gtk-demo: Add a spinbutton to the path walk

Let the user pick how many arrows to show, to explore performance implications.
Add the randomized segment test
2023-08-17 12:43:46 -04:00 · 2023-08-17 06:37:03 -04:00 · 2023-08-17 06:37:03 -04:00 · 2023-08-17 06:37:03 -04:00 · 2023-08-17 06:37:03 -04:00 · 2023-08-17 06:37:03 -04:00
16 changed files with 1415 additions and 68 deletions
--- a/demos/gtk-demo/demo.gresource.xml
+++ b/demos/gtk-demo/demo.gresource.xml
@@ -337,6 +337,7 @@
    <file>password_entry.c</file>
    <file>path_fill.c</file>
    <file>path_walk.c</file>
+    <file>path_text.c</file>
    <file>peg_solitaire.c</file>
    <file>pickers.c</file>
    <file>printing.c</file>
@@ -426,6 +427,9 @@
    <file>path_walk.ui</file>
    <file compressed="true">path_world.txt</file>
  </gresource>
+  <gresource prefix="/path_text">
+    <file>path_text.ui</file>
+  </gresource>
  <gresource prefix="/org/gtk/Demo4">
    <file>icons/16x16/actions/application-exit.png</file>
    <file>icons/16x16/actions/document-new.png</file>
--- a/demos/gtk-demo/meson.build
+++ b/demos/gtk-demo/meson.build
@@ -74,6 +74,7 @@ demos = files([
  'password_entry.c',
  'path_fill.c',
  'path_walk.c',
+  'path_text.c',
  'peg_solitaire.c',
  'pickers.c',
  'printing.c',
--- a/demos/gtk-demo/path_text.c
+++ b/demos/gtk-demo/path_text.c
@@ -0,0 +1,568 @@
+/* Path/Text
+ *
+ * This demo shows how to use GskPath to transform a path along another path.
+ */
+
+#include <glib/gi18n.h>
+#include <gtk/gtk.h>
+
+#define GTK_TYPE_PATH_WIDGET (gtk_path_widget_get_type ())
+G_DECLARE_FINAL_TYPE (GtkPathWidget, gtk_path_widget, GTK, PATH_WIDGET, GtkWidget)
+
+#define POINT_SIZE 8
+
+enum {
+  PROP_0,
+  PROP_TEXT,
+  PROP_EDITABLE,
+  N_PROPS
+};
+
+struct _GtkPathWidget
+{
+  GtkWidget parent_instance;
+
+  char *text;
+  gboolean editable;
+
+  graphene_point_t points[4];
+
+  guint active_point;
+
+  GskPath *line_path;
+  GskPath *text_path;
+
+  GdkPaintable *background;
+};
+
+struct _GtkPathWidgetClass
+{
+  GtkWidgetClass parent_class;
+};
+
+static GParamSpec *properties[N_PROPS] = { NULL, };
+
+G_DEFINE_TYPE (GtkPathWidget, gtk_path_widget, GTK_TYPE_WIDGET)
+
+static GskPath *
+create_path_from_text (GtkWidget  *widget,
+                       const char *text,
+                       graphene_point_t *out_offset)
+{
+  PangoLayout *layout;
+  PangoFontDescription *desc;
+  GskPathBuilder *builder;
+  GskPath *result;
+
+  layout = gtk_widget_create_pango_layout (widget, text);
+  desc = pango_font_description_from_string ("sans bold 36");
+  pango_layout_set_font_description (layout, desc);
+  pango_font_description_free (desc);
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_layout (builder, layout);
+  result = gsk_path_builder_free_to_path (builder);
+
+  if (out_offset)
+    graphene_point_init (out_offset, 0, - pango_layout_get_baseline (layout) / (double) PANGO_SCALE);
+  g_object_unref (layout);
+
+  return result;
+}
+
+typedef struct
+{
+  GskPath *path;
+  GskPathBuilder *builder;
+  graphene_point_t offset;
+  double scale;
+} GtkPathTransform;
+
+static void
+gtk_path_transform_point (GskPath                *path,
+                          const graphene_point_t *pt,
+                          const graphene_point_t *offset,
+                          float                   scale,
+                          graphene_point_t       *res)
+{
+  graphene_vec2_t tangent;
+  GskPathPoint point;
+
+  if (gsk_path_get_point (path, (pt->x + offset->x) * scale, &point))
+    {
+      gsk_path_point_get_position (&point, path, res);
+      gsk_path_point_get_tangent (&point, path, GSK_PATH_TO_END, &tangent);
+
+      res->x -= (pt->y + offset->y) * scale * graphene_vec2_get_y (&tangent);
+      res->y += (pt->y + offset->y) * scale * graphene_vec2_get_x (&tangent);
+    }
+}
+
+static gboolean
+gtk_path_transform_op (GskPathOperation        op,
+                       const graphene_point_t *pts,
+                       gsize                   n_pts,
+                       gpointer                data)
+{
+  GtkPathTransform *transform = data;
+
+  switch (op)
+  {
+    case GSK_PATH_MOVE:
+      {
+        graphene_point_t res;
+        gtk_path_transform_point (transform->path, &pts[0], &transform->offset, transform->scale, &res);
+        gsk_path_builder_move_to (transform->builder, res.x, res.y);
+      }
+      break;
+
+    case GSK_PATH_LINE:
+      {
+        graphene_point_t res;
+        gtk_path_transform_point (transform->path, &pts[1], &transform->offset, transform->scale, &res);
+        gsk_path_builder_line_to (transform->builder, res.x, res.y);
+      }
+      break;
+
+    case GSK_PATH_QUAD:
+      {
+        graphene_point_t res[2];
+        gtk_path_transform_point (transform->path, &pts[1], &transform->offset, transform->scale, &res[0]);
+        gtk_path_transform_point (transform->path, &pts[2], &transform->offset, transform->scale, &res[1]);
+        gsk_path_builder_quad_to (transform->builder, res[0].x, res[0].y, res[1].x, res[1].y);
+      }
+      break;
+
+    case GSK_PATH_CUBIC:
+      {
+        graphene_point_t res[3];
+        gtk_path_transform_point (transform->path, &pts[1], &transform->offset, transform->scale, &res[0]);
+        gtk_path_transform_point (transform->path, &pts[2], &transform->offset, transform->scale, &res[1]);
+        gtk_path_transform_point (transform->path, &pts[3], &transform->offset, transform->scale, &res[2]);
+        gsk_path_builder_cubic_to (transform->builder, res[0].x, res[0].y, res[1].x, res[1].y, res[2].x, res[2].y);
+      }
+      break;
+
+    case GSK_PATH_CLOSE:
+      gsk_path_builder_close (transform->builder);
+      break;
+
+    default:
+      g_assert_not_reached();
+      return FALSE;
+  }
+
+  return TRUE;
+}
+
+static GskPath *
+gtk_path_transform (GskPath                *line_path,
+                    GskPath                *path,
+                    const graphene_point_t *offset)
+{
+  GtkPathTransform transform = { line_path, gsk_path_builder_new (), *offset };
+  graphene_rect_t bounds;
+
+  gsk_path_get_bounds (path, &bounds);
+  if (bounds.origin.x + bounds.size.width > 0)
+    transform.scale = gsk_path_get_length (line_path) / (bounds.origin.x + bounds.size.width);
+  else
+    transform.scale = 1.0f;
+
+  gsk_path_foreach (path, -1, gtk_path_transform_op, &transform);
+
+  return gsk_path_builder_free_to_path (transform.builder);
+}
+
+static void
+gtk_path_widget_clear_text_path (GtkPathWidget *self)
+{
+  g_clear_pointer (&self->text_path, gsk_path_unref);
+}
+
+static void
+gtk_path_widget_clear_paths (GtkPathWidget *self)
+{
+  gtk_path_widget_clear_text_path (self);
+
+  g_clear_pointer (&self->line_path, gsk_path_unref);
+}
+
+static void
+gtk_path_widget_create_text_path (GtkPathWidget *self)
+{
+  GskPath *path;
+  graphene_point_t offset;
+
+  gtk_path_widget_clear_text_path (self);
+
+  path = create_path_from_text (GTK_WIDGET (self), self->text, &offset);
+  self->text_path = gtk_path_transform (self->line_path, path, &offset);
+
+  gsk_path_unref (path);
+}
+
+static void
+gtk_path_widget_create_paths (GtkPathWidget *self)
+{
+  double width = gtk_widget_get_width (GTK_WIDGET (self));
+  double height = gtk_widget_get_height (GTK_WIDGET (self));
+  GskPathBuilder *builder;
+
+  gtk_path_widget_clear_paths (self);
+
+  if (width <= 0 || height <= 0)
+    return;
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_move_to (builder,
+                            self->points[0].x * width, self->points[0].y * height);
+  gsk_path_builder_cubic_to (builder,
+                             self->points[1].x * width, self->points[1].y * height,
+                             self->points[2].x * width, self->points[2].y * height,
+                             self->points[3].x * width, self->points[3].y * height);
+  self->line_path = gsk_path_builder_free_to_path (builder);
+
+  gtk_path_widget_create_text_path (self);
+}
+
+static void
+gtk_path_widget_allocate (GtkWidget *widget,
+                          int        width,
+                          int        height,
+                          int        baseline)
+{
+  GtkPathWidget *self = GTK_PATH_WIDGET (widget);
+
+  GTK_WIDGET_CLASS (gtk_path_widget_parent_class)->size_allocate (widget, width, height, baseline);
+
+  gtk_path_widget_create_paths (self);
+}
+
+static void
+gtk_path_widget_snapshot (GtkWidget   *widget,
+                          GtkSnapshot *snapshot)
+{
+  GtkPathWidget *self = GTK_PATH_WIDGET (widget);
+  double width = gtk_widget_get_width (widget);
+  double height = gtk_widget_get_height (widget);
+  GskPath *path;
+  GskStroke *stroke;
+  gsize i;
+
+  /* frosted glass the background */
+  gtk_snapshot_push_blur (snapshot, 100);
+  gdk_paintable_snapshot (self->background, snapshot, width, height);
+  gtk_snapshot_append_color (snapshot, &(GdkRGBA) { 1, 1, 1, 0.6 }, &GRAPHENE_RECT_INIT (0, 0, width, height));
+  gtk_snapshot_pop (snapshot);
+
+  /* draw the text */
+  if (self->text_path)
+    {
+      gtk_snapshot_push_fill (snapshot, self->text_path, GSK_FILL_RULE_WINDING);
+      gdk_paintable_snapshot (self->background, snapshot, width, height);
+
+      /* ... with an emboss effect */
+      stroke = gsk_stroke_new (2.0);
+      gtk_snapshot_translate (snapshot, &GRAPHENE_POINT_INIT(1, 1));
+      gtk_snapshot_push_stroke (snapshot, self->text_path, stroke);
+      gtk_snapshot_append_color (snapshot, &(GdkRGBA) { 0, 0, 0, 0.2 }, &GRAPHENE_RECT_INIT (0, 0, width, height));
+      gsk_stroke_free (stroke);
+      gtk_snapshot_pop (snapshot);
+
+      gtk_snapshot_pop (snapshot);
+    }
+
+  if (self->editable && self->line_path)
+    {
+      GskPathBuilder *builder;
+
+      /* draw the control line */
+      stroke = gsk_stroke_new (1.0);
+      gtk_snapshot_push_stroke (snapshot, self->line_path, stroke);
+      gsk_stroke_free (stroke);
+      gtk_snapshot_append_color (snapshot, &(GdkRGBA) { 0, 0, 0, 1 }, &GRAPHENE_RECT_INIT (0, 0, width, height));
+      gtk_snapshot_pop (snapshot);
+
+      /* draw the points */
+      builder = gsk_path_builder_new ();
+      for (i = 0; i < 4; i++)
+        {
+          gsk_path_builder_add_circle (builder, &GRAPHENE_POINT_INIT (self->points[i].x * width, self->points[i].y * height), POINT_SIZE);
+        }
+      path = gsk_path_builder_free_to_path (builder);
+
+      gtk_snapshot_push_fill (snapshot, path, GSK_FILL_RULE_WINDING);
+      gtk_snapshot_append_color (snapshot, &(GdkRGBA) { 1, 1, 1, 1 }, &GRAPHENE_RECT_INIT (0, 0, width, height));
+      gtk_snapshot_pop (snapshot);
+
+      stroke = gsk_stroke_new (1.0);
+      gtk_snapshot_push_stroke (snapshot, path, stroke);
+      gsk_stroke_free (stroke);
+      gtk_snapshot_append_color (snapshot, &(GdkRGBA) { 0, 0, 0, 1 }, &GRAPHENE_RECT_INIT (0, 0, width, height));
+      gtk_snapshot_pop (snapshot);
+
+      gsk_path_unref (path);
+    }
+}
+
+static void
+gtk_path_widget_set_text (GtkPathWidget *self,
+                          const char    *text)
+{
+  if (g_strcmp0 (self->text, text) == 0)
+    return;
+
+  g_free (self->text);
+  self->text = g_strdup (text);
+
+  gtk_path_widget_create_paths (self);
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_TEXT]);
+}
+
+static void
+gtk_path_widget_set_editable (GtkPathWidget *self,
+                              gboolean       editable)
+{
+  if (self->editable == editable)
+    return;
+
+  self->editable = editable;
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_EDITABLE]);
+}
+
+static void
+gtk_path_widget_set_property (GObject      *object,
+                              guint         prop_id,
+                              const GValue *value,
+                              GParamSpec   *pspec)
+
+{
+  GtkPathWidget *self = GTK_PATH_WIDGET (object);
+
+  switch (prop_id)
+    {
+    case PROP_TEXT:
+      gtk_path_widget_set_text (self, g_value_get_string (value));
+      break;
+
+    case PROP_EDITABLE:
+      gtk_path_widget_set_editable (self, g_value_get_boolean (value));
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_path_widget_get_property (GObject    *object,
+                              guint       prop_id,
+                              GValue     *value,
+                              GParamSpec *pspec)
+{
+  GtkPathWidget *self = GTK_PATH_WIDGET (object);
+
+  switch (prop_id)
+    {
+    case PROP_TEXT:
+      g_value_set_string (value, self->text);
+      break;
+
+    case PROP_EDITABLE:
+      g_value_set_boolean (value, self->editable);
+      break;
+
+    default:
+      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
+      break;
+    }
+}
+
+static void
+gtk_path_widget_dispose (GObject *object)
+{
+  GtkPathWidget *self = GTK_PATH_WIDGET (object);
+
+  gtk_path_widget_clear_paths (self);
+
+  G_OBJECT_CLASS (gtk_path_widget_parent_class)->dispose (object);
+}
+
+static void
+gtk_path_widget_class_init (GtkPathWidgetClass *klass)
+{
+  GtkWidgetClass *widget_class = GTK_WIDGET_CLASS (klass);
+  GObjectClass *object_class = G_OBJECT_CLASS (klass);
+
+  object_class->dispose = gtk_path_widget_dispose;
+  object_class->set_property = gtk_path_widget_set_property;
+  object_class->get_property = gtk_path_widget_get_property;
+
+  widget_class->size_allocate = gtk_path_widget_allocate;
+  widget_class->snapshot = gtk_path_widget_snapshot;
+
+  properties[PROP_TEXT] =
+    g_param_spec_string ("text",
+                         "text",
+                         "Text transformed along a path",
+                         NULL,
+                         G_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY | G_PARAM_STATIC_STRINGS);
+
+  properties[PROP_EDITABLE] =
+    g_param_spec_boolean ("editable",
+                          "editable",
+                          "If the path can be edited by the user",
+                          FALSE,
+                          G_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY | G_PARAM_STATIC_STRINGS);
+
+  g_object_class_install_properties (object_class, N_PROPS, properties);
+}
+
+static void
+drag_begin (GtkGestureDrag *gesture,
+            double          x,
+            double          y,
+            GtkPathWidget  *self)
+{
+  graphene_point_t mouse = GRAPHENE_POINT_INIT (x, y);
+  double width = gtk_widget_get_width (GTK_WIDGET (self));
+  double height = gtk_widget_get_height (GTK_WIDGET (self));
+  gsize i;
+
+  for (i = 0; i < 4; i++)
+    {
+      if (graphene_point_distance (&GRAPHENE_POINT_INIT (self->points[i].x * width, self->points[i].y * height), &mouse, NULL, NULL) <= POINT_SIZE)
+        {
+          self->active_point = i;
+          break;
+        }
+    }
+  if (i == 4)
+    {
+      gtk_gesture_set_state (GTK_GESTURE (gesture), GTK_EVENT_SEQUENCE_DENIED);
+      return;
+    }
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+drag_update (GtkGestureDrag *drag,
+             double          offset_x,
+             double          offset_y,
+             GtkPathWidget  *self)
+{
+  double width = gtk_widget_get_width (GTK_WIDGET (self));
+  double height = gtk_widget_get_height (GTK_WIDGET (self));
+  double start_x, start_y;
+
+  gtk_gesture_drag_get_start_point (drag, &start_x, &start_y);
+
+  self->points[self->active_point] = GRAPHENE_POINT_INIT ((start_x + offset_x) / width,
+                                                          (start_y + offset_y) / height);
+  self->points[self->active_point].x = CLAMP (self->points[self->active_point].x, 0, 1);
+  self->points[self->active_point].y = CLAMP (self->points[self->active_point].y, 0, 1);
+
+  gtk_path_widget_create_paths (self);
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+pointer_motion (GtkEventControllerMotion *controller,
+                double                    x,
+                double                    y,
+                GtkPathWidget            *self)
+{
+  GskPathPoint point;
+  graphene_point_t pos;
+
+  if (gsk_path_get_closest_point (self->line_path,
+                                  &GRAPHENE_POINT_INIT (x, y),
+                                  INFINITY,
+                                  &point))
+    {
+      gsk_path_point_get_position (&point, self->line_path, &pos);
+
+      gtk_widget_queue_draw (GTK_WIDGET (self));
+    }
+}
+
+static void
+pointer_leave (GtkEventControllerMotion *controller,
+               GtkPathWidget            *self)
+{
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+}
+
+static void
+gtk_path_widget_init (GtkPathWidget *self)
+{
+  GtkEventController *controller;
+
+  controller = GTK_EVENT_CONTROLLER (gtk_gesture_drag_new ());
+  g_signal_connect (controller, "drag-begin", G_CALLBACK (drag_begin), self);
+  g_signal_connect (controller, "drag-update", G_CALLBACK (drag_update), self);
+  g_signal_connect (controller, "drag-end", G_CALLBACK (drag_update), self);
+  gtk_widget_add_controller (GTK_WIDGET (self), controller);
+
+  controller = GTK_EVENT_CONTROLLER (gtk_event_controller_motion_new ());
+  g_signal_connect (controller, "enter", G_CALLBACK (pointer_motion), self);
+  g_signal_connect (controller, "motion", G_CALLBACK (pointer_motion), self);
+  g_signal_connect (controller, "leave", G_CALLBACK (pointer_leave), self);
+  gtk_widget_add_controller (GTK_WIDGET (self), controller);
+
+  self->points[0] = GRAPHENE_POINT_INIT (0.1, 0.9);
+  self->points[1] = GRAPHENE_POINT_INIT (0.3, 0.1);
+  self->points[2] = GRAPHENE_POINT_INIT (0.7, 0.1);
+  self->points[3] = GRAPHENE_POINT_INIT (0.9, 0.9);
+
+  self->background = GDK_PAINTABLE (gdk_texture_new_from_resource ("/sliding_puzzle/portland-rose.jpg"));
+
+  gtk_path_widget_set_text (self, "It's almost working");
+}
+
+GtkWidget *
+gtk_path_widget_new (void)
+{
+  GtkPathWidget *self;
+
+  self = g_object_new (GTK_TYPE_PATH_WIDGET, NULL);
+
+  return GTK_WIDGET (self);
+}
+
+GtkWidget *
+do_path_text (GtkWidget *do_widget)
+{
+  static GtkWidget *window = NULL;
+
+  if (!window)
+    {
+      GtkBuilder *builder;
+
+      g_type_ensure (GTK_TYPE_PATH_WIDGET);
+
+      builder = gtk_builder_new_from_resource ("/path_text/path_text.ui");
+      window = GTK_WIDGET (gtk_builder_get_object (builder, "window"));
+      gtk_window_set_display (GTK_WINDOW (window),
+                              gtk_widget_get_display (do_widget));
+      g_object_add_weak_pointer (G_OBJECT (window), (gpointer *) &window);
+      g_object_unref (builder);
+    }
+
+  if (!gtk_widget_get_visible (window))
+    gtk_window_present (GTK_WINDOW (window));
+  else
+    gtk_window_destroy (GTK_WINDOW (window));
+
+  return window;
+}
--- a/demos/gtk-demo/path_text.ui
+++ b/demos/gtk-demo/path_text.ui
@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<interface>
+  <object class="GtkWindow" id="window">
+    <property name="title" translatable="yes">Text along a Path</property>
+    <child type="titlebar">
+      <object class="GtkHeaderBar">
+        <child type="end">
+          <object class="GtkToggleButton" id="edit-toggle">
+            <property name="icon-name">document-edit-symbolic</property>
+          </object>
+        </child>
+      </object>
+    </child>
+    <child>
+      <object class="GtkBox">
+        <property name="orientation">vertical</property>
+        <child>
+          <object class="GtkRevealer">
+            <property name="reveal-child" bind-source="edit-toggle" bind-property="active" bind-flags="sync-create"></property>
+            <child>
+              <object class="GtkEntry" id="text">
+                <property name="text">Through the looking glass</property>
+              </object>
+            </child>
+          </object>
+        </child>
+        <child>
+          <object class="GtkPathWidget" id="view">
+            <property name="editable" bind-source="edit-toggle" bind-property="active" bind-flags="sync-create"></property>
+            <property name="text" bind-source="text" bind-property="text" bind-flags="sync-create"></property>
+            <property name="hexpand">true</property>
+            <property name="vexpand">true</property>
+          </object>
+        </child>
+      </object>
+    </child>
+  </object>
+</interface>
--- a/demos/gtk-demo/path_walk.c
+++ b/demos/gtk-demo/path_walk.c
@@ -1,6 +1,6 @@
-/* Path/Map
+/* Path/Walk
 *
- * This demo shows how to draw a map using paths.
+ * This demo draws a world map and shows how to animate objects along a GskPath.
 *
 * The world map that is used here is a path with 211 lines and 1569 cubic
 * Bėzier segments in 121 contours.
@@ -16,6 +16,7 @@ G_DECLARE_FINAL_TYPE (GtkPathWalk, gtk_path_walk, GTK, PATH_WALK, GtkWidget)

 enum {
  PROP_0,
+  PROP_N_POINTS,
  PROP_PATH,
  N_PROPS
 };
@@ -26,6 +27,8 @@ struct _GtkPathWalk

  GskPath *path;
  graphene_rect_t bounds;
+  GskPath *arrow_path;
+  guint n_points;
 };

 struct _GtkPathWalkClass
@@ -37,6 +40,74 @@ static GParamSpec *properties[N_PROPS] = { NULL, };

 G_DEFINE_TYPE (GtkPathWalk, gtk_path_walk, GTK_TYPE_WIDGET)

+static void
+rgba_init_from_hsla (GdkRGBA *rgba,
+                     float    hue,
+                     float    saturation,
+                     float    lightness,
+                     float    alpha)
+{
+  float m1, m2;
+
+  if (lightness <= 0.5)
+    m2 = lightness * (1 + saturation);
+  else
+    m2 = lightness + saturation - lightness * saturation;
+  m1 = 2 * lightness - m2;
+
+  rgba->alpha = alpha;
+
+  if (saturation == 0)
+    {
+      rgba->red = lightness;
+      rgba->green = lightness;
+      rgba->blue = lightness;
+    }
+  else
+    {
+      hue = hue + 120;
+      while (hue > 360)
+        hue -= 360;
+      while (hue < 0)
+        hue += 360;
+
+      if (hue < 60)
+        rgba->red = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        rgba->red = m2;
+      else if (hue < 240)
+        rgba->red = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        rgba->red = m1;
+
+      hue -= 120;
+      if (hue < 0)
+        hue += 360;
+
+      if (hue < 60)
+        rgba->green = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        rgba->green = m2;
+      else if (hue < 240)
+        rgba->green = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        rgba->green = m1;
+
+      hue -= 120;
+      if (hue < 0)
+        hue += 360;
+
+      if (hue < 60)
+        rgba->blue = m1 + (m2 - m1) * hue / 60;
+      else if (hue < 180)
+        rgba->blue = m2;
+      else if (hue < 240)
+        rgba->blue = m1 + (m2 - m1) * (240 - hue) / 60;
+      else
+        rgba->blue = m1;
+    }
+}
+
 static void
 gtk_path_walk_snapshot (GtkWidget   *widget,
                        GtkSnapshot *snapshot)
@@ -44,7 +115,9 @@ gtk_path_walk_snapshot (GtkWidget   *widget,
  GtkPathWalk *self = GTK_PATH_WALK (widget);
  double width = gtk_widget_get_width (widget);
  double height = gtk_widget_get_height (widget);
+  float length, progress;
  GskStroke *stroke;
+  guint i;

  if (self->path == NULL)
    return;
@@ -57,6 +130,35 @@ gtk_path_walk_snapshot (GtkWidget   *widget,
  gtk_snapshot_pop (snapshot);
  gsk_stroke_free (stroke);

+  length = gsk_path_get_length (self->path);
+  progress = 25.f * gdk_frame_clock_get_frame_time (gtk_widget_get_frame_clock (widget)) / G_USEC_PER_SEC;
+
+  stroke = gsk_stroke_new (1.0);
+  for (i = 0; i < self->n_points; i++)
+    {
+      GskPathPoint point;
+      graphene_point_t position;
+      float angle;
+      GdkRGBA color;
+      float distance;
+
+      distance = i * length / self->n_points;
+      distance = fmod (distance + progress, length);
+
+      gsk_path_get_point (self->path, distance, &point);
+      gsk_path_point_get_position (&point, self->path, &position);
+      angle = gsk_path_point_get_rotation (&point, self->path, GSK_PATH_FROM_START);
+      rgba_init_from_hsla (&color, 360.f * i / self->n_points, 1, 0.5, 1);
+
+      gtk_snapshot_save (snapshot);
+      gtk_snapshot_translate (snapshot, &position);
+      gtk_snapshot_rotate (snapshot, angle);
+      gtk_snapshot_append_fill (snapshot, self->arrow_path, GSK_FILL_RULE_EVEN_ODD, &color);
+      gtk_snapshot_append_stroke (snapshot, self->arrow_path, stroke, &(GdkRGBA) { 0, 0, 0, 1 });
+      gtk_snapshot_restore (snapshot);
+    }
+
+  gsk_stroke_free (stroke);
  gtk_snapshot_restore (snapshot);
 }

@@ -77,6 +179,20 @@ gtk_path_walk_measure (GtkWidget      *widget,
    *minimum = *natural = (int) ceilf (self->bounds.size.height);
 }

+static void
+gtk_path_walk_set_n_points (GtkPathWalk *self,
+                            gsize        n_points)
+{
+  if (self->n_points == n_points)
+    return;
+
+  self->n_points = n_points;
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_N_POINTS]);
+}
+
 static void
 gtk_path_walk_set_path (GtkPathWalk *self,
                        GskPath     *path)
@@ -112,6 +228,10 @@ gtk_path_walk_set_property (GObject      *object,

  switch (prop_id)
    {
+    case PROP_N_POINTS:
+      gtk_path_walk_set_n_points (self, g_value_get_uint (value));
+      break;
+
    case PROP_PATH:
      gtk_path_walk_set_path (self, g_value_get_boxed (value));
      break;
@@ -132,6 +252,10 @@ gtk_path_walk_get_property (GObject    *object,

  switch (prop_id)
    {
+    case PROP_N_POINTS:
+      g_value_set_uint (value, self->n_points);
+      break;
+
    case PROP_PATH:
      g_value_set_boxed (value, self->path);
      break;
@@ -148,6 +272,7 @@ gtk_path_walk_dispose (GObject *object)
  GtkPathWalk *self = GTK_PATH_WALK (object);

  g_clear_pointer (&self->path, gsk_path_unref);
+  g_clear_pointer (&self->arrow_path, gsk_path_unref);

  G_OBJECT_CLASS (gtk_path_walk_parent_class)->dispose (object);
 }
@@ -165,6 +290,13 @@ gtk_path_walk_class_init (GtkPathWalkClass *klass)
  widget_class->snapshot = gtk_path_walk_snapshot;
  widget_class->measure = gtk_path_walk_measure;

+  properties[PROP_N_POINTS] =
+    g_param_spec_uint ("n-points",
+                       NULL, NULL,
+                       1, G_MAXUINT,
+                       500,
+                       G_PARAM_READWRITE | G_PARAM_EXPLICIT_NOTIFY | G_PARAM_STATIC_STRINGS);
+
  properties[PROP_PATH] =
    g_param_spec_boxed ("path",
                        NULL, NULL,
@@ -174,6 +306,16 @@ gtk_path_walk_class_init (GtkPathWalkClass *klass)
  g_object_class_install_properties (object_class, N_PROPS, properties);
 }

+static gboolean
+tick_tick_tick (GtkWidget     *self,
+                GdkFrameClock *frame_clock,
+                gpointer       unused)
+{
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+
+  return G_SOURCE_CONTINUE;
+}
+
 static void
 gtk_path_walk_init (GtkPathWalk *self)
 {
@@ -185,6 +327,9 @@ gtk_path_walk_init (GtkPathWalk *self)
  g_bytes_unref (data);
  gtk_path_walk_set_path (self, path);
  gsk_path_unref (path);
+  self->arrow_path = gsk_path_parse ("M 5 0 L 0 -5. 0 -2, -5 -2, -5 2, 0 2, 0 5 Z");
+  self->n_points = 500;
+  gtk_widget_add_tick_callback (GTK_WIDGET (self), tick_tick_tick, NULL, NULL);
 }

 GtkWidget *
--- a/demos/gtk-demo/path_walk.ui
+++ b/demos/gtk-demo/path_walk.ui
@@ -2,16 +2,32 @@
 <interface>
  <object class="GtkWindow" id="window">
    <property name="title" translatable="yes">World Map</property>
-    <child>
+    <property name="titlebar">
+      <object class="GtkHeaderBar">
+        <child type="end">
+          <object class="GtkSpinButton">
+            <property name="adjustment">
+              <object class="GtkAdjustment" id="adjustment">
+                <property name="lower">0</property>
+                <property name="upper">2000</property>
+                <property name="value">500</property>
+              </object>
+            </property>
+          </object>
+        </child>
+      </object>
+    </property>
+    <property name="child">
      <object class="GtkBox">
        <property name="orientation">vertical</property>
        <child>
          <object class="GtkPathWalk" id="view">
+            <property name="n-points" bind-source="adjustment" bind-property="value"/>
            <property name="hexpand">true</property>
            <property name="vexpand">true</property>
          </object>
        </child>
      </object>
-    </child>
+    </property>
  </object>
 </interface>
--- a/gsk/ct-values.c
+++ b/gsk/ct-values.c
@@ -0,0 +1,133 @@
+static const double T[] = {
+	-0.0243502926634244325089558428537156614268871093149758091634531663960566965166295288529853061657116894882370493013671717560479926679408068852617342586968190919443025679363843727751902756254975073084367002129407854253246662805532069172532219089321005870178809284335033318073251039701073379759,
+	0.0243502926634244325089558428537156614268871093149758091634531663960566965166295288529853061657116894882370493013671717560479926679408068852617342586968190919443025679363843727751902756254975073084367002129407854253246662805532069172532219089321005870178809284335033318073251039701073379759,
+	-0.0729931217877990394495429419403374932441261816687788533563163323377395217254429050181833064967505478802134768007678458612956459126148837496307967995621683597067400860540057918571357609346700883624064782909888895547912499697295335516804810990011835717296819569741981551097569810739977931249,
+	0.0729931217877990394495429419403374932441261816687788533563163323377395217254429050181833064967505478802134768007678458612956459126148837496307967995621683597067400860540057918571357609346700883624064782909888895547912499697295335516804810990011835717296819569741981551097569810739977931249,
+	-0.1214628192961205544703764634922478782186836383371912940423495826006931832245070944213952236889690237679661122848626352437115925113582515415979746598665681268376919737373113667247142315234607397986222184384307059013512155412722263090766858403726100735651684437098923088469949297570988091677,
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+};
+
+static const double C[] = {
+	0.0486909570091397203833653907347499124426286922838743305086688042456914190998246107310291565645676057401607079939845156005172257043376703767287395573765236401039685866479381075274920900511719320271157129622463682509122641788910270632229694394595885032921037399187298767076084601033342936131,
+	0.0486909570091397203833653907347499124426286922838743305086688042456914190998246107310291565645676057401607079939845156005172257043376703767287395573765236401039685866479381075274920900511719320271157129622463682509122641788910270632229694394595885032921037399187298767076084601033342936131,
+	0.0485754674415034269347990667839781136875565447049294857111516761025158193093697039229163427633930410186232149083923688162761488505704450697417589593116703853157329164894580165517236877241308351214870169600093357854651930986960906313726182992933363325614247750209880050786299287510692780499,
+	0.0485754674415034269347990667839781136875565447049294857111516761025158193093697039229163427633930410186232149083923688162761488505704450697417589593116703853157329164894580165517236877241308351214870169600093357854651930986960906313726182992933363325614247750209880050786299287510692780499,
+	0.048344762234802957169769527158017809703692550609501080629442201445249828946429202156764153264348308119169811534137999799779908820312744765416129733427088646813066886130539178187597540312913636916139844188190193872629488730769015964208394624398401975043997268903006190530430762197842013971,
+	0.048344762234802957169769527158017809703692550609501080629442201445249828946429202156764153264348308119169811534137999799779908820312744765416129733427088646813066886130539178187597540312913636916139844188190193872629488730769015964208394624398401975043997268903006190530430762197842013971,
+	0.0479993885964583077281261798713460699543167134714936209446323930933335214619650277588138568504103427609283146728470455041360837549685364869161566863222680599110109210456299588352028330169041000166382937545505655464884266691630625402297821494221827392164049587946530563778771030124675514431,
+	0.0479993885964583077281261798713460699543167134714936209446323930933335214619650277588138568504103427609283146728470455041360837549685364869161566863222680599110109210456299588352028330169041000166382937545505655464884266691630625402297821494221827392164049587946530563778771030124675514431,
+	0.0475401657148303086622822069442231716408252512625387521584740318784735191312349586041971325618543660076682369564304738487584849740943805934034367382833518752314207901993991333786062812015195073547884746598535775062676699885664167707011249029305697669004958515813436770491520105115843742005,
+	0.0475401657148303086622822069442231716408252512625387521584740318784735191312349586041971325618543660076682369564304738487584849740943805934034367382833518752314207901993991333786062812015195073547884746598535775062676699885664167707011249029305697669004958515813436770491520105115843742005,
+	0.0469681828162100173253262857545810751998975284738125649829240886861900500181800807437012381630302198876925642461830694029139318555787845567143614289552410495903601238284556145544858090965965782916339169651505119399637862876053945518410353459767034026687936026945199383607112976484520939933,
+	0.0469681828162100173253262857545810751998975284738125649829240886861900500181800807437012381630302198876925642461830694029139318555787845567143614289552410495903601238284556145544858090965965782916339169651505119399637862876053945518410353459767034026687936026945199383607112976484520939933,
+	0.0462847965813144172959532492322611849696503075324468007778340818364698861774606986244241539105685321088517142947579291476238551538798963436740600968513359005801910700069462154098456091711311098901749803777735222026075473081311483686560830539773763176758567914860207820170792365910140063798,
+	0.0462847965813144172959532492322611849696503075324468007778340818364698861774606986244241539105685321088517142947579291476238551538798963436740600968513359005801910700069462154098456091711311098901749803777735222026075473081311483686560830539773763176758567914860207820170792365910140063798,
+	0.0454916279274181444797709969712690588873234618023998968168834081606504637618082102750954507142497706775055424364453740562113890878382679420378787427100982909191308430750899201141096789461078632697297091763378573830284133736378128577579722120264252594541491899441765769262904055702701625378,
+	0.0454916279274181444797709969712690588873234618023998968168834081606504637618082102750954507142497706775055424364453740562113890878382679420378787427100982909191308430750899201141096789461078632697297091763378573830284133736378128577579722120264252594541491899441765769262904055702701625378,
+	0.0445905581637565630601347100309448432940237999912217256432193286861948363377761089569585678875932857237669096941854082976565514031401996407675401022860761183118504326746863327792604337217763335682212515058414863183914930810334329596384915832703655935958010948424747251920190851700662833367,
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+	0.032057928354851553585467504347898716966221573881398062250169407854535275399124366530227987935629046729162364779969274126431870966979526186907589490002269660893281421728773647001279141626157958271220102615163092206489916992120482595587916535390136003611498634162765724522022671474313619317,
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+	0.030234657072402478867974059819548659158281397768481241636026542045969161851838118212761980885178641520596873511042783163461341979185470882574743804555268086640389062237383427702813367624714014426121485626242067362445894463989335423458464954799181190120473168677930333898873084606011285311,
+	0.030234657072402478867974059819548659158281397768481241636026542045969161851838118212761980885178641520596873511042783163461341979185470882574743804555268086640389062237383427702813367624714014426121485626242067362445894463989335423458464954799181190120473168677930333898873084606011285311,
+	0.0283396726142594832275113052002373519812075841257543359907955185084500175712880712901834579816476269393013386531176072296695948860841466158639973753393323262188023471133258509422081952937349849822864752636994881600343083839805990853930436233762729622213044478376753949590318846038229829528,
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+	0.0263774697150546586716917926252251856755993308422457184496156736853021592428967790284780487213653480867620409279447766944383920384284787790772384251090745670478105870527396429136326932261251511732466974897397268573168068852344129736214469830280087710575094607457344820944885011053938108899,
+	0.0263774697150546586716917926252251856755993308422457184496156736853021592428967790284780487213653480867620409279447766944383920384284787790772384251090745670478105870527396429136326932261251511732466974897397268573168068852344129736214469830280087710575094607457344820944885011053938108899,
+	0.0243527025687108733381775504090689876499784155133784119819985685535536787083770723737264828464464223276155821319330210193549896426801083040150047332857692873011433649334477370145389017577189505240415125600908800786897201425473757275187332157593198572919772969833130729981971352463730545469,
+	0.0243527025687108733381775504090689876499784155133784119819985685535536787083770723737264828464464223276155821319330210193549896426801083040150047332857692873011433649334477370145389017577189505240415125600908800786897201425473757275187332157593198572919772969833130729981971352463730545469,
+	0.0222701738083832541592983303841550024229592905997594051455205429744914460867081990116647982811451138592401156680063927909718825845915896692701716212710541472344073624315399429951255221519263275095347974129106415903376085208797420439500915674568159744176912567285070988940509294826076696882,
+	0.0222701738083832541592983303841550024229592905997594051455205429744914460867081990116647982811451138592401156680063927909718825845915896692701716212710541472344073624315399429951255221519263275095347974129106415903376085208797420439500915674568159744176912567285070988940509294826076696882,
+	0.0201348231535302093723403167285438970895266801007919519220072343276769828211923597982299498416998597995443052252531684909219367615574440281549241161294448697202959593344989612626641188010558013085389491205901106884167596038790695150496733123662891637942237462337673353651179115491957031948,
+	0.0201348231535302093723403167285438970895266801007919519220072343276769828211923597982299498416998597995443052252531684909219367615574440281549241161294448697202959593344989612626641188010558013085389491205901106884167596038790695150496733123662891637942237462337673353651179115491957031948,
+	0.0179517157756973430850453020011193688971673570364158572977184273569247295870620984743089140579199272107974903016785911970727080884655646148340637373001805876560334052431930062983734905886704331100259778249929425439377011315288821865303197904492848823994202996722656114004109123107733596987,
+	0.0179517157756973430850453020011193688971673570364158572977184273569247295870620984743089140579199272107974903016785911970727080884655646148340637373001805876560334052431930062983734905886704331100259778249929425439377011315288821865303197904492848823994202996722656114004109123107733596987,
+	0.0157260304760247193219659952975397944260290098431565121528943932284210502164124556525745628476326997189475680077625258949765335021586482683126547283634704087193102431454662772463321304938516661086261262080252305539171654570677889578063634007609097342035360186636479612243231917699790225637,
+	0.0157260304760247193219659952975397944260290098431565121528943932284210502164124556525745628476326997189475680077625258949765335021586482683126547283634704087193102431454662772463321304938516661086261262080252305539171654570677889578063634007609097342035360186636479612243231917699790225637,
+	0.0134630478967186425980607666859556841084257719773496708184682785221983598894666268489697837056105038485845901773961664652581563686185523959473293683490869846700009741156668864960127745507806046701586435579547632680339906665338521813319281296935586498194608460412423723103161161922347608637,
+	0.0134630478967186425980607666859556841084257719773496708184682785221983598894666268489697837056105038485845901773961664652581563686185523959473293683490869846700009741156668864960127745507806046701586435579547632680339906665338521813319281296935586498194608460412423723103161161922347608637,
+	0.011168139460131128818590493019208135072778797816827287215251362273969701224836131369547661822970774719521543690039908073147476182135228738610704246958518755712518444434075738269866120460156365855324768445411463643114925829148750923090201475035559533993035986264487097245733097728698218563,
+	0.011168139460131128818590493019208135072778797816827287215251362273969701224836131369547661822970774719521543690039908073147476182135228738610704246958518755712518444434075738269866120460156365855324768445411463643114925829148750923090201475035559533993035986264487097245733097728698218563,
+	0.0088467598263639477230309146597306476951762660792204997984715769296110380005985367341694286322550520156167431790573509593010611842062630262878798782558974712042810219159674181580449655112696028911646066461502678711637780164986283350190669684468398617127841853445303466680698660632269500149,
+	0.0088467598263639477230309146597306476951762660792204997984715769296110380005985367341694286322550520156167431790573509593010611842062630262878798782558974712042810219159674181580449655112696028911646066461502678711637780164986283350190669684468398617127841853445303466680698660632269500149,
+	0.0065044579689783628561173603999812667711317610549523400952448792575685125717613068203530526491113296049409911387320826711045787146267036866881961532403342811327869183281273743976710008917886491097375367147212074243884772614562628844975421736416404173672075979097191581386023407454532945934,
+	0.0065044579689783628561173603999812667711317610549523400952448792575685125717613068203530526491113296049409911387320826711045787146267036866881961532403342811327869183281273743976710008917886491097375367147212074243884772614562628844975421736416404173672075979097191581386023407454532945934,
+	0.0041470332605624676352875357285514153133028192536848024628763661431834776690157393776820933106187137592011723199002845429836606307797425496666456172753165824787973801175029578301513761259541022471768825518482406145696380621686627285992715643614469568410535180218496973657001203470470418364,
+	0.0041470332605624676352875357285514153133028192536848024628763661431834776690157393776820933106187137592011723199002845429836606307797425496666456172753165824787973801175029578301513761259541022471768825518482406145696380621686627285992715643614469568410535180218496973657001203470470418364,
+	0.0017832807216964329472960791449719331799593472719279556695308063655858546954239803486698215802150348282744786016134857283616955449868451969230490863774274598030023211055562492709717566919237924255297982774711177411074145151155610163293142044147991553384925940046957893721166251082473659733,
+	0.0017832807216964329472960791449719331799593472719279556695308063655858546954239803486698215802150348282744786016134857283616955449868451969230490863774274598030023211055562492709717566919237924255297982774711177411074145151155610163293142044147991553384925940046957893721166251082473659733
+};
--- a/gsk/gskcontour.c
+++ b/gsk/gskcontour.c
@@ -82,6 +82,13 @@ struct _GskContourClass
                                                 gboolean                emit_move_to,
                                                 GskRealPathPoint       *start,
                                                 GskRealPathPoint       *end);
+  void                  (* get_point)           (const GskContour       *contour,
+                                                 float                   distance,
+                                                 float                   precision,
+                                                 GskRealPathPoint       *result);
+  float                 (* get_distance)        (const GskContour       *contour,
+                                                 GskRealPathPoint       *point);
+  float                 (* get_length)          (const GskContour       *contour);
 };

 /* {{{ Utilities */
@@ -119,9 +126,13 @@ struct _GskStandardContour

  GskPathFlags flags;

+  float length;
+  gsize has_length;
+
  gsize n_ops;
  gsize n_points;
  graphene_point_t *points;
+  float *lengths;
  gskpathop ops[];
 };

@@ -134,6 +145,7 @@ gsk_standard_contour_compute_size (gsize n_ops,
                          G_ALIGNOF (GskStandardContour)));
  gsize s = sizeof (GskStandardContour)
          + sizeof (gskpathop) * n_ops
+          + sizeof (float) * n_ops
          + sizeof (graphene_point_t) * n_points;
  return s + (align - (s % align));
 }
@@ -164,6 +176,29 @@ gsk_standard_contour_get_size (const GskContour *contour)
  return gsk_standard_contour_compute_size (self->n_ops, self->n_points);
 }

+static void
+gsk_standard_contour_ensure_lengths (const GskContour *contour)
+{
+  GskStandardContour *self = (GskStandardContour *) contour;
+
+  if (g_once_init_enter (&self->has_length))
+    {
+      GskCurve curve;
+
+      self->lengths[0] = 0;
+
+      for (gsize i = 1; i < self->n_ops; i++)
+        {
+          gsk_curve_init (&curve, self->ops[i]);
+          self->lengths[i] = self->lengths[i - 1] + gsk_curve_get_length (&curve);
+        }
+
+      self->length = self->lengths[self->n_ops - 1];
+
+      g_once_init_leave (&self->has_length, 1);
+    }
+}
+
 static gboolean
 gsk_standard_contour_foreach (const GskContour   *contour,
                              float               tolerance,
@@ -633,6 +668,91 @@ gsk_standard_contour_add_segment (const GskContour *contour,
    }
 }

+static void
+gsk_standard_contour_get_point (const GskContour *contour,
+                                float             distance,
+                                float             precision,
+                                GskRealPathPoint *result)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  gsize i, i0, i1;
+
+  gsk_standard_contour_ensure_lengths (contour);
+
+  distance = CLAMP (distance, 0, self->length);
+
+  i0 = 0;
+  i1 = self->n_ops - 1;
+  while (i0 + 1 < i1)
+    {
+      i = (i0 + i1) / 2;
+
+      if (self->lengths[i] < distance)
+        i0 = i;
+      else
+        i1 = i;
+    }
+
+  g_assert (self->lengths[i0] <= distance && distance <= self->lengths[i1]);
+
+  if (distance >= self->lengths[i1])
+    {
+      if (i1 == self->n_ops - 1)
+        {
+          result->idx = i1;
+          result->t = 1;
+        }
+      else
+        {
+          result->idx = i1 + 1;
+          result->t = 0;
+        }
+    }
+  else
+    {
+      GskCurve curve;
+
+      gsk_curve_init (&curve, self->ops[i1]);
+
+      result->idx = i1;
+      result->t = gsk_curve_at_length (&curve, distance - self->lengths[i1 - 1], precision);
+    }
+}
+
+static float
+gsk_standard_contour_get_distance (const GskContour *contour,
+                                   GskRealPathPoint *point)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  GskCurve curve, curve1;
+
+  if (G_UNLIKELY (point->idx == 0))
+    return 0;
+
+  gsk_standard_contour_ensure_lengths (contour);
+
+  if (point->t == 0)
+    return self->lengths[point->idx - 1];
+  else if (point->t == 1)
+    return self->lengths[point->idx];
+  else
+    {
+      gsk_curve_init (&curve, self->ops[point->idx]);
+      gsk_curve_split (&curve, point->t, &curve1, NULL);
+      return self->lengths[point->idx - 1] + gsk_curve_get_length (&curve1);
+    }
+}
+
+static float
+gsk_standard_contour_get_length (const GskContour *contour)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+
+  gsk_standard_contour_ensure_lengths (contour);
+
+  return self->length;
+}
+
 static const GskContourClass GSK_STANDARD_CONTOUR_CLASS =
 {
  sizeof (GskStandardContour),
@@ -653,6 +773,9 @@ static const GskContourClass GSK_STANDARD_CONTOUR_CLASS =
  gsk_standard_contour_get_tangent,
  gsk_standard_contour_get_curvature,
  gsk_standard_contour_add_segment,
+  gsk_standard_contour_get_point,
+  gsk_standard_contour_get_distance,
+  gsk_standard_contour_get_length,
 };

 /* You must ensure the contour has enough size allocated,
@@ -677,14 +800,17 @@ gsk_standard_contour_init (GskContour             *contour,
  self->n_ops = n_ops;
  self->n_points = n_points;
  self->points = (graphene_point_t *) &self->ops[n_ops];
+  self->lengths = (float *) &self->points[n_points];
  memcpy (self->points, points, sizeof (graphene_point_t) * n_points);
+  memset (self->lengths, 0, sizeof (float) * n_ops);

  offset += self->points - points;
  for (i = 0; i < n_ops; i++)
-    {
-      self->ops[i] = gsk_pathop_encode (gsk_pathop_op (ops[i]),
-                                        gsk_pathop_points (ops[i]) + offset);
-    }
+    self->ops[i] = gsk_pathop_encode (gsk_pathop_op (ops[i]),
+                                      gsk_pathop_points (ops[i]) + offset);
+
+  self->length = 0.f;
+  self->has_length = 0;
 }

 GskContour *
@@ -840,6 +966,28 @@ gsk_contour_add_segment (const GskContour *self,
  self->klass->add_segment (self, builder, emit_move_to, start, end);
 }

+void
+gsk_contour_get_point (const GskContour       *self,
+                       float                   distance,
+                       float                   precision,
+                       GskRealPathPoint       *result)
+{
+  self->klass->get_point (self, distance, precision, result);
+}
+
+float
+gsk_contour_get_distance (const GskContour *self,
+                          GskRealPathPoint *point)
+{
+  return self->klass->get_distance (self, point);
+}
+
+float
+gsk_contour_get_length (const GskContour *self)
+{
+  return self->klass->get_length (self);
+}
+
 /* }}} */

 /* vim:set foldmethod=marker expandtab: */
--- a/gsk/gskcontourprivate.h
+++ b/gsk/gskcontourprivate.h
@@ -79,5 +79,13 @@ void                    gsk_contour_add_segment                 (const GskContou
                                                                 GskRealPathPoint       *start,
                                                                 GskRealPathPoint       *end);

+void                    gsk_contour_get_point                   (const GskContour       *self,
+                                                                 float                   distance,
+                                                                 float                   precision,
+                                                                 GskRealPathPoint       *result);
+float                   gsk_contour_get_distance                (const GskContour       *self,
+                                                                 GskRealPathPoint       *point);
+float                   gsk_contour_get_length                  (const GskContour       *self);
+

 G_END_DECLS
--- a/gsk/gskcurve.c
+++ b/gsk/gskcurve.c
@@ -76,6 +76,8 @@ struct _GskCurveClass
                                                         GskBoundingBox         *bounds);
  void                          (* get_tight_bounds)    (const GskCurve         *curve,
                                                         GskBoundingBox         *bounds);
+  void                          (* get_derivative)      (const GskCurve         *curve,
+                                                         GskCurve               *derivative);
 };

 /* {{{ Utilities */
@@ -311,6 +313,19 @@ gsk_line_curve_get_bounds (const GskCurve  *curve,
  gsk_bounding_box_init (bounds, &pts[0], &pts[1]);
 }

+static void
+gsk_line_curve_get_derivative (const GskCurve *curve,
+                               GskCurve       *deriv)
+{
+  const GskLineCurve *self = &curve->line;
+  graphene_point_t p;
+
+  p.x = self->points[1].x - self->points[0].x;
+  p.y = self->points[1].y - self->points[0].y;
+
+  gsk_line_curve_init_from_points (&deriv->line, GSK_PATH_LINE, &p, &p);
+}
+
 static const GskCurveClass GSK_LINE_CURVE_CLASS = {
  gsk_line_curve_init,
  gsk_line_curve_init_foreach,
@@ -330,6 +345,7 @@ static const GskCurveClass GSK_LINE_CURVE_CLASS = {
  gsk_line_curve_decompose_curve,
  gsk_line_curve_get_bounds,
  gsk_line_curve_get_bounds,
+  gsk_line_curve_get_derivative,
 };

 /* }}} */
@@ -670,6 +686,21 @@ gsk_quad_curve_get_tight_bounds (const GskCurve  *curve,
    }
 }

+static void
+gsk_quad_curve_get_derivative (const GskCurve *curve,
+                               GskCurve       *deriv)
+{
+  const GskQuadCurve *self = &curve->quad;
+  graphene_point_t p[2];
+
+  p[0].x = 2.f * (self->points[1].x - self->points[0].x);
+  p[0].y = 2.f * (self->points[1].y - self->points[0].y);
+  p[1].x = 2.f * (self->points[2].x - self->points[1].x);
+  p[1].y = 2.f * (self->points[2].y - self->points[1].y);
+
+  gsk_line_curve_init_from_points (&deriv->line, GSK_PATH_LINE, &p[0], &p[1]);
+}
+
 static const GskCurveClass GSK_QUAD_CURVE_CLASS = {
  gsk_quad_curve_init,
  gsk_quad_curve_init_foreach,
@@ -689,6 +720,7 @@ static const GskCurveClass GSK_QUAD_CURVE_CLASS = {
  gsk_quad_curve_decompose_curve,
  gsk_quad_curve_get_bounds,
  gsk_quad_curve_get_tight_bounds,
+  gsk_quad_curve_get_derivative,
 };

 /* }}} */
@@ -859,61 +891,6 @@ gsk_cubic_curve_reverse (const GskCurve *curve,
  reverse->cubic.has_coefficients = FALSE;
 }

-static void
-gsk_curve_get_derivative (const GskCurve *curve,
-                          GskCurve       *deriv)
-{
-  switch (curve->op)
-    {
-    case GSK_PATH_LINE:
-      {
-        const GskLineCurve *self = &curve->line;
-        graphene_point_t p;
-
-        p.x = self->points[1].x - self->points[0].x;
-        p.y = self->points[1].y - self->points[0].y;
-
-        gsk_line_curve_init_from_points (&deriv->line, GSK_PATH_LINE, &p, &p);
-      }
-      break;
-
-    case GSK_PATH_QUAD:
-      {
-        const GskQuadCurve *self = &curve->quad;
-        graphene_point_t p[2];
-
-        p[0].x = 2.f * (self->points[1].x - self->points[0].x);
-        p[0].y = 2.f * (self->points[1].y - self->points[0].y);
-        p[1].x = 2.f * (self->points[2].x - self->points[1].x);
-        p[1].y = 2.f * (self->points[2].y - self->points[1].y);
-
-        gsk_line_curve_init_from_points (&deriv->line, GSK_PATH_LINE, &p[0], &p[1]);
-      }
-      break;
-
-    case GSK_PATH_CUBIC:
-      {
-        const GskCubicCurve *self = &curve->cubic;
-        graphene_point_t p[3];
-
-        p[0].x = 3.f * (self->points[1].x - self->points[0].x);
-        p[0].y = 3.f * (self->points[1].y - self->points[0].y);
-        p[1].x = 3.f * (self->points[2].x - self->points[1].x);
-        p[1].y = 3.f * (self->points[2].y - self->points[1].y);
-        p[2].x = 3.f * (self->points[3].x - self->points[2].x);
-        p[2].y = 3.f * (self->points[3].y - self->points[2].y);
-
-        gsk_quad_curve_init_from_points (&deriv->quad, p);
-      }
-      break;
-
-    case GSK_PATH_MOVE:
-    case GSK_PATH_CLOSE:
-    default:
-      g_assert_not_reached ();
-    }
-}
-
 static inline float
 cross (const graphene_vec2_t *v1,
       const graphene_vec2_t *v2)
@@ -928,6 +905,9 @@ pow3 (float w)
  return w * w * w;
 }

+static void gsk_cubic_curve_get_derivative (const GskCurve *curve,
+                                            GskCurve       *deriv);
+
 static float
 gsk_cubic_curve_get_curvature (const GskCurve *curve,
                               float           t)
@@ -937,8 +917,8 @@ gsk_cubic_curve_get_curvature (const GskCurve *curve,
  graphene_vec2_t d, dd;
  float num, denom;

-  gsk_curve_get_derivative (curve, &c1);
-  gsk_curve_get_derivative (&c1, &c2);
+  gsk_cubic_curve_get_derivative (curve, &c1);
+  gsk_quad_curve_get_derivative (&c1, &c2);

  gsk_curve_get_point (&c1, t, &p);
  gsk_curve_get_point (&c2, t, &pp);
@@ -1150,6 +1130,23 @@ gsk_cubic_curve_get_tight_bounds (const GskCurve  *curve,
    }
 }

+static void
+gsk_cubic_curve_get_derivative (const GskCurve *curve,
+                                GskCurve       *deriv)
+{
+  const GskCubicCurve *self = &curve->cubic;
+  graphene_point_t p[3];
+
+  p[0].x = 3.f * (self->points[1].x - self->points[0].x);
+  p[0].y = 3.f * (self->points[1].y - self->points[0].y);
+  p[1].x = 3.f * (self->points[2].x - self->points[1].x);
+  p[1].y = 3.f * (self->points[2].y - self->points[1].y);
+  p[2].x = 3.f * (self->points[3].x - self->points[2].x);
+  p[2].y = 3.f * (self->points[3].y - self->points[2].y);
+
+  gsk_quad_curve_init_from_points (&deriv->quad, p);
+}
+
 static const GskCurveClass GSK_CUBIC_CURVE_CLASS = {
  gsk_cubic_curve_init,
  gsk_cubic_curve_init_foreach,
@@ -1169,6 +1166,7 @@ static const GskCurveClass GSK_CUBIC_CURVE_CLASS = {
  gsk_cubic_curve_decompose_curve,
  gsk_cubic_curve_get_bounds,
  gsk_cubic_curve_get_tight_bounds,
+  gsk_cubic_curve_get_derivative,
 };

 /* }}} */
@@ -1359,6 +1357,13 @@ gsk_curve_get_tight_bounds (const GskCurve  *curve,
  get_class (curve->op)->get_tight_bounds (curve, bounds);
 }

+void
+gsk_curve_get_derivative (const GskCurve *curve,
+                          GskCurve       *deriv)
+{
+  get_class (curve->op)->get_derivative (curve, deriv);
+}
+
 static inline int
 line_get_crossing (const graphene_point_t *p,
                   const graphene_point_t *p1,
@@ -1528,6 +1533,80 @@ gsk_curve_get_closest_point (const GskCurve         *curve,
    return find_closest_point (curve, point, threshold, 0, 1, out_dist, out_t);
 }

+/* Legendre-Gauss values for n=64,
+ * see https://pomax.github.io/bezierinfo/legendre-gauss.html
+ */
+
+#include "ct-values.c"
+
+/* Compute arclength by using Gauss quadrature on
+ *
+ * \int_0^z \sqrt{ (dx/dt)^2 + (dy/dt)^2 } dt
+ */
+float
+gsk_curve_get_length (const GskCurve *curve)
+{
+  double z = 0.5;
+  double sum;
+  GskCurve derivative;
+  graphene_point_t d;
+
+  if (curve->op == GSK_PATH_LINE ||
+      curve->op == GSK_PATH_CLOSE)
+    return graphene_point_distance (gsk_curve_get_start_point (curve),
+                                    gsk_curve_get_end_point (curve),
+                                    NULL, NULL);
+
+  gsk_curve_get_derivative (curve, &derivative);
+
+  sum = 0;
+
+  for (unsigned int i = 0; i < G_N_ELEMENTS (T); i++)
+    {
+      double t = z * T[i] + z;
+      gsk_curve_get_point (&derivative, t, &d);
+      sum += C[i] * sqrt (d.x * d.x + d.y * d.y);
+    }
+
+  return z * sum;
+}
+
+/* Compute the inverse of the arclength using bisection,
+ * to a given precision
+ */
+float
+gsk_curve_at_length (const GskCurve *curve,
+                     float           length,
+                     float           epsilon)
+{
+  float t1, t2, t, l;
+  GskCurve c1;
+
+  g_assert (epsilon >= FLT_EPSILON);
+
+  t1 = 0;
+  t2 = 1;
+
+  while (t1 < t2)
+    {
+      t = (t1 + t2) / 2;
+      if (t == t1 || t == t2)
+        break;
+
+      gsk_curve_split (curve, t, &c1, NULL);
+
+      l = gsk_curve_get_length (&c1);
+      if (fabsf (length - l) < epsilon)
+        break;
+      else if (l < length)
+        t1 = t;
+      else
+        t2 = t;
+    }
+
+  return t;
+}
+
 /* }}} */

 /* vim:set foldmethod=marker expandtab: */
--- a/gsk/gskcurveprivate.h
+++ b/gsk/gskcurveprivate.h
@@ -145,6 +145,8 @@ void                    gsk_curve_get_bounds                    (const GskCurve
 void                    gsk_curve_get_tight_bounds              (const GskCurve         *curve,
                                                                 GskBoundingBox         *bounds);

+void                    gsk_curve_get_derivative                (const GskCurve         *curve,
+                                                                 GskCurve               *derivative);
 int                     gsk_curve_get_crossing                  (const GskCurve         *curve,
                                                                 const graphene_point_t *point);
 gboolean                gsk_curve_get_closest_point             (const GskCurve         *curve,
@@ -152,6 +154,11 @@ gboolean                gsk_curve_get_closest_point             (const GskCurve
                                                                 float                   threshold,
                                                                 float                  *out_dist,
                                                                 float                  *out_t);
+float                  gsk_curve_get_length                     (const GskCurve         *curve);
+float                  gsk_curve_at_length                      (const GskCurve         *curve, 
+                                                                 float                   distance,
+                                                                 float                   epsilon);
+

 G_END_DECLS

--- a/gsk/gskpath.c
+++ b/gsk/gskpath.c
@@ -1413,3 +1413,107 @@ error:

  return NULL;
 }
+
+/**
+ * gsk_path_get_length:
+ * @self: a `GskPath`
+ *
+ * Returns the length of the path.
+ *
+ * Returns: the length of @self
+ *
+ * Since: 4.14
+ */
+float
+gsk_path_get_length (GskPath *self)
+{
+  float length = 0;
+
+  g_return_val_if_fail (self != NULL, 0);
+
+  for (gsize i = 0; i < self->n_contours; i++)
+    {
+      length += gsk_contour_get_length (self->contours[i]);
+    }
+
+  return length;
+}
+
+/**
+ * gsk_path_get_point:
+ * @self: a `GskPath`
+ * @distance: the distance
+ * @result: (out caller-allocates): return location for the point
+ *
+ * Computes the point that is at the given
+ * distance from the beginning of the path.
+ *
+ * An empty path has no points, so `FALSE`
+ * is returned in this case.
+ *
+ * Returns: `TRUE` if @result was filled
+ *
+ * Since: 4.14
+ */
+gboolean
+gsk_path_get_point (GskPath      *self,
+                    float         distance,
+                    GskPathPoint *result)
+{
+  GskRealPathPoint *res = (GskRealPathPoint *) result;
+  gsize i;
+
+  g_return_val_if_fail (self != NULL, 0);
+  g_return_val_if_fail (result != NULL, 0);
+
+  if (self->n_contours == 0)
+    return FALSE;
+
+  for (i = 0; i < self->n_contours - 1; i++)
+    {
+      float length = gsk_contour_get_length (self->contours[i]);
+      if (distance < length)
+        break;
+
+      distance -= length;
+    }
+
+  gsk_contour_get_point (self->contours[i], distance, 0.0001, res);
+  res->contour = i;
+
+  return TRUE;
+}
+
+/**
+ * gsk_path_point_get_distance:
+ * @point: a `GskPathPoint
+ * @path: the `GskPath` that @point is on
+ *
+ * Returns the distance from the beginning of the path to @point.
+ *
+ * Returns: the distance of @point
+ *
+ * Since: 4.14
+ */
+float
+gsk_path_point_get_distance (const GskPathPoint *point,
+                             GskPath            *path)
+{
+  GskRealPathPoint *p = (GskRealPathPoint *)point;
+  float distance = 0;
+
+  g_return_val_if_fail (point != NULL, 0);
+  g_return_val_if_fail (path != NULL, 0);
+  g_return_val_if_fail (p->contour < path->n_contours, 0);
+
+  for (gsize i = 0; i < path->n_contours; i++)
+    {
+      if (i == p->contour)
+        return distance + gsk_contour_get_distance (path->contours[i], p);
+
+      distance += gsk_contour_get_length (path->contours[i]);
+    }
+
+  g_return_val_if_reached (0);
+}
+
--- a/gsk/gskpath.h
+++ b/gsk/gskpath.h
@@ -131,6 +131,14 @@ gboolean                gsk_path_foreach                        (GskPath
                                                                 GskPathForeachFunc      func,
                                                                 gpointer                user_data);

+GDK_AVAILABLE_IN_4_14
+float                  gsk_path_get_length                      (GskPath                *self);
+
+GDK_AVAILABLE_IN_4_14
+gboolean               gsk_path_get_point                       (GskPath                *self,                                                                 float                   distance,
+                                                                 GskPathPoint           *result);
+
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(GskPath, gsk_path_unref)

 G_END_DECLS
--- a/gsk/gskpathpoint.h
+++ b/gsk/gskpathpoint.h
@@ -68,14 +68,17 @@ void                    gsk_path_point_get_tangent     (const GskPathPoint *poin
                                                        graphene_vec2_t    *tangent);

 GDK_AVAILABLE_IN_4_14
-float                   gsk_path_point_get_rotation    (const GskPathPoint     *point,
-                                                        GskPath                *path,
-                                                        GskPathDirection        direction);
+float                   gsk_path_point_get_rotation    (const GskPathPoint *point,
+                                                        GskPath            *path,
+                                                        GskPathDirection    direction);

 GDK_AVAILABLE_IN_4_14
 float                   gsk_path_point_get_curvature   (const GskPathPoint *point,
                                                        GskPath            *path,
                                                        graphene_point_t   *center);

+GDK_AVAILABLE_IN_4_14
+float                   gsk_path_point_get_distance    (const GskPathPoint *point,
+                                                        GskPath            *path);

 G_END_DECLS
--- a/testsuite/gsk/curve-special-cases.c
+++ b/testsuite/gsk/curve-special-cases.c
@@ -145,6 +145,23 @@ test_curve_crossing (void)
    }
 }

+static void
+test_curve_length (void)
+{
+  GskCurve c, c1, c2;
+  float l, l1, l2;
+
+  parse_curve (&c, "M 1462.632080 -1593.118896 C 751.533630 -74.179169 -914.280090 956.537720 -83.091866 207.213776");
+
+  gsk_curve_split (&c, 0.5, &c1, &c2);
+
+  l = gsk_curve_get_length (&c);
+  l1 = gsk_curve_get_length (&c1);
+  l2 = gsk_curve_get_length (&c2);
+
+  g_assert_cmpfloat_with_epsilon (l, l1 + l2, 0.01);
+}
+
 int
 main (int   argc,
      char *argv[])
@@ -154,6 +171,7 @@ main (int   argc,
  g_test_add_func ("/curve/special/tangents", test_curve_tangents);
  g_test_add_func ("/curve/special/degenerate-tangents", test_curve_degenerate_tangents);
  g_test_add_func ("/curve/special/crossing", test_curve_crossing);
+  g_test_add_func ("/curve/special/length", test_curve_length);

  return g_test_run ();
 }
--- a/testsuite/gsk/path.c
+++ b/testsuite/gsk/path.c
@@ -742,6 +742,72 @@ test_in_fill_rotated (void)
 #undef N_FILL_RULES
 }

+static void
+test_segment (void)
+{
+  GskPath *path, *path1, *path2, *path3;
+  GskPathBuilder *builder;
+  guint i;
+  float split1, split2, epsilon, length;
+  GskPathPoint point0, point1, point2, point3;
+
+  if (!g_test_slow ())
+    {
+      g_test_skip ("Skipping slow test");
+      return;
+    }
+
+  for (i = 0; i < 50000; i++)
+    {
+      path = create_random_path (G_MAXUINT);
+
+      length = gsk_path_get_length (path);
+      /* chosen high enough to stop the testsuite from failing */
+      epsilon = MAX (length / 64, 1.f / 1024);
+
+      split1 = g_test_rand_double_range (0, length);
+      split2 = g_test_rand_double_range (split1, length);
+
+      if (!gsk_path_get_start_point (path, &point0) ||
+          !gsk_path_get_point (path, split1, &point1) ||
+          !gsk_path_get_point (path, split2, &point2) ||
+          !gsk_path_get_end_point (path, &point3))
+        {
+          gsk_path_unref (path);
+          continue;
+        }
+
+      if (gsk_path_point_equal (&point0, &point1) ||
+          gsk_path_point_equal (&point1, &point2) ||
+          gsk_path_point_equal (&point2, &point3))
+        {
+          gsk_path_unref (path);
+          continue;
+        }
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point0, &point1);
+      path1 = gsk_path_builder_free_to_path (builder);
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point1, &point2);
+      path2 = gsk_path_builder_free_to_path (builder);
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point2, &point3);
+      path3 = gsk_path_builder_free_to_path (builder);
+
+      g_assert_cmpfloat_with_epsilon (split1, gsk_path_get_length (path1), epsilon);
+      g_assert_cmpfloat_with_epsilon (split2 - split1, gsk_path_get_length (path2), epsilon);
+      g_assert_cmpfloat_with_epsilon (length - split2, gsk_path_get_length (path3), epsilon);
+
+      gsk_path_unref (path3);
+      gsk_path_unref (path2);
+      gsk_path_unref (path1);
+      gsk_path_unref (path);
+    }
+}
+
 int
 main (int   argc,
      char *argv[])
@@ -752,6 +818,7 @@ main (int   argc,
  g_test_add_func ("/path/parse", test_parse);
  g_test_add_func ("/path/in-fill-union", test_in_fill_union);
  g_test_add_func ("/path/in-fill-rotated", test_in_fill_rotated);
+  g_test_add_func ("/path/segment", test_segment);

  return g_test_run ();
 }
Author	SHA1	Message	Date
Matthias Clasen	0f0fe317a3	gtk-demo: Add a spinbutton to the path walk Let the user pick how many arrows to show, to explore performance implications.	2023-08-17 12:43:46 -04:00
Matthias Clasen	348391cd0e	Add the randomized segment test This produces bad split examples quickly.	2023-08-17 06:37:03 -04:00
Matthias Clasen	334b1215d0	Add a test for bad lengths with splits	2023-08-17 06:37:03 -04:00
Benjamin Otte	48b47cd518	demos: Add a text-on-path demo	2023-08-17 06:37:03 -04:00
Matthias Clasen	ce692d391c	Make the map demo more interesting Add path walking to it.	2023-08-17 06:37:03 -04:00
Matthias Clasen	1d6724c075	path: Add length<>point api	2023-08-17 06:37:03 -04:00
Matthias Clasen	bba5dd047e	contour: Add length<>point api	2023-08-17 06:37:03 -04:00
Matthias Clasen	7eef8b514c	curve: Add length computation Add api to go t<>length.	2023-08-17 06:37:03 -04:00
Matthias Clasen	d56b6062cf	curve: Add a get_derivative vfunc	2023-08-16 21:56:28 -04:00