Support bottom-right anchored fixed-position elements during a pinch gesture

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/heads_up_display_layer_impl.h"
@@ skipping 389 matching lines @@
         if (!layer->renderSurface()->drawTransform().GetInverse(&inverseSurfaceDrawTransform)) {
             // TODO(shawnsingh): Either we need to handle uninvertible transforms
             // here, or DCHECK that the transform is invertible.
         }
         nextScrollCompensationMatrix = inverseSurfaceDrawTransform * nextScrollCompensationMatrix * layer->renderSurface()->drawTransform();
     }
 
     return nextScrollCompensationMatrix;
 }
 
+static gfx::Vector2dF computeFixedContainerSizeDeltaForChildren(Layer*, const gfx::Vector2dF&)
+{
+  return gfx::Vector2dF();
+}
+
+static gfx::Vector2dF computeFixedContainerSizeDeltaForChildren(LayerImpl* layer, const gfx::Vector2dF& currentFixedContainerSizeDelta)
+{
+    if (layer->isContainerForFixedPositionLayers())
+        return layer->fixedContainerSizeDelta();
+    return currentFixedContainerSizeDelta;
+}
+
 template<typename LayerType>
 static inline void calculateContentsScale(LayerType* layer, float contentsScale, bool animatingTransformToScreen)
 {
     layer->calculateContentsScale(
         contentsScale,
         animatingTransformToScreen,
         &layer->drawProperties().contents_scale_x,
         &layer->drawProperties().contents_scale_y,
         &layer->drawProperties().content_bounds);
 
@@ skipping 117 matching lines @@
     }
 
     layer->drawProperties().num_descendants_that_draw_content = numDescendantsThatDrawContent;
     layer->drawProperties().descendants_can_clip_selves = descendantsCanClipSelves;
 }
 
 // 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::Transform& fullHierarchyMatrix, const gfx::Transform& currentScrollCompensationMatrix, const gfx::Vector2dF& currentFixedContainerSizeDelta,
     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,
     gfx::Rect& drawableContentRectOfSubtree, bool updateTilePriorities)
 {
     // This function computes the new matrix transformations recursively for this
     // layer and all its descendants. It also computes the appropriate render surfaces.
     // Some important points to remember:
     //
     // 0. Here, transforms are notated in Matrix x Vector order, and in words we describe what
@@ skipping 135 matching lines @@
     // computation of contentsScale above.
     // Note carefully: this is Concat, not Preconcat (implTransform * combinedTransform).
     combinedTransform.ConcatTransform(layer->implTransform());
 
     if (layer->fixedToContainerLayer()) {
         // Special case: this layer is a composited fixed-position layer; we need to
         // explicitly compensate for all ancestors' nonzero scrollDeltas to keep this layer
         // fixed correctly.
         // Note carefully: this is Concat, not Preconcat (currentScrollCompensation * combinedTransform).
         combinedTransform.ConcatTransform(currentScrollCompensationMatrix);
+
+        gfx::Transform bottomRightAnchorCompensation;
+        bottomRightAnchorCompensation.Translate(
+            layer->fixedToRightEdge() ? currentFixedContainerSizeDelta.x() : 0,
+            layer->fixedToBottomEdge() ? currentFixedContainerSizeDelta.y() : 0);
+        combinedTransform.PreconcatTransform(bottomRightAnchorCompensation);

[shawnsingh, 2013/03/07 09:57:06]

Chances are, once we do this correctly, that this will be Concat instead of
Preconcat.  Better yet, I think the right way to do this will be to fold this
computation into the scroll compensation, and re-name scrollCompensation to
something more generic.  More explanation at the beginning of this review =)

     }
 
     // The drawTransform that gets computed below is effectively the layer's drawTransform, unless
     // the layer itself creates a renderSurface. In that case, the renderSurface re-parents the transforms.
     layerDrawProperties.target_space_transform = combinedTransform;
     // M[draw] = M[parent] * LT * S[layer2content]
     layerDrawProperties.target_space_transform.Scale(1.0 / layer->contentsScaleX(), 1.0 / layer->contentsScaleY());
 
     // layerScreenSpaceTransform represents the transform between root layer's "screen space" and local content space.
     layerDrawProperties.screen_space_transform = fullHierarchyMatrix;
@@ skipping 163 matching lines @@
 
     LayerList& descendants = (layer->renderSurface() ? layer->renderSurface()->layerList() : layerList);
 
     // Any layers that are appended after this point are in the layer's subtree and should be included in the sorting process.
     unsigned sortingStartIndex = descendants.size();
 
     if (!layerShouldBeSkipped(layer))
         descendants.push_back(layer);
 
     gfx::Transform nextScrollCompensationMatrix = computeScrollCompensationMatrixForChildren(layer, parentMatrix, currentScrollCompensationMatrix);;
+    gfx::Vector2dF nextFixedContainerSizeDelta = computeFixedContainerSizeDeltaForChildren(layer, currentFixedContainerSizeDelta);
 
     gfx::Rect accumulatedDrawableContentRectOfChildren;
     for (size_t i = 0; i < layer->children().size(); ++i) {
         LayerType* child = LayerTreeHostCommon::getChildAsRawPtr(layer->children(), i);
         gfx::Rect drawableContentRectOfChildSubtree;
-        calculateDrawPropertiesInternal<LayerType, LayerList, RenderSurfaceType>(child, sublayerMatrix, nextHierarchyMatrix, nextScrollCompensationMatrix,
+        calculateDrawPropertiesInternal<LayerType, LayerList, RenderSurfaceType>(child, sublayerMatrix, nextHierarchyMatrix, nextScrollCompensationMatrix, nextFixedContainerSizeDelta,
                                                                                  clipRectForSubtree, clipRectForSubtreeInDescendantSpace, subtreeShouldBeClipped, nearestAncestorThatMovesPixels,
                                                                                  renderSurfaceLayerList, descendants, layerSorter, maxTextureSize, deviceScaleFactor, pageScaleFactor,
                                                                                  subtreeCanUseLCDText, drawableContentRectOfChildSubtree, updateTilePriorities);
         if (!drawableContentRectOfChildSubtree.IsEmpty()) {
             accumulatedDrawableContentRectOfChildren.Union(drawableContentRectOfChildSubtree);
             if (child->renderSurface())
                 descendants.push_back(child);
         }
     }
 
@@ skipping 122 matching lines @@
     // The root layer's renderSurface should receive the deviceViewport as the initial clipRect.
     bool subtreeShouldBeClipped = true;
     gfx::Rect deviceViewportRect(gfx::Point(), deviceViewportSize);
     bool updateTilePriorities = false;
 
     // This function should have received a root layer.
     DCHECK(isRootLayer(rootLayer));
 
     preCalculateMetaInformation<Layer>(rootLayer);
     calculateDrawPropertiesInternal<Layer, std::vector<scoped_refptr<Layer> >, RenderSurface>(
-        rootLayer, deviceScaleTransform, identityMatrix, identityMatrix,
+        rootLayer, deviceScaleTransform, identityMatrix, identityMatrix, gfx::Vector2dF(),
         deviceViewportRect, deviceViewportRect, subtreeShouldBeClipped, 0, renderSurfaceLayerList,
         dummyLayerList, 0, maxTextureSize,
         deviceScaleFactor, pageScaleFactor, canUseLCDText, totalDrawableContentRect,
         updateTilePriorities);
 
     // The dummy layer list should not have been used.
     DCHECK(dummyLayerList.size() == 0);
     // A root layer renderSurface should always exist after calculateDrawProperties.
     DCHECK(rootLayer->renderSurface());
 }
 
 void LayerTreeHostCommon::calculateDrawProperties(LayerImpl* rootLayer, const gfx::Size& deviceViewportSize, float deviceScaleFactor, float pageScaleFactor, int maxTextureSize, bool canUseLCDText, std::vector<LayerImpl*>& renderSurfaceLayerList, bool updateTilePriorities)
 {
     gfx::Rect totalDrawableContentRect;
     gfx::Transform identityMatrix;
     gfx::Transform deviceScaleTransform;
     deviceScaleTransform.Scale(deviceScaleFactor, deviceScaleFactor);
     std::vector<LayerImpl*> dummyLayerList;
     LayerSorter layerSorter;
     
     // The root layer's renderSurface should receive the deviceViewport as the initial clipRect.
     bool subtreeShouldBeClipped = true;
     gfx::Rect deviceViewportRect(gfx::Point(), deviceViewportSize);
 
     // This function should have received a root layer.
     DCHECK(isRootLayer(rootLayer));
 
     preCalculateMetaInformation<LayerImpl>(rootLayer);
     calculateDrawPropertiesInternal<LayerImpl, std::vector<LayerImpl*>, RenderSurfaceImpl>(
-        rootLayer, deviceScaleTransform, identityMatrix, identityMatrix,
+        rootLayer, deviceScaleTransform, identityMatrix, identityMatrix, gfx::Vector2dF(),
         deviceViewportRect, deviceViewportRect, subtreeShouldBeClipped, 0, renderSurfaceLayerList,
         dummyLayerList, &layerSorter, maxTextureSize,
         deviceScaleFactor, pageScaleFactor, canUseLCDText, totalDrawableContentRect,
         updateTilePriorities);
 
     // The dummy layer list should not have been used.
     DCHECK(dummyLayerList.size() == 0);
     // A root layer renderSurface should always exist after calculateDrawProperties.
     DCHECK(rootLayer->renderSurface());
 }
@@ skipping 127 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