Fix GPU-only snapping bug in mask blur rendering

The existing mask effect code in Ganesh is subject to snapping issues (when the created mask is redrawn). This artifact can be seen by rendering the original geometry (w/o blurs) and comparing that result to a rendering of the unblurred masks. W/o this patch the results do not match up (they are arbitrarily shifted by a pixel).

This patch will require rebaselining and suppressions.

Chromium layout tests suppressions are here:
https://codereview.chromium.org/1342683003/ (Add layout test suppressions for upcoming Skia roll)

Review URL: https://codereview.chromium.org/1338183002

1 files changed, 13 insertions, 7 deletions

diff --git a/src/gpu/GrBlurUtils.cpp b/src/gpu/GrBlurUtils.cpp
index 039a12c3c8..a96d92e764 100644
--- a/src/gpu/GrBlurUtils.cpp
+++ b/src/gpu/GrBlurUtils.cpp
@@ -97,15 +97,20 @@ static bool draw_with_mask_filter(GrDrawContext* drawContext,
 
 // Create a mask of 'devPath' and place the result in 'mask'.
 static GrTexture* create_mask_GPU(GrContext* context,
-                                  const SkRect& maskRect,
+                                  SkRect* maskRect,
                                   const SkPath& devPath,
                                   const GrStrokeInfo& strokeInfo,
                                   bool doAA,
                                   int sampleCnt) {
+    // This mask will ultimately be drawn as a non-AA rect (see draw_mask). 
+    // Non-AA rects have a bad habit of snapping arbitrarily. Integerize here 
+    // so the mask draws in a reproducible manner.
+    *maskRect = SkRect::Make(maskRect->roundOut());
+
     GrSurfaceDesc desc;
     desc.fFlags = kRenderTarget_GrSurfaceFlag;
-    desc.fWidth = SkScalarCeilToInt(maskRect.width());
-    desc.fHeight = SkScalarCeilToInt(maskRect.height());
+    desc.fWidth = SkScalarCeilToInt(maskRect->width());
+    desc.fHeight = SkScalarCeilToInt(maskRect->height());
     desc.fSampleCnt = doAA ? sampleCnt : 0;
     // We actually only need A8, but it often isn't supported as a
     // render target so default to RGBA_8888
@@ -120,7 +125,7 @@ static GrTexture* create_mask_GPU(GrContext* context,
         return nullptr;
     }
 
-    SkRect clipRect = SkRect::MakeWH(maskRect.width(), maskRect.height());
+    SkRect clipRect = SkRect::MakeWH(maskRect->width(), maskRect->height());
 
     SkAutoTUnref<GrDrawContext> drawContext(context->drawContext());
     if (!drawContext) {
@@ -136,9 +141,10 @@ static GrTexture* create_mask_GPU(GrContext* context,
     // setup new clip
     GrClip clip(clipRect);
 
-    // Draw the mask into maskTexture with the path's top-left at the origin using tempPaint.
+    // Draw the mask into maskTexture with the path's integerized top-left at
+    // the origin using tempPaint.
     SkMatrix translate;
-    translate.setTranslate(-maskRect.fLeft, -maskRect.fTop);
+    translate.setTranslate(-maskRect->fLeft, -maskRect->fTop);
     drawContext->drawPath(mask->asRenderTarget(), clip, tempPaint, translate, devPath, strokeInfo);
     return mask;
 }
@@ -254,7 +260,7 @@ void GrBlurUtils::drawPathWithMaskFilter(GrContext* context,
             }
 
             SkAutoTUnref<GrTexture> mask(create_mask_GPU(context,
-                                                         maskRect,
+                                                         &maskRect,
                                                          *devPathPtr,
                                                          strokeInfo,
                                                          grPaint.isAntiAlias(),