK_TRANSFORM_CATEGORY_IDENTITY
 } GskTransformCategory;
 
+/**
+ * GskGLUniformType:
+ * @GSK_GLUNIFORM_TYPE_NONE: No type, used for uninitialized or unspecified values.
+ * @GSK_GLUNIFORM_TYPE_FLOAT: A float uniform
+ * @GSK_GLUNIFORM_TYPE_INT: A GLSL int / gint32 uniform
+ * @GSK_GLUNIFORM_TYPE_UINT: A GLSL uint / guint32 uniform
+ * @GSK_GLUNIFORM_TYPE_BOOL: A GLSL bool / gboolean uniform
+ * @GSK_GLUNIFORM_TYPE_VEC2: A GLSL vec2 / graphene_vec2_t uniform
+ * @GSK_GLUNIFORM_TYPE_VEC3: A GLSL vec3 / graphene_vec3_t uniform
+ * @GSK_GLUNIFORM_TYPE_VEC4: A GLSL vec4 / graphene_vec4_t uniform
+ *
+ * This defines the types of the uniforms that #GskGLShaders
+ * declare. It defines both what the type is called in the GLSL shader
+ * code, and what the corresponding C type is on the Gtk side.
+ */
+typedef enum
+{
+  GSK_GLUNIFORM_TYPE_NONE,
+  GSK_GLUNIFORM_TYPE_FLOAT,
+  GSK_GLUNIFORM_TYPE_INT,
+  GSK_GLUNIFORM_TYPE_UINT,
+  GSK_GLUNIFORM_TYPE_BOOL,
+  GSK_GLUNIFORM_TYPE_VEC2,
+  GSK_GLUNIFORM_TYPE_VEC3,
+  GSK_GLUNIFORM_TYPE_VEC4,
+} GskGLUniformType;
+
+
 #endif /* __GSK_TYPES_H__ */

gsk/gskglshader.c

@@ -0,0 +1,529 @@
+/* GSK - The GTK Scene Kit
+ *
+ * Copyright 2020, Red Hat Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/**
+ * SECTION:GskGLShader
+ * @Title: GskGLShader
+ * @Short_description: A description of GskGLShader
+ *
+ * A #GskGLShader is a snippet of GLSL that is meant to run in the
+ * fragment shader of the rendering pipeline. A fragment shaader it
+ * gets the coordinates being rendered as input and produces a the
+ * pixel values for that particular pixel. Additionally the
+ * shader can declare a set of other input arguments, called
+ * uniforms (as they are uniform over all the calls to your shader in
+ * each instance of use). A shader can also receieve up to 4
+ * textures that it can use as input when producing the pixel data.
+ *
+ * The typical way a #GskGLShader is used is as an argument to a
+ * #GskGLShaderNode in the rendering hierarchy, and then the textures
+ * it gets as input are constructed by rendering the child nodes to
+ * textures before rendering the shader node itself. (Although you can
+ * also pass texture nodes as children if you want to directly use a
+ * texture as input). Note that the #GskGLShaderNode API is a bit
+ * lowlevel, and highlevel code normally uses
+ * gtk_snapshot_push_glshader() to produce the nodes.
+ *
+ * The actual shader code is GLSL code that gets combined with
+ * some other code into the fragment shader. Since the exact
+ * capabilities of the GPU driver differs between different OpenGL
+ * drivers and hardware Gtk adds some defines that you can use
+ * to ensure your GLSL code runs on as many drivers as it can.
+ *
+ * If the OpenGL driver is GLES, then the shader language version
+ * is set to 100, and GSK_GLES will be defined in the shader.
+ *
+ * Otherwise, if the OpenGL driver does not support the 3.2 core profile,
+ * then the shader will run with language version 110 for GL2 and 130 for GL3,
+ * and GSK_LEGACY will be defined in the shader.
+ *
+ * If the OpenGL driver supports the 3.2 code profile, it will be used,
+ * the shader language version is set to 150, and GSK_GL3 will be defined
+ * in the shader.
+ *
+ * The main function the shader should implement is:
+ *
+ * |[<!-- language="plain" -->
+ *  void mainImage(out vec4 fragColor,
+ *                 in vec2 fragCoord,
+ *                 in vec2 resolution,
+ *                 in vec2 uv)
+ * ]|
+ * 
+ * Where the input @fragCoord is the coordinate of the pixel we're
+ * currently rendering, relative to the boundary rectangle that was
+ * specified in the #GskGLShaderNode, and @resolution is the width and
+ * height of that rectangle. This is in the typical Gtk+ coordinate
+ * system with the origin in the top left. @uv contains the u and v
+ * coordinates that can be used to index a texture at the
+ * corresponding point. These coordinates are in the [0..1]x[0..1]
+ * region, with 0, 0 being in the lower left cornder (which is typical
+ * for OpenGL).
+ *
+ * The output @fragColor should be a RGBA color (and alpha) that will
+ * be used as the output for the specified pixel location. Note that
+ * this output will be automatically clipped to the clip region of the
+ * glshader node.
+ *
+ * In addition to the function arguments the shader can use one of the
+ * pre-defined uniforms for tetxure sources (u_source, u_source2,
+ * u_source3 or u_source4), as well as any custom uniforms you
+ * declare.
+ *
+ * Gtk uses the the "gsk" namespace in the symbols it uses in the
+ * shader, so your code should not use any symbols with the prefix gsk
+ * or GSK. There are some helper functions declared that you can use:
+ *
+ * |[<!-- language="plain" -->
+ * vec4 GskTexture(sampler2D sampler, vec2 texCoords);
+ * ]|
+ *
+ * This samples a texture (e.g. u_source) at the specified
+ * coordinates, and containes some helper ifdefs to ensure that
+ * it works on all OpenGL versions.
+ */
+
+#include "config.h"
+#include "gskglshader.h"
+#include "gskglshaderprivate.h"
+
+struct _GskGLShader
+{
+  GObject parent_instance;
+  char *sourcecode;
+  int n_required_sources;
+  int uniforms_size;
+  GArray *uniforms;
+};
+
+G_DEFINE_TYPE (GskGLShader, gsk_glshader, G_TYPE_OBJECT)
+
+enum {
+  GLSHADER_PROP_0,
+  GLSHADER_PROP_SOURCECODE,
+  GLSHADER_PROP_N_REQUIRED_SOURCES,
+  GLSHADER_N_PROPS
+};
+static GParamSpec *gsk_glshader_properties[GLSHADER_N_PROPS];
+
+static void
+gsk_glshader_get_property (GObject    *object,
+                           guint       prop_id,
+                           GValue     *value,
+                           GParamSpec *pspec)
+{
+  GskGLShader *shader = GSK_GLSHADER (object);
+
+  switch (prop_id)
+    {
+    case GLSHADER_PROP_SOURCECODE:
+      g_value_set_string (value, shader->sourcecode);
+      break;
+
+    case GLSHADER_PROP_N_REQUIRED_SOURCES:
+      g_value_set_int (value, shader->n_required_sources);
+      break;
+
+    default:
+      g_assert_not_reached ();
+    }
+}
+
+static void
+gsk_glshader_set_property (GObject      *object,
+                           guint         prop_id,
+                           const GValue *value,
+                           GParamSpec   *pspec)
+{
+  GskGLShader *shader = GSK_GLSHADER (object);
+
+  switch (prop_id)
+    {
+    case GLSHADER_PROP_SOURCECODE:
+      g_free (shader->sourcecode);
+      shader->sourcecode = g_value_dup_string (value);
+      break;
+
+    case GLSHADER_PROP_N_REQUIRED_SOURCES:
+      gsk_glshader_set_n_required_sources (shader, g_value_get_int (value));
+      break;
+
+    default:
+      g_assert_not_reached ();
+    }
+}
+
+static void
+gsk_glshader_finalize (GObject *object)
+{
+  GskGLShader *shader = GSK_GLSHADER (object);
+
+  g_free (shader->sourcecode);
+  for (int i = 0; i < shader->uniforms->len; i ++)
+    g_free (g_array_index (shader->uniforms, GskGLUniform, i).name);
+  g_array_free (shader->uniforms, TRUE);
+
+  G_OBJECT_CLASS (gsk_glshader_parent_class)->finalize (object);
+}
+
+static void
+gsk_glshader_class_init (GskGLShaderClass *klass)
+{
+   GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->get_property = gsk_glshader_get_property;
+  object_class->set_property = gsk_glshader_set_property;
+  object_class->finalize = gsk_glshader_finalize;
+
+  /**
+   * GskGLShader:sourcecode:
+   *
+   * The source code for the shader.
+   */
+  gsk_glshader_properties[GLSHADER_PROP_SOURCECODE] =
+    g_param_spec_string ("sourcecode",
+                         "Sourcecode",
+                         "The sourcecode code for the shader",
+                         NULL,
+                         G_PARAM_READWRITE |
+                         G_PARAM_CONSTRUCT_ONLY |
+                         G_PARAM_STATIC_STRINGS);
+
+  /**
+   * GskGLShader:n-required-sources:
+   *
+   * The number of texture sources (u_source*) that are required to be set for the
+   * shader to work.
+   */
+  gsk_glshader_properties[GLSHADER_PROP_N_REQUIRED_SOURCES] =
+    g_param_spec_int ("n-required-sources",
+                      "Number of required sources",
+                      "Minimum number of source textures required for the shader to work",
+                      0, 4, 0,
+                      G_PARAM_READWRITE |
+                      G_PARAM_STATIC_STRINGS);
+
+  g_object_class_install_properties (object_class, GLSHADER_N_PROPS, gsk_glshader_properties);
+}
+
+static void
+gsk_glshader_init (GskGLShader *shader)
+{
+  shader->uniforms = g_array_new (FALSE, FALSE, sizeof (GskGLUniform));
+}
+
+/**
+ * gsk_glshader_new:
+ * @sourcecode: The sourcecode for the shader
+ *
+ * Creates a #GskGLShader that will render pixels using the specified code.
+ *
+ * Returns: (transfer full): A new #GskGLShader
+ */
+GskGLShader *
+gsk_glshader_new (const char *sourcecode)
+{
+   GskGLShader *shader = g_object_new (GSK_TYPE_GLSHADER,
+                                       "sourcecode", sourcecode,
+                                       NULL);
+   return shader;
+}
+
+/**
+ * gsk_glshader_get_sourcecode:
+ * @shader: A #GskGLShader
+ *
+ * Get the source code being used to render this shader.
+ *
+ * Returns: (transfer none): The source code for the shader
+ */
+const char *
+gsk_glshader_get_sourcecode (GskGLShader *shader)
+{
+  return shader->sourcecode;
+}
+
+/**
+ * gsk_glshader_get_n_required_sources:
+ * @shader: A #GskGLShader
+ *
+ * Returns the number of texture sources that the shader requires. This can be set
+ * with gsk_glshader_set_n_required_sources() and can be used to check that the
+ * a passed shader works in your usecase.
+ *
+ * Returns: (transfer none): The set nr of texture sources this shader requires.
+ */
+int
+gsk_glshader_get_n_required_sources (GskGLShader  *shader)
+{
+  return shader->n_required_sources;
+}
+
+/**
+ * gsk_glshader_set_n_required_sources:
+ * @shader: A #GskGLShader
+ * @n_required_sources: The number of sources.
+ *
+ * Sets the number of texture sources that the shader requires. This can be used
+ * to signal to other users that this shader needs this much input. 
+ */
+void
+gsk_glshader_set_n_required_sources (GskGLShader  *shader,
+                                     int           n_required_sources)
+{
+  shader->n_required_sources = n_required_sources;
+}
+
+static int
+uniform_type_size (GskGLUniformType type)
+{
+  switch (type)
+    {
+    case GSK_GLUNIFORM_TYPE_FLOAT:
+      return sizeof (float);
+
+    case GSK_GLUNIFORM_TYPE_INT:
+      return sizeof (gint32);
+
+    case GSK_GLUNIFORM_TYPE_UINT:
+    case GSK_GLUNIFORM_TYPE_BOOL:
+      return sizeof (guint32);
+
+    case GSK_GLUNIFORM_TYPE_VEC2:
+      return sizeof (float) * 2;
+
+    case GSK_GLUNIFORM_TYPE_VEC3:
+      return sizeof (float) * 3;
+
+    case GSK_GLUNIFORM_TYPE_VEC4:
+      return sizeof (float) * 4;
+
+    case GSK_GLUNIFORM_TYPE_NONE:
+    default:
+      g_assert_not_reached ();
+      return 0;
+
+    }
+}
+
+/**
+ * gsk_glshader_add_uniform:
+ * @shader: A #GskGLShader
+ * @name: Then name of the uniform.
+ * @type: The uniform type
+ *
+ * This declares that the shader uses a uniform of a particular @name
+ * and @type. You need to declare each uniform that your shader
+ * uses or you will not be able to pass data to it.
+ */
+void
+gsk_glshader_add_uniform (GskGLShader     *shader,
+                          const char      *name,
+                          GskGLUniformType type)
+{
+  GskGLUniform uniform = {
+    g_strdup (name),
+    type,
+    shader->uniforms_size
+  };
+
+  shader->uniforms_size += uniform_type_size (type);
+
+  g_array_append_val (shader->uniforms, uniform);
+}
+
+/**
+ * gsk_glshader_get_n_uniforms:
+ * @shader: A #GskGLShader
+ *
+ * Get the number of declared uniforms for this shader.
+ *
+ * Returns: The nr of declared uniforms
+ */
+int
+gsk_glshader_get_n_uniforms (GskGLShader     *shader)
+{
+  return shader->uniforms->len;
+}
+
+/**
+ * gsk_glshader_get_uniform_name:
+ * @shader: A #GskGLShader
+ * @idx: A zero-based index of the uniforms
+ *
+ * Get the name of a declared uniforms for this shader at index @indx.
+ *
+ * Returns: (transfer none): The name of the declared uniform
+ */
+const char *
+gsk_glshader_get_uniform_name (GskGLShader     *shader,
+                                int              idx)
+{
+  return g_array_index (shader->uniforms, GskGLUniform, idx).name;
+}
+
+/**
+ * gsk_glshader_get_uniform_type:
+ * @shader: A #GskGLShader
+ * @idx: A zero-based index of the uniforms
+ *
+ * Get the type of a declared uniforms for this shader at index @indx.
+ *
+ * Returns: The type of the declared uniform
+ */
+GskGLUniformType
+gsk_glshader_get_uniform_type (GskGLShader     *shader,
+                                  int              idx)
+{
+  return g_array_index (shader->uniforms, GskGLUniform, idx).type;
+}
+
+/**
+ * gsk_glshader_get_uniform_offset:
+ * @shader: A #GskGLShader
+ * @idx: A zero-based index of the uniforms
+ *
+ * Get the offset into the data block where data for this uniforms is stored.
+ *
+ * Returns: The data offset
+ */
+int
+gsk_glshader_get_uniform_offset (GskGLShader     *shader,
+                                 int              idx)
+{
+  return g_array_index (shader->uniforms, GskGLUniform, idx).offset;
+}
+
+const GskGLUniform *
+gsk_glshader_get_uniforms (GskGLShader *shader,
+                           int         *n_uniforms)
+{
+  *n_uniforms = shader->uniforms->len;
+  return &g_array_index (shader->uniforms, GskGLUniform, 0);
+}
+
+/**
+ * gsk_glshader_get_uniforms_size:
+ * @shader: A #GskGLShader
+ *
+ * Get the size of the data block used to specify uniform data for this shader.
+ *
+ * Returns: The size of the data block
+ */
+int
+gsk_glshader_get_uniforms_size (GskGLShader *shader)
+{
+  return shader->uniforms_size;
+}
+
+static const GskGLUniform *
+gsk_glshader_find_uniform (GskGLShader *shader,
+                           const char *name)
+{
+  int i;
+  for (i = 0; i < shader->uniforms->len; i++)
+    {
+      const GskGLUniform *u = &g_array_index (shader->uniforms, GskGLUniform, i);
+      if (strcmp (u->name, name) == 0)
+        return u;
+    }
+
+  return NULL;
+}
+
+/**
+ * gsk_glshader_format_uniform_data_va:
+ * @shader: A #GskGLShader
+ * @uniforms: %NULL terminated va_list with (name, pointer-to-data) arguments pairs
+ *
+ * Formats the uniform data as needed for feeding the named uniforms values into the shader.
+ * The argument list is a list of pairs of names, and pointers to data of the types
+ * that match the declared uniforms (i.e. `float *` for float uniforms and `graphene_vec4_t *` f
+ * or vec3 uniforms).
+ *
+ * Returns: (transfer full): A newly allocated block of data which can be passed to gsk_glshader_node_new().
+ */
+guchar *
+gsk_glshader_format_uniform_data_va (GskGLShader *shader,
+                                     va_list uniforms)
+{
+  guchar *args = g_malloc0 (shader->uniforms_size);
+  const char *name;
+
+  while ((name = va_arg (uniforms, const char *)) != NULL)
+    {
+      const GskGLUniform *u;
+      gpointer value = va_arg (uniforms, gpointer);
+      guchar *args_dest;
+
+      u = gsk_glshader_find_uniform (shader, name);
+      if (u == NULL)
+        {
+          /* This isn't really an error, because we can easily imaging
+             a shader interface that have input which isn't needed for
+             a particular shader */
+          g_debug ("No uniform named `%s` in shader", name);
+          continue;
+        }
+
+      args_dest = args + u->offset;
+
+      /* We use pointers-to-value so that all values are the same
+         size, otherwise we couldn't handle the missing uniform case above */
+
+      switch (u->type)
+        {
+        case GSK_GLUNIFORM_TYPE_FLOAT:
+          *(float *)args_dest = *(float *)value;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_INT:
+          *(gint32 *)args_dest = *(gint32 *)value;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_UINT:
+          *(guint32 *)args_dest = *(guint32 *)value;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_BOOL:
+          *(guint32 *)args_dest = *(gboolean *)value;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_VEC2:
+          graphene_vec2_to_float ((const graphene_vec2_t *)value,
+                                  (float *)args_dest);
+          break;
+
+        case GSK_GLUNIFORM_TYPE_VEC3:
+          graphene_vec3_to_float ((const graphene_vec3_t *)value,
+                                  (float *)args_dest);
+          break;
+
+        case GSK_GLUNIFORM_TYPE_VEC4:
+          graphene_vec4_to_float ((const graphene_vec4_t *)value,
+                                  (float *)args_dest);
+          break;
+
+        case GSK_GLUNIFORM_TYPE_NONE:
+        default:
+          g_assert_not_reached ();
+        }
+    }
+
+  return args;
+}

gsk/gskglshader.h

@@ -0,0 +1,70 @@
+/* GSK - The GTK Scene Kit
+ *
+ * Copyright 2020  Red Hat Inc
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef __GSK_GLSHADER_H__
+#define __GSK_GLSHADER_H__
+
+#if !defined (__GSK_H_INSIDE__) && !defined (GTK_COMPILATION)
+#error "Only <gsk/gsk.h> can be included directly."
+#endif
+
+#include <stdarg.h>
+
+#include <gsk/gsktypes.h>
+#include <gsk/gskenums.h>
+
+G_BEGIN_DECLS
+
+#define GSK_TYPE_GLSHADER (gsk_glshader_get_type ())
+
+GDK_AVAILABLE_IN_ALL
+G_DECLARE_FINAL_TYPE (GskGLShader, gsk_glshader, GSK, GLSHADER, GObject)
+
+GDK_AVAILABLE_IN_ALL
+GskGLShader *    gsk_glshader_new                     (const char       *sourcecode);
+GDK_AVAILABLE_IN_ALL
+const char *     gsk_glshader_get_sourcecode          (GskGLShader      *shader);
+GDK_AVAILABLE_IN_ALL
+int              gsk_glshader_get_n_required_sources  (GskGLShader      *shader);
+GDK_AVAILABLE_IN_ALL
+void             gsk_glshader_set_n_required_sources  (GskGLShader      *shader,
+                                                       int               n_required_sources);
+GDK_AVAILABLE_IN_ALL
+void             gsk_glshader_add_uniform             (GskGLShader      *shader,
+                                                       const char       *name,
+                                                       GskGLUniformType  type);
+GDK_AVAILABLE_IN_ALL
+int              gsk_glshader_get_n_uniforms          (GskGLShader      *shader);
+GDK_AVAILABLE_IN_ALL
+const char *     gsk_glshader_get_uniform_name        (GskGLShader      *shader,
+                                                       int               idx);
+GDK_AVAILABLE_IN_ALL
+GskGLUniformType gsk_glshader_get_uniform_type        (GskGLShader      *shader,
+                                                       int               idx);
+GDK_AVAILABLE_IN_ALL
+int              gsk_glshader_get_uniform_offset      (GskGLShader      *shader,
+                                                       int               idx);
+GDK_AVAILABLE_IN_ALL
+int              gsk_glshader_get_uniforms_size       (GskGLShader      *shader);
+GDK_AVAILABLE_IN_ALL
+guchar *         gsk_glshader_format_uniform_data_va  (GskGLShader  *shader,
+                                                       va_list       uniforms);
+
+G_END_DECLS
+
+#endif /* __GSK_GLSHADER_H__ */

gsk/gskglshaderprivate.h

@@ -0,0 +1,17 @@
+#ifndef __GSK_GL_UNIFORM_H__
+#define __GSK_GL_UNIFORM_H__
+
+#include "gskglshader.h"
+
+typedef struct
+{
+  char *name;
+  GskGLUniformType type;
+  int offset;
+} GskGLUniform;
+
+
+const GskGLUniform *gsk_glshader_get_uniforms (GskGLShader *shader,
+                                               int         *n_uniforms);
+
+#endif

gsk/gskrendernode.h

@@ -25,6 +25,7 @@
 
 #include <gsk/gskroundedrect.h>
 #include <gsk/gsktypes.h>
+#include <gsk/gskglshader.h>
 #include <gtk/css/gtkcss.h>
 
 G_BEGIN_DECLS
@@ -122,6 +123,7 @@ GskRenderNode *         gsk_render_node_deserialize             (GBytes
 #define GSK_TYPE_CROSS_FADE_NODE                (gsk_cross_fade_node_get_type())
 #define GSK_TYPE_TEXT_NODE                      (gsk_text_node_get_type())
 #define GSK_TYPE_BLUR_NODE                      (gsk_blur_node_get_type())
+#define GSK_TYPE_GLSHADER_NODE                  (gsk_glshader_node_get_type())
 
 typedef struct _GskDebugNode                    GskDebugNode;
 typedef struct _GskColorNode                    GskColorNode;
@@ -146,6 +148,7 @@ typedef struct _GskBlendNode                    GskBlendNode;
 typedef struct _GskCrossFadeNode                GskCrossFadeNode;
 typedef struct _GskTextNode                     GskTextNode;
 typedef struct _GskBlurNode                     GskBlurNode;
+typedef struct _GskGLShaderNode                 GskGLShaderNode;
 
 GDK_AVAILABLE_IN_ALL
 GType                   gsk_debug_node_get_type                 (void) G_GNUC_CONST;
@@ -451,6 +454,28 @@ GskRenderNode *         gsk_blur_node_get_child                 (GskRenderNode
 GDK_AVAILABLE_IN_ALL
 float                   gsk_blur_node_get_radius                (GskRenderNode            *node);
 
+GDK_AVAILABLE_IN_ALL
+GType                   gsk_glshader_node_get_type              (void) G_GNUC_CONST;
+GDK_AVAILABLE_IN_ALL
+GskRenderNode *         gsk_glshader_node_new                   (GskGLShader              *shader,
+                                                                 const graphene_rect_t    *bounds,
+                                                                 guchar                   *uniform_data,
+                                                                 GskRenderNode            *fallback,
+                                                                 GskRenderNode           **children,
+                                                                 int                       n_children);
+GDK_AVAILABLE_IN_ALL
+GskRenderNode *         gsk_glshader_node_get_fallback_child    (GskRenderNode            *node);
+GDK_AVAILABLE_IN_ALL
+guint                   gsk_glshader_node_get_n_children        (GskRenderNode            *node);
+GDK_AVAILABLE_IN_ALL
+GskRenderNode *         gsk_glshader_node_get_child             (GskRenderNode            *node,
+                                                                 int                       idx);
+GDK_AVAILABLE_IN_ALL
+const guchar *          gsk_glshader_node_get_uniform_data      (GskRenderNode            *node);
+GDK_AVAILABLE_IN_ALL
+GskGLShader *           gsk_glshader_node_get_shader            (GskRenderNode            *node);
+
+
 G_END_DECLS
 
 #endif /* __GSK_RENDER_NODE_H__ */

gsk/gskrendernodeimpl.c

@@ -4470,6 +4470,244 @@ gsk_debug_node_get_message (GskRenderNode *node)
   return self->message;
 }
 
+/*** GSK_GLSHADER_NODE ***/
+
+struct _GskGLShaderNode
+{
+  GskRenderNode render_node;
+
+  GskGLShader *shader;
+  union {
+    guchar inlined[8]; /* Most shaders have few args, so avoid extra alloc */
+    guchar *external;
+  } args;
+  GskRenderNode *fallback;
+  GskRenderNode **children;
+  guint n_children;
+};
+
+static void
+gsk_glshader_node_finalize (GskRenderNode *node)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+  GskRenderNodeClass *parent_class = g_type_class_peek (g_type_parent (GSK_TYPE_GLSHADER_NODE));
+  int uniforms_size;
+
+  for (guint i = 0; i < self->n_children; i++)
+    gsk_render_node_unref (self->children[i]);
+  g_free (self->children);
+
+  gsk_render_node_unref (self->fallback);
+
+  uniforms_size = gsk_glshader_get_uniforms_size (self->shader);
+  if (uniforms_size > sizeof (self->args.inlined))
+    g_free (self->args.external);
+
+  g_object_unref (self->shader);
+
+  parent_class->finalize (node);
+}
+
+static void
+gsk_glshader_node_draw (GskRenderNode *node,
+                        cairo_t       *cr)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+
+  gsk_render_node_draw (self->fallback, cr);
+}
+
+static void
+gsk_glshader_node_diff (GskRenderNode  *node1,
+                        GskRenderNode  *node2,
+                        cairo_region_t *region)
+{
+  GskGLShaderNode *self1 = (GskGLShaderNode *) node1;
+  GskGLShaderNode *self2 = (GskGLShaderNode *) node2;
+  int uniforms_size = gsk_glshader_get_uniforms_size (self1->shader);
+
+  if (graphene_rect_equal (&node1->bounds, &node2->bounds) &&
+      self1->shader == self2->shader &&
+      ((uniforms_size <= sizeof (self1->args.inlined)) ?
+       memcmp (&self1->args.inlined[0], &self2->args.inlined[0], uniforms_size) == 0:
+       memcmp (self1->args.external, self2->args.external, uniforms_size) == 0) &&
+      self1->n_children == self2->n_children)
+    {
+      gsk_render_node_diff (self1->fallback, self2->fallback, region);
+
+      for (guint i = 0; i < self1->n_children; i++)
+        {
+          if (self1->children[i] != self2->children[i])
+            {
+              gsk_render_node_diff_impossible (node1, node2, region);
+              break;
+            }
+        }
+    }
+  else
+    {
+      gsk_render_node_diff_impossible (node1, node2, region);
+    }
+}
+
+/**
+ * gsk_glshader_node_new:
+ * @shader: the #GskGLShader
+ * @bounds: the rectangle to render the shader into
+ * @uniform_data: Data for the uniforms
+ * @fallback: Render node to use if OpenGL is not supported
+ * @children: List of child nodes, these will be rendered to textures and used as input.
+ * @n_children: Length of @children (currenly the GL backend only supports max 4 children)
+ *
+ * Creates a #GskRenderNode that will render the given @gl_program into the area given by @bounds.
+ * The @uniform_data is a block of data to use for uniform input, as per types and offsets
+ * defined by the @shader. Normally this is generated by gsk_glshader_format_uniform_data_va().
+ *
+ * See #GskGLShader for details about how the shader should be written.
+ *
+ * All the children will be rendered into textures, if they aren't already #GskTextureNode:s
+ * then they will be used directly. These textures will be sent as input to the shader.
+ *
+ * If the backend doesn't support GL shaders, or if there is any problem when compiling
+ * the shader, then the fallback shader node will be used instead.
+ *
+ * Returns: (transfer full) (type GskGLShaderNode): A new #GskRenderNode
+ */
+GskRenderNode *
+gsk_glshader_node_new (GskGLShader           *shader,
+                       const graphene_rect_t *bounds,
+                       guchar                *uniform_data,
+                       GskRenderNode         *fallback,
+                       GskRenderNode        **children,
+                       int                    n_children)
+{
+  GskGLShaderNode *self;
+  GskRenderNode *node;
+  int uniforms_size;
+
+  g_return_val_if_fail (bounds != NULL, NULL);
+
+  self = gsk_render_node_alloc (GSK_GLSHADER_NODE);
+  node = (GskRenderNode *) self;
+
+  graphene_rect_init_from_rect (&node->bounds, bounds);
+  self->shader = g_object_ref (shader);
+
+  uniforms_size = gsk_glshader_get_uniforms_size (shader);
+  if (uniforms_size <= sizeof (self->args.inlined))
+    memcpy (self->args.inlined, uniform_data, uniforms_size);
+  else
+    self->args.external = g_memdup (uniform_data, uniforms_size);
+
+  self->fallback = gsk_render_node_ref (fallback);
+
+  self->n_children = n_children;
+  if (n_children > 0)
+    {
+      self->children = g_malloc_n (n_children, sizeof (GskRenderNode *));
+      for (guint i = 0; i < n_children; i++)
+        self->children[i] = gsk_render_node_ref (children[i]);
+    }
+
+  return node;
+}
+
+/**
+ * gsk_glshader_node_get_fallback_child:
+ * @node: (type GskGLShaderNode): a #GskRenderNode for a gl shader
+ *
+ * Gets the fallback child node
+ *
+ * Returns: (transfer none): The fallback node
+ */
+GskRenderNode *
+gsk_glshader_node_get_fallback_child (GskRenderNode *node)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_GLSHADER_NODE), NULL);
+
+  return self->fallback;
+}
+
+/**
+ * gsk_glshader_node_get_n_children:
+ * @node: (type GskGLShaderNode): a #GskRenderNode for a gl shader
+ *
+ * Returns the number of (non-fallback) children
+ *
+ * Returns: The number of children
+ */
+guint
+gsk_glshader_node_get_n_children (GskRenderNode *node)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_GLSHADER_NODE), 0);
+
+  return self->n_children;
+}
+
+/**
+ * gsk_glshader_node_get_child:
+ * @node: (type GskGLShaderNode): a #GskRenderNode for a gl shader
+ * @idx: the position of the child to get
+ *
+ * Gets one of the (non-fallback) children.
+ *
+ * Returns: (transfer none): the @idx'th child of @node
+ */
+GskRenderNode *
+gsk_glshader_node_get_child (GskRenderNode *node,
+                             int            idx)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_GLSHADER_NODE), NULL);
+  g_return_val_if_fail (idx < self->n_children, NULL);
+
+  return self->children[idx];
+}
+
+/**
+ * gsk_glshader_node_get_shader:
+ * @node: (type GskGLShaderNode): a #GskRenderNode for a gl shader
+ *
+ * Gets shader code for the node.
+ *
+ * Returns: (transfer none): the #GskGLShader shader
+ */
+GskGLShader *
+gsk_glshader_node_get_shader (GskRenderNode *node)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_GLSHADER_NODE), 0);
+
+  return self->shader;
+}
+
+/**
+ * gsk_glshader_node_get_uniform_data:
+ * @node: (type GskGLShaderNode): a #GskRenderNode for a gl shader
+ *
+ * Gets args for the node.
+ */
+const guchar *
+gsk_glshader_node_get_uniform_data (GskRenderNode *node)
+{
+  GskGLShaderNode *self = (GskGLShaderNode *) node;
+  int uniforms_size;
+
+  g_return_val_if_fail (GSK_IS_RENDER_NODE_TYPE (node, GSK_GLSHADER_NODE), NULL);
+
+  uniforms_size = gsk_glshader_get_uniforms_size (self->shader);
+  if (uniforms_size > sizeof (self->args.inlined))
+    return self->args.external;
+  else
+    return &self->args.inlined[0];
+}
+
 GType gsk_render_node_types[GSK_RENDER_NODE_TYPE_N_TYPES];
 
 #ifndef I_
@@ -4506,6 +4744,7 @@ GSK_DEFINE_RENDER_NODE_TYPE (gsk_blend_node, GSK_BLEND_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_cross_fade_node, GSK_CROSS_FADE_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_text_node, GSK_TEXT_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_blur_node, GSK_BLUR_NODE)
+GSK_DEFINE_RENDER_NODE_TYPE (gsk_glshader_node, GSK_GLSHADER_NODE)
 GSK_DEFINE_RENDER_NODE_TYPE (gsk_debug_node, GSK_DEBUG_NODE)
 
 static void
@@ -4863,6 +5102,22 @@ gsk_render_node_init_types_once (void)
     gsk_render_node_types[GSK_BLUR_NODE] = node_type;
   }
 
+  {
+    const GskRenderNodeTypeInfo node_info =
+    {
+      GSK_GLSHADER_NODE,
+      sizeof (GskGLShaderNode),
+      NULL,
+      gsk_glshader_node_finalize,
+      gsk_glshader_node_draw,
+      NULL,
+      gsk_glshader_node_diff,
+    };
+
+    GType node_type = gsk_render_node_type_register_static (I_("GskGLShaderNode"), &node_info);
+    gsk_render_node_types[GSK_GLSHADER_NODE] = node_type;
+  }
+
   {
     const GskRenderNodeTypeInfo node_info =
     {

gsk/gskrendernodeparser.c

@@ -358,6 +358,13 @@ parse_double (GtkCssParser *parser,
   return gtk_css_parser_consume_number (parser, out_double);
 }
 
+static gboolean
+parse_int (GtkCssParser *parser,
+           gpointer      out_int)
+{
+  return gtk_css_parser_consume_integer (parser, out_int);
+}
+
 static gboolean
 parse_point (GtkCssParser *parser,
              gpointer      out_point)
@@ -824,9 +831,9 @@ clear_node (gpointer inout_node)
 static GskRenderNode *
 parse_container_node (GtkCssParser *parser)
 {
-  GskRenderNode *node;
   GPtrArray *nodes;
   const GtkCssToken *token;
+  GskRenderNode *node;
 
   nodes = g_ptr_array_new_with_free_func ((GDestroyNotify) gsk_render_node_unref);
 
@@ -1089,6 +1096,251 @@ parse_inset_shadow_node (GtkCssParser *parser)
   return gsk_inset_shadow_node_new (&outline, &color, dx, dy, spread, blur);
 }
 
+typedef struct {
+  GskGLUniformType type;
+  char *name;
+  union {
+    int i;
+    double v[4];
+  } value;
+} Uniform;
+
+static gboolean
+parse_uniform_decl (GtkCssParser *parser, Uniform *decl)
+{
+  Uniform decls[] = {
+    { GSK_GLUNIFORM_TYPE_FLOAT, (char *) "float" },
+    { GSK_GLUNIFORM_TYPE_INT, (char *) "int" },
+    { GSK_GLUNIFORM_TYPE_UINT, (char*) "uint" },
+    { GSK_GLUNIFORM_TYPE_BOOL, (char *) "bool" },
+    { GSK_GLUNIFORM_TYPE_VEC2, (char *) "vec2" },
+    { GSK_GLUNIFORM_TYPE_VEC3, (char *) "vec3" },
+    { GSK_GLUNIFORM_TYPE_VEC4, (char *) "vec4" },
+  };
+  int i;
+
+  for (i = 0; i < G_N_ELEMENTS (decls); i++)
+    {
+      if (gtk_css_parser_try_ident (parser, decls[i].name))
+        {
+          decl->type = decls[i].type;
+          decl->name = gtk_css_parser_consume_ident (parser);
+
+          gtk_css_parser_try_token (parser, GTK_CSS_TOKEN_COMMA);
+
+          return TRUE;
+        }
+    }
+
+  return FALSE;
+}
+
+static void
+clear_uniform_decl (gpointer data)
+{
+  Uniform *decl = data;
+  g_free (decl->name);
+}
+
+static gboolean
+parse_uniforms (GtkCssParser *parser, gpointer data)
+{
+  GArray *uniforms = data;
+  Uniform decl;
+
+  while (parse_uniform_decl (parser, &decl))
+    g_array_append_val (uniforms, decl);
+
+  return TRUE;
+}
+
+static void
+clear_array (gpointer data)
+{
+  GArray *array = data;
+  g_array_set_size (array, 0);
+}
+
+static gboolean
+parse_uniform_value (GtkCssParser *parser, Uniform *uniform)
+{
+  switch (uniform->type)
+    {
+    case GSK_GLUNIFORM_TYPE_FLOAT:
+      if (!gtk_css_parser_consume_number (parser, &uniform->value.v[0]))
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_INT:
+      if (!gtk_css_parser_consume_integer (parser, &uniform->value.i))
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_UINT:
+      if (!gtk_css_parser_consume_integer (parser, &uniform->value.i) ||
+          uniform->value.i < 0)
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_BOOL:
+      if (!gtk_css_parser_consume_integer (parser, &uniform->value.i) ||
+          (uniform->value.i != 0 && uniform->value.i != 1))
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_VEC2:
+      if (!gtk_css_parser_consume_number (parser, &uniform->value.v[0]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[1]))
+          return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_VEC3:
+      if (!gtk_css_parser_consume_number (parser, &uniform->value.v[0]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[1]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[2]))
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_VEC4:
+      if (!gtk_css_parser_consume_number (parser, &uniform->value.v[0]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[1]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[2]) ||
+          !gtk_css_parser_consume_number (parser, &uniform->value.v[3]))
+        return FALSE;
+      break;
+
+    case GSK_GLUNIFORM_TYPE_NONE:
+    default:
+      g_assert_not_reached ();
+      break;
+    }
+
+  gtk_css_parser_try_token (parser, GTK_CSS_TOKEN_COMMA);
+
+  return TRUE;
+}
+
+static gboolean
+parse_uniform_data (GtkCssParser *parser, gpointer data)
+{
+  GArray *uniforms = data;
+  int i;
+
+  for (i = 0; i < uniforms->len; i++)
+    {
+      Uniform *uniform = &g_array_index (uniforms, Uniform, i);
+      if (!parse_uniform_value (parser, uniform))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
+static GskRenderNode *
+parse_glshader_node (GtkCssParser *parser)
+{
+  graphene_rect_t bounds = GRAPHENE_RECT_INIT (0, 0, 50, 50);
+  char *sourcecode = NULL;
+  int required_sources = 0;
+  GskRenderNode *fallback = NULL;
+  GskRenderNode *child[4] = { NULL, };
+  GArray *uniforms = g_array_new (FALSE, FALSE, sizeof (Uniform));
+  const Declaration declarations[] = {
+    { "bounds", parse_rect, NULL, &bounds },
+    { "sourcecode", parse_string, NULL, &sourcecode },
+    { "required-sources", parse_int, NULL, &required_sources },
+    { "uniforms", parse_uniforms, clear_array, uniforms },
+    { "uniform-data", parse_uniform_data, clear_array, uniforms },
+    { "fallback", parse_node, clear_node, &fallback },
+    { "child1", parse_node, clear_node, &child[0] },
+    { "child2", parse_node, clear_node, &child[1] },
+    { "child3", parse_node, clear_node, &child[2] },
+    { "child4", parse_node, clear_node, &child[3] },
+  };
+  GskGLShader *shader;
+  GskRenderNode *node;
+  guchar *uniform_data;
+  int len, i;
+
+  g_array_set_clear_func (uniforms, clear_uniform_decl);
+
+  parse_declarations (parser, declarations, G_N_ELEMENTS(declarations));
+
+  for (len = 0; len < 4; len++)
+    {
+      if (child[len] == NULL)
+        break;
+    }
+
+  shader = gsk_glshader_new (sourcecode);
+  gsk_glshader_set_n_required_sources (shader, required_sources);
+  for (i = 0; i < uniforms->len; i++)
+    {
+      Uniform *uniform = &g_array_index (uniforms, Uniform, i);
+      gsk_glshader_add_uniform (shader, uniform->name, uniform->type);
+    }
+
+  uniform_data = g_new (guchar, gsk_glshader_get_uniforms_size (shader));
+  for (i = 0; i < uniforms->len; i++)
+    {
+      Uniform *uniform = &g_array_index (uniforms, Uniform, i);
+      guchar *dest;
+
+      dest = uniform_data + gsk_glshader_get_uniform_offset (shader, i);
+
+      switch (uniform->type)
+        {
+        case GSK_GLUNIFORM_TYPE_FLOAT:
+          *(float *)dest = uniform->value.v[0];
+          break;
+
+        case GSK_GLUNIFORM_TYPE_INT:
+          *(gint32 *)dest = uniform->value.i;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_UINT:
+          *(guint32 *)dest = uniform->value.i;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_BOOL:
+          *(guint32 *)dest = uniform->value.i;
+          break;
+
+        case GSK_GLUNIFORM_TYPE_VEC4:
+          ((float *)dest)[3] = uniform->value.v[3];
+          G_GNUC_FALLTHROUGH;
+
+        case GSK_GLUNIFORM_TYPE_VEC3:
+          ((float *)dest)[2] = uniform->value.v[2];
+          G_GNUC_FALLTHROUGH;
+
+        case GSK_GLUNIFORM_TYPE_VEC2:
+          ((float *)dest)[1] = uniform->value.v[1];
+          ((float *)dest)[0] = uniform->value.v[0];
+          break;
+
+        case GSK_GLUNIFORM_TYPE_NONE:
+        default:
+          g_assert_not_reached ();
+        }
+    }
+
+  node = gsk_glshader_node_new (shader, &bounds, uniform_data,
+                                fallback, child, len);
+
+  g_array_unref (uniforms);
+  g_free (uniform_data);
+  g_object_unref (shader);
+
+  for (i = 0; i < 4; i++)
+    {
+      if (child[i])
+        gsk_render_node_unref (child[i]);
+    }
+
+  return node;
+}
+
 static GskRenderNode *
 parse_border_node (GtkCssParser *parser)
 {
@@ -1603,6 +1855,7 @@ parse_node (GtkCssParser *parser,
     { "text", parse_text_node },
     { "texture", parse_texture_node },
     { "transform", parse_transform_node },
+    { "glshader", parse_glshader_node },
   };
   GskRenderNode **node_p = out_node;
   guint i;
@@ -1837,6 +2090,51 @@ append_point (GString                *str,
   string_append_double (str, p->y);
 }
 
+static void
+append_string (GString    *str,
+               const char *string)
+{
+  gsize len;
+
+  g_return_if_fail (str != NULL);
+  g_return_if_fail (string != NULL);
+
+  g_string_append_c (str, '"');
+
+  do {
+    len = strcspn (string, "\\\"\n\r\f");
+    g_string_append_len (str, string, len);
+    string += len;
+    switch (*string)
+      {
+      case '\0':
+        goto out;
+      case '\n':
+        g_string_append (str, "\\A ");
+        break;
+      case '\r':
+        g_string_append (str, "\\D ");
+        break;
+      case '\f':
+        g_string_append (str, "\\C ");
+        break;
+      case '\"':
+        g_string_append (str, "\\\"");
+        break;
+      case '\\':
+        g_string_append (str, "\\\\");
+        break;
+      default:
+        g_assert_not_reached ();
+        break;
+      }
+    string++;
+  } while (*string);
+
+out:
+  g_string_append_c (str, '"');
+}
+
 static void
 append_vec4 (GString               *str,
              const graphene_vec4_t *v)
@@ -1866,6 +2164,19 @@ append_float_param (Printer    *p,
   g_string_append (p->str, ";\n");
 }
 
+static void
+append_int_param (Printer    *p,
+                  const char *param_name,
+                  int         value,
+                  int         default_value)
+{
+  if (value == default_value)
+    return;
+
+  _indent (p);
+  g_string_append_printf (p->str, "%s: %d;\n", param_name, value);
+}
+
 static void
 append_rgba_param (Printer       *p,
                    const char    *param_name,
@@ -1914,6 +2225,18 @@ append_point_param (Printer                *p,
   g_string_append_c (p->str, '\n');
 }
 
+static void
+append_string_param (Printer    *p,
+                     const char *param_name,
+                     const char *value)
+{
+  _indent (p);
+  g_string_append_printf (p->str, "%s: ", param_name);
+  append_string (p->str, value);
+  g_string_append_c (p->str, ';');
+  g_string_append_c (p->str, '\n');
+}
+
 static void
 append_vec4_param (Printer               *p,
                    const char            *param_name,
@@ -2441,6 +2764,131 @@ render_node_print (Printer       *p,
       }
       break;
 
+    case GSK_GLSHADER_NODE:
+      {
+        GskGLShader *shader = gsk_glshader_node_get_shader (node);
+        const guchar *uniform_data = gsk_glshader_node_get_uniform_data (node);
+
+        start_node (p, "glshader");
+
+        append_rect_param (p, "bounds", &node->bounds);
+
+        append_string_param (p, "sourcecode", gsk_glshader_get_sourcecode (shader));
+        append_int_param (p, "required-sources", gsk_glshader_get_n_required_sources (shader), 0);
+
+        if (gsk_glshader_get_n_uniforms (shader) > 0)
+          {
+            GString *decl = g_string_new ("");
+            GString *data = g_string_new ("");
+
+            for (guint i = 0; i < gsk_glshader_get_n_uniforms (shader); i++)
+              {
+                const char *name = gsk_glshader_get_uniform_name (shader, i);
+                int offset = gsk_glshader_get_uniform_offset (shader, i);
+
+                if (i > 0)
+                  {
+                    g_string_append (decl, ", ");
+                    g_string_append (data, ", ");
+                  }
+
+                switch (gsk_glshader_get_uniform_type (shader, i))
+                  {
+                  case GSK_GLUNIFORM_TYPE_NONE:
+                  default:
+                    g_assert_not_reached ();
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_FLOAT:
+                    {
+                      float value = *(float *)(uniform_data + offset);
+                      g_string_append_printf (decl, "float %s", name);
+                      g_string_append_printf (data, "%f", value);
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_INT:
+                    {
+                      gint32 value = *(gint32 *)(uniform_data + offset);
+                      g_string_append_printf (decl, "int %s", name);
+                      g_string_append_printf (data, "%d", value);
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_UINT:
+                    {
+                      guint32 value = *(guint32 *)(uniform_data + offset);
+                      g_string_append_printf (decl, "uint %s", name);
+                      g_string_append_printf (data, "%u", value);
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_BOOL:
+                    {
+                      gboolean value = *(gboolean *)(uniform_data + offset);
+                      g_string_append_printf (decl, "bool %s", name);
+                      g_string_append_printf (data, "%d", value);
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_VEC2:
+                    {
+                      graphene_vec2_t *v = (graphene_vec2_t *)(uniform_data + offset);
+                      g_string_append_printf (decl, "vec2 %s", name);
+                      g_string_append_printf (data, "%f %f",
+                                              graphene_vec2_get_x (v),
+                                              graphene_vec2_get_y (v));
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_VEC3:
+                    {
+                      graphene_vec3_t *v = (graphene_vec3_t *)(uniform_data + offset);
+                      g_string_append_printf (decl, "vec3 %s", name);
+                      g_string_append_printf (data, "%f %f %f",
+                                              graphene_vec3_get_x (v),
+                                              graphene_vec3_get_y (v),
+                                              graphene_vec3_get_z (v));
+                    }
+                    break;
+
+                  case GSK_GLUNIFORM_TYPE_VEC4:
+                    {
+                      graphene_vec4_t *v = (graphene_vec4_t *)(uniform_data + offset);
+                      g_string_append_printf (decl, "vec4 %s", name);
+                      g_string_append_printf (data, "%f %f %f %f",
+                                              graphene_vec4_get_x (v),
+                                              graphene_vec4_get_y (v),
+                                              graphene_vec4_get_z (v),
+                                              graphene_vec4_get_w (v));
+                    }
+                    break;
+                  }
+              }
+            _indent (p);
+            g_string_append_printf (p->str, "uniforms: %s;\n", decl->str);
+            _indent (p);
+            g_string_append_printf (p->str, "uniform-data: %s;\n", data->str);
+
+            g_string_free (decl, TRUE);
+            g_string_free (data, TRUE);
+          }
+
+        append_node_param (p, "fallback", gsk_glshader_node_get_fallback_child (node));
+        for (guint i = 0; i < gsk_glshader_node_get_n_children (node); i ++)
+          {
+            GskRenderNode *child = gsk_glshader_node_get_child (node, i);
+            char *name;
+
+            name = g_strdup_printf ("child%d", i + 1);
+            append_node_param (p, name, child);
+            g_free (name);
+          }
+
+        end_node (p);
+      }
+      break;
+
     case GSK_REPEAT_NODE:
       {
         GskRenderNode *child = gsk_repeat_node_get_child (node);

gsk/gskrendernodeprivate.h

@@ -13,7 +13,7 @@ typedef struct _GskRenderNodeClass GskRenderNodeClass;
  * We don't add an "n-types" value to avoid having to handle
  * it in every single switch.
  */
-#define GSK_RENDER_NODE_TYPE_N_TYPES    (GSK_DEBUG_NODE + 1)
+#define GSK_RENDER_NODE_TYPE_N_TYPES    (GSK_GLSHADER_NODE + 1)
 
 extern GType gsk_render_node_types[];
 

gsk/meson.build

@@ -16,11 +16,13 @@ gsk_private_gl_shaders = [
   'resources/glsl/cross_fade.glsl',
   'resources/glsl/blend.glsl',
   'resources/glsl/repeat.glsl',
+  'resources/glsl/custom.glsl',
 ]
 
 gsk_public_sources = files([
   'gskdiff.c',
   'gskcairorenderer.c',
+  'gskglshader.c',
   'gskrenderer.c',
   'gskrendernode.c',
   'gskrendernodeimpl.c',
@@ -52,6 +54,7 @@ gsk_private_sources = files([
 gsk_public_headers = files([
   'gskcairorenderer.h',
   'gskenums.h',
+  'gskglshader.h',
   'gskrenderer.h',
   'gskrendernode.h',
   'gskroundedrect.h',

gsk/resources/glsl/custom.glsl

@@ -0,0 +1,21 @@
+// VERTEX_SHADER:
+void main() {
+  gl_Position = u_projection * u_modelview * vec4(aPosition, 0.0, 1.0);
+  vUv = vec2(aUv.x, aUv.y);
+}
+
+// FRAGMENT_SHADER:
+// The shader supplies:
+void mainImage(out vec4 fragColor, in vec2 fragCoord, in vec2 resolution, in vec2 uv);
+
+uniform vec2 u_size;
+uniform sampler2D u_source2;
+uniform sampler2D u_source3;
+uniform sampler2D u_source4;
+
+void main() {
+  vec4 fragColor;
+  vec2 fragCoord = vec2(vUv.x * u_size.x, (1.0-vUv.y) * u_size.y);
+  mainImage(fragColor, fragCoord, u_size, vUv);
+  gskSetOutputColor(fragColor);
+}

gsk/vulkan/gskvulkanrenderpass.c

@@ -539,6 +539,10 @@ gsk_vulkan_render_pass_add_node (GskVulkanRenderPass           *self,
       }
       return;
 
+    case GSK_GLSHADER_NODE:
+     gsk_vulkan_render_pass_add_node (self, render, constants, gsk_glshader_node_get_fallback_child (node));
+      return;
+
     case GSK_DEBUG_NODE:
       gsk_vulkan_render_pass_add_node (self, render, constants, gsk_debug_node_get_child (node));
       return;

gtk/gtksnapshot.c

@@ -91,6 +91,14 @@ struct _GtkSnapshotState {
     struct {
       graphene_rect_t bounds;
     } clip;
+    struct {
+      GskGLShader *shader;
+      guchar *args;
+      graphene_rect_t bounds;
+      int n_children;
+      int node_idx;
+      GskRenderNode **nodes;
+    } glshader;
     struct {
       GskRoundedRect bounds;
     } rounded_clip;
@@ -812,6 +820,154 @@ gtk_snapshot_push_clip (GtkSnapshot           *snapshot,
   gtk_graphene_rect_scale_affine (bounds, scale_x, scale_y, dx, dy, &state->data.clip.bounds);
 }
 
+static GskRenderNode *
+maybe_clip (GskRenderNode         *node,
+            const graphene_rect_t *bounds)
+{
+  if (node &&
+      !graphene_rect_contains_rect (bounds, &node->bounds))
+    {
+      return gsk_clip_node_new (node, bounds);
+    }
+
+  return gsk_render_node_ref (node);
+}
+
+static GskRenderNode *
+gtk_snapshot_collect_glshader (GtkSnapshot      *snapshot,
+                               GtkSnapshotState *state,
+                               GskRenderNode   **nodes,
+                               guint             n_nodes)
+{
+  GskRenderNode *shader_node = NULL, *child_node;
+  GdkRGBA transparent = { 0, 0, 0, 0 };
+
+  child_node = gtk_snapshot_collect_default (snapshot, state, nodes, n_nodes);
+
+  if (child_node == NULL)
+    child_node = gsk_color_node_new (&transparent, &state->data.glshader.bounds);
+
+  state->data.glshader.nodes[state->data.glshader.node_idx] = child_node;
+
+  if (state->data.glshader.node_idx != state->data.glshader.n_children)
+    return NULL; /* Not last */
+
+  /* This is the last pop */
+
+  shader_node = NULL;
+
+  if (state->data.glshader.bounds.size.width != 0 &&
+      state->data.glshader.bounds.size.height != 0)
+    {
+      GskRenderNode *fallback_node = maybe_clip (state->data.glshader.nodes[0],
+                                  &state->data.glshader.bounds);
+      shader_node = gsk_glshader_node_new (state->data.glshader.shader,
+                                           &state->data.glshader.bounds,
+                                           state->data.glshader.args,
+                                           fallback_node,
+                                           &state->data.glshader.nodes[1],
+                                           state->data.glshader.n_children);
+      gsk_render_node_unref (fallback_node);
+    }
+
+  g_object_unref (state->data.glshader.shader);
+  for (guint i = 0; i  < state->data.glshader.n_children + 1; i++)
+    gsk_render_node_unref (state->data.glshader.nodes[i]);
+  g_free (state->data.glshader.nodes);
+
+  return shader_node;
+}
+
+/**
+ * gtk_snapshot_push_glshader_va:
+ * @snapshot: a #GtkSnapshot
+ * @shader: The code to run
+ * @bounds: the rectangle to render into
+ * @n_children: The number of extra nodes given as argument to the shader as textures.
+ * @uniforms: Values for the uniforms of the shader in this instance, ending with NULL
+ *
+ * Renders a rectangle with output from a GLSL shader. This is the same as
+ * gtk_snapshot_push_glshader() but with a va_list instead of a varargs argument,
+ * so see that for details.
+ */
+void
+gtk_snapshot_push_glshader_va (GtkSnapshot           *snapshot,
+                               GskGLShader           *shader,
+                               const graphene_rect_t *bounds,
+                               int                    n_children,
+                               va_list                uniforms)
+{
+  GtkSnapshotState *state;
+  float scale_x, scale_y, dx, dy;
+  GskRenderNode **nodes;
+  int node_idx;
+  graphene_rect_t transformed_bounds;
+
+  gtk_snapshot_ensure_affine (snapshot, &scale_x, &scale_y, &dx, &dy);
+
+  state = gtk_snapshot_push_state (snapshot,
+                                   gtk_snapshot_get_current_state (snapshot)->transform,
+                                   gtk_snapshot_collect_glshader);
+  gtk_graphene_rect_scale_affine (bounds, scale_x, scale_y, dx, dy, &transformed_bounds);
+  state->data.glshader.bounds = transformed_bounds;
+  state->data.glshader.shader = g_object_ref (shader);
+  state->data.glshader.args = gsk_glshader_format_uniform_data_va (shader, uniforms);
+  state->data.glshader.n_children = n_children;
+  nodes = g_new0 (GskRenderNode *, n_children + 1);
+  node_idx = n_children; /* We pop in reverse order */
+
+  state->data.glshader.node_idx = node_idx--;
+  state->data.glshader.nodes = nodes;
+
+  for (int i = 0; i  < n_children; i++)
+    {
+      state = gtk_snapshot_push_state (snapshot,
+                                       gtk_snapshot_get_current_state (snapshot)->transform,
+                                       gtk_snapshot_collect_glshader);
+      state->data.glshader.node_idx = node_idx--;
+      state->data.glshader.n_children = n_children;
+      state->data.glshader.nodes = nodes;
+      state->data.glshader.bounds = transformed_bounds;
+    }
+}
+
+/**
+ * gtk_snapshot_push_glshader:
+ * @snapshot: a #GtkSnapshot
+ * @shader: The code to run
+ * @bounds: the rectangle to render into
+ * @n_children: The number of extra nodes given as argument to the shader as textures.
+ * @uniforms: Values for the uniforms of the shader in this instance, ending with NULL
+ *
+ * Push a #GskGLShaderNode with a specific #GskGLShader and a set of uniform values
+ * to use while rendering. Additionally this takes a fallback node and a list of
+ * @n_children other nodes which will be passed to the #GskGLShaderNode.
+ *
+ * The fallback node is used if GLSL shaders are not supported by the backend, or if
+ * there is any problem compiling the shader. The fallback node needs to be pushed
+ * directly after the gtk_snapshot_push_glshader() call up until the first  call to gtk_snapshot_pop().
+ *
+ * If @n_children > 0, then it is expected that you (after the fallback call gtk_snapshot_pop()
+ * @n_children times. Each of these will generate a node that is passed as a child to the
+ * glshader node, which in turn will render these to textures and pass as arguments to the
+ * shader.
+ *
+ * For details on how to write shaders, see #GskGLShader.
+ */
+void
+gtk_snapshot_push_glshader (GtkSnapshot           *snapshot,
+                            GskGLShader           *shader,
+                            const graphene_rect_t *bounds,
+                            int                    n_children,
+                            ...)
+{
+  va_list args;
+
+  va_start (args, n_children);
+  gtk_snapshot_push_glshader_va (snapshot, shader, bounds, n_children, args);
+  va_end (args);
+}
+
 static GskRenderNode *
 gtk_snapshot_collect_rounded_clip (GtkSnapshot      *snapshot,
                                    GtkSnapshotState *state,

gtk/gtksnapshot.h

@@ -99,6 +99,18 @@ GDK_AVAILABLE_IN_ALL
 void            gtk_snapshot_push_cross_fade            (GtkSnapshot            *snapshot,
                                                          double                  progress);
 GDK_AVAILABLE_IN_ALL
+void            gtk_snapshot_push_glshader              (GtkSnapshot            *snapshot,
+                                                         GskGLShader            *shader,
+                                                         const graphene_rect_t  *bounds,
+                                                         int                     n_children,
+                                                         ...);
+GDK_AVAILABLE_IN_ALL
+void            gtk_snapshot_push_glshader_va           (GtkSnapshot            *snapshot,
+                                                         GskGLShader            *shader,
+                                                         const graphene_rect_t  *bounds,
+                                                         int                     n_children,
+                                                         va_list                 uniforms);
+GDK_AVAILABLE_IN_ALL
 void            gtk_snapshot_pop                        (GtkSnapshot            *snapshot);
 
 GDK_AVAILABLE_IN_ALL

gtk/inspector/recorder.c

@@ -171,6 +171,25 @@ create_list_model_for_render_node (GskRenderNode *node)
       return create_render_node_list_model ((GskRenderNode *[2]) { gsk_cross_fade_node_get_start_child (node),
                                                                    gsk_cross_fade_node_get_end_child (node) }, 2);
 
+    case GSK_GLSHADER_NODE:
+      {
+        GListStore *store = G_LIST_STORE (create_render_node_list_model ((GskRenderNode *[1]) { gsk_glshader_node_get_fallback_child (node) }, 1));
+
+        for (guint i = 0; i < gsk_glshader_node_get_n_children (node); i++)
+          {
+            GskRenderNode *child = gsk_glshader_node_get_child (node, i);
+            graphene_rect_t bounds;
+            GdkPaintable *paintable;
+
+            gsk_render_node_get_bounds (child, &bounds);
+            paintable = gtk_render_node_paintable_new (child, &bounds);
+            g_list_store_append (store, paintable);
+            g_object_unref (paintable);
+          }
+
+        return G_LIST_MODEL (store);
+      }
+
     case GSK_CONTAINER_NODE:
       {
         GListStore *store;
@@ -270,6 +289,8 @@ node_type_name (GskRenderNodeType type)
       return "Text";
     case GSK_BLUR_NODE:
       return "Blur";
+    case GSK_GLSHADER_NODE:
+      return "GLShader";
     }
 }
 
@@ -301,6 +322,7 @@ node_name (GskRenderNode *node)
     case GSK_CROSS_FADE_NODE:
     case GSK_TEXT_NODE:
     case GSK_BLUR_NODE:
+    case GSK_GLSHADER_NODE:
       return g_strdup (node_type_name (gsk_render_node_get_node_type (node)));
 
     case GSK_DEBUG_NODE:
@@ -511,6 +533,34 @@ add_color_row (GtkListStore  *store,
   g_object_unref (texture);
 }
 
+static void
+add_int_row (GtkListStore  *store,
+             const char    *name,
+             int            value)
+{
+  char *text = g_strdup_printf ("%d", value);
+  add_text_row (store, name, text);
+  g_free (text);
+}
+
+static void
+add_uint_row (GtkListStore  *store,
+              const char    *name,
+              guint          value)
+{
+  char *text = g_strdup_printf ("%u", value);
+  add_text_row (store, name, text);
+  g_free (text);
+}
+
+static void
+add_boolean_row (GtkListStore  *store,
+                 const char    *name,
+                 gboolean       value)
+{
+  add_text_row (store, name, value ? "TRUE" : "FALSE");
+}
+
 static void
 add_float_row (GtkListStore  *store,
                const char    *name,
@@ -759,6 +809,88 @@ populate_render_node_properties (GtkListStore  *store,
       add_float_row (store, "Radius", gsk_blur_node_get_radius (node));
       break;
 
+    case GSK_GLSHADER_NODE:
+      {
+        GskGLShader *shader = gsk_glshader_node_get_shader (node);
+        const guchar *uniform_data = gsk_glshader_node_get_uniform_data (node);
+        int i;
+
+        add_int_row (store, "Required sources", gsk_glshader_get_n_required_sources (shader));
+        for (i = 0; i < gsk_glshader_get_n_uniforms (shader); i++)
+          {
+            const char *name;
+            int offset;
+            char *title;
+
+            name = gsk_glshader_get_uniform_name (shader, i);
+            title = g_strdup_printf ("Uniform %s", name);
+
+            offset = gsk_glshader_get_uniform_offset (shader, i);
+
+            switch (gsk_glshader_get_uniform_type (shader, i))
+              {
+              case GSK_GLUNIFORM_TYPE_NONE:
+              default:
+                g_assert_not_reached ();
+                break;
+
+              case GSK_GLUNIFORM_TYPE_FLOAT:
+                add_float_row (store, title, *(float *)(uniform_data + offset));
+                break;
+
+              case GSK_GLUNIFORM_TYPE_INT:
+                add_int_row (store, title, *(gint32 *)(uniform_data + offset));
+                break;
+
+              case GSK_GLUNIFORM_TYPE_UINT:
+                add_uint_row (store, title, *(guint32 *)(uniform_data + offset));
+                break;
+
+              case GSK_GLUNIFORM_TYPE_BOOL:
+                add_boolean_row (store, title, *(gboolean *)(uniform_data + offset));
+                break;
+
+              case GSK_GLUNIFORM_TYPE_VEC2:
+                {
+                  graphene_vec2_t *v = (graphene_vec2_t *)(uniform_data + offset);
+                  float x = graphene_vec2_get_x (v);
+                  float y = graphene_vec2_get_x (v);
+                  char *s = g_strdup_printf ("%.2f %.2f", x, y);
+                  add_text_row (store, title, s);
+                  g_free (s);
+                }
+                break;
+
+              case GSK_GLUNIFORM_TYPE_VEC3:
+                {
+                  graphene_vec3_t *v = (graphene_vec3_t *)(uniform_data + offset);
+                  float x = graphene_vec3_get_x (v);
+                  float y = graphene_vec3_get_y (v);
+                  float z = graphene_vec3_get_z (v);
+                  char *s = g_strdup_printf ("%.2f %.2f %.2f", x, y, z);
+                  add_text_row (store, title, s);
+                  g_free (s);
+                }
+                break;
+
+              case GSK_GLUNIFORM_TYPE_VEC4:
+                {
+                  graphene_vec4_t *v = (graphene_vec4_t *)(uniform_data + offset);
+                  float x = graphene_vec4_get_x (v);
+                  float y = graphene_vec4_get_y (v);
+                  float z = graphene_vec4_get_z (v);
+                  float w = graphene_vec4_get_w (v);
+                  char *s = g_strdup_printf ("%.2f %.2f %.2f %.2f", x, y, z, w);
+                  add_text_row (store, title, s);
+                  g_free (s);
+                }
+                break;
+              }
+            g_free (title);
+          }
+      }
+      break;
+
     case GSK_INSET_SHADOW_NODE:
       {
         const GdkRGBA *color = gsk_inset_shadow_node_peek_color (node);