optimize computing bounds by calling SkMatrix44::map2()

cc/math_util.cc

Index: cc/math_util.cc
===================================================================
--- cc/math_util.cc	(revision 171493)
+++ cc/math_util.cc	(working copy)
@@ -109,15 +109,22 @@
 {
     if (transform.IsIdentityOrTranslation())
         return srcRect + gfx::Vector2dF(static_cast<float>(transform.matrix().getDouble(0, 3)), static_cast<float>(transform.matrix().getDouble(1, 3)));
-
+    
     // Apply the transform, but retain the result in homogeneous coordinates.
-    gfx::QuadF q = gfx::QuadF(srcRect);
-    HomogeneousCoordinate h1 = mapHomogeneousPoint(transform, gfx::Point3F(q.p1()));
-    HomogeneousCoordinate h2 = mapHomogeneousPoint(transform, gfx::Point3F(q.p2()));
-    HomogeneousCoordinate h3 = mapHomogeneousPoint(transform, gfx::Point3F(q.p3()));
-    HomogeneousCoordinate h4 = mapHomogeneousPoint(transform, gfx::Point3F(q.p4()));
 
-    return computeEnclosingClippedRect(h1, h2, h3, h4);
+    double quad[4 * 2]; // input: 4 x 2D points
+    quad[0] = srcRect.x();     quad[1] = srcRect.y();
+    quad[2] = srcRect.right(); quad[3] = srcRect.y();
+    quad[4] = srcRect.x();     quad[5] = srcRect.bottom();
+    quad[6] = srcRect.right(); quad[7] = srcRect.bottom();
+
+    double result[4 * 4];   // output: 4 x 4D homogeneous points
+    transform.matrix().map2(quad, 4, result);
+
+    return computeEnclosingClippedRect(*(const HomogeneousCoordinate*)&result[0],

[jamesr, 2012/12/07 04:30:39]

chromium code never uses c-style casts.  I'd suggest hoisting the cast to result
out of this call and using a static_cast<>, if that compiles, or even better
just doing member-by-member initialization and trust the compiler to fold it
together.

+                                       *(const HomogeneousCoordinate*)&result[4],
+                                       *(const HomogeneousCoordinate*)&result[8],
+                                       *(const HomogeneousCoordinate*)&result[12]);
 }
 
 gfx::RectF MathUtil::projectClippedRect(const gfx::Transform& transform, const gfx::RectF& srcRect)