shaped-texture: Turn blending off when drawing entirely opaque regions

When drawing entirely opaque regions, we traditionally kept blending on
simply because it made the code more convenient and obvious to handle.
However, this can cause lots of performance issues on GPUs that aren't
too powerful, as they have to readback the buffer underneath.

Keep track of the opaque region set by windows (through _NET_WM_OPAQUE_REGION,
Wayland opaque_region hints, standard RGB32 frame masks or similar), and draw
those rectangles separately through a different path with blending turned off.

https://bugzilla.gnome.org/show_bug.cgi?id=707019

3 files changed, 152 insertions, 26 deletions

diff --git a/src/compositor/meta-shaped-texture.c b/src/compositor/meta-shaped-texture.c
index eb448ba9b..838e3fe22 100644
--- a/src/compositor/meta-shaped-texture.c
+++ b/src/compositor/meta-shaped-texture.c
@@ -94,6 +94,7 @@ struct _MetaShapedTexturePrivate
 
   cairo_region_t *clip_region;
   cairo_region_t *input_shape_region;
+  cairo_region_t *opaque_region;
 
   guint tex_width, tex_height;
 
@@ -172,6 +173,55 @@ get_masked_pipeline (CoglContext *ctx)
   return cogl_pipeline_copy (template);
 }
 
+static CoglPipeline *
+get_unblended_pipeline (CoglContext *ctx)
+{
+  static CoglPipeline *template = NULL;
+  if (G_UNLIKELY (template == NULL))
+    {
+      CoglColor color;
+      template = cogl_pipeline_new (ctx);
+      cogl_color_init_from_4ub (&color, 255, 255, 255, 255);
+      cogl_pipeline_set_blend (template,
+                               "RGBA = ADD (SRC_COLOR, 0)",
+                               NULL);
+      cogl_pipeline_set_color (template, &color);
+    }
+
+  return cogl_pipeline_copy (template);
+}
+
+static void
+paint_clipped_rectangle (CoglFramebuffer       *fb,
+                         CoglPipeline          *pipeline,
+                         cairo_rectangle_int_t *rect,
+                         ClutterActorBox       *alloc)
+{
+  float coords[8];
+  float x1, y1, x2, y2;
+
+  x1 = rect->x;
+  y1 = rect->y;
+  x2 = rect->x + rect->width;
+  y2 = rect->y + rect->height;
+
+  coords[0] = rect->x / (alloc->x2 - alloc->x1);
+  coords[1] = rect->y / (alloc->y2 - alloc->y1);
+  coords[2] = (rect->x + rect->width) / (alloc->x2 - alloc->x1);
+  coords[3] = (rect->y + rect->height) / (alloc->y2 - alloc->y1);
+
+  coords[4] = coords[0];
+  coords[5] = coords[1];
+  coords[6] = coords[2];
+  coords[7] = coords[3];
+
+  cogl_framebuffer_draw_multitextured_rectangle (fb, pipeline,
+                                                 x1, y1, x2, y2,
+                                                 &coords[0], 8);
+
+}
+
+
 static void
 set_cogl_texture (MetaShapedTexture *stex,
                   CoglTexture       *cogl_tex)
@@ -222,11 +272,13 @@ meta_shaped_texture_paint (ClutterActor *actor)
   MetaShapedTexture *stex = (MetaShapedTexture *) actor;
   MetaShapedTexturePrivate *priv = stex->priv;
   guint tex_width, tex_height;
+  guchar opacity;
   CoglContext *ctx;
   CoglFramebuffer *fb;
   CoglPipeline *pipeline = NULL;
   CoglTexture *paint_tex;
   ClutterActorBox alloc;
+  cairo_region_t *blended_region = NULL;
 
   if (priv->clip_region && cairo_region_is_empty (priv->clip_region))
     return;
@@ -266,6 +318,64 @@ meta_shaped_texture_paint (ClutterActor *actor)
   ctx = clutter_backend_get_cogl_context (clutter_get_default_backend ());
   fb = cogl_get_draw_framebuffer ();
 
+  opacity = clutter_actor_get_paint_opacity (actor);
+  clutter_actor_get_allocation_box (actor, &alloc);
+
+  if (priv->opaque_region != NULL && opacity == 255)
+    {
+      CoglPipeline *opaque_pipeline;
+      cairo_region_t *region;
+      int n_rects;
+      int i;
+
+      if (priv->clip_region != NULL)
+        {
+          region = cairo_region_copy (priv->clip_region);
+          cairo_region_intersect (region, priv->opaque_region);
+        }
+      else
+        {
+          region = cairo_region_reference (priv->opaque_region);
+        }
+
+      if (cairo_region_is_empty (region))
+        goto paint_blended;
+
+      opaque_pipeline = get_unblended_pipeline (ctx);
+      cogl_pipeline_set_layer_texture (opaque_pipeline, 0, paint_tex);
+
+      n_rects = cairo_region_num_rectangles (region);
+      for (i = 0; i < n_rects; i++)
+        {
+          cairo_rectangle_int_t rect;
+          cairo_region_get_rectangle (region, i, &rect);
+          paint_clipped_rectangle (fb, opaque_pipeline, &rect, &alloc);
+        }
+
+      cogl_object_unref (opaque_pipeline);
+
+      if (priv->clip_region != NULL)
+        {
+          blended_region = cairo_region_copy (priv->clip_region);
+        }
+      else
+        {
+          cairo_rectangle_int_t rect = { 0, 0, tex_width, tex_height };
+          blended_region = cairo_region_create_rectangle (&rect);
+        }
+
+      cairo_region_subtract (blended_region, priv->opaque_region);
+
+    paint_blended:
+      cairo_region_destroy (region);
+    }
+
+  if (blended_region == NULL && priv->clip_region != NULL)
+    blended_region = cairo_region_reference (priv->clip_region);
+
+  if (blended_region != NULL && cairo_region_is_empty (blended_region))
+    goto out;
+
   if (priv->mask_texture == NULL)
     {
       pipeline = get_unmasked_pipeline (ctx);
@@ -280,18 +390,13 @@ meta_shaped_texture_paint (ClutterActor *actor)
 
   {
     CoglColor color;
-    guchar opacity = clutter_actor_get_paint_opacity (actor);
     cogl_color_init_from_4ub (&color, opacity, opacity, opacity, opacity);
     cogl_pipeline_set_color (pipeline, &color);
   }
 
-  clutter_actor_get_allocation_box (actor, &alloc);
-
-  if (priv->clip_region)
+  if (blended_region != NULL)
     {
       int n_rects;
-      int i;
-      cairo_rectangle_int_t tex_rect = { 0, 0, tex_width, tex_height };
 
       /* Limit to how many separate rectangles we'll draw; beyond this just
        * fall back and draw the whole thing */
@@ -300,8 +405,8 @@ meta_shaped_texture_paint (ClutterActor *actor)
       n_rects = cairo_region_num_rectangles (priv->clip_region);
       if (n_rects <= MAX_RECTS)
 	{
-	  float coords[8];
-          float x1, y1, x2, y2;
+          int i;
+          cairo_rectangle_int_t tex_rect = { 0, 0, tex_width, tex_height };
 
 	  for (i = 0; i < n_rects; i++)
 	    {
@@ -312,24 +417,7 @@ meta_shaped_texture_paint (ClutterActor *actor)
 	      if (!gdk_rectangle_intersect (&tex_rect, &rect, &rect))
 		continue;
 
-	      x1 = rect.x;
-	      y1 = rect.y;
-	      x2 = rect.x + rect.width;
-	      y2 = rect.y + rect.height;
-
-	      coords[0] = rect.x / (alloc.x2 - alloc.x1);
-	      coords[1] = rect.y / (alloc.y2 - alloc.y1);
-	      coords[2] = (rect.x + rect.width) / (alloc.x2 - alloc.x1);
-	      coords[3] = (rect.y + rect.height) / (alloc.y2 - alloc.y1);
-
-              coords[4] = coords[0];
-              coords[5] = coords[1];
-              coords[6] = coords[2];
-              coords[7] = coords[3];
-
-              cogl_framebuffer_draw_multitextured_rectangle (fb, pipeline,
-                                                             x1, y1, x2, y2,
-                                                             &coords[0], 8);
+              paint_clipped_rectangle (fb, pipeline, &rect, &alloc);
             }
 
           goto out;
@@ -344,6 +432,8 @@ meta_shaped_texture_paint (ClutterActor *actor)
  out:
   if (pipeline != NULL)
     cogl_object_unref (pipeline);
+  if (blended_region != NULL)
+    cairo_region_destroy (blended_region);
 }
 
 static void
@@ -845,6 +935,36 @@ meta_shaped_texture_set_clip_region (MetaShapedTexture *stex,
 }
 
 /**
+ * meta_shaped_texture_set_opaque_region:
+ * @stex: a #MetaShapedTexture
+ * @opaque_region: (transfer full): the region of the texture that
+ *   can have blending turned off.
+ *
+ * As most windows have a large portion that does not require blending,
+ * we can easily turn off blending if we know the areas that do not
+ * require blending. This sets the region where we will not blend for
+ * optimization purposes.
+ */
+void
+meta_shaped_texture_set_opaque_region (MetaShapedTexture *stex,
+                                       cairo_region_t    *opaque_region)
+{
+  MetaShapedTexturePrivate *priv;
+
+  g_return_if_fail (META_IS_SHAPED_TEXTURE (stex));
+
+  priv = stex->priv;
+
+  if (priv->opaque_region)
+    cairo_region_destroy (priv->opaque_region);
+
+  if (opaque_region)
+    priv->opaque_region = cairo_region_reference (opaque_region);
+  else
+    priv->opaque_region = NULL;
+}
+
+/**
  * meta_shaped_texture_get_image:
  * @stex: A #MetaShapedTexture
  * @clip: A clipping rectangle, to help prevent extra processing.
diff --git a/src/compositor/meta-window-actor.c b/src/compositor/meta-window-actor.c
index e7ca3f61e..12043227c 100644
--- a/src/compositor/meta-window-actor.c
+++ b/src/compositor/meta-window-actor.c
@@ -2286,6 +2286,9 @@ meta_window_actor_update_opaque_region (MetaWindowActor *self)
     priv->opaque_region = NULL;
   else
     priv->opaque_region = cairo_region_reference (priv->shape_region);
+
+  meta_shaped_texture_set_opaque_region (META_SHAPED_TEXTURE (priv->actor),
+                                         priv->opaque_region);
 }
 
 static void
diff --git a/src/meta/meta-shaped-texture.h b/src/meta/meta-shaped-texture.h
index 080554198..2b6d3254a 100644
--- a/src/meta/meta-shaped-texture.h
+++ b/src/meta/meta-shaped-texture.h
@@ -84,6 +84,9 @@ void meta_shaped_texture_set_input_shape_region (MetaShapedTexture *stex,
 void meta_shaped_texture_set_clip_region (MetaShapedTexture *stex,
 					  cairo_region_t    *clip_region);
 
+void meta_shaped_texture_set_opaque_region (MetaShapedTexture *stex,
+                                            cairo_region_t    *opaque_region);
+
 cairo_surface_t * meta_shaped_texture_get_image (MetaShapedTexture     *stex,
                                                  cairo_rectangle_int_t *clip);