renderer: Track the previous node

... and diff the previous node with the current one to determine the
clip region.

This doubles the work necessary to track clip regions, but the following
commits will clean that up.

diff --git a/gsk/gskrenderer.c b/gsk/gskrenderer.c
index c011fb6cf233d9eb9d0fdcac9d68bc9e3514fa26..e4945feb5ebbef456e49a229f695e7591d853bc0 100644 (file)
--- a/gsk/gskrenderer.c
+++ b/gsk/gskrenderer.c
@@ -66,6 +66,7 @@ typedef struct
   GObject parent_instance;
 
   GdkSurface *surface;
+  GskRenderNode *prev_node;
   GskRenderNode *root_node;
   GdkDisplay *display;
 
@@ -375,6 +376,8 @@ gsk_renderer_unrealize (GskRenderer *renderer)
 
   GSK_RENDERER_GET_CLASS (renderer)->unrealize (renderer);
 
+  g_clear_pointer (&priv->prev_node, gsk_render_node_unref);
+
   priv->is_realized = FALSE;
 }
 
@@ -465,32 +468,37 @@ gsk_renderer_render (GskRenderer          *renderer,
                      const cairo_region_t *region)
 {
   GskRendererPrivate *priv = gsk_renderer_get_instance_private (renderer);
-  cairo_region_t *real_region;
+  cairo_region_t *clip;
 
   g_return_if_fail (GSK_IS_RENDERER (renderer));
   g_return_if_fail (priv->is_realized);
   g_return_if_fail (GSK_IS_RENDER_NODE (root));
   g_return_if_fail (priv->root_node == NULL);
 
-  priv->root_node = gsk_render_node_ref (root);
-
-  if (region == NULL || GSK_RENDERER_DEBUG_CHECK (renderer, FULL_REDRAW))
+  if (region == NULL || priv->prev_node == NULL || GSK_RENDERER_DEBUG_CHECK (renderer, FULL_REDRAW))
     {
-      real_region = cairo_region_create_rectangle (&(GdkRectangle) {
-                                                       0, 0,
-                                                       gdk_surface_get_width (priv->surface),
-                                                       gdk_surface_get_height (priv->surface)
-                                                   });
-
-      GSK_RENDERER_GET_CLASS (renderer)->render (renderer, root, real_region);
-
-      cairo_region_destroy (real_region);
+      clip = cairo_region_create_rectangle (&(GdkRectangle) {
+                                                0, 0,
+                                                gdk_surface_get_width (priv->surface),
+                                                gdk_surface_get_height (priv->surface)
+                                            });
     }
   else
     {
-      GSK_RENDERER_GET_CLASS (renderer)->render (renderer, root, region);
+      clip = cairo_region_copy (region);
+      gsk_render_node_diff (priv->prev_node, root, clip);
+
+      if (cairo_region_is_empty (clip))
+        {
+          cairo_region_destroy (clip);
+          return;
+        }
     }
 
+  priv->root_node = gsk_render_node_ref (root);
+
+  GSK_RENDERER_GET_CLASS (renderer)->render (renderer, root, clip);
+
 #ifdef G_ENABLE_DEBUG
   if (GSK_RENDERER_DEBUG_CHECK (renderer, RENDERER))
     {
@@ -508,7 +516,9 @@ gsk_renderer_render (GskRenderer          *renderer,
     }
 #endif
 
-  g_clear_pointer (&priv->root_node, gsk_render_node_unref);
+  g_clear_pointer (&priv->prev_node, gsk_render_node_unref);
+  priv->prev_node = priv->root_node;
+  priv->root_node = NULL;
 }
 
 /*< private >