Fix masks when scaling is in the tree

cc/render_surface_impl.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/render_surface_impl.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "base/stringprintf.h"
@@ skipping 206 matching lines @@
         maskLayer = 0;
 
     if (!maskLayer && forReplica) {
         maskLayer = m_owningLayer->replicaLayer()->maskLayer();
         if (maskLayer && (!maskLayer->drawsContent() || maskLayer->bounds().IsEmpty()))
             maskLayer = 0;
     }
 
     gfx::RectF maskUVRect(0.0f, 0.0f, 1.0f, 1.0f);
     if (maskLayer) {
-        float scaleX = contentRect().width() / maskLayer->contentsScaleX() / maskLayer->bounds().width();
-        float scaleY = contentRect().height() / maskLayer->contentsScaleY() / maskLayer->bounds().height();
+        // Because the RenderSurface is sized base on the screen footprint,
+        // there can be a scale between the RenderSurface and the owning layer,
+        // as well as the mask. While the mask doesn't have a drawTransform, the
+        // owning layer has it (and should be pure scaling), so use that to
+        // scale the mask to the right size.
+        gfx::Vector2dF maskDrawScale = MathUtil::computeTransform2dScaleComponents(m_owningLayer->drawTransform(), 1.f);

[enne (OOO), 2013/01/15 04:12:43]

This will work given the current implementation of LTHCommon, but I had once
hoped that we could separate the scale of the owning layer from the scale of the
surface (in case you had some image with a bizarre scale that created a surface,
and then everything inside would get scaled to it).  It almost seems like the
mask layer's content's scale should just take this surface scale into account
and then this owning layer detail could be entirely hidden in
LayerTreeHostCommon.

[danakj, 2013/01/15 16:31:11]

I'm not sure I agree. My POV is that the mask is assumed to share the same
contents scale as the owning layer, so I think the mask needs to be drawn with
the same scale as the owning layer is. The "surface's scale" is in theory
independent of the owning layer's draw transform, but the mask layer should
continue to draw at the same scale as the owning layer to have its pixel
positions aligned.

[danakj, 2013/01/15 17:11:53]

Ok I take this back. I had developed an impression that the mask only applies to
its layer. But enne@ pointed me to https://www.webkit.org/blog/181/css-masks/
where it states:

"The mask will therefore overlay the child and all of its descendants"

So I guess we want to scale it to fill the entire render surface.

Which makes me then wonder why this wasn't working for this case. Is it because
the mask layer was being added to the root layer, so the contentRect of the
surface didn't match the size of the subtree? or because aura is drawing a mask
assuming it matches the size of the owning layer and not its subtree?

+        float scaleX = contentRect().width() / maskLayer->contentsScaleX() / maskLayer->bounds().width() / maskDrawScale.x();
+        float scaleY = contentRect().height() / maskLayer->contentsScaleY() / maskLayer->bounds().height() / maskDrawScale.y();
 
         maskUVRect = gfx::RectF(static_cast<float>(contentRect().x()) / contentRect().width() * scaleX,
                                 static_cast<float>(contentRect().y()) / contentRect().height() * scaleY,
                                 scaleX,
                                 scaleY);
     }
 
     ResourceProvider::ResourceId maskResourceId = maskLayer ? maskLayer->contentsResourceId() : 0;
     gfx::Rect contentsChangedSinceLastFrame = contentsChanged() ? m_contentRect : gfx::Rect();
 
     scoped_ptr<RenderPassDrawQuad> quad = RenderPassDrawQuad::Create();
     quad->SetNew(sharedQuadState, contentRect(), renderPassId, forReplica, maskResourceId, contentsChangedSinceLastFrame, maskUVRect, m_owningLayer->filters(), m_owningLayer->filter(), m_owningLayer->backgroundFilters());
     quadSink.append(quad.PassAs<DrawQuad>(), appendQuadsData);
 }
 
 }  // namespace cc