Add the randomized segment test

This produces bad split examples quickly.

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>

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',

demos/gtk-demo/path_text.c

@@ -0,0 +1,573 @@
+/* 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
+{
+  GskPathMeasure *measure;
+  GskPathBuilder *builder;
+  graphene_point_t offset;
+  double scale;
+} GtkPathTransform;
+
+static void
+gtk_path_transform_point (GskPathMeasure         *measure,
+                          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_measure_get_point (measure, (pt->x + offset->x) * scale, TRUE, &point))
+    {
+      GskPath *path = gsk_path_measure_get_path (measure);
+
+      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->measure, &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->measure, &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->measure, &pts[1], &transform->offset, transform->scale, &res[0]);
+        gtk_path_transform_point (transform->measure, &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->measure, &pts[1], &transform->offset, transform->scale, &res[0]);
+        gtk_path_transform_point (transform->measure, &pts[2], &transform->offset, transform->scale, &res[1]);
+        gtk_path_transform_point (transform->measure, &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)
+{
+  GskPathMeasure *measure = gsk_path_measure_new (line_path);
+  GtkPathTransform transform = { measure, 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_measure_get_length (measure) / (bounds.origin.x + bounds.size.width);
+  else
+    transform.scale = 1.0f;
+
+  gsk_path_foreach (path, -1, gtk_path_transform_op, &transform);
+
+  gsk_path_measure_unref (measure);
+
+  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;
+}

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>

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
 };
@@ -25,7 +26,10 @@ struct _GtkPathWalk
   GtkWidget parent_instance;
 
   GskPath *path;
+  GskPathMeasure *measure;
   graphene_rect_t bounds;
+  GskPath *arrow_path;
+  guint n_points;
 };
 
 struct _GtkPathWalkClass
@@ -37,6 +41,74 @@ 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 +116,9 @@ 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 +131,35 @@ gtk_path_walk_snapshot (GtkWidget   *widget,
   gtk_snapshot_pop (snapshot);
   gsk_stroke_free (stroke);
 
+  length = gsk_path_measure_get_length (self->measure);
+  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_measure_get_point (self->measure, distance, FALSE, &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 +180,20 @@ 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)
@@ -94,6 +211,7 @@ gtk_path_walk_set_path (GtkPathWalk *self,
       stroke = gsk_stroke_new (2.0);
       gsk_path_get_stroke_bounds (path, stroke, &self->bounds);
       gsk_stroke_free (stroke);
+      self->measure = gsk_path_measure_new (self->path);
     }
 
   gtk_widget_queue_resize (GTK_WIDGET (self));
@@ -112,6 +230,10 @@ 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 +254,10 @@ 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 +274,8 @@ gtk_path_walk_dispose (GObject *object)
   GtkPathWalk *self = GTK_PATH_WALK (object);
 
   g_clear_pointer (&self->path, gsk_path_unref);
+  g_clear_pointer (&self->measure, gsk_path_measure_unref);
+  g_clear_pointer (&self->arrow_path, gsk_path_unref);
 
   G_OBJECT_CLASS (gtk_path_walk_parent_class)->dispose (object);
 }
@@ -165,6 +293,13 @@ 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 +309,16 @@ 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 +330,9 @@ 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 *

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">5000</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>

gsk/ct-values.c

@@ -0,0 +1,209 @@
+#if 0
+/* n = 64 */
+static const double T[] = {
+	-0.0243502926634244325089558428537156614268871093149758091634531663960566965166295288529853061657116894882370493013671717560479926679408068852617342586968190919443025679363843727751902756254975073084367002129407854253246662805532069172532219089321005870178809284335033318073251039701073379759,
+	0.0243502926634244325089558428537156614268871093149758091634531663960566965166295288529853061657116894882370493013671717560479926679408068852617342586968190919443025679363843727751902756254975073084367002129407854253246662805532069172532219089321005870178809284335033318073251039701073379759,
+	-0.0729931217877990394495429419403374932441261816687788533563163323377395217254429050181833064967505478802134768007678458612956459126148837496307967995621683597067400860540057918571357609346700883624064782909888895547912499697295335516804810990011835717296819569741981551097569810739977931249,
+	0.0729931217877990394495429419403374932441261816687788533563163323377395217254429050181833064967505478802134768007678458612956459126148837496307967995621683597067400860540057918571357609346700883624064782909888895547912499697295335516804810990011835717296819569741981551097569810739977931249,
+	-0.1214628192961205544703764634922478782186836383371912940423495826006931832245070944213952236889690237679661122848626352437115925113582515415979746598665681268376919737373113667247142315234607397986222184384307059013512155412722263090766858403726100735651684437098923088469949297570988091677,
+	0.1214628192961205544703764634922478782186836383371912940423495826006931832245070944213952236889690237679661122848626352437115925113582515415979746598665681268376919737373113667247142315234607397986222184384307059013512155412722263090766858403726100735651684437098923088469949297570988091677,
+	-0.1696444204239928180373136297482698441999902667343778505894178746884342357796505591325925801106834127602396624627746208498838190598644711533868179088757129652678801285453336384132061358206434768209251779433993367981112053126660575920785488821886662635718276505127786854167528795165050389903,
+	0.1696444204239928180373136297482698441999902667343778505894178746884342357796505591325925801106834127602396624627746208498838190598644711533868179088757129652678801285453336384132061358206434768209251779433993367981112053126660575920785488821886662635718276505127786854167528795165050389903,
+	-0.217423643740007084149648748988822617578485831141222348630380401885689634737659235537163737740243604800759921292790013642836998201691226098978544332296437547642195961469059807833597096166848933098833151166287901339013986496737408125314858259377210847115061960167857239951500335854820530586,
+	0.217423643740007084149648748988822617578485831141222348630380401885689634737659235537163737740243604800759921292790013642836998201691226098978544332296437547642195961469059807833597096166848933098833151166287901339013986496737408125314858259377210847115061960167857239951500335854820530586,
+	-0.2646871622087674163739641725100201179804131362950932439559895448126206429452852982016450901649805445999078728714943692622330016257776575354105370883948495294882935681426154386660616476411740312465060150591301869544672050088454083442813632094277160007745547301572849406353682760306061929911,
+	0.2646871622087674163739641725100201179804131362950932439559895448126206429452852982016450901649805445999078728714943692622330016257776575354105370883948495294882935681426154386660616476411740312465060150591301869544672050088454083442813632094277160007745547301572849406353682760306061929911,
+	-0.3113228719902109561575126985601568835577153578680501269954571709858169098868398268719654999460149709757804582988077747605532896065842023340674450299515989484487746153929299031759475919924980452933324186984188982046762542556035347023744560814177013801414889023264804693830155588690576492164,
+	0.3113228719902109561575126985601568835577153578680501269954571709858169098868398268719654999460149709757804582988077747605532896065842023340674450299515989484487746153929299031759475919924980452933324186984188982046762542556035347023744560814177013801414889023264804693830155588690576492164,
+	-0.357220158337668115950442615046202531626264464640909112021237019340099177403802509741325589540743874845093675632547750287037622834793938695456980400958079292460482315821150714268593539935795231095157602025909339384694681190969656053235824652679875951093689200190014853543993102190088381483,
+	0.357220158337668115950442615046202531626264464640909112021237019340099177403802509741325589540743874845093675632547750287037622834793938695456980400958079292460482315821150714268593539935795231095157602025909339384694681190969656053235824652679875951093689200190014853543993102190088381483,
+	-0.4022701579639916036957667712601588487132652056150208082760431843129087214967261515969669708970990221669508217089555714806012046537594438323569293594638517933840725639831594134038262580440842200076281605641993773325072728778928440394419613403725280285705765326861533477990551765453978736181,
+	0.4022701579639916036957667712601588487132652056150208082760431843129087214967261515969669708970990221669508217089555714806012046537594438323569293594638517933840725639831594134038262580440842200076281605641993773325072728778928440394419613403725280285705765326861533477990551765453978736181,
+	-0.4463660172534640879849477147589151892067507578262501763082606820212937626970791295735937384813941473610238854736863966831464694923749954564921955859791688348936235671762050333408576202492209167272366373825152067680845198006626563761196191045700093968519269790165913301841545609485952718504,
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+	-0.4894031457070529574785263070219213908493732974637398373316540793240315585537584844752851087115581833443158831657759501916744927211636581386025171070582998790865902140901838128045602667002106847665927788023098753138400106615804847725751247952878407027140260429761863258319891988431055536872,
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+	-0.531279464019894545658013903544455247408525588734180238053268047166041778398245121448843253296460411619816073385211875151397248937264089998182375345915413219579220233566173902955487674957069948591213673456625912506280248298229907928060620469290406581396192419570799497688513058132396498814,
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+	-0.5718956462026340342838781166591886431831910060912509932273284719418912212643223327597417735844776972648163821225207266145263395898251858906124801356522395225326954546582593857056725545247314092886133249957455688586118199388064447508712958637376347457406936802691416300157802889354368128467,
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+	-0.7528199072605318966118637748856939855517142713220871932461987761167722639636968539390413583009467924995905147153923286347693864945784890119950315095740891764880991728646942920208355501445550654259850385377192973526980795946453961077798744753892199929235882097232836682421729944934586281945,
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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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+};
+#else
+/* n = 32 */
+
+static double T[] = {
+	-0.0483076656877383162348125704405021636908472517308488971677937345463685926042778777794060365911173780988289503411375793689757446357461295741679964108035347980667582792392651327368009453047606446744575790523465655622949909588624860214137051585425884056992683442137333250625173849291299678673,
+	0.0483076656877383162348125704405021636908472517308488971677937345463685926042778777794060365911173780988289503411375793689757446357461295741679964108035347980667582792392651327368009453047606446744575790523465655622949909588624860214137051585425884056992683442137333250625173849291299678673,
+	-0.1444719615827964934851863735988106522038459913156355521379528938242184438164519731102406769974924713989580220758441301598578946580142268413547299935841673092513202403499286272686350814272974392746706128556678811982653393383080797337231702069432462445053984587997153683967433095128570624414,
+	0.1444719615827964934851863735988106522038459913156355521379528938242184438164519731102406769974924713989580220758441301598578946580142268413547299935841673092513202403499286272686350814272974392746706128556678811982653393383080797337231702069432462445053984587997153683967433095128570624414,
+	-0.2392873622521370745446032091655015206088554219602530155470960995597029133039943915553593695844147813728958071901224632260145752503694970545640339873418480550362677768010887468668377893757173424222709744116861683634989914911762187599464033126988486345234374380695224452457957624756811128321,
+	0.2392873622521370745446032091655015206088554219602530155470960995597029133039943915553593695844147813728958071901224632260145752503694970545640339873418480550362677768010887468668377893757173424222709744116861683634989914911762187599464033126988486345234374380695224452457957624756811128321,
+	-0.3318686022821276497799168057301879961957751368050598360182296306285376829657438169809731852312743263005943551508559377834274303920771100489026913715847854727626540340157368609696698131829681988642689780208633461925468064919389286805624602715005948661328152252049795463242055567997437182143,
+	0.3318686022821276497799168057301879961957751368050598360182296306285376829657438169809731852312743263005943551508559377834274303920771100489026913715847854727626540340157368609696698131829681988642689780208633461925468064919389286805624602715005948661328152252049795463242055567997437182143,
+	-0.4213512761306353453641194361724264783358772886324433305416613404557190462549837315607633055675740638739884093394574651160978879545562247406839036854173715776910866941643197988581928900702286425821151586000969947406313405310082646561917980302543820974679501841964453794193724645925031841919,
+	0.4213512761306353453641194361724264783358772886324433305416613404557190462549837315607633055675740638739884093394574651160978879545562247406839036854173715776910866941643197988581928900702286425821151586000969947406313405310082646561917980302543820974679501841964453794193724645925031841919,
+	-0.5068999089322293900237474743778212301802836995994354639743662809707712640478764442266190213124522047999876916596854537447047905434649918210338296049592120273725464263651562560829050004258268002241145951271730860506703690843719936432852920782304931272053564539127514959875734718036950073563,
+	0.5068999089322293900237474743778212301802836995994354639743662809707712640478764442266190213124522047999876916596854537447047905434649918210338296049592120273725464263651562560829050004258268002241145951271730860506703690843719936432852920782304931272053564539127514959875734718036950073563,
+	-0.5877157572407623290407454764018268584509401154544205727031788473129228586684474311408145102018661764979429510790747919023774933113319119601088669936958908618326367715806216053155906936017362413244183150445492317940727345571648726363597097311647731726438279098059670236086983675374932643925,
+	0.5877157572407623290407454764018268584509401154544205727031788473129228586684474311408145102018661764979429510790747919023774933113319119601088669936958908618326367715806216053155906936017362413244183150445492317940727345571648726363597097311647731726438279098059670236086983675374932643925,
+	-0.6630442669302152009751151686632383689770222859605053010170834964924461749232229404368981536611965356686820332804126742949900731319113817214392193185613161549689934301410316417342588149871686184296988807305719690974644891055567340650986465615021143958920599684258616066247948224049997371166,
+	0.6630442669302152009751151686632383689770222859605053010170834964924461749232229404368981536611965356686820332804126742949900731319113817214392193185613161549689934301410316417342588149871686184296988807305719690974644891055567340650986465615021143958920599684258616066247948224049997371166,
+	-0.732182118740289680387426665091267146630270483506629100821139573270385253587797727611292298988652560055905228466313310601075333829094630570926240639601009902567982815376254840388565733846030450161774620971196087756484387383432502715118096615117242484073636640563609696801484680439912327302,
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+	0.9647622555875064307738119281182749603888952204430187193220113218370995254867038008243801877562227002840740910741483519987441236283464394249183812395373150090695515823078220949436846111682404866338388944248976976566275875721000356873959697266702651250019105084704924793016185368873243713355,
+	-0.9856115115452683354001750446309019786323957143358063182107821705820305847193755946663846485510970266115353839862364606643634021712823093784875255943834038377710426488328772047833289470320023596895438028281274741367781028592272459887917924171204666683239464005128153533797603112851826904814,
+	0.9856115115452683354001750446309019786323957143358063182107821705820305847193755946663846485510970266115353839862364606643634021712823093784875255943834038377710426488328772047833289470320023596895438028281274741367781028592272459887917924171204666683239464005128153533797603112851826904814,
+	-0.9972638618494815635449811286650407271385376637294611593011185457862359083917418520130456693085426416474280482200936551645510686196373231416035137741332968299789863385253514914078766236061488136738023162574655835389902337937054326098485227311719825229066712510246574949376367552421728646398,
+	0.9972638618494815635449811286650407271385376637294611593011185457862359083917418520130456693085426416474280482200936551645510686196373231416035137741332968299789863385253514914078766236061488136738023162574655835389902337937054326098485227311719825229066712510246574949376367552421728646398
+};
+
+static double C[] = {
+	0.0965400885147278005667648300635757947368606312355700687323182099577497758679466512968173871061464644599963197828969869820251559172455698832434930732077927850876632725829187045819145660710266452161095406358159608874152584850413283587913891015545638518881205600825069096855488296437485836866,
+	0.0965400885147278005667648300635757947368606312355700687323182099577497758679466512968173871061464644599963197828969869820251559172455698832434930732077927850876632725829187045819145660710266452161095406358159608874152584850413283587913891015545638518881205600825069096855488296437485836866,
+	0.0956387200792748594190820022041311005948905081620055509529898509437067444366006256133614167190847508238474888230077112990752876436158047205555474265705582078453283640212465537132165041268773645168746774530146140911679782502276289938840330631903789120176765314495900053061764438990021439069,
+	0.0956387200792748594190820022041311005948905081620055509529898509437067444366006256133614167190847508238474888230077112990752876436158047205555474265705582078453283640212465537132165041268773645168746774530146140911679782502276289938840330631903789120176765314495900053061764438990021439069,
+	0.0938443990808045656391802376681172600361000757462364500506275696355695118623098075097804207682530277555307864917078828352419853248607668520631751470962234105835015158485760721979732297206950719908744248285672032436598213262204039212897239890934116841559005147755270269705682414708355646603,
+	0.0938443990808045656391802376681172600361000757462364500506275696355695118623098075097804207682530277555307864917078828352419853248607668520631751470962234105835015158485760721979732297206950719908744248285672032436598213262204039212897239890934116841559005147755270269705682414708355646603,
+	0.0911738786957638847128685771116370625448614132753900053231278739777031520613017513597426417145878622654027367650308019870251963114683369110451524174258161390823876554910693202594383388549640738095422966058367070348943662290656339592299608558384147559830707904449930677260444604329157917977,
+	0.0911738786957638847128685771116370625448614132753900053231278739777031520613017513597426417145878622654027367650308019870251963114683369110451524174258161390823876554910693202594383388549640738095422966058367070348943662290656339592299608558384147559830707904449930677260444604329157917977,
+	0.0876520930044038111427714627518022875484497217017572223192228034747061150211380239263021665771581379364685191248848158059408000065275041643745927401342920150588893827207354226012701872322225514682178439577327346929209121046816487338309068375228210705166692551938339727096609740531893725675,
+	0.0876520930044038111427714627518022875484497217017572223192228034747061150211380239263021665771581379364685191248848158059408000065275041643745927401342920150588893827207354226012701872322225514682178439577327346929209121046816487338309068375228210705166692551938339727096609740531893725675,
+	0.0833119242269467552221990746043486115387468839428344598401864047287594069244380966536255650452315042012372905572506028852130723585016898197140339352228963465326746426938359210160503509807644396182380868089959855742801355208471205261406307895519604387550841954817025499019984032594036141439,
+	0.0833119242269467552221990746043486115387468839428344598401864047287594069244380966536255650452315042012372905572506028852130723585016898197140339352228963465326746426938359210160503509807644396182380868089959855742801355208471205261406307895519604387550841954817025499019984032594036141439,
+	0.078193895787070306471740918828306671039786798482159190307481553869493700115196435401943819761440851294456424770323467367505109006517482028994114252939401250416132320553639542341400437522236191275346323130525969269563653003188829786549728825182082678498917784036375053244425839341945385297,
+	0.078193895787070306471740918828306671039786798482159190307481553869493700115196435401943819761440851294456424770323467367505109006517482028994114252939401250416132320553639542341400437522236191275346323130525969269563653003188829786549728825182082678498917784036375053244425839341945385297,
+	0.0723457941088485062253993564784877916043369833018248707397632823511765345816800402874475958591657429073027694582930574378890633404841054620298756279975430795706338162404545590689277985270140590721779502609564199074051863640176937117952488466002340085264819537808079947788437998042296495822,
+	0.0723457941088485062253993564784877916043369833018248707397632823511765345816800402874475958591657429073027694582930574378890633404841054620298756279975430795706338162404545590689277985270140590721779502609564199074051863640176937117952488466002340085264819537808079947788437998042296495822,
+	0.0658222227763618468376500637069387728775364473732465153710916696852412442018627316280044447764609054151761388378861151807154113495715653711918644796313239555117970398473141615070299152284100887258072240524028885129828725430021172354299810423059697133688823072212214503334259555369485963074,
+	0.0658222227763618468376500637069387728775364473732465153710916696852412442018627316280044447764609054151761388378861151807154113495715653711918644796313239555117970398473141615070299152284100887258072240524028885129828725430021172354299810423059697133688823072212214503334259555369485963074,
+	0.0586840934785355471452836373001708867501204674575467587150032786132877518019090643743123653437052116901895704813134467814193905269714480573030647540887991405215103758723074481312705449946311993670933802369300463315125015975216910705047901943865293781921122370996257470349807212516159332678,
+	0.0586840934785355471452836373001708867501204674575467587150032786132877518019090643743123653437052116901895704813134467814193905269714480573030647540887991405215103758723074481312705449946311993670933802369300463315125015975216910705047901943865293781921122370996257470349807212516159332678,
+	0.0509980592623761761961632446895216952601847767397628437069071236525030510385137821267442193868358292147899714519363571211100873456269865150186456681043804358654826791768545393024953758025593924464295555854744882720755747096079325496814455853004350452095212995888025282619932613606999567133,
+	0.0509980592623761761961632446895216952601847767397628437069071236525030510385137821267442193868358292147899714519363571211100873456269865150186456681043804358654826791768545393024953758025593924464295555854744882720755747096079325496814455853004350452095212995888025282619932613606999567133,
+	0.0428358980222266806568786466061255284928108575989407395620219408911043916962572261359138025961596979511472539467367407419206021900868371610612953162236233351132214438513203223655531564777278515080476421262443325932320214191168239648611793958596884827086182431203349730049744697408543115307,
+	0.0428358980222266806568786466061255284928108575989407395620219408911043916962572261359138025961596979511472539467367407419206021900868371610612953162236233351132214438513203223655531564777278515080476421262443325932320214191168239648611793958596884827086182431203349730049744697408543115307,
+	0.0342738629130214331026877322523727069948402029116274337814057454192310522168984446294442724624445760666244242305266023810860790282088335398182296698622433517061843276344829146573593201201081743714879684153735672789104567624853712011151505225193933019375481618760594889854480408562043658635,
+	0.0342738629130214331026877322523727069948402029116274337814057454192310522168984446294442724624445760666244242305266023810860790282088335398182296698622433517061843276344829146573593201201081743714879684153735672789104567624853712011151505225193933019375481618760594889854480408562043658635,
+	0.0253920653092620594557525897892240292875540475469487209362512822192154788532376645960457016338988332029324531233401833547954942765653767672102838323550828207273795044402516181251040411735351747299230615776597356956641506445501689924551185923348003766988424170511157069264716719906995309826,
+	0.0253920653092620594557525897892240292875540475469487209362512822192154788532376645960457016338988332029324531233401833547954942765653767672102838323550828207273795044402516181251040411735351747299230615776597356956641506445501689924551185923348003766988424170511157069264716719906995309826,
+	0.0162743947309056706051705622063866181795429637952095664295931749613369651752917857651844425586692833071042366002861684552859449530958901379260437604156888337987656773068694383447504913457771896770689760342192010638946676879735404121702279005140285599424477022083127753774756520463311689155,
+	0.0162743947309056706051705622063866181795429637952095664295931749613369651752917857651844425586692833071042366002861684552859449530958901379260437604156888337987656773068694383447504913457771896770689760342192010638946676879735404121702279005140285599424477022083127753774756520463311689155,
+	0.0070186100094700966004070637388531825133772207289396032320082356192151241454178686953297376907573215077936155545790593837513204206518026084505878987243348925784479817181234617862457418214505322067610482902501455504204433524520665822704844582452877416001060465891907497519632353148380799619,
+	0.0070186100094700966004070637388531825133772207289396032320082356192151241454178686953297376907573215077936155545790593837513204206518026084505878987243348925784479817181234617862457418214505322067610482902501455504204433524520665822704844582452877416001060465891907497519632353148380799619
+};
+
+#endif

gsk/gsk.h

@@ -22,6 +22,7 @@
 #include <gsk/gskenums.h>
 #include <gsk/gskpath.h>
 #include <gsk/gskpathbuilder.h>
+#include <gsk/gskpathmeasure.h>
 #include <gsk/gskpathpoint.h>
 #include <gsk/gskrenderer.h>
 #include <gsk/gskrendernode.h>

gsk/gskcontour.c

@@ -82,6 +82,20 @@ struct _GskContourClass
                                                  gboolean                emit_move_to,
                                                  GskRealPathPoint       *start,
                                                  GskRealPathPoint       *end);
+  gpointer              (* init_measure)        (const GskContour       *contour,
+                                                 float                   tolerance,
+                                                 float                  *out_length);
+  void                  (* free_measure)        (const GskContour       *contour,
+                                                 gpointer                measure_data);
+  void                  (* get_point)           (const GskContour       *contour,
+                                                 gpointer                measure_data,
+                                                 float                   distance,
+                                                 gboolean                precise,
+                                                 GskRealPathPoint       *result);
+  float                 (* get_distance)        (const GskContour       *contour,
+                                                 GskRealPathPoint       *point,
+                                                 gpointer                measure_data,
+                                                 gboolean                precise);
 };
 
 /* {{{ Utilities */
@@ -112,6 +126,18 @@ _g_string_append_point (GString                *string,
 /* }}} */
 /* {{{ Standard */
 
+typedef struct
+{
+  float t;
+  float length;
+} CurvePoint;
+
+typedef struct
+{
+  float length;
+  CurvePoint lut[32];
+} CurveMeasure;
+
 typedef struct _GskStandardContour GskStandardContour;
 struct _GskStandardContour
 {
@@ -602,6 +628,186 @@ gsk_standard_contour_add_segment (const GskContour *contour,
     }
 }
 
+static gpointer
+gsk_standard_contour_init_measure (const GskContour *contour,
+                                   float             tolerance,
+                                   float            *out_length)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  GskCurve curve, curve1;
+  CurveMeasure *measure;
+  CurvePoint *lut;
+
+  measure = g_new (CurveMeasure, self->n_ops);
+
+  measure[0].length = 0;
+
+  for (gsize i = 1; i < self->n_ops; i++)
+    {
+      gsk_curve_init (&curve, self->ops[i]);
+      measure[i].length = measure[i - 1].length + gsk_curve_get_length (&curve);
+
+      lut = measure[i].lut;
+      for (gsize j = 0; j < 32; j++)
+        {
+          lut[j].t = (j + 1) / 32.f;
+
+          gsk_curve_split (&curve, lut[j].t, &curve1, NULL);
+          lut[j].length = gsk_curve_get_length (&curve1);
+        }
+    }
+
+  *out_length = measure[self->n_ops - 1].length;
+
+  return measure;
+}
+
+static void
+gsk_standard_contour_free_measure (const GskContour *contour,
+                                   gpointer          data)
+{
+  g_free (data);
+}
+
+static void
+gsk_standard_contour_get_point (const GskContour *contour,
+                                gpointer          measure_data,
+                                float             distance,
+                                gboolean          precise,
+                                GskRealPathPoint *result)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  CurveMeasure *measure = (CurveMeasure *)measure_data;
+  gsize i, i0, i1;
+
+  distance = CLAMP (distance, 0, measure[self->n_ops - 1].length);
+
+  i0 = 0;
+  i1 = self->n_ops - 1;
+  while (i0 + 1 < i1)
+    {
+      i = (i0 + i1) / 2;
+
+      if (measure[i].length < distance)
+        i0 = i;
+      else
+        i1 = i;
+    }
+
+  g_assert (measure[i0].length <= distance && distance <= measure[i1].length);
+
+  if (distance >= measure[i1].length)
+    {
+      if (i1 == self->n_ops - 1)
+        {
+          result->idx = i1;
+          result->t = 1;
+        }
+      else
+        {
+          result->idx = i1 + 1;
+          result->t = 0;
+        }
+    }
+  else if (precise)
+    {
+      GskCurve curve;
+
+      gsk_curve_init (&curve, self->ops[i1]);
+
+      result->idx = i1;
+      result->t = gsk_curve_at_length (&curve, distance - measure[i1 - 1].length, FLT_EPSILON);
+    }
+  else
+    {
+      float length, fraction, l1, t1;
+      gsize j;
+      CurvePoint *lut;
+
+      length = distance - measure[i1 - 1].length;
+
+      result->idx = i1;
+
+      lut = measure[i1].lut;
+
+      for (j = 0; j < 32; j++)
+        {
+          if (lut[j].length >= length)
+            break;
+        }
+
+      if (j > 0)
+        {
+          l1 = lut[j - 1].length;
+          t1 = lut[j - 1].t;
+        }
+      else
+        {
+          l1 = 0;
+          t1 = 0;
+        }
+
+      fraction = (length - l1) / (lut[j].length - l1);
+      g_assert (fraction >= 0.f && fraction <= 1.f);
+      result->t = t1 * (1 - fraction) + lut[j].t * fraction;
+      g_assert (result->t >= 0.f && result->t <= 1.f);
+    }
+}
+
+static float
+gsk_standard_contour_get_distance (const GskContour *contour,
+                                   GskRealPathPoint *point,
+                                   gpointer          measure_data,
+                                   gboolean          precise)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  CurveMeasure *measure = (CurveMeasure *)measure_data;
+  GskCurve curve, curve1;
+
+  if (G_UNLIKELY (point->idx == 0))
+    return 0;
+
+  if (point->t == 0)
+    return measure[point->idx - 1].length;
+  else if (point->t == 1)
+    return measure[point->idx].length;
+  else if (precise)
+    {
+      gsk_curve_init (&curve, self->ops[point->idx]);
+      gsk_curve_split (&curve, point->t, &curve1, NULL);
+      return measure[point->idx - 1].length + gsk_curve_get_length (&curve1);
+    }
+  else
+    {
+      float fraction, l1, t1;
+      gsize j;
+      CurvePoint *lut;
+
+      lut = measure[point->idx].lut;
+
+      for (j = 0; j < 32; j++)
+        {
+          if (lut[j].t >= point->t)
+            break;
+        }
+
+      if (j > 0)
+        {
+          l1 = lut[j - 1].length;
+          t1 = lut[j - 1].t;
+        }
+      else
+        {
+          l1 = 0;
+          t1 = 0;
+        }
+
+      fraction = (point->t - t1) / (lut[j].t - t1);
+      g_assert (fraction >= 0.f && fraction <= 1.f);
+      return measure[point->idx - 1].length + l1 * (1 - fraction) + lut[j].length * fraction;
+    }
+}
+
 static const GskContourClass GSK_STANDARD_CONTOUR_CLASS =
 {
   sizeof (GskStandardContour),
@@ -622,6 +828,10 @@ 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_init_measure,
+  gsk_standard_contour_free_measure,
+  gsk_standard_contour_get_point,
+  gsk_standard_contour_get_distance,
 };
 
 /* You must ensure the contour has enough size allocated,
@@ -810,6 +1020,40 @@ gsk_contour_add_segment (const GskContour *self,
   self->klass->add_segment (self, builder, emit_move_to, start, end);
 }
 
+gpointer
+gsk_contour_init_measure (const GskContour *self,
+                          float             tolerance,
+                          float            *out_length)
+{
+  return self->klass->init_measure (self, tolerance, out_length);
+}
+
+void
+gsk_contour_free_measure (const GskContour *self,
+                          gpointer          data)
+{
+  self->klass->free_measure (self, data);
+}
+
+void
+gsk_contour_get_point (const GskContour *self,
+                       gpointer          measure_data,
+                       float             distance,
+                       gboolean          precise,
+                       GskRealPathPoint *result)
+{
+  self->klass->get_point (self, measure_data, distance, precise, result);
+}
+
+float
+gsk_contour_get_distance (const GskContour *self,
+                          GskRealPathPoint *point,
+                          gpointer          measure_data,
+                          gboolean          precise)
+{
+  return self->klass->get_distance (self, point, measure_data, precise);
+}
+
 /* }}} */
 
 /* vim:set foldmethod=marker expandtab: */

gsk/gskcontourprivate.h

@@ -79,5 +79,19 @@ void                    gsk_contour_add_segment                 (const GskContou
                                                                  GskRealPathPoint       *start,
                                                                  GskRealPathPoint       *end);
 
+gpointer                gsk_contour_init_measure                (const GskContour       *self,
+                                                                 float                   tolerance,
+                                                                 float                  *out_length);
+void                    gsk_contour_free_measure                (const GskContour       *self,
+                                                                 gpointer                data);
+void                    gsk_contour_get_point                   (const GskContour       *self,
+                                                                 gpointer                measure_data,
+                                                                 float                   distance,
+                                                                 gboolean                precise,
+                                                                 GskRealPathPoint       *result);
+float                   gsk_contour_get_distance                (const GskContour       *self,
+                                                                 GskRealPathPoint       *point,
+                                                                 gpointer                measure_data,
+                                                                 gboolean                precise);
 
 G_END_DECLS

gsk/gskcurve.c

@@ -1563,6 +1563,80 @@ 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: */

gsk/gskcurveprivate.h

@@ -154,6 +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
 

gsk/gskpathmeasure.c

@@ -0,0 +1,334 @@
+/*
+ * Copyright © 2020 Benjamin Otte
+ *
+ * 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 2.1 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/>.
+ *
+ * Authors: Benjamin Otte <otte@gnome.org>
+ */
+
+#include "config.h"
+
+#include "gskpathmeasure.h"
+
+#include "gskpathbuilder.h"
+#include "gskpathpointprivate.h"
+#include "gskpathprivate.h"
+
+/**
+ * GskPathMeasure:
+ *
+ * `GskPathMeasure` is an object that allows measurements
+ * on `GskPath`s such as determining the length of the path.
+ *
+ * Many measuring operations require approximating the path
+ * with simpler shapes. Therefore, a `GskPathMeasure` has
+ * a tolerance that determines what precision is required
+ * for such approximations.
+ *
+ * A `GskPathMeasure` struct is a reference counted struct
+ * and should be treated as opaque.
+ */
+
+typedef struct _GskContourMeasure GskContourMeasure;
+
+struct _GskContourMeasure
+{
+  float length;
+  gpointer contour_data;
+};
+
+struct _GskPathMeasure
+{
+  /*< private >*/
+  guint ref_count;
+
+  GskPath *path;
+  float tolerance;
+
+  float length;
+  gsize n_contours;
+  GskContourMeasure measures[];
+};
+
+G_DEFINE_BOXED_TYPE (GskPathMeasure, gsk_path_measure,
+                     gsk_path_measure_ref,
+                     gsk_path_measure_unref)
+
+/**
+ * gsk_path_measure_new:
+ * @path: the path to measure
+ *
+ * Creates a measure object for the given @path.
+ *
+ * Returns: a new `GskPathMeasure` representing @path
+ *
+ * Since: 4.14
+ */
+GskPathMeasure *
+gsk_path_measure_new (GskPath *path)
+{
+  return gsk_path_measure_new_with_tolerance (path, GSK_PATH_TOLERANCE_DEFAULT);
+}
+
+/**
+ * gsk_path_measure_new_with_tolerance:
+ * @path: the path to measure
+ * @tolerance: the tolerance for measuring operations
+ *
+ * Creates a measure object for the given @path and @tolerance.
+ *
+ * Returns: a new `GskPathMeasure` representing @path
+ *
+ * Since: 4.14
+ */
+GskPathMeasure *
+gsk_path_measure_new_with_tolerance (GskPath *path,
+                                     float    tolerance)
+{
+  GskPathMeasure *self;
+  gsize i, n_contours;
+
+  g_return_val_if_fail (path != NULL, NULL);
+  g_return_val_if_fail (tolerance > 0, NULL);
+
+  n_contours = gsk_path_get_n_contours (path);
+
+  self = g_malloc0 (sizeof (GskPathMeasure) + n_contours * sizeof (GskContourMeasure));
+
+  self->ref_count = 1;
+  self->path = gsk_path_ref (path);
+  self->tolerance = tolerance;
+  self->n_contours = n_contours;
+
+  for (i = 0; i < n_contours; i++)
+    {
+      self->measures[i].contour_data = gsk_contour_init_measure (gsk_path_get_contour (path, i),
+                                                                 self->tolerance,
+                                                                 &self->measures[i].length);
+      self->length += self->measures[i].length;
+    }
+
+  return self;
+}
+
+/**
+ * gsk_path_measure_ref:
+ * @self: a `GskPathMeasure`
+ *
+ * Increases the reference count of a `GskPathMeasure` by one.
+ *
+ * Returns: the passed in `GskPathMeasure`.
+ *
+ * Since: 4.14
+ */
+GskPathMeasure *
+gsk_path_measure_ref (GskPathMeasure *self)
+{
+  g_return_val_if_fail (self != NULL, NULL);
+
+  self->ref_count++;
+
+  return self;
+}
+
+/**
+ * gsk_path_measure_unref:
+ * @self: a `GskPathMeasure`
+ *
+ * Decreases the reference count of a `GskPathMeasure` by one.
+ *
+ * If the resulting reference count is zero, frees the object.
+ *
+ * Since: 4.14
+ */
+void
+gsk_path_measure_unref (GskPathMeasure *self)
+{
+  gsize i;
+
+  g_return_if_fail (self != NULL);
+  g_return_if_fail (self->ref_count > 0);
+
+  self->ref_count--;
+  if (self->ref_count > 0)
+    return;
+
+  for (i = 0; i < self->n_contours; i++)
+    {
+      gsk_contour_free_measure (gsk_path_get_contour (self->path, i),
+                                self->measures[i].contour_data);
+    }
+
+  gsk_path_unref (self->path);
+  g_free (self);
+}
+
+/**
+ * gsk_path_measure_get_path:
+ * @self: a `GskPathMeasure`
+ *
+ * Returns the path that the measure was created for.
+ *
+ * Returns: (transfer none): the path of @self
+ *
+ * Since: 4.14
+ */
+GskPath *
+gsk_path_measure_get_path (GskPathMeasure *self)
+{
+  return self->path;
+}
+
+/**
+ * gsk_path_measure_get_tolerance:
+ * @self: a `GskPathMeasure`
+ *
+ * Returns the tolerance that the measure was created with.
+ *
+ * Returns: the tolerance of @self
+ *
+ * Since: 4.14
+ */
+float
+gsk_path_measure_get_tolerance (GskPathMeasure *self)
+{
+  return self->tolerance;
+}
+
+/**
+ * gsk_path_measure_get_length:
+ * @self: a `GskPathMeasure`
+ *
+ * Gets the length of the path being measured.
+ *
+ * The length is cached, so this function does not do any work.
+ *
+ * Returns: The length of the path measured by @self
+ *
+ * Since: 4.14
+ */
+float
+gsk_path_measure_get_length (GskPathMeasure *self)
+{
+  g_return_val_if_fail (self != NULL, 0);
+
+  return self->length;
+}
+
+static float
+gsk_path_measure_clamp_distance (GskPathMeasure *self,
+                                 float           distance)
+{
+  if (isnan (distance))
+    return 0;
+
+  return CLAMP (distance, 0, self->length);
+}
+
+/**
+ * gsk_path_measure_get_point:
+ * @self: a `GskPathMeasure`
+ * @distance: the distance
+ * @precise: whether to do expensive calculations to produce
+ *   a very accurate result
+ * @result: (out caller-allocates): return location for the result
+ *
+ * Sets @result to the point at the given distance into the path.
+ *
+ * An empty path has no points, so `FALSE` is returned in that case.
+ *
+ * Returns: `TRUE` if @result was set
+ *
+ * Since: 4.14
+ */
+gboolean
+gsk_path_measure_get_point (GskPathMeasure *self,
+                            float           distance,
+                            gboolean        precise,
+                            GskPathPoint   *result)
+{
+  GskRealPathPoint *res = (GskRealPathPoint *) result;
+  gsize i;
+  const GskContour *contour;
+
+  g_return_val_if_fail (self != NULL, FALSE);
+  g_return_val_if_fail (result != NULL, FALSE);
+
+  if (self->n_contours == 0)
+    return FALSE;
+
+  distance = gsk_path_measure_clamp_distance (self, distance);
+
+  for (i = 0; i < self->n_contours - 1; i++)
+    {
+      if (distance < self->measures[i].length)
+        break;
+
+      distance -= self->measures[i].length;
+    }
+
+  g_assert (0 <= i && i < self->n_contours);
+
+  distance = CLAMP (distance, 0, self->measures[i].length);
+
+  contour = gsk_path_get_contour (self->path, i);
+
+  gsk_contour_get_point (contour, self->measures[i].contour_data, distance, precise, res);
+  res->contour = i;
+
+  return TRUE;
+}
+
+/**
+ * gsk_path_point_get_distance:
+ * @point: a `GskPathPoint on the path
+ * @measure: a `GskPathMeasure` for the path
+ * @precise: whether to do expensive calculations to produce
+ *   a very accurate result
+ *
+ * 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,
+                             GskPathMeasure     *measure,
+                             gboolean            precise)
+{
+  GskRealPathPoint *p = (GskRealPathPoint *)point;
+  const GskContour *contour;
+  float contour_offset = 0;
+
+  g_return_val_if_fail (point != NULL, 0);
+  g_return_val_if_fail (measure != NULL, 0);
+  g_return_val_if_fail (p->contour < measure->n_contours, 0);
+
+  contour = gsk_path_get_contour (measure->path, p->contour);
+
+  for (gsize i = 0; i < measure->n_contours; i++)
+    {
+      if (contour == gsk_path_get_contour (measure->path, i))
+        return contour_offset + gsk_contour_get_distance (contour,
+                                                          p,
+                                                          measure->measures[i].contour_data,
+                                                          precise);
+
+      contour_offset += measure->measures[i].length;
+    }
+
+  g_return_val_if_reached (0);
+}

gsk/gskpathmeasure.h

@@ -0,0 +1,63 @@
+/*
+ * Copyright © 2020 Benjamin Otte
+ *
+ * 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 2.1 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/>.
+ *
+ * Authors: Benjamin Otte <otte@gnome.org>
+ */
+
+#pragma once
+
+#if !defined (__GSK_H_INSIDE__) && !defined (GTK_COMPILATION)
+#error "Only <gsk/gsk.h> can be included directly."
+#endif
+
+
+#include <gsk/gskpath.h>
+#include <gsk/gskpathpoint.h>
+
+G_BEGIN_DECLS
+
+#define GSK_TYPE_PATH_MEASURE (gsk_path_measure_get_type ())
+
+GDK_AVAILABLE_IN_4_14
+GType                   gsk_path_measure_get_type               (void) G_GNUC_CONST;
+GDK_AVAILABLE_IN_4_14
+GskPathMeasure *        gsk_path_measure_new                    (GskPath                *path);
+GDK_AVAILABLE_IN_4_14
+GskPathMeasure *        gsk_path_measure_new_with_tolerance     (GskPath                *path,
+                                                                 float                   tolerance);
+
+GDK_AVAILABLE_IN_4_14
+GskPathMeasure *        gsk_path_measure_ref                    (GskPathMeasure         *self);
+GDK_AVAILABLE_IN_4_14
+void                    gsk_path_measure_unref                  (GskPathMeasure         *self);
+
+GDK_AVAILABLE_IN_4_14
+GskPath *               gsk_path_measure_get_path               (GskPathMeasure         *self) G_GNUC_PURE;
+GDK_AVAILABLE_IN_4_14
+float                   gsk_path_measure_get_tolerance          (GskPathMeasure         *self) G_GNUC_PURE;
+
+GDK_AVAILABLE_IN_4_14
+float                   gsk_path_measure_get_length             (GskPathMeasure         *self);
+
+GDK_AVAILABLE_IN_4_14
+gboolean                gsk_path_measure_get_point              (GskPathMeasure         *self,
+                                                                 float                   distance,
+                                                                 gboolean                precise,
+                                                                 GskPathPoint           *result);
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(GskPathMeasure, gsk_path_measure_unref)
+
+G_END_DECLS

gsk/gskpathpoint.h

@@ -77,5 +77,9 @@ float                   gsk_path_point_get_curvature   (const GskPathPoint *poin
                                                         GskPath            *path,
                                                         graphene_point_t   *center);
 
+GDK_AVAILABLE_IN_4_14
+float                   gsk_path_point_get_distance    (const GskPathPoint *point,
+                                                        GskPathMeasure     *measure,
+                                                        gboolean            precise);
 
 G_END_DECLS

gsk/gsktypes.h

@@ -27,6 +27,7 @@
 
 typedef struct _GskPath                 GskPath;
 typedef struct _GskPathBuilder          GskPathBuilder;
+typedef struct _GskPathMeasure          GskPathMeasure;
 typedef struct _GskPathPoint            GskPathPoint;
 typedef struct _GskRenderer             GskRenderer;
 typedef struct _GskRenderNode           GskRenderNode;

gsk/meson.build

@@ -28,6 +28,7 @@ gsk_public_sources = files([
   'gskglshader.c',
   'gskpath.c',
   'gskpathbuilder.c',
+  'gskpathmeasure.c',
   'gskpathpoint.c',
   'gskrenderer.c',
   'gskrendernode.c',
@@ -75,6 +76,7 @@ gsk_public_headers = files([
   'gskglshader.h',
   'gskpath.h',
   'gskpathbuilder.h',
+  'gskpathmeasure.h',
   'gskpathpoint.h',
   'gskrenderer.h',
   'gskrendernode.h',

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, 0.5);
+}
+
 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 ();
 }

testsuite/gsk/path.c

@@ -742,6 +742,84 @@ test_in_fill_rotated (void)
 #undef N_FILL_RULES
 }
 
+static void
+test_segment (void)
+{
+  GskPath *path, *path1, *path2, *path3;
+  GskPathMeasure *measure, *measure1, *measure2, *measure3;
+  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 < 1000; i++)
+    {
+      path = create_random_path (G_MAXUINT);
+      measure = gsk_path_measure_new (path);
+
+      length = gsk_path_measure_get_length (measure);
+      /* chosen high enough to stop the testsuite from failing */
+      epsilon = MAX (length / 1000, 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_measure_get_point (measure, split1, TRUE, &point1) ||
+          !gsk_path_measure_get_point (measure, split2, TRUE, &point2) ||
+          !gsk_path_get_end_point (path, &point3))
+        {
+          gsk_path_unref (path);
+          gsk_path_measure_unref (measure);
+          continue;
+        }
+
+      if (gsk_path_point_equal (&point0, &point1) ||
+          gsk_path_point_equal (&point1, &point2) ||
+          gsk_path_point_equal (&point2, &point3))
+        {
+          gsk_path_unref (path);
+          gsk_path_measure_unref (measure);
+          continue;
+        }
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point0, &point1);
+      path1 = gsk_path_builder_free_to_path (builder);
+      measure1 = gsk_path_measure_new (path1);
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point1, &point2);
+      path2 = gsk_path_builder_free_to_path (builder);
+      measure2 = gsk_path_measure_new (path2);
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_segment (builder, path, &point2, &point3);
+      path3 = gsk_path_builder_free_to_path (builder);
+      measure3 = gsk_path_measure_new (path3);
+
+      g_assert_cmpfloat_with_epsilon (split1, gsk_path_measure_get_length (measure1), epsilon);
+      g_assert_cmpfloat_with_epsilon (split2 - split1, gsk_path_measure_get_length (measure2), epsilon);
+      g_assert_cmpfloat_with_epsilon (length - split2, gsk_path_measure_get_length (measure3), epsilon);
+
+      gsk_path_unref (path3);
+      gsk_path_unref (path2);
+      gsk_path_unref (path1);
+      gsk_path_unref (path);
+
+      gsk_path_measure_unref (measure3);
+      gsk_path_measure_unref (measure2);
+      gsk_path_measure_unref (measure1);
+      gsk_path_measure_unref (measure);
+    }
+}
+
 int
 main (int   argc,
       char *argv[])
@@ -752,6 +830,7 @@ 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 ();
 }