Make non-AA hairline stroke rects snap to pixels centers so they close.

src/gpu/GrContext.cpp

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrContext.h"
 
@@ skipping 780 matching lines @@
         geometry.fColor = color;
         geometry.fRect = rect;
         geometry.fStrokeWidth = width;
 
         SkAutoTUnref<GrBatch> batch(StrokeRectBatch::Create(geometry));
 
         SkRect bounds = rect;
         SkScalar rad = SkScalarHalf(width);
         bounds.outset(rad, rad);
         viewMatrix.mapRect(&bounds);
+        // Depending on sub-pixel coordinates and the particular GPU, we may lose a corner of
+        // hairline rects. We jam all the vertices to pixel centers to avoid this, but not when MSAA
+        // is enabled because it can cause ugly artifacts.
+        pipelineBuilder.setState(GrPipelineBuilder::kSnapVerticesToPixelCenters_Flag,
+                                 0 == width && !rt->isMultisampled());
         target->drawBatch(&pipelineBuilder, batch, &bounds);
     } else {
         // filled BW rect
         target->drawSimpleRect(&pipelineBuilder, color, viewMatrix, rect);
     }
 }
 
 void GrContext::drawNonAARectToRect(GrRenderTarget* rt,
                                     const GrClip& clip,
                                     const GrPaint& paint,
@@ skipping 1220 matching lines @@
     }
 }
 
 void GrContext::removeGpuTraceMarker(const GrGpuTraceMarker* marker) {
     fGpu->removeGpuTraceMarker(marker);
     if (fDrawBuffer) {
         fDrawBuffer->removeGpuTraceMarker(marker);
     }
 }