antialias matrix-image-filter to get smooth diagonals

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 34d6aaa0ab4ddbb9ae5f158a846d77636c326642..8849aba9151f5475dc1a6cec25cdde8e2370375e 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -992,6 +992,8 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
     flags |= kClipToLayer_SaveFlag;
 #endif
 
+    SkImageFilter* imgf = paint ? paint->getImageFilter() : NULL;
+
     // do this before we create the layer. We don't call the public save() since
     // that would invoke a possibly overridden virtual
     this->internalSave();
@@ -999,7 +1001,7 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
     fDeviceCMDirty = true;
 
     SkIRect ir;
-    if (!this->clipRectBounds(bounds, flags, &ir, paint ? paint->getImageFilter() : NULL)) {
+    if (!this->clipRectBounds(bounds, flags, &ir, imgf)) {
         return;
     }
 
@@ -1013,7 +1015,7 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
     SkPixelGeometry geo = fProps.pixelGeometry();
     if (paint) {
         // TODO: perhaps add a query to filters so we might preserve opaqueness...
-        if (paint->getImageFilter() || paint->getColorFilter()) {
+        if (imgf || paint->getColorFilter()) {
             isOpaque = false;
             geo = kUnknown_SkPixelGeometry;
         }
@@ -1029,7 +1031,10 @@ void SkCanvas::internalSaveLayer(const SkRect* bounds, const SkPaint* paint, Sav
 
     bool forceSpriteOnRestore = false;
     {
-        const SkBaseDevice::TileUsage usage = SkBaseDevice::kNever_TileUsage;
+        SkBaseDevice::TileUsage usage = SkBaseDevice::kNever_TileUsage;
+        if (imgf && imgf->mayDrawWithMatrix()) {
+            usage = SkBaseDevice::kPossible_TileUsage;
+        }
         const SkBaseDevice::CreateInfo createInfo = SkBaseDevice::CreateInfo(info, usage, geo);
         SkBaseDevice* newDev = device->onCreateDevice(createInfo, paint);
         if (NULL == newDev) {