Neuter some tests that assume special contours

This is a function like gsk_path_foreach, but
it provides a dashed version of the path instead
of the original.

LOG

@@ -0,0 +1,150 @@
+TAP version 13
+# random seed: R02S22611f6aefc1121b0ab2dc5286960449
+# GLib-GIO-DEBUG: _g_io_module_get_default: Found default implementation dconf (DConfSettingsBackend) for ‘gsettings-backend’
+# GLib-GIO-DEBUG: Using cross-namespace EXTERNAL authentication (this will deadlock if server is GDBus < 2.73.3)
+# GLib-GIO-DEBUG: Using cross-namespace EXTERNAL authentication (this will deadlock if server is GDBus < 2.73.3)
+1..1
+# Start of ops tests
+# testcase 0 op 0
+collecting# 
+    Cubic 0: # M 100.000000 100.000000 C 150.000000 100.000000 200.000000 100.000000 250.000000 100.000000 
+    Cubic 1: # M 250.000000 100.000000 C 300.000000 100.000000 350.000000 100.000000 400.000000 100.000000 
+    Line 2: # M 400 100 L 200 300 
+    Line 3: # M 200 300 L 100 100 
+    Cubic 4: # M 200.000000 100.000000 C 250.000000 100.000000 300.000000 100.000000 350.000000 100.000000 
+    Cubic 5: # M 350.000000 100.000000 C 400.000000 100.000000 450.000000 100.000000 500.000000 100.000000 
+    Line 6: # M 500 100 L 300 300 
+    Line 7: # M 300 300 L 200 100 
+splitting# 
+1 intersections between Cubic 0 and Cubic 1# 
+1 intersections between Cubic 0 and Line 3# 
+9 intersections between Cubic 0 and Cubic 4# 
+# split Cubic 0.0 from Cubic 0 at 0.666666: M 100.000000 100.000000 C 133.333298 100.000000 166.666595 100.000000 199.999893 100.000000
+split Cubic 0.1 from Cubic 0 at 0.666666: M 199.999893 100.000000 C 216.666595 100.000000 233.333298 100.000000 250.000000 100.000000split Cubic 0.4 from Cubic 0 at 0.00600814: M 200.300323 100.000000 C 216.866882 100.000000 233.433441 100.000000 250.000000 100.000000split Cubic 0.7 from Cubic 0 at 0.00604445: M 200.600708 100.000000 C 217.067139 100.000000 233.533569 100.000000 250.000000 100.000000# split Cubic 4.9 from Cubic 4 at 0.00533867: M 200.800812 100.000000 C 250.533875 100.000000 300.266937 100.000000 350.000000 100.000000
+1 intersections between Cubic 0.1 and Line 7# 
+1 intersections between Cubic 1 and Line 2# 
+9 intersections between Cubic 1 and Cubic 4.9# 
+split Cubic 1.9 from Cubic 1 at 0.00534248: M 250.801361 100.000000 C 300.534241 100.000000 350.267120 100.000000 400.000000 100.000000# split Cubic 4.9.0 from Cubic 4.9 at 0.329756: M 200.800812 100.000000 C 217.200577 100.000000 233.600342 100.000000 250.000122 100.000000
+# split Cubic 4.9.1 from Cubic 4.9 at 0.329756: M 250.000122 100.000000 C 283.333435 100.000000 316.666718 100.000000 350.000000 100.000000
+# split Cubic 4.9.6 from Cubic 4.9 at 0.00500283: M 250.500412 100.000000 C 283.666931 100.000000 316.833466 100.000000 350.000000 100.000000
+9 intersections between Cubic 1.9 and Cubic 5# 
+# split Cubic 1.9.0 from Cubic 1.9 at 0.664877: M 250.801361 100.000000 C 283.867615 100.000000 316.933868 100.000000 350.000122 100.000000
+split Cubic 1.9.1 from Cubic 1.9 at 0.664877: M 350.000122 100.000000 C 366.666748 100.000000 383.333374 100.000000 400.000000 100.000000split Cubic 1.9.4 from Cubic 1.9 at 0.00601021: M 350.300598 100.000000 C 366.867065 100.000000 383.433533 100.000000 400.000000 100.000000split Cubic 1.9.7 from Cubic 1.9 at 0.00604655: M 350.601074 100.000000 C 367.067383 100.000000 383.533691 100.000000 400.000000 100.000000# split Cubic 5.9 from Cubic 5 at 0.00534248: M 350.801361 100.000000 C 400.534241 100.000000 450.267120 100.000000 500.000000 100.000000
+1 intersections between Line 2 and Line 3# 
+1 intersections between Line 2 and Line 7# 
+# split Line 2.0 from Line 2 at 0.666667: M 400 100 L 266.667 233.333
+split Line 2.1 from Line 2 at 0.666667: M 266.667 233.333 L 200 300# split Line 7.0 from Line 7 at 0.333333: M 300 300 L 266.667 233.333
+# split Line 7.1 from Line 7 at 0.333333: M 266.667 233.333 L 200 100
+1 intersections between Cubic 4 and Cubic 4.9.0# 
+1 intersections between Cubic 4 and Line 7.1# 
+1 intersections between Cubic 4.9.0 and Cubic 4.9.1# 
+1 intersections between Cubic 4.9.1 and Cubic 4.9.6# 
+1 intersections between Cubic 4.9.6 and Cubic 5# 
+1 intersections between Cubic 5 and Cubic 5.9# 
+1 intersections between Cubic 5.9 and Line 6# 
+1 intersections between Line 6 and Line 7.0# 
+    Cubic 0.0: # M 100.000000 100.000000 C 133.333298 100.000000 166.666595 100.000000 199.999893 100.000000 
+    Cubic 0.1: # M 199.999893 100.000000 C 200.100037 100.000000 200.200180 100.000000 200.300323 100.000000 
+    Cubic 0.4: # M 200.300323 100.000000 C 200.400452 100.000000 200.500580 100.000000 200.600708 100.000000 
+    Cubic 0.7: # M 200.600708 100.000000 C 217.067139 100.000000 233.533569 100.000000 250.000000 100.000000 
+    Cubic 1: # M 250.000000 100.000000 C 250.267120 100.000000 250.534241 100.000000 250.801361 100.000000 
+    Cubic 1.9.0: # M 250.801361 100.000000 C 283.867615 100.000000 316.933868 100.000000 350.000122 100.000000 
+    Cubic 1.9.1: # M 350.000122 100.000000 C 350.100281 100.000000 350.200439 100.000000 350.300598 100.000000 
+    Cubic 1.9.4: # M 350.300598 100.000000 C 350.400757 100.000000 350.500916 100.000000 350.601074 100.000000 
+    Cubic 1.9.7: # M 350.601074 100.000000 C 367.067383 100.000000 383.533691 100.000000 400.000000 100.000000 
+    Line 2.0: # M 400 100 L 266.667 233.333 
+    Line 2.1: # M 266.667 233.333 L 200 300 
+    Line 3: # M 200 300 L 100 100 
+    Cubic 4: # M 200.000000 100.000000 C 200.266937 100.000000 200.533875 100.000000 200.800812 100.000000 
+    Cubic 4.9.0: # M 200.800812 100.000000 C 217.200577 100.000000 233.600342 100.000000 250.000122 100.000000 
+    Cubic 4.9.1: # M 250.000122 100.000000 C 250.166885 100.000000 250.333649 100.000000 250.500412 100.000000 
+    Cubic 4.9.6: # M 250.500412 100.000000 C 283.666931 100.000000 316.833466 100.000000 350.000000 100.000000 
+    Cubic 5: # M 350.000000 100.000000 C 350.267120 100.000000 350.534241 100.000000 350.801361 100.000000 
+    Cubic 5.9: # M 350.801361 100.000000 C 400.534241 100.000000 450.267120 100.000000 500.000000 100.000000 
+    Line 6: # M 500 100 L 300 300 
+    Line 7.0: # M 300 300 L 266.667 233.333 
+    Line 7.1: # M 266.667 233.333 L 200 100 
+classifying# 
+ 01 Cubic 0.0: # M 100.000000 100.000000 C 133.333298 100.000000 166.666595 100.000000 199.999893 100.000000 
+[11 Cubic 0.7: # M 200.600708 100.000000 C 217.067139 100.000000 233.533569 100.000000 250.000000 100.000000 ]
+[11 Cubic 1.9.0: # M 250.801361 100.000000 C 283.867615 100.000000 316.933868 100.000000 350.000122 100.000000 ]
+[11 Cubic 1.9.7: # M 350.601074 100.000000 C 367.067383 100.000000 383.533691 100.000000 400.000000 100.000000 ]
+[11 Line 2.0: # M 400 100 L 266.667 233.333 ]
+ 01 Line 2.1: # M 266.667 233.333 L 200 300 
+ 01 Line 3: # M 200 300 L 100 100 
+[11 Cubic 4: # M 200.000000 100.000000 C 200.266937 100.000000 200.533875 100.000000 200.800812 100.000000 ]
+[11 Cubic 4.9.0: # M 200.800812 100.000000 C 217.200577 100.000000 233.600342 100.000000 250.000122 100.000000 ]
+[11 Cubic 4.9.6: # M 250.500412 100.000000 C 283.666931 100.000000 316.833466 100.000000 350.000000 100.000000 ]
+[11 Cubic 5: # M 350.000000 100.000000 C 350.267120 100.000000 350.534241 100.000000 350.801361 100.000000 ]
+ 01 Cubic 5.9: # M 350.801361 100.000000 C 400.534241 100.000000 450.267120 100.000000 500.000000 100.000000 
+ 01 Line 6: # M 500 100 L 300 300 
+ 01 Line 7.0: # M 300 300 L 266.667 233.333 
+[11 Line 7.1: # M 266.667 233.333 L 200 100 ]
+fixups# 
+# found 3 bad nodes
+# split Cubic 0/Cubic 4 BAD 200.600723 100.000000
+# 	[11 Line 7.1 ] 116.565
+# 	[11 Cubic 0.7 ] 180
+# 	[11 Cubic 4 ] 180
+# 	[11 Cubic 4 ] 180
+# 	[11 Cubic 4.9.0 ] 180
+# 	>01 Cubic 0.0  360
+# split Cubic 1/Cubic 4.9 BAD 250.801376 100.000000
+# 	[11 Cubic 1.9.0 ] 180
+# 	[11 Cubic 4.9.6 ] 180
+# 	[11 Cubic 0.7 ] 360
+# 	[11 Cubic 4.9.0 ] 360
+# split Cubic 1.9/Cubic 5 BAD 350.601105 100.000000
+# 	[11 Cubic 1.9.7 ] 180
+# 	[11 Cubic 5 ] 180
+# 	[11 Cubic 5 ] 180
+# 	<01 Cubic 5.9  180
+# 	[11 Cubic 1.9.0 ] 360
+# 	[11 Cubic 4.9.6 ] 360
+reassembling# 
+start new contour Cubic 0.0# 
+# Cubic 0.0 ends at: 
+# start 0 100.000000 100.000000
+# 	>01 Line 3  116.565
+# 	(10 Cubic 0.0 ) 180
+picking cw# 
+append Line 3# 
+# Line 3 ends at: 
+# end 2 200.000000 300.000000
+# 	>01 Line 2.1  225
+# 	(10 Line 3 ) 296.565
+picking cw# 
+append Line 2.1# 
+# Line 2.1 ends at: 
+# split Line 2/Line 7 266.666656 233.333344
+# 	(10 Line 2.1 ) 45
+# 	>01 Line 7.0  116.565
+# 	[11 Line 2.0 ] 225
+# 	[11 Line 7.1 ] 296.565
+picking cw# 
+append Line 7.0# 
+# Line 7.0 ends at: 
+# end 6 300.000000 300.000000
+# 	>01 Line 6  225
+# 	(10 Line 7.0 ) 296.565
+picking cw# 
+append Line 6# 
+# Line 6 ends at: 
+# end 5 500.000000 100.000000
+# 	(10 Line 6 ) 45
+# 	>01 Cubic 5.9  360
+picking cw# 
+append Cubic 5.9# 
+# Cubic 5.9 ends at: 
+# split Cubic 1.9/Cubic 5 BAD 350.601105 100.000000
+# 	[11 Cubic 1.9.7 ] 180
+# 	[11 Cubic 5 ] 180
+# 	[11 Cubic 5 ] 180
+# 	(10 Cubic 5.9 ) 180
+# 	[11 Cubic 1.9.0 ] 360
+# 	[11 Cubic 4.9.6 ] 360
+picking cw# 
+**
+ERROR:../testsuite/gsk/path-ops.c:359:test_ops_simple: assertion failed (s == tests[i].out): ("M 354.60110473632812 100 A 4 4 0 0 0 346.60110473632812 100 A 4 4 0 0 0 354.60110473632812 100 z M 252.80137634277344 100 A 2 2 0 0 0 248.80137634277344 100 A 2 2 0 0 0 252.80137634277344 100 z M 204.60072326660156 100 A 4 4 0 0 0 196.60072326660156 100 A 4 4 0 0 0 204.60072326660156 100 z" == "M 100 100 z")
+not ok /ops/simple - ERROR:../testsuite/gsk/path-ops.c:359:test_ops_simple: assertion failed (s == tests[i].out): ("M 354.60110473632812 100 A 4 4 0 0 0 346.60110473632812 100 A 4 4 0 0 0 354.60110473632812 100 z M 252.80137634277344 100 A 2 2 0 0 0 248.80137634277344 100 A 2 2 0 0 0 252.80137634277344 100 z M 204.60072326660156 100 A 4 4 0 0 0 196.60072326660156 100 A 4 4 0 0 0 204.60072326660156 100 z" == "M 100 100 z")
+Bail out!

demos/gtk-demo/demo.gresource.xml

@@ -336,6 +336,7 @@
     <file>panes.c</file>
     <file>password_entry.c</file>
     <file>path_fill.c</file>
+    <file>path_text.c</file>
     <file>peg_solitaire.c</file>
     <file>pickers.c</file>
     <file>printing.c</file>
@@ -421,6 +422,9 @@
   <gresource prefix="/fontrendering">
     <file>fontrendering.ui</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

@@ -73,6 +73,7 @@ demos = files([
   'panes.c',
   'password_entry.c',
   'path_fill.c',
+  'path_text.c',
   'peg_solitaire.c',
   'pickers.c',
   'printing.c',

demos/gtk-demo/path_text.c

@@ -0,0 +1,604 @@
+/* Path/Text
+ *
+ * This demo shows how to use GskPath to animate 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;
+  float line_closest;
+
+  GskPath *line_path;
+  GskPathMeasure *line_measure;
+  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, &point))
+    {
+      GskPath *path = gsk_path_measure_get_path (measure);
+
+      gsk_path_point_get_position (path, &point, res);
+      gsk_path_point_get_tangent (path, &point, GSK_PATH_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 (GskPathMeasure         *measure,
+                    GskPath                *path,
+                    const graphene_point_t *offset)
+{
+  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);
+
+  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);
+  g_clear_pointer (&self->line_measure, gsk_path_measure_unref);
+}
+
+static void
+gtk_path_widget_create_text_path (GtkPathWidget *self)
+{
+  GskPath *path;
+  graphene_point_t offset;
+
+  gtk_path_widget_clear_text_path (self);
+
+  if (self->line_measure == NULL)
+    return;
+
+  path = create_path_from_text (GTK_WIDGET (self), self->text, &offset);
+  self->text_path = gtk_path_transform (self->line_measure, 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);
+
+  self->line_measure = gsk_path_measure_new (self->line_path);
+
+  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);
+    }
+
+  if (self->line_closest >= 0)
+    {
+      GskPathBuilder *builder;
+      GskPathPoint point;
+      graphene_point_t closest;
+
+      builder = gsk_path_builder_new ();
+      if (gsk_path_measure_get_point (self->line_measure, self->line_closest, &point))
+        {
+          gsk_path_point_get_position (self->line_path, &point, &closest);
+          gsk_path_builder_add_circle (builder, &closest, 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) { 0, 0, 1, 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 (gsk_path_measure_get_path (self->line_measure),
+                                  &GRAPHENE_POINT_INIT (x, y),
+                                  INFINITY,
+                                  &point))
+    {
+      gsk_path_point_get_position (self->line_path, &point, &pos);
+      self->line_closest = graphene_point_distance (&pos, &GRAPHENE_POINT_INIT (x, y), NULL, NULL);
+    
+      gtk_widget_queue_draw (GTK_WIDGET (self));
+    }
+}
+
+static void
+pointer_leave (GtkEventControllerMotion *controller,
+               GtkPathWidget            *self)
+{
+  self->line_closest = -1;
+
+  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->line_closest = -1;
+
+  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>

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 +82,18 @@ 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                   offset,
+                                                 GskRealPathPoint       *result);
+  float                 (* get_distance)        (const GskContour       *contour,
+                                                 GskRealPathPoint       *point,
+                                                 gpointer                measure_data);
 };
 
 /* {{{ Utilities */
@@ -230,6 +242,38 @@ gsk_standard_contour_reverse (const GskContour *contour)
   return res;
 }
 
+static int
+gsk_standard_contour_get_winding (const GskContour       *contour,
+                                  const graphene_point_t *point)
+{
+  GskStandardContour *self = (GskStandardContour *) contour;
+  int winding = 0;
+
+  for (gsize i = 0; i < self->n_ops; i ++)
+    {
+      GskCurve c;
+
+      if (gsk_pathop_op (self->ops[i]) == GSK_PATH_MOVE)
+        continue;
+
+      gsk_curve_init (&c, self->ops[i]);
+      winding += gsk_curve_get_crossing (&c, point);
+    }
+
+  if ((self->flags & GSK_PATH_CLOSED) == 0)
+    {
+      GskCurve c;
+
+      gsk_curve_init (&c, gsk_pathop_encode (GSK_PATH_CLOSE,
+                                             (const graphene_point_t[]) { self->points[self->n_points - 1],
+                                                                          self->points[0] }));
+
+      winding += gsk_curve_get_crossing (&c, point);
+    }
+
+  return winding;
+}
+
 static GskPathFlags
 gsk_standard_contour_get_flags (const GskContour *contour)
 {
@@ -373,38 +417,6 @@ gsk_standard_contour_get_start_end (const GskContour *contour,
     *end = self->points[self->n_points - 1];
 }
 
-static int
-gsk_standard_contour_get_winding (const GskContour       *contour,
-                                  const graphene_point_t *point)
-{
-  GskStandardContour *self = (GskStandardContour *) contour;
-  int winding = 0;
-
-  for (gsize i = 0; i < self->n_ops; i ++)
-    {
-      GskCurve c;
-
-      if (gsk_pathop_op (self->ops[i]) == GSK_PATH_MOVE)
-        continue;
-
-      gsk_curve_init (&c, self->ops[i]);
-      winding += gsk_curve_get_crossing (&c, point);
-    }
-
-  if ((self->flags & GSK_PATH_CLOSED) == 0)
-    {
-      GskCurve c;
-
-      gsk_curve_init (&c, gsk_pathop_encode (GSK_PATH_CLOSE,
-                                             (const graphene_point_t[]) { self->points[self->n_points - 1],
-                                                                          self->points[0] }));
-
-      winding += gsk_curve_get_crossing (&c, point);
-    }
-
-  return winding;
-}
-
 static gsize
 gsk_standard_contour_get_n_points (const GskContour *contour)
 {
@@ -622,6 +634,164 @@ gsk_standard_contour_add_segment (const GskContour *contour,
     }
 }
 
+typedef struct
+{
+  float start;
+  float end;
+  float start_progress;
+  float end_progress;
+  GskCurveLineReason reason;
+  gsize op;
+} GskStandardContourMeasure;
+
+typedef struct
+{
+  GArray *array;
+  GskStandardContourMeasure measure;
+} LengthDecompose;
+
+static gboolean
+gsk_standard_contour_measure_add_point (const graphene_point_t *from,
+                                        const graphene_point_t *to,
+                                        float                   from_progress,
+                                        float                   to_progress,
+                                        GskCurveLineReason      reason,
+                                        gpointer                user_data)
+{
+  LengthDecompose *decomp = user_data;
+  float seg_length;
+
+  seg_length = graphene_point_distance (from, to, NULL, NULL);
+
+  decomp->measure.end += seg_length;
+
+  if (decomp->measure.end <= decomp->measure.start)
+    return TRUE;
+
+  decomp->measure.start_progress = from_progress;
+  decomp->measure.end_progress = to_progress;
+  decomp->measure.reason = reason;
+
+  g_array_append_val (decomp->array, decomp->measure);
+
+  decomp->measure.start += seg_length;
+
+  return TRUE;
+}
+
+static gpointer
+gsk_standard_contour_init_measure (const GskContour *contour,
+                                   float             tolerance,
+                                   float            *out_length)
+{
+  const GskStandardContour *self = (const GskStandardContour *) contour;
+  gsize i;
+  float length;
+  GArray *array;
+
+  array = g_array_new (FALSE, FALSE, sizeof (GskStandardContourMeasure));
+  length = 0;
+
+  for (i = 1; i < self->n_ops; i ++)
+    {
+      GskCurve curve;
+      LengthDecompose decomp = { array, { length, length, 0, 0, GSK_CURVE_LINE_REASON_SHORT, i } };
+
+      gsk_curve_init (&curve, self->ops[i]);
+      gsk_curve_decompose (&curve, tolerance, gsk_standard_contour_measure_add_point, &decomp);
+      length = decomp.measure.start;
+    }
+
+  *out_length = length;
+
+  return array;
+}
+
+static void
+gsk_standard_contour_free_measure (const GskContour *contour,
+                                   gpointer          data)
+{
+  g_array_free (data, TRUE);
+}
+
+static int
+gsk_standard_contour_find_measure (gconstpointer m,
+                                   gconstpointer l)
+{
+  const GskStandardContourMeasure *measure = m;
+  float length = *(const float *) l;
+
+  if (measure->start > length)
+    return 1;
+  else if (measure->end <= length)
+    return -1;
+  else
+    return 0;
+}
+
+static void
+gsk_standard_contour_get_point (const GskContour *contour,
+                                gpointer          measure_data,
+                                float             distance,
+                                GskRealPathPoint *result)
+{
+  GArray *array = measure_data;
+  unsigned int idx;
+  GskStandardContourMeasure *measure;
+  float fraction, t;
+
+  if (array->len == 0)
+    {
+      result->idx = 0;
+      result->t = 0;
+      return;
+    }
+
+  if (!g_array_binary_search (array, &distance, gsk_standard_contour_find_measure, &idx))
+    idx = array->len - 1;
+
+  measure = &g_array_index (array, GskStandardContourMeasure, idx);
+
+  fraction = (distance - measure->start) / (measure->end - measure->start);
+  t = measure->start_progress + fraction * (measure->end_progress - measure->start_progress);
+
+  g_assert (t >= 0 && t <= 1);
+
+  result->idx = measure->op;
+  result->t = t;
+}
+
+static float
+gsk_standard_contour_get_distance (const GskContour *contour,
+                                   GskRealPathPoint *point,
+                                   gpointer          measure_data)
+{
+  GArray *array = measure_data;
+
+  if (G_UNLIKELY (point->idx == 0))
+    return 0;
+
+  for (unsigned int i = 0; i < array->len; i++)
+    {
+      GskStandardContourMeasure *measure = &g_array_index (array, GskStandardContourMeasure, i);
+      float fraction;
+
+      if (measure->op != point->idx)
+        continue;
+
+      if (measure->end_progress < point->t)
+        continue;
+
+      g_assert (measure->op == point->idx);
+      g_assert (measure->start_progress <= point->t && point->t <= measure->end_progress);
+
+      fraction = (point->t - measure->start_progress) / (measure->end_progress - measure->start_progress);
+      return measure->start + fraction * (measure->end - measure->start);
+    }
+
+  return 0;
+}
+
 static const GskContourClass GSK_STANDARD_CONTOUR_CLASS =
 {
   sizeof (GskStandardContour),
@@ -642,6 +812,10 @@ 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,
@@ -778,6 +952,12 @@ gsk_contour_get_winding (const GskContour       *self,
   return self->klass->get_winding (self, point);
 }
 
+gsize
+gsk_contour_get_n_points (const GskContour *self)
+{
+  return self->klass->get_n_points (self);
+}
+
 gboolean
 gsk_contour_get_closest_point (const GskContour       *self,
                                const graphene_point_t *point,
@@ -788,12 +968,6 @@ gsk_contour_get_closest_point (const GskContour       *self,
   return self->klass->get_closest_point (self, point, threshold, result, out_dist);
 }
 
-gsize
-gsk_contour_get_n_points (const GskContour *self)
-{
-  return self->klass->get_n_points (self);
-}
-
 void
 gsk_contour_get_position (const GskContour *self,
                           GskRealPathPoint *point,
@@ -829,6 +1003,38 @@ 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             offset,
+                       GskRealPathPoint *result)
+{
+  self->klass->get_point (self, measure_data, offset, result);
+}
+
+float
+gsk_contour_get_distance (const GskContour *self,
+                          GskRealPathPoint *point,
+                          gpointer          measure_data)
+{
+  return self->klass->get_distance (self, point, measure_data);
+}
+
 /* }}} */
 
 /* vim:set foldmethod=marker expandtab: */

gsk/gskcontourprivate.h

@@ -63,9 +63,11 @@ gboolean                gsk_contour_get_closest_point           (const GskContou
                                                                  float                   threshold,
                                                                  GskRealPathPoint       *result,
                                                                  float                  *out_dist);
+
 void                    gsk_contour_get_position                (const GskContour       *self,
                                                                  GskRealPathPoint       *point,
                                                                  graphene_point_t       *pos);
+
 void                    gsk_contour_get_tangent                 (const GskContour       *self,
                                                                  GskRealPathPoint       *point,
                                                                  GskPathDirection        direction,
@@ -73,6 +75,7 @@ void                    gsk_contour_get_tangent                 (const GskContou
 float                   gsk_contour_get_curvature               (const GskContour       *self,
                                                                  GskRealPathPoint       *point,
                                                                  graphene_point_t       *center);
+
 void                    gsk_contour_add_segment                 (const GskContour       *self,
                                                                  GskPathBuilder         *builder,
                                                                  gboolean                emit_move_to,
@@ -80,4 +83,22 @@ void                    gsk_contour_add_segment                 (const GskContou
                                                                  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                   offset,
+                                                                 GskRealPathPoint       *result);
+float                   gsk_contour_get_distance                (const GskContour       *self,
+                                                                 GskRealPathPoint       *point,
+                                                                 gpointer                measure_data);
+gboolean                gsk_contour_dash                        (const GskContour       *contour,
+                                                                 GskStroke              *stroke,
+                                                                 float                   tolerance,
+                                                                 GskPathForeachFunc      func,
+                                                                 gpointer                user_data);
+
 G_END_DECLS

gsk/gskcurve.c

@@ -24,7 +24,7 @@
 
 /* GskCurve collects all the functionality we need for Bézier segments */
 
-#define MIN_PROGRESS (1/1024.f)
+#define MIN_PROGRESS (1/2048.f)
 
 typedef struct _GskCurveClass GskCurveClass;
 
@@ -524,20 +524,6 @@ gsk_quad_curve_segment (const GskCurve *curve,
   gsk_quad_curve_split (&tmp, (end - start) / (1.0f - start), segment, NULL);
 }
 
-/* taken from Skia, including the very descriptive name */
-static gboolean
-gsk_quad_curve_too_curvy (const GskQuadCurve *self,
-                               float          tolerance)
-{
-  const graphene_point_t *pts = self->points;
-  float dx, dy;
-
-  dx = fabs (pts[1].x / 2 - (pts[0].x + pts[2].x) / 4);
-  dy = fabs (pts[1].y / 2 - (pts[0].y + pts[2].y) / 4);
-
-  return MAX (dx, dy) > tolerance;
-}
-
 static gboolean
 gsk_quad_curve_decompose_step (const GskCurve      *curve,
                                float                start_progress,
@@ -550,8 +536,8 @@ gsk_quad_curve_decompose_step (const GskCurve      *curve,
   GskCurve left, right;
   float mid_progress;
 
-  if (!gsk_quad_curve_too_curvy (self, tolerance))
-    return add_line_func (&self->points[0], &self->points[2], start_progress, end_progress, GSK_CURVE_LINE_REASON_STRAIGHT, user_data);
+  if (graphene_point_distance (&self->points[0], &self->points[2], NULL, NULL) < tolerance)
+    return add_line_func (&self->points[0], &self->points[2], start_progress, end_progress, GSK_CURVE_LINE_REASON_SHORT, user_data);
   if (end_progress - start_progress <= MIN_PROGRESS)
     return add_line_func (&self->points[0], &self->points[2], start_progress, end_progress, GSK_CURVE_LINE_REASON_SHORT, user_data);
 
@@ -994,25 +980,6 @@ gsk_cubic_curve_segment (const GskCurve *curve,
   gsk_cubic_curve_split (&tmp, (end - start) / (1.0f - start), segment, NULL);
 }
 
-/* taken from Skia, including the very descriptive name */
-static gboolean
-gsk_cubic_curve_too_curvy (const GskCubicCurve *self,
-                           float                tolerance)
-{
-  const graphene_point_t *pts = self->points;
-  graphene_point_t p;
-
-  graphene_point_interpolate (&pts[0], &pts[3], 1.0f / 3, &p);
-  if (MAX (ABS (p.x - pts[1].x), ABS (p.y - pts[1].y)) > tolerance)
-    return TRUE;
-
-  graphene_point_interpolate (&pts[0], &pts[3], 2.0f / 3, &p);
-  if (MAX (ABS (p.x - pts[2].x), ABS (p.y - pts[2].y)) > tolerance)
-    return TRUE;
-
-  return FALSE;
-}
-
 static gboolean
 gsk_cubic_curve_decompose_step (const GskCurve      *curve,
                                 float                start_progress,
@@ -1025,8 +992,8 @@ gsk_cubic_curve_decompose_step (const GskCurve      *curve,
   GskCurve left, right;
   float mid_progress;
 
-  if (!gsk_cubic_curve_too_curvy (self, tolerance))
-    return add_line_func (&self->points[0], &self->points[3], start_progress, end_progress, GSK_CURVE_LINE_REASON_STRAIGHT, user_data);
+  if (graphene_point_distance (&self->points[0], &self->points[3], NULL, NULL) < tolerance)
+    return add_line_func (&self->points[0], &self->points[3], start_progress, end_progress, GSK_CURVE_LINE_REASON_SHORT, user_data);
   if (end_progress - start_progress <= MIN_PROGRESS)
     return add_line_func (&self->points[0], &self->points[3], start_progress, end_progress, GSK_CURVE_LINE_REASON_SHORT, user_data);
 

gsk/gskpath.h

@@ -131,6 +131,13 @@ gboolean                gsk_path_foreach                        (GskPath
                                                                  GskPathForeachFunc      func,
                                                                  gpointer                user_data);
 
+GDK_AVAILABLE_IN_4_14
+gboolean                gsk_path_dash                           (GskPath                *self,
+                                                                 GskStroke              *stroke,
+                                                                 float                   tolerance,
+                                                                 GskPathForeachFunc      func,
+                                                                 gpointer                user_data);
+
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(GskPath, gsk_path_unref)
 
 G_END_DECLS

gsk/gskpathbuilder.h

@@ -73,6 +73,7 @@ void                    gsk_path_builder_add_segment            (GskPathBuilder
                                                                  GskPath                *path,
                                                                  const GskPathPoint     *start,
                                                                  const GskPathPoint     *end);
+
 GDK_AVAILABLE_IN_4_14
 void                    gsk_path_builder_move_to                (GskPathBuilder         *self,
                                                                  float                   x,

gsk/gskpathdash.c

@@ -0,0 +1,304 @@
+/*
+ * 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 "gskcontourprivate.h"
+#include "gskcurveprivate.h"
+#include "gskpathprivate.h"
+#include "gskstrokeprivate.h"
+
+typedef struct
+{
+  float offset;                 /* how much of the current dash we've spent */
+  gsize dash_index;             /* goes from 0 to n_dash * 2, so we don't have to care about on/off
+                                   for uneven dashes */
+  gboolean on;                  /* If we're currently dashing or not */
+  gboolean may_close;           /* TRUE if we haven't turned the dash off in this contour */
+  gboolean needs_move_to;       /* If we have emitted the initial move_to() yet */
+  enum {
+    NORMAL, /* no special behavior required */
+    SKIP,   /* skip the next dash */
+    ONLY,   /* only do the first dash */
+    DONE    /* done with the first dash */
+  } first_dash_behavior;        /* How to handle the first dash in the loop. We loop closed contours
+                                   twice to make sure the first dash and the last dash can get joined */
+
+  GskCurve curve;               /* Curve we are currently processing */
+
+  float collect_start;          /* We're collecting multiple line segments when decomposing. */
+  float collect_length;         /* No need to emit a curve for every line segment when the dash is long enough. */
+
+  /* from the stroke */
+  float *dash;
+  gsize n_dash;
+  float dash_length;
+  float dash_offset;
+
+  float tolerance;
+  GskPathForeachFunc func;
+  gpointer user_data;
+} GskPathDash;
+
+static void
+gsk_path_dash_setup (GskPathDash *self)
+{
+  self->offset = fmodf (self->dash_offset, 2 * self->dash_length);
+
+  self->dash_index = 0;
+  self->on = TRUE;
+  self->may_close = TRUE;
+  while (self->offset > self->dash[self->dash_index % self->n_dash])
+    {
+      self->offset -= self->dash[self->dash_index % self->n_dash];
+      self->dash_index++;
+      self->on = !self->on;
+    }
+  if (self->first_dash_behavior != ONLY)
+    self->needs_move_to = TRUE;
+}
+
+static gboolean
+gsk_path_dash_ensure_move_to (GskPathDash            *self,
+                              const graphene_point_t *pt)
+{
+  if (!self->needs_move_to)
+    return TRUE;
+
+  if (!self->func (GSK_PATH_MOVE, pt, 1, self->user_data))
+    return FALSE;
+
+  self->needs_move_to = FALSE;
+  return TRUE;
+}
+
+static gboolean
+gsk_path_dash_add_line_segment (const graphene_point_t *start,
+                                const graphene_point_t *end,
+                                float                   t_start,
+                                float                   t_end,
+                                GskCurveLineReason      reason,
+                                gpointer                user_data)
+{
+  GskPathDash *self = user_data;
+  float remaining, length, t_step;
+
+  length = graphene_point_distance (start, end, NULL, NULL);
+  if (self->collect_length)
+    {
+      t_start = self->collect_start;
+      length += self->collect_length;
+      self->collect_length = 0;
+    }
+
+  t_step = t_end - t_start;
+  remaining = length;
+
+  while (remaining)
+    {
+      float piece;
+
+      if (self->offset + remaining <= self->dash[self->dash_index % self->n_dash])
+        {
+          /* try collecting multiple line segments */
+          if (t_end < 1.0)
+            {
+              self->collect_start = t_start + t_step * (length - remaining) / length;
+              self->collect_length = remaining;
+              return TRUE;
+            }
+
+          piece = remaining;
+        }
+      else
+        piece = self->dash[self->dash_index % self->n_dash] - self->offset;
+
+      if (self->on)
+        {
+          if (self->first_dash_behavior != SKIP)
+            {
+              GskCurve segment;
+
+              if (piece)
+                {
+                  gsk_curve_segment (&self->curve,
+                                     t_start + t_step * (length - remaining) / length,
+                                     t_start + t_step * (length - (remaining - piece)) / length,
+                                     &segment);
+                  if (!gsk_path_dash_ensure_move_to (self, gsk_curve_get_start_point (&segment)))
+                    return FALSE;
+
+                  if (!gsk_pathop_foreach (gsk_curve_pathop (&segment), self->func, self->user_data))
+                    return FALSE;
+                }
+              else
+                {
+                  graphene_point_t p;
+
+                  gsk_curve_get_point (&self->curve, t_start + t_step * (length - remaining) / length, &p);
+                  if (!gsk_path_dash_ensure_move_to (self, &p))
+                    return FALSE;
+                }
+            }
+        }
+      else
+        {
+          self->may_close = FALSE;
+          if (self->first_dash_behavior == ONLY)
+            {
+              self->first_dash_behavior = DONE;
+              return FALSE;
+            }
+          self->first_dash_behavior = NORMAL;
+        }
+
+      if (self->offset + remaining <= self->dash[self->dash_index % self->n_dash])
+        {
+          self->offset += remaining;
+          remaining = 0;
+        }
+      else
+        {
+          remaining -= piece;
+          self->offset = 0;
+          self->dash_index++;
+          self->dash_index %= 2 * self->n_dash;
+          self->on = !self->on;
+          self->needs_move_to = TRUE;
+        }
+    }
+
+  return TRUE;
+}
+
+static gboolean
+gsk_path_dash_foreach (GskPathOperation        op,
+                       const graphene_point_t *pts,
+                       gsize                   n_pts,
+                       gpointer                user_data)
+{
+  GskPathDash *self = user_data;
+
+  switch (op)
+  {
+    case GSK_PATH_MOVE:
+      gsk_path_dash_setup (self);
+      break;
+
+    case GSK_PATH_CLOSE:
+      if (self->may_close)
+        {
+          if (graphene_point_equal (&pts[0], &pts[1]))
+            return self->func (GSK_PATH_CLOSE, pts, 2, self->user_data);
+        }
+      else
+        op = GSK_PATH_LINE;
+      G_GNUC_FALLTHROUGH;
+
+    case GSK_PATH_LINE:
+    case GSK_PATH_QUAD:
+    case GSK_PATH_CUBIC:
+      gsk_curve_init_foreach (&self->curve, op, pts, n_pts);
+      if (!gsk_curve_decompose (&self->curve, self->tolerance, gsk_path_dash_add_line_segment, self))
+        return FALSE;
+      break;
+
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+
+  return TRUE;
+}
+
+gboolean
+gsk_contour_dash (const GskContour   *contour,
+                  GskStroke          *stroke,
+                  float               tolerance,
+                  GskPathForeachFunc  func,
+                  gpointer            user_data)
+{
+  GskPathDash self = {
+    .offset = 0,
+    .dash = stroke->dash,
+    .n_dash = stroke->n_dash,
+    .dash_length = stroke->dash_length,
+    .dash_offset = stroke->dash_offset,
+    .tolerance = tolerance,
+    .func = func,
+    .user_data = user_data
+  };
+  gboolean is_closed = gsk_contour_get_flags (contour) & GSK_PATH_CLOSED ? TRUE : FALSE;
+
+  self.first_dash_behavior = is_closed ? SKIP : NORMAL;
+  if (!gsk_contour_foreach (contour, tolerance, gsk_path_dash_foreach, &self))
+    return FALSE;
+
+  if (is_closed)
+    {
+      if (self.first_dash_behavior == NORMAL)
+        self.first_dash_behavior = ONLY;
+      else
+        self.first_dash_behavior = NORMAL;
+      self.needs_move_to = !self.on;
+      if (!gsk_contour_foreach (contour, tolerance, gsk_path_dash_foreach, &self) &&
+          self.first_dash_behavior != DONE)
+        return FALSE;
+    }
+
+  return TRUE;
+}
+
+/**
+ * gsk_path_dash:
+ * @self: the `GskPath` to dash
+ * @stroke: the stroke containing the dash parameters
+ * @tolerance: tolerance to use while dashing
+ * @func: (scope call) (closure user_data): the function to call for operations
+ * @user_data: (nullable): user data passed to @func
+ *
+ * Calls @func for every operation of the path that is the result
+ * of dashing @self with the dash pattern from @stroke.
+ *
+ * Returns: `FALSE` if @func returned FALSE`, `TRUE` otherwise.
+ *
+ * Since: 4.14
+ */
+gboolean
+gsk_path_dash (GskPath            *self,
+               GskStroke          *stroke,
+               float               tolerance,
+               GskPathForeachFunc  func,
+               gpointer            user_data)
+{
+  gsize i;
+
+  /* Dashing disabled, no need to do any work */
+  if (stroke->dash_length <= 0)
+    return gsk_path_foreach (self, -1, func, user_data);
+
+  for (i = 0; i < gsk_path_get_n_contours (self); i++)
+    {
+      if (!gsk_contour_dash (gsk_path_get_contour (self, i), stroke, tolerance, func, user_data))
+        return FALSE;
+    }
+
+  return TRUE;
+}
+

gsk/gskpathmeasure.c

@@ -0,0 +1,328 @@
+/*
+ * 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
+ * @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,
+                            GskPathPoint   *result)
+{
+  GskRealPathPoint *res = (GskRealPathPoint *) result;
+  gsize i;
+  float offset;
+  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;
+
+  offset = gsk_path_measure_clamp_distance (self, distance);
+
+  for (i = 0; i < self->n_contours - 1; i++)
+    {
+      if (offset < self->measures[i].length)
+        break;
+
+      offset -= self->measures[i].length;
+    }
+
+  g_assert (0 <= i && i < self->n_contours);
+
+  offset = CLAMP (offset, 0, self->measures[i].length);
+
+  contour = gsk_path_get_contour (self->path, i);
+
+  gsk_contour_get_point (contour, self->measures[i].contour_data, offset, res);
+  res->contour = i;
+
+  return TRUE;
+}
+
+/**
+ * gsk_path_point_get_distance:
+ * @measure: a `GskPathMeasure`
+ * @point: a `GskPathPoint on the path of @self
+ *
+ * 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 (GskPathMeasure     *measure,
+                             const GskPathPoint *point)
+{
+  GskRealPathPoint *p = (GskRealPathPoint *)point;
+  const GskContour *contour;
+  float contour_offset = 0;
+
+  g_return_val_if_fail (measure != NULL, 0);
+  g_return_val_if_fail (point != 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);
+
+      contour_offset += measure->measures[i].length;
+    }
+
+  g_return_val_if_reached (0);
+}

gsk/gskpathmeasure.h

@@ -0,0 +1,62 @@
+/*
+ * 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,
+                                                                 GskPathPoint           *result);
+
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(GskPathMeasure, gsk_path_measure_unref)
+
+G_END_DECLS

gsk/gskpathpoint.c

@@ -22,6 +22,7 @@
 #include "gskpathpointprivate.h"
 
 #include "gskcontourprivate.h"
+#include "gskpathmeasure.h"
 
 #include "gdk/gdkprivate.h"
 
@@ -33,7 +34,8 @@
  * It can be queried for properties of the path at that point, such as its
  * tangent or its curvature.
  *
- * To obtain a `GskPathPoint`, use [method@Gsk.Path.get_closest_point].
+ * To obtain a `GskPathPoint`, use [method@Gsk.Path.get_closest_point]
+ * or [method@Gsk.PathMeasure.get_point].
  *
  * Note that `GskPathPoint` structs are meant to be stack-allocated, and
  * don't a reference to the path object they are obtained from. It is the

gsk/gskpathpoint.h

@@ -72,5 +72,8 @@ float                   gsk_path_point_get_curvature   (GskPath            *path
                                                         const GskPathPoint *point,
                                                         graphene_point_t   *center);
 
+GDK_AVAILABLE_IN_4_14
+float                   gsk_path_point_get_distance    (GskPathMeasure     *measure,
+                                                        const GskPathPoint *point);
 
 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 _GskStroke               GskStroke;

gsk/meson.build

@@ -27,7 +27,9 @@ gsk_public_sources = files([
   'gskdiff.c',
   'gskglshader.c',
   'gskpath.c',
+  'gskpathdash.c',
   'gskpathbuilder.c',
+  'gskpathmeasure.c',
   'gskpathpoint.c',
   'gskrenderer.c',
   'gskrendernode.c',
@@ -75,6 +77,7 @@ gsk_public_headers = files([
   'gskglshader.h',
   'gskpath.h',
   'gskpathbuilder.h',
+  'gskpathmeasure.h',
   'gskpathpoint.h',
   'gskrenderer.h',
   'gskrendernode.h',

testsuite/gsk/dash.c

@@ -0,0 +1,186 @@
+/*
+ * 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 <gtk/gtk.h>
+
+static gboolean
+build_path (GskPathOperation        op,
+            const graphene_point_t *pts,
+            gsize                   n_pts,
+            gpointer                user_data)
+{
+  GskPathBuilder *builder = user_data;
+
+  switch (op)
+  {
+    case GSK_PATH_MOVE:
+      gsk_path_builder_move_to (builder, pts[0].x, pts[0].y);
+      break;
+
+    case GSK_PATH_CLOSE:
+      gsk_path_builder_close (builder);
+      break;
+
+    case GSK_PATH_LINE:
+      gsk_path_builder_line_to (builder, pts[1].x, pts[1].y);
+      break;
+
+    case GSK_PATH_QUAD:
+      gsk_path_builder_quad_to (builder, pts[1].x, pts[1].y, pts[2].x, pts[2].y);
+      break;
+
+    case GSK_PATH_CUBIC:
+      gsk_path_builder_cubic_to (builder, pts[1].x, pts[1].y, pts[2].x, pts[2].y, pts[3].x, pts[3].y);
+      break;
+
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+
+  return TRUE;
+}
+
+static void
+test_simple (void)
+{
+  const struct {
+    const char *test;
+    float dash[4];
+    gsize n_dash;
+    float dash_offset;
+    const char *result;
+  } tests[] = {
+    /* a line with a dash of a quarter its size, very simple test */
+    {
+      "M 0 0 L 20 0",
+      { 5, }, 1, 0.f,
+      "M 0 0 L 5 0 M 10 0 L 15 0",
+    },
+    /* a square with a dash of half its size, another simple test */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 5, }, 1, 0.f,
+      "M 10 0 L 10 5 M 10 10 L 5 10 M 0 10 L 0 5 M 0 0 L 5 0"
+    },
+    /* a square smaller than the dash, make sure it closes */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 50, }, 1, 0.f,
+      "M 0 0 L 10 0 L 10 10 L 0 10 Z"
+    },
+    /* a square exactly the dash's size, make sure it still closes */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 40, }, 1, 0.f,
+      "M 0 0 L 10 0 L 10 10 L 0 10 Z"
+    },
+    /* a dash with offset */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 5, }, 1, 2.5f,
+      "M 7.5 0 L 10 0 L 10 2.5 M 10 7.5 L 10 10 L 7.5 10 M 2.5 10 L 0 10 L 0 7.5 M 0 2.5 L 0 0 L 2.5 0"
+    },
+    /* a dash with offset, but this time the rect isn't closed */
+    {
+      "M 0 0 L 10 0 L 10 10 L 0 10 L 0 0",
+      { 5, }, 1, 2.5f,
+      "M 0 0 L 2.5 0 M 7.5 0 L 10 0 L 10 2.5 M 10 7.5 L 10 10 L 7.5 10 M 2.5 10 L 0 10 L 0 7.5 M 0 2.5 L 0 0"
+    },
+    /* a dash with offset into an empty dash */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 5, }, 1, 7.5f,
+      "M 2.5 0 L 7.5 0 M 10 2.5 L 10 7.5 M 7.5 10 L 2.5 10 M 0 7.5 L 0 2.5"
+    },
+    /* a dash with offset where the whole rectangle fits into one element - make sure it closes */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 1, 1, 100 }, 3, 3.f,
+      "M 0 0 L 10 0 L 10 10 L 0 10 Z"
+    },
+    /* a dash with 0-length elements, aka dotting */
+    {
+      "M 0 0 h 10 v 10 h -10 z",
+      { 0, 5 }, 2, 0.f,
+      "M 5 0 M 10 0 M 10 5 M 10 10 M 5 10 M 0 10 M 0 5 M 0 0"
+    },
+#if 0
+    /* a dash of a circle */
+    {
+      "M 10 5 O 10 10, 5 10, 0.70710676908493042 O 0 10, 0 5, 0.70710676908493042 O 0 0, 5 0, 0.70710676908493042 O 10 0, 10 5, 0.70710676908493042 Z",
+      { 32, }, 1, 0.f,
+      "M 10 5 O 10 10, 5 10, 0.70710676908493042 O 0 10, 0 5, 0.70710676908493042 O 0 0, 5 0, 0.70710676908493042 O 10 0, 10 5, 0.70710676908493042 Z",
+    },
+#endif
+    /* a dash with offset and 2 contours */
+    {
+      "M 10 10 h 10 v 10 h -10 z M 20 20 h 10 v 10 h -10 z",
+      { 5, }, 1, 2.5f,
+      "M 17.5 10 L 20 10 L 20 12.5 M 20 17.5 L 20 20 L 17.5 20 M 12.5 20 L 10 20 L 10 17.5 M 10 12.5 L 10 10 L 12.5 10 "
+      "M 27.5 20 L 30 20 L 30 22.5 M 30 27.5 L 30 30 L 27.5 30 M 22.5 30 L 20 30 L 20 27.5 M 20 22.5 L 20 20 L 22.5 20"
+    },
+  };
+  GskPath *path, *result;
+  GskPathBuilder *builder;
+  GskStroke *stroke;
+  char *s;
+
+  for (gsize i = 0; i < G_N_ELEMENTS(tests); i++)
+    {
+      if (g_test_verbose ())
+        g_test_message ("%lu: %s", i, tests[i].test);
+
+      stroke = gsk_stroke_new (1);
+      gsk_stroke_set_dash (stroke, tests[i].dash, tests[i].n_dash);
+      gsk_stroke_set_dash_offset (stroke, tests[i].dash_offset);
+
+      path = gsk_path_parse (tests[i].test);
+      g_assert_nonnull (path);
+#if 0
+      /* This assumes that we have rectangle contours */
+      s = gsk_path_to_string (path);
+      g_assert_cmpstr (s, ==, tests[i].test);
+      g_free (s);
+#endif
+
+      builder = gsk_path_builder_new ();
+      gsk_path_dash (path, stroke, 0.5, build_path, builder);
+      result = gsk_path_builder_free_to_path (builder);
+
+      s = gsk_path_to_string (result);
+      g_assert_cmpstr (s, ==, tests[i].result);
+      g_free (s);
+
+      gsk_path_unref (result);
+      gsk_stroke_free (stroke);
+      gsk_path_unref (path);
+    }
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  gtk_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/dash/simple", test_simple);
+
+  return g_test_run ();
+}

testsuite/gsk/measure-special-cases.c

@@ -0,0 +1,272 @@
+/*
+ * 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 <gtk/gtk.h>
+
+
+static void
+test_basics (void)
+{
+  GskPath *path;
+  GskPathMeasure *measure;
+  GskPathPoint point, point1;
+  float epsilon = 0.001;
+  float length;
+
+  path = gsk_path_parse ("M 0 0 L 100 0 C 100 100 200 100 200 0");
+  measure = gsk_path_measure_new (path);
+
+  gsk_path_measure_get_point (measure, 0, &point);
+  gsk_path_get_start_point (path, &point1);
+  g_assert_true (gsk_path_point_equal (&point, &point1));
+
+  g_assert_cmpfloat_with_epsilon (gsk_path_point_get_distance (measure, &point), 0, epsilon);
+
+  gsk_path_measure_get_point (measure, 50, &point);
+  g_assert_cmpfloat_with_epsilon (gsk_path_point_get_distance (measure, &point), 50, epsilon);
+
+  gsk_path_measure_get_point (measure, 100, &point);
+  g_assert_cmpfloat_with_epsilon (gsk_path_point_get_distance (measure, &point), 100, epsilon);
+
+  gsk_path_measure_get_point (measure, 150, &point);
+  g_assert_cmpfloat_with_epsilon (gsk_path_point_get_distance (measure, &point), 150, epsilon);
+
+  length = gsk_path_measure_get_length (measure);
+  gsk_path_measure_get_point (measure, length, &point);
+  gsk_path_get_end_point (path, &point1);
+  g_assert_true (gsk_path_point_equal (&point, &point1));
+
+  g_assert_cmpfloat_with_epsilon (gsk_path_point_get_distance (measure, &point), length, epsilon);
+
+  gsk_path_measure_unref (measure);
+  gsk_path_unref (path);
+}
+
+static void
+test_bad_split (void)
+{
+  GskPath *path, *path1;
+  GskPathMeasure *measure, *measure1;
+  GskPathBuilder *builder;
+  float split, length, epsilon;
+  GskPathPoint point1, point2;
+
+  /* An example that was isolated from the /path/segment test path.c
+   * It shows how uneven parametrization of cubics can lead to bad
+   * lengths reported by the measure.
+   */
+
+  path = gsk_path_parse ("M 0 0 C 2 0 4 0 4 0");
+
+  measure = gsk_path_measure_new (path);
+  split = 2.962588;
+  length = gsk_path_measure_get_length (measure);
+  epsilon = MAX (length / 256, 1.f / 1024);
+
+  gsk_path_get_start_point (path, &point1);
+  gsk_path_measure_get_point (measure, split, &point2);
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_segment (builder, path, &point1, &point2);
+  path1 = gsk_path_builder_free_to_path (builder);
+  measure1 = gsk_path_measure_new (path1);
+
+  g_assert_cmpfloat_with_epsilon (split, gsk_path_measure_get_length (measure1), epsilon);
+
+  gsk_path_measure_unref (measure1);
+  gsk_path_unref (path1);
+  gsk_path_measure_unref (measure);
+  gsk_path_unref (path);
+}
+
+static void
+test_rect (void)
+{
+  GskPathBuilder *builder;
+  GskPath *path;
+  GskPathMeasure *measure;
+  GskPathPoint point;
+  graphene_point_t p;
+  graphene_vec2_t tangent, expected_tangent;
+  float length;
+  gboolean ret;
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (0, 0, 100, 50));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 300);
+
+#define TEST_POS_AT(distance, X, Y) \
+  ret = gsk_path_measure_get_point (measure, distance, &point); \
+  g_assert_true (ret); \
+  gsk_path_point_get_position (path, &point, &p); \
+  g_assert_true (graphene_point_near (&p, &GRAPHENE_POINT_INIT (X, Y), 0.01)); \
+  ret = gsk_path_get_closest_point (path, &GRAPHENE_POINT_INIT (X, Y), INFINITY, &point); \
+  g_assert_true (ret); \
+  if (distance < length) \
+    g_assert_true (fabs (gsk_path_point_get_distance (measure, &point) - distance) < 0.01); \
+  else \
+    g_assert_true (fabs (gsk_path_point_get_distance (measure, &point)) < 0.01); \
+  gsk_path_point_get_position (path, &point, &p); \
+  g_assert_true (graphene_point_near (&p, &GRAPHENE_POINT_INIT (X, Y), 0.01)); \
+
+#define TEST_TANGENT_AT(distance, x1, y1, x2, y2) \
+  ret = gsk_path_measure_get_point (measure, distance, &point); \
+  g_assert_true (ret); \
+  gsk_path_point_get_tangent (path, &point, GSK_PATH_START, &tangent); \
+  g_assert_true (graphene_vec2_near (&tangent, graphene_vec2_init (&expected_tangent, x1, y1), 0.01)); \
+  gsk_path_point_get_tangent (path, &point, GSK_PATH_END, &tangent); \
+  g_assert_true (graphene_vec2_near (&tangent, graphene_vec2_init (&expected_tangent, x2, y2), 0.01)); \
+
+#define TEST_POS_AT2(distance, X, Y, expected_distance) \
+  ret = gsk_path_measure_get_point (measure, distance, &point); \
+  g_assert_true (ret); \
+  gsk_path_point_get_position (path, &point, &p); \
+  g_assert_true (graphene_point_near (&p, &GRAPHENE_POINT_INIT (X, Y), 0.01)); \
+  ret = gsk_path_get_closest_point (path, &GRAPHENE_POINT_INIT (X, Y), INFINITY, &point); \
+  g_assert_true (ret); \
+  g_assert_true (fabs (gsk_path_point_get_distance (measure, &point) - expected_distance) < 0.01); \
+  gsk_path_point_get_position (path, &point, &p); \
+  g_assert_true (graphene_point_near (&p, &GRAPHENE_POINT_INIT (X, Y), 0.01)); \
+
+  TEST_POS_AT (0, 0, 0)
+  TEST_POS_AT (25, 25, 0)
+  TEST_POS_AT (100, 100, 0)
+  TEST_POS_AT (110, 100, 10)
+  TEST_POS_AT (150, 100, 50)
+  TEST_POS_AT (175, 75, 50)
+  TEST_POS_AT (250, 0, 50)
+  TEST_POS_AT (260, 0, 40)
+  TEST_POS_AT2 (300, 0, 0, 0)
+
+  TEST_TANGENT_AT (0, 0, -1, 1, 0)
+  TEST_TANGENT_AT (50, 1, 0, 1, 0)
+  TEST_TANGENT_AT (100, 1, 0, 0, 1)
+  TEST_TANGENT_AT (125, 0, 1, 0, 1)
+  TEST_TANGENT_AT (150, 0, 1, -1, 0)
+  TEST_TANGENT_AT (200, -1, 0, -1, 0)
+  TEST_TANGENT_AT (250, -1, 0, 0, -1)
+  TEST_TANGENT_AT (275, 0, -1, 0, -1)
+
+  gsk_path_measure_unref (measure);
+  gsk_path_unref (path);
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (100, 50, -100, -50));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 300);
+
+  TEST_POS_AT (0, 100, 50)
+  TEST_POS_AT (25, 75, 50)
+  TEST_POS_AT (100, 0, 50)
+  TEST_POS_AT (110, 0, 40)
+  TEST_POS_AT (150, 0, 0)
+  TEST_POS_AT (175, 25, 0)
+  TEST_POS_AT (250, 100, 0)
+  TEST_POS_AT (260, 100, 10)
+  TEST_POS_AT (300, 100, 50)
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (100, 0, -100, 50));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 300);
+
+  TEST_POS_AT (0, 100, 0)
+  TEST_POS_AT (25, 75, 0)
+  TEST_POS_AT (100, 0, 0)
+  TEST_POS_AT (110, 0, 10)
+  TEST_POS_AT (150, 0, 50)
+  TEST_POS_AT (175, 25, 50)
+  TEST_POS_AT (250, 100, 50)
+  TEST_POS_AT (260, 100, 40)
+  TEST_POS_AT (300, 100, 0)
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (0, 0, 100, 0));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 200);
+
+  TEST_POS_AT2 (0, 0, 0, 0)
+  TEST_POS_AT2 (25, 25, 0, 25)
+  TEST_POS_AT2 (100, 100, 0, 100)
+  TEST_POS_AT2 (110, 90, 0, 90)
+  TEST_POS_AT2 (200, 0, 0, 0)
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (100, 0, -100, 0));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 200);
+
+  /* These cases are ambiguous */
+  TEST_POS_AT2 (0, 100, 0, 0)
+  TEST_POS_AT2 (25, 75, 0, 25)
+  TEST_POS_AT2 (100, 0, 0, 100)
+  TEST_POS_AT2 (110, 10, 0, 110)
+  TEST_POS_AT2 (200, 100, 0, 0)
+
+  builder = gsk_path_builder_new ();
+  gsk_path_builder_add_rect (builder, &GRAPHENE_RECT_INIT (0, 100, 0, -100));
+  path = gsk_path_builder_free_to_path (builder);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  g_assert_true (length == 200);
+
+  /* These cases are ambiguous */
+  TEST_POS_AT2 (0, 0, 100, 0)
+  TEST_POS_AT2 (25, 0, 75, 25)
+  TEST_POS_AT2 (100, 0, 0, 100)
+  TEST_POS_AT2 (110, 0, 10, 110)
+  TEST_POS_AT2 (200, 0, 100, 0)
+
+#undef TEST_POS_AT
+#undef TEST_POS_AT2
+#undef TEST_TANGENT_AT
+
+  gsk_path_measure_unref (measure);
+  gsk_path_unref (path);
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  gtk_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/measure/basics", test_basics);
+  g_test_add_func ("/measure/bad-split", test_bad_split);
+  g_test_add_func ("/measure/rect", test_rect);
+
+  return g_test_run ();
+}

testsuite/gsk/measure.c

@@ -0,0 +1,555 @@
+/*
+ * 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 <gtk/gtk.h>
+
+static GskPath *
+create_random_degenerate_path (guint max_contours)
+{
+#define N_DEGENERATE_PATHS 14
+  GskPathBuilder *builder;
+  guint i;
+
+  builder = gsk_path_builder_new ();
+
+  switch (g_test_rand_int_range (0, N_DEGENERATE_PATHS))
+  {
+    case 0:
+      /* empty path */
+      break;
+
+    case 1:
+      /* a single point */
+      gsk_path_builder_move_to (builder, 
+                                g_test_rand_double_range (-1000, 1000),
+                                g_test_rand_double_range (-1000, 1000));
+      break;
+
+    case 2:
+      /* N points */
+      for (i = 0; i < MIN (10, max_contours); i++)
+        {
+          gsk_path_builder_move_to (builder, 
+                                    g_test_rand_double_range (-1000, 1000),
+                                    g_test_rand_double_range (-1000, 1000));
+        }
+      break;
+
+    case 3:
+      /* 1 closed point */
+      gsk_path_builder_move_to (builder, 
+                                g_test_rand_double_range (-1000, 1000),
+                                g_test_rand_double_range (-1000, 1000));
+      gsk_path_builder_close (builder);
+      break;
+
+    case 4:
+      /* the same point closed N times */
+      gsk_path_builder_move_to (builder, 
+                                g_test_rand_double_range (-1000, 1000),
+                                g_test_rand_double_range (-1000, 1000));
+      for (i = 0; i < MIN (10, max_contours); i++)
+        {
+          gsk_path_builder_close (builder);
+        }
+      break;
+
+    case 5:
+      /* a zero-width and zero-height rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      0, 0));
+      break;
+
+    case 6:
+      /* a zero-width rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      0,
+                                                      g_test_rand_double_range (-1000, 1000)));
+      break;
+
+    case 7:
+      /* a zero-height rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      0));
+      break;
+
+    case 8:
+      /* a negative-size rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 0),
+                                                      g_test_rand_double_range (-1000, 0)));
+      break;
+
+    case 9:
+      /* an absolutely random rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000)));
+      break;
+
+    case 10:
+      /* an absolutely random rect */
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000)));
+      break;
+
+    case 11:
+      /* an absolutely random circle */
+      gsk_path_builder_add_circle (builder,
+                                   &GRAPHENE_POINT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                         g_test_rand_double_range (-1000, 1000)),
+                                   g_test_rand_double_range (1, 1000));
+      break;
+
+    case 12:
+      /* a zero-length line */
+      {
+        graphene_point_t point = GRAPHENE_POINT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000));
+        gsk_path_builder_move_to (builder, point.x, point.y);
+        gsk_path_builder_line_to (builder, point.x, point.y);
+      }
+      break;
+
+    case 13:
+      /* a curve with start == end */
+      {
+        graphene_point_t point = GRAPHENE_POINT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000));
+        gsk_path_builder_move_to (builder, point.x, point.y);
+        gsk_path_builder_cubic_to (builder,
+                                   g_test_rand_double_range (-1000, 1000),
+                                   g_test_rand_double_range (-1000, 1000),
+                                   g_test_rand_double_range (-1000, 1000),
+                                   g_test_rand_double_range (-1000, 1000),
+                                   point.x, point.y);
+      }
+      break;
+
+    case N_DEGENERATE_PATHS:
+    default:
+      g_assert_not_reached ();
+  }
+
+  return gsk_path_builder_free_to_path (builder);
+}
+
+static GskPath *
+create_random_path (guint max_contours);
+
+static void
+add_shape_contour (GskPathBuilder *builder)
+{
+#define N_SHAPE_CONTOURS 3
+  switch (g_test_rand_int_range (0, N_SHAPE_CONTOURS))
+  {
+    case 0:
+      gsk_path_builder_add_rect (builder,
+                                 &GRAPHENE_RECT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (-1000, 1000),
+                                                      g_test_rand_double_range (1, 1000),
+                                                      g_test_rand_double_range (1, 1000)));
+      break;
+
+    case 1:
+      gsk_path_builder_add_circle (builder,
+                                   &GRAPHENE_POINT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                         g_test_rand_double_range (-1000, 1000)),
+                                   g_test_rand_double_range (1, 1000));
+      break;
+
+    case 2:
+      {
+        GskPath *path = create_random_path (1);
+        gsk_path_builder_add_path (builder, path);
+        gsk_path_unref (path);
+      }
+      break;
+
+    case N_SHAPE_CONTOURS:
+    default:
+      g_assert_not_reached ();
+      break;
+  }
+}
+
+static void
+add_standard_contour (GskPathBuilder *builder)
+{
+  guint i, n;
+
+  if (g_test_rand_bit ())
+    {
+      if (g_test_rand_bit ())
+        gsk_path_builder_move_to (builder,
+                                  g_test_rand_double_range (-1000, 1000),
+                                  g_test_rand_double_range (-1000, 1000));
+      else
+        gsk_path_builder_rel_move_to (builder,
+                                      g_test_rand_double_range (-1000, 1000),
+                                      g_test_rand_double_range (-1000, 1000));
+    }
+
+  /* that 20 is random, but should be enough to get some
+   * crazy self-intersecting shapes */
+  n = g_test_rand_int_range (1, 20);
+  for (i = 0; i < n; i++)
+    {
+      switch (g_test_rand_int_range (0, 6))
+      {
+        case 0:
+          gsk_path_builder_line_to (builder,
+                                    g_test_rand_double_range (-1000, 1000),
+                                    g_test_rand_double_range (-1000, 1000));
+          break;
+
+        case 1:
+          gsk_path_builder_rel_line_to (builder,
+                                        g_test_rand_double_range (-1000, 1000),
+                                        g_test_rand_double_range (-1000, 1000));
+          break;
+
+        case 2:
+          gsk_path_builder_quad_to (builder,
+                                    g_test_rand_double_range (-1000, 1000),
+                                    g_test_rand_double_range (-1000, 1000),
+                                    g_test_rand_double_range (-1000, 1000),
+                                    g_test_rand_double_range (-1000, 1000));
+          break;
+
+        case 3:
+          gsk_path_builder_rel_quad_to (builder,
+                                        g_test_rand_double_range (-1000, 1000),
+                                        g_test_rand_double_range (-1000, 1000),
+                                        g_test_rand_double_range (-1000, 1000),
+                                        g_test_rand_double_range (-1000, 1000));
+          break;
+
+        case 4:
+          gsk_path_builder_cubic_to (builder,
+                                     g_test_rand_double_range (-1000, 1000),
+                                     g_test_rand_double_range (-1000, 1000),
+                                     g_test_rand_double_range (-1000, 1000),
+                                     g_test_rand_double_range (-1000, 1000),
+                                     g_test_rand_double_range (-1000, 1000),
+                                     g_test_rand_double_range (-1000, 1000));
+          break;
+
+        case 5:
+          gsk_path_builder_rel_cubic_to (builder,
+                                         g_test_rand_double_range (-1000, 1000),
+                                         g_test_rand_double_range (-1000, 1000),
+                                         g_test_rand_double_range (-1000, 1000),
+                                         g_test_rand_double_range (-1000, 1000),
+                                         g_test_rand_double_range (-1000, 1000),
+                                         g_test_rand_double_range (-1000, 1000));
+          break;
+
+        default:
+          g_assert_not_reached();
+          break;
+      }
+    }
+
+  if (g_test_rand_bit ())
+    gsk_path_builder_close (builder);
+}
+
+static GskPath *
+create_random_path (guint max_contours)
+{
+  GskPathBuilder *builder;
+  guint i, n;
+
+  /* 5% chance for a weird shape */
+  if (!g_test_rand_int_range (0, 20))
+    return create_random_degenerate_path (max_contours);
+
+  builder = gsk_path_builder_new ();
+  n = g_test_rand_int_range (1, 10);
+  n = MIN (n, max_contours);
+
+  for (i = 0; i < n; i++)
+    {
+      /* 2/3 of shapes are standard contours */
+      if (g_test_rand_int_range (0, 3))
+        add_standard_contour (builder);
+      else
+        add_shape_contour (builder);
+    }
+
+  return gsk_path_builder_free_to_path (builder);
+}
+
+static void
+test_roundtrip (void)
+{
+  GskPath *path;
+  GskPathMeasure *measure;
+  float length, seg_length;
+  int i;
+  GskPathPoint point;
+  float epsilon = 0.5;
+
+  path = create_random_path (10);
+  measure = gsk_path_measure_new (path);
+  length = gsk_path_measure_get_length (measure);
+
+  for (i = 0; i <= 100; i++)
+    {
+      seg_length = length * i / 100.0f;
+
+      gsk_path_measure_get_point (measure, seg_length, &point);
+
+      g_assert_cmpfloat_with_epsilon (seg_length, gsk_path_point_get_distance (measure, &point), epsilon);
+    }
+
+  gsk_path_measure_unref (measure);
+  gsk_path_unref (path);
+}
+
+static void
+test_get_point (void)
+{
+  static const guint max_contours = 5;
+  static const float tolerance = 1.0;
+  GskPath *path;
+  GskPathMeasure *measure;
+  GskPathPoint point;
+  guint n_discontinuities;
+  float length, offset, last_offset;
+  graphene_point_t p, last_point;
+  guint i, j;
+  gboolean ret;
+
+  for (i = 0; i < 10; i++)
+    {
+      path = create_random_path (max_contours);
+      measure = gsk_path_measure_new_with_tolerance (path, tolerance);
+      length = gsk_path_measure_get_length (measure);
+      n_discontinuities = 0;
+
+      ret = gsk_path_measure_get_point (measure, 0, &point);
+      if (!ret)
+        {
+          g_assert_true (gsk_path_is_empty (path));
+          continue;
+        }
+      gsk_path_point_get_position (path, &point, &last_point);
+
+      /* FIXME: anything we can test with tangents here? */
+      last_offset = 0;
+
+      for (j = 1; j <= 1024; j++)
+        {
+          offset = length * j / 1024;
+          ret = gsk_path_measure_get_point (measure, offset, &point);
+          g_assert_true (ret);
+          gsk_path_point_get_position (path, &point, &p);
+
+          if (graphene_point_distance (&last_point, &p, NULL, NULL) > 2 * (offset - last_offset))
+            {
+              n_discontinuities++;
+              g_assert_cmpint (n_discontinuities, <, max_contours);
+            }
+
+          last_offset = offset;
+          last_point = p;
+        }
+
+      gsk_path_measure_unref (measure);
+      gsk_path_unref (path);
+    }
+}
+
+static void
+test_closest_point (void)
+{
+  static const float tolerance = 0.5;
+  GskPath *path, *path1, *path2;
+  GskPathMeasure *measure, *measure1, *measure2;
+  GskPathBuilder *builder;
+  GskPathPoint point;
+  guint i, j;
+  gboolean ret;
+
+  if (!g_test_slow ())
+    {
+      g_test_skip ("Skipping slow test");
+      return;
+    }
+
+  for (i = 0; i < 10; i++)
+    {
+      path1 = create_random_path (G_MAXUINT);
+      measure1 = gsk_path_measure_new_with_tolerance (path1, tolerance);
+      path2 = create_random_path (G_MAXUINT);
+      measure2 = gsk_path_measure_new_with_tolerance (path2, tolerance);
+
+      builder = gsk_path_builder_new ();
+      gsk_path_builder_add_path (builder, path1);
+      gsk_path_builder_add_path (builder, path2);
+      path = gsk_path_builder_free_to_path (builder);
+      measure = gsk_path_measure_new_with_tolerance (path, tolerance);
+
+      for (j = 0; j < 100; j++)
+        {
+          graphene_point_t test = GRAPHENE_POINT_INIT (g_test_rand_double_range (-1000, 1000),
+                                                       g_test_rand_double_range (-1000, 1000));
+          graphene_point_t p1, p2, p;
+          graphene_vec2_t t1, t2, t;
+          float offset1, offset2, offset;
+          float distance1, distance2, distance;
+
+          offset1 = offset2 = offset = 0;
+          distance1 = distance2 = distance = 0;
+          ret = gsk_path_get_closest_point (path1, &test, INFINITY, &point);
+          g_assert_true (ret);
+
+          gsk_path_point_get_position (path1, &point, &p1);
+          gsk_path_point_get_tangent (path1, &point, GSK_PATH_END, &t1);
+          offset1 = gsk_path_point_get_distance (measure1, &point);
+          distance1 = graphene_point_distance (&p1, &test, NULL, NULL);
+
+          ret = gsk_path_get_closest_point (path2, &test, INFINITY, &point);
+          g_assert_true (ret);
+
+          gsk_path_point_get_position (path2, &point, &p2);
+          gsk_path_point_get_tangent (path2, &point, GSK_PATH_END, &t2);
+          offset2 = gsk_path_point_get_distance (measure2, &point);
+          distance2 = graphene_point_distance (&p2, &test, NULL, NULL);
+
+          ret = gsk_path_get_closest_point (path, &test, INFINITY, &point);
+          g_assert_true (ret);
+
+          gsk_path_point_get_position (path, &point, &p);
+          gsk_path_point_get_tangent (path, &point, GSK_PATH_END, &t);
+          offset = gsk_path_point_get_distance (measure, &point);
+          distance = graphene_point_distance (&p, &test, NULL, NULL);
+
+          if (distance1 == distance)
+            {
+              g_assert_cmpfloat (distance1, ==, distance);
+              g_assert_cmpfloat (p1.x, ==, p.x);
+              g_assert_cmpfloat (p1.y, ==, p.y);
+              g_assert_cmpfloat (offset1, ==, offset);
+              g_assert_true (graphene_vec2_equal (&t1, &t));
+            }
+          else
+            {
+              g_assert_cmpfloat (distance2, ==, distance);
+              g_assert_cmpfloat (p2.x, ==, p.x);
+              g_assert_cmpfloat (p2.y, ==, p.y);
+              g_assert_cmpfloat_with_epsilon (offset2 + gsk_path_measure_get_length (measure1), offset, MAX (G_MINFLOAT, offset / 1024));
+              g_assert_true (graphene_vec2_equal (&t2, &t));
+            }
+        }
+
+      gsk_path_measure_unref (measure2);
+      gsk_path_measure_unref (measure1);
+      gsk_path_measure_unref (measure);
+      gsk_path_unref (path2);
+      gsk_path_unref (path1);
+      gsk_path_unref (path);
+    }
+}
+
+static void
+test_closest_point_for_point (void)
+{
+  static const float tolerance = 0.5;
+  GskPath *path;
+  GskPathMeasure *measure;
+  GskPathPoint point;
+  float length, offset, distance;
+  graphene_point_t p, closest_point;
+  guint i, j;
+  gboolean ret;
+
+  if (!g_test_slow ())
+    {
+      g_test_skip ("Skipping slow test");
+      return;
+    }
+
+  for (i = 0; i < 100; i++)
+    {
+      path = create_random_path (G_MAXUINT);
+      if (gsk_path_is_empty (path))
+        {
+          /* empty paths have no closest point to anything */
+          gsk_path_unref (path);
+          continue;
+        }
+
+      measure = gsk_path_measure_new_with_tolerance (path, tolerance);
+      length = gsk_path_measure_get_length (measure);
+
+      for (j = 0; j < 100; j++)
+        {
+          offset = g_test_rand_double_range (0, length);
+          ret = gsk_path_measure_get_point (measure, offset, &point);
+          g_assert_true (ret);
+          gsk_path_point_get_position (path, &point, &p);
+          ret = gsk_path_get_closest_point (path, &p, 2 * tolerance, &point);
+          g_assert_true (ret);
+          gsk_path_point_get_position (path, &point, &closest_point);
+          //closest_offset = gsk_path_point_get_distance (measure, &point);
+          distance = graphene_point_distance (&p, &closest_point, NULL, NULL);
+
+          /* should be given due to the TRUE return above, but who knows... */
+          g_assert_cmpfloat (distance, <=, 2 * tolerance);
+          g_assert_cmpfloat (graphene_point_distance (&p, &closest_point, NULL, NULL), <=, 2 * tolerance);
+          /* we can't check offsets here, since we might hit self-intersections
+          g_assert_cmpfloat_with_epsilon (closest_offset, offset, 2 * tolerance);
+          */
+        }
+
+      gsk_path_measure_unref (measure);
+      gsk_path_unref (path);
+    }
+}
+
+int
+main (int   argc,
+      char *argv[])
+{
+  gtk_test_init (&argc, &argv, NULL);
+
+  g_test_add_func ("/measure/roundtrip", test_roundtrip);
+  g_test_add_func ("/measure/get_point", test_get_point);
+  g_test_add_func ("/measure/closest_point", test_closest_point);
+  g_test_add_func ("/measure/closest_point_for_point", test_closest_point_for_point);
+
+  return g_test_run ();
+}

testsuite/gsk/meson.build

@@ -371,6 +371,9 @@ tests = [
   ['shader'],
   ['path'],
   ['path-special-cases'],
+  ['measure'],
+  ['measure-special-cases'],
+  ['dash'],
 ]
 
 test_cargs = []