Use antialiasing and bitmap filtering when needed in software compositor.

cc/CCRendererSoftware.cpp

Index: cc/CCRendererSoftware.cpp
diff --git a/cc/CCRendererSoftware.cpp b/cc/CCRendererSoftware.cpp
index 89a758b4f55c6cc6c9cff52b4bc678512d089a13..2cd65360fd6eba1efc5e8c55b6159d23c23c6f9a 100644
--- a/cc/CCRendererSoftware.cpp
+++ b/cc/CCRendererSoftware.cpp
@@ -19,6 +19,7 @@
 #include <public/WebImage.h>
 #include <public/WebSize.h>
 #include <public/WebTransformationMatrix.h>
+#include <limits>
 
 using WebKit::WebCompositorSoftwareOutputDevice;
 using WebKit::WebImage;
@@ -53,6 +54,20 @@ void toSkMatrix(SkMatrix* flattened, const WebTransformationMatrix& m)
     flattened->set(8, m.m44());
 }
 
+bool isZero(float f)

[aelias_OOO_until_Jul13, 2012/10/12 21:26:56]

No need for this method.  You can use SkScalarNearlyZero and SkScalarNearlyEqual
from SkScalar.h.

+{
+    return abs(f) < std::numeric_limits<float>::epsilon();

[danakj, 2012/10/12 21:24:37]

thanks! i think this should be std::abs() as well or it might break when we
remove webcore headers.

+}
+
+bool isScaleAndTranslate(const SkMatrix& matrix)
+{
+    return isZero(matrix[SkMatrix::kMSkewX]) &&
+           isZero(matrix[SkMatrix::kMSkewY]) &&
+           isZero(matrix[SkMatrix::kMPersp0]) &&
+           isZero(matrix[SkMatrix::kMPersp1]) &&
+           isZero(matrix[SkMatrix::kMPersp2] - 1.0f);
+}
+
 } // anonymous namespace
 
 PassOwnPtr<CCRendererSoftware> CCRendererSoftware::create(CCRendererClient* client, CCResourceProvider* resourceProvider, WebCompositorSoftwareOutputDevice* outputDevice)
@@ -178,6 +193,10 @@ void CCRendererSoftware::drawQuad(DrawingFrame& frame, const CCDrawQuad* quad)
     m_skCurrentCanvas->setMatrix(skDeviceMatrix);
 
     m_skCurrentPaint.reset();
+    if (!isScaleAndTranslate(skDeviceMatrix)) {
+        m_skCurrentPaint.setAntiAlias(true);
+        m_skCurrentPaint.setFilterBitmap(true);
+    }
     if (quad->needsBlending()) {
         m_skCurrentPaint.setAlpha(quad->opacity() * 255);
         m_skCurrentPaint.setXfermodeMode(SkXfermode::kSrcOver_Mode);