gsk: Prepare subsurface offload

Use a GskOffloadInfo to update subsurfaces (and collect info about
them). Pass that info to both the diff and the render vfuncs.

gsk/broadway/gskbroadwayrenderer.c

@@ -919,7 +919,8 @@ gsk_broadway_renderer_add_node (GskRenderer *renderer,
 static void
 gsk_broadway_renderer_render (GskRenderer          *renderer,
                               GskRenderNode        *root,
-                              const cairo_region_t *update_area)
+                              const cairo_region_t *update_area,
+                              GskOffload           *offload)
 {
   GskBroadwayRenderer *self = GSK_BROADWAY_RENDERER (renderer);
 

gsk/gl/gskglrenderer.c

@@ -272,7 +272,8 @@ update_area_requires_clear (GdkSurface           *surface,
 static void
 gsk_gl_renderer_render (GskRenderer          *renderer,
                         GskRenderNode        *root,
-                        const cairo_region_t *update_area)
+                        const cairo_region_t *update_area,
+                        GskOffload           *offload)
 {
   GskGLRenderer *self = (GskGLRenderer *)renderer;
   cairo_region_t *render_region;

gsk/gskcairorenderer.c

@@ -152,7 +152,8 @@ gsk_cairo_renderer_render_texture (GskRenderer           *renderer,
 static void
 gsk_cairo_renderer_render (GskRenderer          *renderer,
                            GskRenderNode        *root,
-                           const cairo_region_t *region)
+                           const cairo_region_t *region,
+                           GskOffload           *offload)
 {
   GskCairoRenderer *self = GSK_CAIRO_RENDERER (renderer);
   cairo_t *cr;

gsk/gskrenderer.c

@@ -41,6 +41,7 @@
 #include "gl/gskglrenderer.h"
 #include "gskprofilerprivate.h"
 #include "gskrendernodeprivate.h"
+#include "gskoffloadprivate.h"
 
 #include "gskenumtypes.h"
 
@@ -128,7 +129,8 @@ gsk_renderer_real_render_texture (GskRenderer           *self,
 static void
 gsk_renderer_real_render (GskRenderer          *self,
                           GskRenderNode        *root,
-                          const cairo_region_t *region)
+                          const cairo_region_t *region,
+                          GskOffload           *offload)
 {
   GSK_RENDERER_WARN_NOT_IMPLEMENTED_METHOD (self, render);
 }
@@ -424,6 +426,7 @@ gsk_renderer_render (GskRenderer          *renderer,
 {
   GskRendererPrivate *priv = gsk_renderer_get_instance_private (renderer);
   cairo_region_t *clip;
+  GskOffload *offload = NULL;
 
   g_return_if_fail (GSK_IS_RENDERER (renderer));
   g_return_if_fail (priv->is_realized);
@@ -433,6 +436,11 @@ gsk_renderer_render (GskRenderer          *renderer,
   if (priv->surface == NULL)
     return;
 
+  priv->root_node = gsk_render_node_ref (root);
+
+  if (!GSK_RENDERER_DEBUG_CHECK (renderer, OFFLOAD_DISABLE))
+    offload = gsk_offload_new (priv->surface, root);
+
   if (region == NULL || priv->prev_node == NULL || GSK_RENDERER_DEBUG_CHECK (renderer, FULL_REDRAW))
     {
       clip = cairo_region_create_rectangle (&(GdkRectangle) {
@@ -444,18 +452,11 @@ gsk_renderer_render (GskRenderer          *renderer,
   else
     {
       clip = cairo_region_copy (region);
-      gsk_render_node_diff (priv->prev_node, root, clip, NULL);
 
-      if (cairo_region_is_empty (clip))
+      gsk_render_node_diff (priv->prev_node, root, clip, offload);
-        {
-          cairo_region_destroy (clip);
-          return;
-        }
     }
 
-  priv->root_node = gsk_render_node_ref (root);
+  GSK_RENDERER_GET_CLASS (renderer)->render (renderer, root, clip, offload);
-
-  GSK_RENDERER_GET_CLASS (renderer)->render (renderer, root, clip);
 
   if (GSK_RENDERER_DEBUG_CHECK (renderer, RENDERER))
     {
@@ -474,6 +475,7 @@ gsk_renderer_render (GskRenderer          *renderer,
 
   g_clear_pointer (&priv->prev_node, gsk_render_node_unref);
   cairo_region_destroy (clip);
+  gsk_offload_free (offload);
   priv->prev_node = priv->root_node;
   priv->root_node = NULL;
 }

gsk/gskrendererprivate.h

@@ -21,6 +21,7 @@
 #include "gskrenderer.h"
 #include "gskprofilerprivate.h"
 #include "gskdebugprivate.h"
+#include "gskoffloadprivate.h"
 
 G_BEGIN_DECLS
 
@@ -47,7 +48,8 @@ struct _GskRendererClass
                                                                  const graphene_rect_t  *viewport);
   void                 (* render)                               (GskRenderer            *renderer,
                                                                  GskRenderNode          *root,
-                                                                 const cairo_region_t   *invalid);
+                                                                 const cairo_region_t   *invalid,
+                                                                 GskOffload             *offload);
 };
 
 GskProfiler *           gsk_renderer_get_profiler               (GskRenderer    *renderer);

gsk/vulkan/gskvulkanrenderer.c

@@ -349,7 +349,8 @@ gsk_vulkan_renderer_render_texture (GskRenderer           *renderer,
 static void
 gsk_vulkan_renderer_render (GskRenderer          *renderer,
                             GskRenderNode        *root,
-                            const cairo_region_t *region)
+                            const cairo_region_t *region,
+                            GskOffload           *offload)
 {
   GskVulkanRenderer *self = GSK_VULKAN_RENDERER (renderer);
   GskVulkanRender *render;