clutter/stage-view: Only paint redraw clip from offscreen

The rest didn't change, so only actually paint the part of the offscreen
that was composited as part of the stage painting. In practice, this
means that, unless a shadow buffer is used, we now only paint the
damaged part of the stage, and copy the damage part of the offscreen to
the onscreen.

https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1237

clutter/clutter/clutter-stage-view-private.h

@@ -20,7 +20,8 @@
 
 #include "clutter/clutter-stage-view.h"
 
-void clutter_stage_view_after_paint (ClutterStageView *view);
+void clutter_stage_view_after_paint (ClutterStageView *view,
+                                     cairo_region_t   *redraw_clip);
 
 gboolean clutter_stage_view_is_dirty_viewport (ClutterStageView *view);
 

clutter/clutter/clutter-stage-view.c

@@ -186,20 +186,84 @@ static void
 paint_transformed_framebuffer (ClutterStageView     *view,
                                CoglPipeline         *pipeline,
                                CoglFramebuffer      *src_framebuffer,
-                               CoglFramebuffer  *dst_framebuffer)
+                               CoglFramebuffer      *dst_framebuffer,
+                               const cairo_region_t *redraw_clip)
 {
   CoglMatrix matrix;
+  unsigned int n_rectangles, i;
+  int dst_width, dst_height;
+  cairo_rectangle_int_t view_layout;
+  cairo_rectangle_int_t onscreen_layout;
+  float view_scale;
+  float *coordinates;
+
+  dst_width = cogl_framebuffer_get_width (dst_framebuffer);
+  dst_height = cogl_framebuffer_get_height (dst_framebuffer);
+  clutter_stage_view_get_layout (view, &view_layout);
+  clutter_stage_view_transform_rect_to_onscreen (view,
+                                                 &(cairo_rectangle_int_t) {
+                                                   .width = view_layout.width,
+                                                   .height = view_layout.height,
+                                                 },
+                                                 view_layout.width,
+                                                 view_layout.height,
+                                                 &onscreen_layout);
+  view_scale = clutter_stage_view_get_scale (view);
 
   cogl_framebuffer_push_matrix (dst_framebuffer);
 
   cogl_matrix_init_identity (&matrix);
-  cogl_matrix_translate (&matrix, -1, 1, 0);
+  cogl_matrix_scale (&matrix,
-  cogl_matrix_scale (&matrix, 2, -2, 0);
+                     1.0 / (dst_width / 2.0),
+                     -1.0 / (dst_height / 2.0), 0);
+  cogl_matrix_translate (&matrix,
+                         -(dst_width / 2.0),
+                         -(dst_height / 2.0), 0);
   cogl_framebuffer_set_projection_matrix (dst_framebuffer, &matrix);
+  cogl_framebuffer_set_viewport (dst_framebuffer,
+                                 0, 0, dst_width, dst_height);
 
-  cogl_framebuffer_draw_rectangle (dst_framebuffer,
+  n_rectangles = cairo_region_num_rectangles (redraw_clip);
+  coordinates = g_newa (float, 2 * 4 * n_rectangles);
+
+  for (i = 0; i < n_rectangles; i++)
+    {
+      cairo_rectangle_int_t src_rect;
+      cairo_rectangle_int_t dst_rect;
+
+      cairo_region_get_rectangle (redraw_clip, i, &src_rect);
+      _clutter_util_rectangle_offset (&src_rect,
+                                      -view_layout.x,
+                                      -view_layout.y,
+                                      &src_rect);
+
+      clutter_stage_view_transform_rect_to_onscreen (view,
+                                                     &src_rect,
+                                                     onscreen_layout.width,
+                                                     onscreen_layout.height,
+                                                     &dst_rect);
+
+      coordinates[i * 8 + 0] = (float) dst_rect.x * view_scale;
+      coordinates[i * 8 + 1] = (float) dst_rect.y * view_scale;
+      coordinates[i * 8 + 2] = ((float) (dst_rect.x + dst_rect.width) *
+                                view_scale);
+      coordinates[i * 8 + 3] = ((float) (dst_rect.y + dst_rect.height) *
+                                view_scale);
+
+      coordinates[i * 8 + 4] = (((float) dst_rect.x / (float) dst_width) *
+                                view_scale);
+      coordinates[i * 8 + 5] = (((float) dst_rect.y / (float) dst_height) *
+                                view_scale);
+      coordinates[i * 8 + 6] = ((float) (dst_rect.x + dst_rect.width) /
+                                (float) dst_width) * view_scale;
+      coordinates[i * 8 + 7] = ((float) (dst_rect.y + dst_rect.height) /
+                                (float) dst_height) * view_scale;
+    }
+
+  cogl_framebuffer_draw_textured_rectangles (dst_framebuffer,
                                              pipeline,
-                                   0, 0, 1, 1);
+                                             coordinates,
+                                             n_rectangles);
 
   cogl_framebuffer_pop_matrix (dst_framebuffer);
 }
@@ -279,7 +343,8 @@ init_shadowfb (ClutterStageView *view)
 }
 
 void
-clutter_stage_view_after_paint (ClutterStageView *view)
+clutter_stage_view_after_paint (ClutterStageView *view,
+                                cairo_region_t   *redraw_clip)
 {
   ClutterStageViewPrivate *priv =
     clutter_stage_view_get_instance_private (view);
@@ -293,14 +358,16 @@ clutter_stage_view_after_paint (ClutterStageView *view)
           paint_transformed_framebuffer (view,
                                          priv->offscreen_pipeline,
                                          priv->offscreen,
-                                         priv->shadow.framebuffer);
+                                         priv->shadow.framebuffer,
+                                         redraw_clip);
         }
       else
         {
           paint_transformed_framebuffer (view,
                                          priv->offscreen_pipeline,
                                          priv->offscreen,
-                                         priv->framebuffer);
+                                         priv->framebuffer,
+                                         redraw_clip);
         }
     }
 

clutter/clutter/cogl/clutter-stage-cogl.c

@@ -512,7 +512,7 @@ paint_stage (ClutterStageCogl *stage_cogl,
   _clutter_stage_maybe_setup_viewport (stage, view);
   clutter_stage_paint_view (stage, view, redraw_clip);
 
-  clutter_stage_view_after_paint (view);
+  clutter_stage_view_after_paint (view, redraw_clip);
 }
 
 static void