commit 3833daaa663db7e655a8077cdab42cca19d3a276
author robertphillips <robertphillips@google.com> Mon Sep 14 11:18:13 2015 -0700
committer Commit bot <commit-bot@chromium.org> Mon Sep 14 11:18:13 2015 -0700
tree fa6b9a0da4910a3dc2dd91274daf8b10b778ec74
parent efd50daa2883ccadbed4bcffc789a76b24536a60

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

src/gpu/GrBlurUtils.cpp

diff --git a/src/gpu/GrBlurUtils.cpp b/src/gpu/GrBlurUtils.cpp
index 039a12c..a96d92e 100644
--- a/src/gpu/GrBlurUtils.cpp
+++ b/src/gpu/GrBlurUtils.cpp
@@ -97,15 +97,20 @@
 
 // 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 @@
         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 @@
     // 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 @@
             }
 
             SkAutoTUnref<GrTexture> mask(create_mask_GPU(context,
-                                                         maskRect,
+                                                         &maskRect,
                                                          *devPathPtr,
                                                          strokeInfo,
                                                          grPaint.isAntiAlias(),