Fix bounds computation for non-aa hairlines when snapping to pixel centers

src/gpu/batches/GrNonAAStrokeRectBatch.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrNonAAStrokeRectBatch.h"
 
 #include "GrBatchTest.h"
@@ skipping 82 matching lines @@
 
 private:
     void setupBounds(SkRect* bounds, const Geometry& geo, bool snapToPixelCenters) {
         *bounds = geo.fRect;
         SkScalar rad = SkScalarHalf(geo.fStrokeWidth);
         bounds->outset(rad, rad);
         geo.fViewMatrix.mapRect(&fBounds);
 
         // If our caller snaps to pixel centers then we have to round out the bounds
         if (snapToPixelCenters) {
+            // We want to be consistent with how we snap non-aa lines. To match what we do in
+            // GrGLSLVertexShaderBuilder, we first floor all the vertex values and then add half a
+            // pixel to force us to pixel centers.
+            bounds->set(SkScalarFloorToScalar(bounds->fLeft),
+                        SkScalarFloorToScalar(bounds->fTop),
+                        SkScalarFloorToScalar(bounds->fRight),
+                        SkScalarFloorToScalar(bounds->fBottom));
+            bounds->offset(0.5f, 0.5f);
+
+            // Round out the bounds to integer values
             bounds->roundOut();

[bsalomon, 2016/07/07 14:19:06]

Do we need this round out? If the rect is rendered at pixel centers the bounds
be at half integers?

         }
     }
 
     void onPrepareDraws(Target* target) const override {
         sk_sp<GrGeometryProcessor> gp;
         {
             using namespace GrDefaultGeoProcFactory;
             Color color(this->color());
             Coverage coverage(this->coverageIgnored() ? Coverage::kSolid_Type :
                                                         Coverage::kNone_Type);
@@ skipping 127 matching lines @@
 DRAW_BATCH_TEST_DEFINE(NonAAStrokeRectBatch) {
     SkMatrix viewMatrix = GrTest::TestMatrix(random);
     GrColor color = GrRandomColor(random);
     SkRect rect = GrTest::TestRect(random);
     SkScalar strokeWidth = random->nextBool() ? 0.0f : 1.0f;
 
     return GrNonAAStrokeRectBatch::Create(color, viewMatrix, rect, strokeWidth, random->nextBool());
 }
 
 #endif