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

[verdre <jonasd src gnome org>]

commit 258f859e8d29016ef6e178ae4b89f04834b59677
Author: Jonas Ådahl <jadahl gmail com>
Date:   Tue May 5 19:22:10 2020 +0200

    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 |  3 +-
 clutter/clutter/clutter-stage-view.c         | 91 ++++++++++++++++++++++++----
 clutter/clutter/cogl/clutter-stage-cogl.c    |  2 +-
 3 files changed, 82 insertions(+), 14 deletions(-)
---
diff --git a/clutter/clutter/clutter-stage-view-private.h b/clutter/clutter/clutter-stage-view-private.h
index b5b65a4df8..0dfc4e94ee 100644
--- a/clutter/clutter/clutter-stage-view-private.h
+++ b/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);
 
diff --git a/clutter/clutter/clutter-stage-view.c b/clutter/clutter/clutter-stage-view.c
index 97aadcc9c8..9a1f0c5c82 100644
--- a/clutter/clutter/clutter-stage-view.c
+++ b/clutter/clutter/clutter-stage-view.c
@@ -183,23 +183,87 @@ clutter_stage_view_transform_rect_to_onscreen (ClutterStageView            *view
 }
 
 static void
-paint_transformed_framebuffer (ClutterStageView *view,
-                               CoglPipeline     *pipeline,
-                               CoglFramebuffer  *src_framebuffer,
-                               CoglFramebuffer  *dst_framebuffer)
+paint_transformed_framebuffer (ClutterStageView     *view,
+                               CoglPipeline         *pipeline,
+                               CoglFramebuffer      *src_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, 2, -2, 0);
+  cogl_matrix_scale (&matrix,
+                     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,
-                                   pipeline,
-                                   0, 0, 1, 1);
+  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,
+                                             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);
         }
     }
 
diff --git a/clutter/clutter/cogl/clutter-stage-cogl.c b/clutter/clutter/cogl/clutter-stage-cogl.c
index fa9d655d31..8d025d008c 100644
--- a/clutter/clutter/cogl/clutter-stage-cogl.c
+++ b/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