texture: Add gdk_texture_diff()

... and use it in rendernodes.

Setting up textures for diffing is done via gdk_texture_set_diff() which
should only be used during texture construction.

Note that the pointers to next/previous are allowed to dangle if one of
the textures is finalized, but that's fine because we always check both
textures' links to each other before we consider the pointer valid.

2 files changed, 57 insertions, 1 deletions

diff --git a/gdk/gdktexture.c b/gdk/gdktexture.c
index 41cb8ea11a..b392b90222 100644
--- a/gdk/gdktexture.c
+++ b/gdk/gdktexture.c
@@ -282,6 +282,8 @@ gdk_texture_dispose (GObject *object)
 {
   GdkTexture *self = GDK_TEXTURE (object);
 
+  g_clear_pointer (&self->diff_to_previous, cairo_region_destroy);
+
   gdk_texture_clear_render_data (self);
 
   G_OBJECT_CLASS (gdk_texture_parent_class)->dispose (object);
@@ -671,7 +673,47 @@ gdk_texture_do_download (GdkTexture      *texture,
                          guchar          *data,
                          gsize            stride)
 {
-  GDK_TEXTURE_GET_CLASS (texture)->download (texture, format, data,stride);
+  GDK_TEXTURE_GET_CLASS (texture)->download (texture, format, data, stride);
+}
+
+void
+gdk_texture_diff (GdkTexture     *self,
+                  GdkTexture     *other,
+                  cairo_region_t *region)
+{
+  if (self == other)
+    return;
+
+  if (self->previous_texture == other &&
+      g_atomic_pointer_get (&other->next_texture) == self)
+    {
+      cairo_region_union (region, self->diff_to_previous);
+    }
+  else if (other->previous_texture == self &&
+           g_atomic_pointer_get (&self->next_texture) == other)
+    {
+      cairo_region_union (region, other->diff_to_previous);
+    }
+  else
+    {
+      cairo_region_union_rectangle (region,
+                                    &(cairo_rectangle_int_t) {
+                                      0,
+                                      0,
+                                      MAX (self->width, other->width),
+                                      MAX (self->height, other->height)
+                                    });
+    }
+}
+
+void
+gdk_texture_set_diff (GdkTexture     *self,
+                      GdkTexture     *previous,
+                      cairo_region_t *diff)
+{
+  self->previous_texture = previous;
+  self->diff_to_previous = diff;
+  g_atomic_pointer_set (&previous->next_texture, self);
 }
 
 cairo_surface_t *
diff --git a/gdk/gdktextureprivate.h b/gdk/gdktextureprivate.h
index fccf380d7c..b0fc2a8785 100644
--- a/gdk/gdktextureprivate.h
+++ b/gdk/gdktextureprivate.h
@@ -21,6 +21,12 @@ struct _GdkTexture
   gpointer render_key;
   gpointer render_data;
   GDestroyNotify render_notify;
+
+  /* for diffing swapchain-like textures.
+   * Links are only valid if both textures agree on them */
+  gpointer next_texture; /* atomic, no reference, may be invalid pointer */
+  gpointer previous_texture; /* no reference, may be invalid pointer */
+  cairo_region_t *diff_to_previous;
 };
 
 struct _GdkTextureClass {
@@ -42,6 +48,14 @@ void                    gdk_texture_do_download         (GdkTexture
                                                          GdkMemoryFormat         format,
                                                          guchar                 *data,
                                                          gsize                   stride);
+void                    gdk_texture_diff                (GdkTexture             *self,
+                                                         GdkTexture             *other,
+                                                         cairo_region_t         *region);
+
+void                    gdk_texture_set_diff            (GdkTexture             *self,
+                                                         GdkTexture             *previous,
+                                                         cairo_region_t         *diff);
+
 gboolean                gdk_texture_set_render_data     (GdkTexture             *self,
                                                          gpointer                key,
                                                          gpointer                data,