Hit test on the layer tree rather than the RSLL

cc/base/math_util.cc

Index: cc/base/math_util.cc
diff --git a/cc/base/math_util.cc b/cc/base/math_util.cc
index ca6e5711760f8b6a16ccfcb9f3e10c82b1f3ada7..641d6499cd147a759453baa86095101851ab5b6e 100644
--- a/cc/base/math_util.cc
+++ b/cc/base/math_util.cc
@@ -41,6 +41,15 @@ static HomogeneousCoordinate ProjectHomogeneousPoint(
   return result;
 }
 
+static HomogeneousCoordinate ProjectHomogeneousPoint(
+    const gfx::Transform& transform,
+    const gfx::PointF& p,
+    bool* clipped) {
+  HomogeneousCoordinate h = ProjectHomogeneousPoint(transform, p);
+  *clipped = h.w() <= 0;
+  return h;
+}
+
 static HomogeneousCoordinate MapHomogeneousPoint(
     const gfx::Transform& transform,
     const gfx::Point3F& p) {
@@ -444,28 +453,27 @@ gfx::QuadF MathUtil::ProjectQuad(const gfx::Transform& transform,
 gfx::PointF MathUtil::ProjectPoint(const gfx::Transform& transform,
                                    const gfx::PointF& p,
                                    bool* clipped) {
-  HomogeneousCoordinate h = ProjectHomogeneousPoint(transform, p);
-
-  if (h.w() > 0) {
-    // The cartesian coordinates will be valid in this case.
-    *clipped = false;
-    return h.CartesianPoint2d();
-  }
-
-  // The cartesian coordinates will be invalid after dividing by w.
-  *clipped = true;
-
+  HomogeneousCoordinate h = ProjectHomogeneousPoint(transform, p, clipped);
   // Avoid dividing by w if w == 0.
   if (!h.w())
     return gfx::PointF();
 
-  // This return value will be invalid because clipped == true, but (1) users of
+  // This return value will be invalid if clipped == true, but (1) users of
   // this code should be ignoring the return value when clipped == true anyway,
   // and (2) this behavior is more consistent with existing behavior of WebKit
   // transforms if the user really does not ignore the return value.
   return h.CartesianPoint2d();
 }
 
+gfx::Point3F MathUtil::ProjectPoint3D(const gfx::Transform& transform,
+                                      const gfx::PointF& p,
+                                      bool* clipped) {
+  HomogeneousCoordinate h = ProjectHomogeneousPoint(transform, p, clipped);
+  if (!h.w())
+    return gfx::Point3F();
+  return h.CartesianPoint3d();

[enne (OOO), 2014/05/06 20:30:58]

What if h is clipped?

[Ian Vollick, 2014/05/06 21:06:20]

In that case, the answer isn't valid, but won't div-by-zero. This mimics the
behavior of ProjectPoint call above; the only exception is that I don't discard
z here. (I omitted the comment because the fn's are similar -- should I put it
back?)

+}
+
 gfx::RectF MathUtil::ScaleRectProportional(const gfx::RectF& input_outer_rect,
                                            const gfx::RectF& scale_outer_rect,
                                            const gfx::RectF& scale_inner_rect) {