Avoid int->float->int conversion in OcclusionTracker for int translates.

If the transform on a layer is an integer translation, we can easily
avoid converting the query rectangle to floats just to convert them
back to integers again. This is super costly.

Added a perftest for this. On an N4 the results are

Before: 20.553817749023438 us
After: 13.440165519714355 us

For about 35% reduction in time in this scnario.

Also renames MapClippedRect(Rect) to MapEnclosingClippedRect(Rect) to
describe what it does better, and audit callsides of MapClippedRect
to change any others that then ToEnclosingRect to call the
MapEnclosingClippedRect instead. Similar for Project.

R=enne
BUG=342848

Review URL: https://codereview.chromium.org/143293005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250739 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 26 insertions, 4 deletions

diff --git a/cc/base/math_util.cc b/cc/base/math_util.cc
index 72b1e7f..e696ea6 100644
--- a/cc/base/math_util.cc
+++ b/cc/base/math_util.cc
@@ -101,8 +101,15 @@ static inline void AddVertexToClippedQuad(const gfx::PointF& new_vertex,
   (*num_vertices_in_clipped_quad)++;
 }
 
-gfx::Rect MathUtil::MapClippedRect(const gfx::Transform& transform,
-                                   const gfx::Rect& src_rect) {
+gfx::Rect MathUtil::MapEnclosingClippedRect(const gfx::Transform& transform,
+                                            const gfx::Rect& src_rect) {
+  if (transform.IsIdentityOrIntegerTranslation()) {
+    return src_rect +
+           gfx::Vector2d(
+               static_cast<int>(SkMScalarToFloat(transform.matrix().get(0, 3))),
+               static_cast<int>(
+                   SkMScalarToFloat(transform.matrix().get(1, 3))));
+  }
   return gfx::ToEnclosingRect(MapClippedRect(transform, gfx::RectF(src_rect)));
 }
 
@@ -136,6 +143,19 @@ gfx::RectF MathUtil::MapClippedRect(const gfx::Transform& transform,
   return ComputeEnclosingClippedRect(hc0, hc1, hc2, hc3);
 }
 
+gfx::Rect MathUtil::ProjectEnclosingClippedRect(const gfx::Transform& transform,
+                                                const gfx::Rect& src_rect) {
+  if (transform.IsIdentityOrIntegerTranslation()) {
+    return src_rect +
+           gfx::Vector2d(
+               static_cast<int>(SkMScalarToFloat(transform.matrix().get(0, 3))),
+               static_cast<int>(
+                   SkMScalarToFloat(transform.matrix().get(1, 3))));
+  }
+  return gfx::ToEnclosingRect(
+      ProjectClippedRect(transform, gfx::RectF(src_rect)));
+}
+
 gfx::RectF MathUtil::ProjectClippedRect(const gfx::Transform& transform,
                                         const gfx::RectF& src_rect) {
   if (transform.IsIdentityOrTranslation()) {
diff --git a/cc/base/math_util.h b/cc/base/math_util.h
index fca08ef..9d6364ae 100644
--- a/cc/base/math_util.h
+++ b/cc/base/math_util.h
@@ -99,10 +99,12 @@ class CC_EXPORT MathUtil {
   //
   // These functions return the axis-aligned rect that encloses the correctly
   // clipped, transformed polygon.
-  static gfx::Rect MapClippedRect(const gfx::Transform& transform,
-                                  const gfx::Rect& rect);
+  static gfx::Rect MapEnclosingClippedRect(const gfx::Transform& transform,
+                                           const gfx::Rect& rect);
   static gfx::RectF MapClippedRect(const gfx::Transform& transform,
                                    const gfx::RectF& rect);
+  static gfx::Rect ProjectEnclosingClippedRect(const gfx::Transform& transform,
+                                               const gfx::Rect& rect);
   static gfx::RectF ProjectClippedRect(const gfx::Transform& transform,
                                        const gfx::RectF& rect);