Changes subtreeShouldRenderToSeparateSurface logic to account for explicit clipping

cc/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/layer_tree_host_common.h"
 
 #include <algorithm>
 
 #include "base/debug/trace_event.h"
 #include "cc/layer.h"
@@ skipping 256 matching lines @@
         return true;
 
     int numDescendantsThatDrawContent = layer->drawProperties().num_descendants_that_draw_content;
 
     // If the layer flattens its subtree (i.e. the layer doesn't preserve-3d), but it is
     // treated as a 3D object by its parent (i.e. parent does preserve-3d).
     if (layerIsInExisting3DRenderingContext(layer) && !layer->preserves3D() && numDescendantsThatDrawContent > 0)
         return true;
 
     // If the layer clips its descendants but it is not axis-aligned with respect to its parent.
-    if (layerClipsSubtree(layer) && !axisAlignedWithRespectToParent && numDescendantsThatDrawContent > 0)
+    if (layerClipsSubtree(layer) && !layer->drawProperties().all_children_can_clip)
         return true;
 
     // If the layer has some translucency and does not have a preserves-3d transform style.
     // This condition only needs a render surface if two or more layers in the
     // subtree overlap. But checking layer overlaps is unnecessarily costly so
     // instead we conservatively create a surface whenever at least two layers
     // draw content for this subtree.
     bool atLeastTwoLayersInSubtreeDrawContent = layer->hasDelegatedContent() ||
         (numDescendantsThatDrawContent > 0 && (layer->drawsContent() || numDescendantsThatDrawContent > 1));
 
@@ skipping 134 matching lines @@
     // layers from the end of the list.
     while (renderSurfaceLayerList.back() != layerToRemove) {
         renderSurfaceLayerList.back()->clearRenderSurface();
         renderSurfaceLayerList.pop_back();
     }
     DCHECK(renderSurfaceLayerList.back() == layerToRemove);
     renderSurfaceLayerList.pop_back();
     layerToRemove->clearRenderSurface();
 }
 
+inline bool isPositiveScaleOrTranslation(const gfx::Transform& xform)
+{
+    if (!xform.IsScaleOrTranslation())
+        return false;
+
+    // Grab our scale and make sure it's positive.
+    float x_scale = xform.matrix().getDouble(0,0);

[jamesr, 2012/12/14 04:31:19]

do we have to do a double->float conversion here?  I suspect it'll compile away,
but since the transform is double and we don't need to do anything but a sign
comparison seems better to keep this doubles

[whunt, 2012/12/14 18:17:01]

There's no reason to do the conversion.  I'm just used to assuming things are
floats.  I'll chnage it.

On 2012/12/14 04:31:19, jamesr wrote:

+    float y_scale = xform.matrix().getDouble(1,1);
+    if (x_scale <= 0.0f || y_scale <= 0.0f)
+        return false;
+
+    return true;
+}
+
 // Recursively walks the layer tree to compute any information that is needed
 // before doing the main recursion.
 template<typename LayerType>
 static void preCalculateMetaInformation(LayerType* layer)
 {
     int numDescendantsThatDrawContent = 0;
+    bool allChildrenCanClip = true;
+
+    bool sublayerPreventsClip = !isPositiveScaleOrTranslation(layer->sublayerTransform());

[jamesr, 2012/12/14 04:31:19]

I'm not sure that this is sufficient.  If the transform on the clipping layer is
a (for instance) rotation then we can clip a texutre_layer_impl, but we don't
have any code (afaik) to clip other types of layers

[shawnsingh, 2012/12/14 07:34:44]

+1 james comment; we do need the additional condition that prevents
sublayerPreventsClip from being true unless the layer is the correct type,
right?

also, naming nit:  sublayerPreventsClip --> descendantPreventsClip

[Ian Vollick, 2012/12/14 12:02:16]

Sorry for the drive-by, but I wanted to mention that we should probably add
SkMatrix44::preservesAxisAlignment to match the already existing SkMatrix::
preservesAxisAlignment. I think this would suit your needs here. Implementing
the SkMatrix44 method should be pretty simple, I think -- correct me if I'm
wrong, but if in the upper-left 3x3 matrix there are only 3 non-zero entries,
one in each row, and one in each column, I think we're ok?

[whunt, 2012/12/14 18:17:01]

I'm aware this isn't sufficient.  I'm working on fixing it.  I just wanted to
get the ball rolling.

On 2012/12/14 04:31:19, jamesr wrote:

[whunt, 2012/12/14 18:17:01]

The clipper wont work on rotations by 90 degrees so the functionality isn't the
same.

On 2012/12/14 12:02:16, vollick wrote:

 
     for (size_t i = 0; i < layer->children().size(); ++i) {
         LayerType* childLayer = layer->children()[i];
         preCalculateMetaInformation<LayerType>(childLayer);
-        numDescendantsThatDrawContent += childLayer->drawsContent() ? 1 : 0;
-        numDescendantsThatDrawContent += childLayer->drawProperties().num_descendants_that_draw_content;
+
+        int numChildDescendantsThatDrawContent = 0;
+        numChildDescendantsThatDrawContent += childLayer->drawsContent() ? 1 : 0;

[shawnsingh, 2012/12/14 07:34:44]

I'm not sure about this rename, how about we omit this particular change from
this patch and discuss it later?  no functionality changed here, right?

[whunt, 2012/12/14 18:17:01]

I need the intermediate value.  I didn't change your variables name.  Look at
the code more closely.

On 2012/12/14 07:34:44, shawnsingh wrote:

+        numChildDescendantsThatDrawContent += childLayer->drawProperties().num_descendants_that_draw_content;
+        numDescendantsThatDrawContent += numChildDescendantsThatDrawContent;
+
+        if (!childLayer->drawProperties().all_children_can_clip ||
+            numChildDescendantsThatDrawContent > 0 && (sublayerPreventsClip || !isPositiveScaleOrTranslation(childLayer->transform())))
+            allChildrenCanClip = false;
     }
 
     layer->drawProperties().num_descendants_that_draw_content = numDescendantsThatDrawContent;
+    layer->drawProperties().all_children_can_clip = allChildrenCanClip;
 }
 
 // Recursively walks the layer tree starting at the given node and computes all the
 // necessary transformations, clipRects, render surfaces, etc.
 template<typename LayerType, typename LayerList, typename RenderSurfaceType>
 static void calculateDrawPropertiesInternal(LayerType* layer, const gfx::Transform& parentMatrix,
     const gfx::Transform& fullHierarchyMatrix, const gfx::Transform& currentScrollCompensationMatrix,
     const gfx::Rect& clipRectFromAncestor, const gfx::Rect& clipRectFromAncestorInDescendantSpace, bool ancestorClipsSubtree,
     RenderSurfaceType* nearestAncestorThatMovesPixels, LayerList& renderSurfaceLayerList, LayerList& layerList,
     LayerSorter* layerSorter, int maxTextureSize, float deviceScaleFactor, float pageScaleFactor, bool subtreeCanUseLCDText,
@@ skipping 638 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(screenSpacePoint, layerImpl))
      return false;
 
   return true;
 }
 }  // namespace cc