fix bounds for BW lines, AA Hairlines

src/gpu/GrContext.cpp

Index: src/gpu/GrContext.cpp
diff --git a/src/gpu/GrContext.cpp b/src/gpu/GrContext.cpp
index b361b671c3b3080b9373ee30a76daf9ce91d7b7a..725cf0359c5938289cb9a90f0b6695dac4a9ecd2 100755
--- a/src/gpu/GrContext.cpp
+++ b/src/gpu/GrContext.cpp
@@ -522,6 +522,12 @@ private:
         SkScalar rad = SkScalarHalf(geometry.fStrokeWidth);
         fBounds.outset(rad, rad);
         geometry.fViewMatrix.mapRect(&fBounds);
+

[robertphillips, 2015/05/07 14:42:02]

For this case, BW hairline rect draw, I believe we just force the lines to pixel
centers.

[bsalomon, 2015/05/07 14:47:45]

Correct. This is an unfortunate case of coupling where the user of this batch
did the snapping rather than the batch itself, but the batch has to know about
it.

+        // This is conservative but, b.c. the hardware can employ somewhat arbitrary
+        // snapping rules to BW lines, it is the best we can do.
+        if (fBatch.fHairline) {
+            fBounds.outset(0.5f, 0.5f);
+        }
     }
 
     /*  create a triangle strip that strokes the specified rect. There are 8
@@ -1021,6 +1027,12 @@ void GrContext::drawVertices(GrRenderTarget* rt,
 
     viewMatrix.mapRect(&bounds);
 
+    // If we don't have AA then we outset for a half pixel in each direction to account for
+    // snapping
+    if (!paint.isAntiAlias()) {
+        bounds.outset(0.5f, 0.5f);
+    }
+
     DrawVerticesBatch::Geometry geometry;
     geometry.fColor = paint.getColor();
     SkAutoTUnref<GrBatch> batch(DrawVerticesBatch::Create(geometry, primitiveType, viewMatrix,