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..1f12830453785e5ca3e3a3ec56a7b1834f349da4 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 +1031,12 @@ 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;
+#ifndef SK_SUPPORT_LEGACY_IMAGEFILTER_TRANSFORM_SCRATCH_LAYTER
+        if (imgf && imgf->mayDrawWithMatrix()) {
+            usage = SkBaseDevice::kPossible_TileUsage;

[Stephen White, 2015/05/15 18:37:22]

This seems like it'll work for the case where we have only a matrix image filter
in the filter chain, and it's drawing the layer device contents rotated. But
what it about a more complex chain, e.g., blur -> matrix. The blur will be
creating a scratch texture, which the matrix will now draw incorrectly.

It seems like we'd have to propagate this flag somehow to
SkDeviceImageFilterProxy::createDevice(), to ensure that all scratch textures
are created with exact dimensions.

+        }
+#endif
         const SkBaseDevice::CreateInfo createInfo = SkBaseDevice::CreateInfo(info, usage, geo);
         SkBaseDevice* newDev = device->onCreateDevice(createInfo, paint);
         if (NULL == newDev) {