Improve computation of ctmScale{X,Y} in NativeImageSkia::drawPattern

Source/platform/graphics/skia/NativeImageSkia.cpp

Index: Source/platform/graphics/skia/NativeImageSkia.cpp
diff --git a/Source/platform/graphics/skia/NativeImageSkia.cpp b/Source/platform/graphics/skia/NativeImageSkia.cpp
index f7e70af0ad4d05d15b9903954a24f59e89866f85..386c507249f22d6798866fa899be3ec50691a0ac 100644
--- a/Source/platform/graphics/skia/NativeImageSkia.cpp
+++ b/Source/platform/graphics/skia/NativeImageSkia.cpp
@@ -412,6 +412,15 @@ static SkBitmap createBitmapWithSpace(const SkBitmap& bitmap, int spaceWidth, in
     return result;
 }
 
+static SkVector computeScaleVector(const SkMatrix& matrix)
+{
+    SkScalar scaleX = matrix.getScaleX();
+    SkScalar scaleY = matrix.getScaleY();
+    SkScalar skewX = matrix.getSkewX();
+    SkScalar skewY = matrix.getSkewY();
+    return SkVector::Make(sqrt(scaleX * scaleX + skewY * skewY), sqrt(scaleY * scaleY + skewX * skewX));

[Stephen White, 2014/04/03 12:25:04]

This looks a lot like AffineTransform::xScale() and AffineTransform::yScale().

[fs, 2014/04/03 14:01:31]

That was the intention...

+}
+
 void NativeImageSkia::drawPattern(
     GraphicsContext* context,
     const FloatRect& floatSrcRect,
@@ -428,8 +437,9 @@ void NativeImageSkia::drawPattern(
         return; // nothing to draw
 
     SkMatrix totalMatrix = context->getTotalMatrix();
-    SkScalar ctmScaleX = totalMatrix.getScaleX();
-    SkScalar ctmScaleY = totalMatrix.getScaleY();
+    SkVector ctmScale = computeScaleVector(totalMatrix);

[Stephen White, 2014/04/03 12:25:04]

Could this be

AffineTransform ctm = context->getCTM();
float ctmScaleX = ctm.xScale();
float ctmScaleY = ctm.yScale();

?

[fs, 2014/04/03 14:01:31]

...because I failed to find this one. Changed to use getCTM.

+    SkScalar ctmScaleX = ctmScale.x();
+    SkScalar ctmScaleY = ctmScale.y();
     totalMatrix.preScale(scale.width(), scale.height());
 
     // Figure out what size the bitmap will be in the destination. The