mix-blend-mode implementation for accelerated layers

cc/trees/layer_tree_host_common.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/base/math_util.h"
@@ skipping 566 matching lines @@
   if (LayerIsInExisting3DRenderingContext(layer) && !layer->preserves_3d() &&
       num_descendants_that_draw_content > 0) {
     TRACE_EVENT_INSTANT0(
         "cc",
         "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface flattening",
         TRACE_EVENT_SCOPE_THREAD);
     DCHECK(!is_root);
     return true;
   }
 
+  // If the layer has blending.
+  // TODO(rosca): this is temporary, until blending is implemented for other
+  // types of quads than RenderPassQuad. Layers having descendants that draw
+  // content will still create a separate rendering surface.
+  if (!layer->uses_default_blend_mode()) {
+    TRACE_EVENT_INSTANT0(
+        "cc",
+        "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface blending",
+        TRACE_EVENT_SCOPE_THREAD);
+    DCHECK(!is_root);
+    return true;
+  }
+
+  // If the layer has isolation.
+  // TODO(rosca): to be optimized - create separate rendering surface only when
+  // the blending descendants might have access to the content behind this layer
+  // (layer has transparent background or descendants overflow)
+  // https://code.google.com/p/chromium/issues/detail?id=301738
+  if (layer->is_root_for_isolated_group()) {
+    TRACE_EVENT_INSTANT0(
+        "cc",
+        "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface isolation",
+        TRACE_EVENT_SCOPE_THREAD);
+    DCHECK(!is_root);
+    return true;
+  }
+
   // If the layer clips its descendants but it is not axis-aligned with respect
   // to its parent.
   bool layer_clips_external_content =
       LayerClipsSubtree(layer) || layer->HasDelegatedContent();
   if (layer_clips_external_content && !axis_aligned_with_respect_to_parent &&
       num_descendants_that_draw_content > 0) {
     TRACE_EVENT_INSTANT0(
         "cc",
         "LayerTreeHostCommon::SubtreeShouldRenderToSeparateSurface clipping",
         TRACE_EVENT_SCOPE_THREAD);
@@ skipping 1248 matching lines @@
     clipped_content_rect.set_width(
         std::min(clipped_content_rect.width(), globals.max_texture_size));
     clipped_content_rect.set_height(
         std::min(clipped_content_rect.height(), globals.max_texture_size));
 
     if (clipped_content_rect.IsEmpty()) {
       RemoveSurfaceForEarlyExit(layer, render_surface_layer_list);
       return;
     }
 
+    // Layers having a non-default blend mode will blend with the content
+    // inside its parent's render target. This render target should be
+    // either root_for_isolated_group, or the root of the layer tree.

[enne (OOO), 2013/11/01 18:49:02]

Can you also mention that if this is not true, then the problem will be that
blending will be incorrect?

[rosca, 2013/11/04 17:14:34]

Done.

+    DCHECK(layer->uses_default_blend_mode() || !layer->parent() ||
+           !layer->parent()->render_target() ||
+           IsRootLayer(layer->parent()->render_target()) ||
+           layer->parent()->render_target()->is_root_for_isolated_group());
+
     render_surface->SetContentRect(clipped_content_rect);
 
     // The owning layer's screen_space_transform has a scale from content to
     // layer space which we need to undo and replace with a scale from the
     // surface's subtree into layer space.
     gfx::Transform screen_space_transform = layer->screen_space_transform();
     screen_space_transform.Scale(
         layer->contents_scale_x() / render_surface_sublayer_scale.x(),
         layer->contents_scale_y() / render_surface_sublayer_scale.y());
     render_surface->SetScreenSpaceTransform(screen_space_transform);
@@ skipping 364 matching lines @@
   // At this point, we think the point does hit the touch event handler region
   // on the layer, but we need to walk up the parents to ensure that the layer
   // was not clipped in such a way that the hit point actually should not hit
   // the layer.
   if (PointIsClippedBySurfaceOrClipRect(screen_space_point, layer_impl))
     return false;
 
   return true;
 }
 }  // namespace cc