Implement preservesAxisAlignment on gfx::Transform

In many cases we would like to check if a rect remains axis-aligned after
having a transform applied to it. This is often done by actually applying the
transform to the rect and then verifying that it is still rectilinear. This
entire map operation can be avoided, instead performing a quicker check over 6
elements of the matrix.

Additionally, this patch fixes a bug where we were unnecessarily creating
renderSurfaces.  This bug was diagnosed and solved by wonsick@chromium.org,
but it was appropriate to do the fix in this patch while it lands.

BUG=258760

Review URL: https://chromiumcodereview.appspot.com/11576036

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@211017 0039d316-1c4b-4281-b951-d872f2087c98

3 files changed, 9 insertions, 12 deletions

diff --git a/cc/trees/layer_tree_host_common.cc b/cc/trees/layer_tree_host_common.cc
index b58340a..2efb20f 100644
--- a/cc/trees/layer_tree_host_common.cc
+++ b/cc/trees/layer_tree_host_common.cc
@@ -1154,7 +1154,7 @@ static void CalculateDrawPropertiesInternal(
       : gfx::Vector2dF(layer_scale_factors, layer_scale_factors);
 
   if (SubtreeShouldRenderToSeparateSurface(
-          layer, combined_transform.IsScaleOrTranslation())) {
+          layer, combined_transform.Preserves2dAxisAlignment())) {
     // Check back-face visibility before continuing with this surface and its
     // subtree
     if (!layer->double_sided() && TransformToParentIsKnown(layer) &&
diff --git a/cc/trees/occlusion_tracker.cc b/cc/trees/occlusion_tracker.cc
index 6b6ea5d..08553a8 100644
--- a/cc/trees/occlusion_tracker.cc
+++ b/cc/trees/occlusion_tracker.cc
@@ -83,17 +83,15 @@ static Region TransformSurfaceOpaqueRegion(const Region& region,
   // surface after applying |transform|. If this is true, then apply |transform|
   // to each rect within |region| in order to transform the entire Region.
 
-  bool clipped;
-  gfx::QuadF transformed_bounds_quad =
-      MathUtil::MapQuad(transform, gfx::QuadF(region.bounds()), &clipped);
   // TODO(danakj): Find a rect interior to each transformed quad.
-  if (clipped || !transformed_bounds_quad.IsRectilinear())
+  if (!transform.Preserves2dAxisAlignment())
     return Region();
 
   // TODO(danakj): If the Region is too complex, degrade gracefully here by
   // skipping rects in it.
   Region transformed_region;
   for (Region::Iterator rects(region); rects.has_rect(); rects.next()) {
+    bool clipped;
     gfx::QuadF transformed_quad =
         MathUtil::MapQuad(transform, gfx::QuadF(rects.rect()), &clipped);
     gfx::Rect transformed_rect =
@@ -422,11 +420,8 @@ void OcclusionTrackerBase<LayerType, RenderSurfaceType>::
 
   DCHECK(layer->visible_content_rect().Contains(opaque_contents.bounds()));
 
-  bool clipped;
-  gfx::QuadF visible_transformed_quad = MathUtil::MapQuad(
-      layer->draw_transform(), gfx::QuadF(opaque_contents.bounds()), &clipped);
   // TODO(danakj): Find a rect interior to each transformed quad.
-  if (clipped || !visible_transformed_quad.IsRectilinear())
+  if (!layer->draw_transform().Preserves2dAxisAlignment())
     return;
 
   gfx::Rect clip_rect_in_target = ScreenSpaceClipRectInTargetSurface(
@@ -441,6 +436,7 @@ void OcclusionTrackerBase<LayerType, RenderSurfaceType>::
   for (Region::Iterator opaque_content_rects(opaque_contents);
        opaque_content_rects.has_rect();
        opaque_content_rects.next()) {
+    bool clipped;
     gfx::QuadF transformed_quad = MathUtil::MapQuad(
         layer->draw_transform(),
         gfx::QuadF(opaque_content_rects.rect()),
@@ -485,6 +481,7 @@ void OcclusionTrackerBase<LayerType, RenderSurfaceType>::
     if (transformed_rect.IsEmpty())
       continue;
 
+    bool clipped;
     gfx::QuadF screen_space_quad = MathUtil::MapQuad(
         layer->render_target()->render_surface()->screen_space_transform(),
         gfx::QuadF(transformed_rect),
diff --git a/cc/trees/occlusion_tracker_unittest.cc b/cc/trees/occlusion_tracker_unittest.cc
index 956b67b..9a5f839 100644
--- a/cc/trees/occlusion_tracker_unittest.cc
+++ b/cc/trees/occlusion_tracker_unittest.cc
@@ -836,7 +836,7 @@ class OcclusionTrackerTestChildInRotatedChild
     typename Types::ContentLayerType* parent = this->CreateRoot(
         this->identity_matrix, gfx::PointF(), gfx::Size(100, 100));
     parent->SetMasksToBounds(true);
-    typename Types::LayerType* child = this->CreateLayer(
+    typename Types::LayerType* child = this->CreateSurface(
         parent, child_transform, gfx::PointF(30.f, 30.f), gfx::Size(500, 500));
     child->SetMasksToBounds(true);
     typename Types::ContentLayerType* layer =
@@ -999,7 +999,7 @@ class OcclusionTrackerTestVisitTargetTwoTimes
     typename Types::ContentLayerType* parent = this->CreateDrawingLayer(
         root, this->identity_matrix, gfx::PointF(), gfx::Size(100, 100), true);
     parent->SetMasksToBounds(true);
-    typename Types::LayerType* child = this->CreateLayer(
+    typename Types::LayerType* child = this->CreateSurface(
         parent, child_transform, gfx::PointF(30.f, 30.f), gfx::Size(500, 500));
     child->SetMasksToBounds(true);
     typename Types::ContentLayerType* layer =
@@ -1236,7 +1236,7 @@ class OcclusionTrackerTestSurfaceWithTwoOpaqueChildren
         root, this->identity_matrix, gfx::PointF(), gfx::Size(100, 100), true);
     parent->SetMasksToBounds(true);
     typename Types::ContentLayerType* child =
-        this->CreateDrawingLayer(parent,
+        this->CreateDrawingSurface(parent,
                                  child_transform,
                                  gfx::PointF(30.f, 30.f),
                                  gfx::Size(500, 500),