Fix artifacts in distance field rendering due to bilerp

src/gpu/GrDistanceFieldTextContext.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrDistanceFieldTextContext.h"
 #include "GrAtlas.h"
 #include "GrDrawTarget.h"
 #include "GrDrawTargetCaps.h"
 #include "GrFontScaler.h"
 #include "SkGlyphCache.h"
 #include "GrIndexBuffer.h"
 #include "GrTextStrike.h"
 #include "GrTextStrike_impl.h"
+#include "SkDistanceFieldGen.h"
 #include "SkDraw.h"
 #include "SkGpuDevice.h"
 #include "SkPath.h"
 #include "SkRTConf.h"
 #include "SkStrokeRec.h"
 #include "effects/GrDistanceFieldTextureEffect.h"
 
 static const int kGlyphCoordsAttributeIndex = 1;
 
 static const int kSmallDFFontSize = 32;
@@ skipping 261 matching lines @@
             fMaxVertices = maxQuadVertices;
         }
         bool success = fDrawTarget->reserveVertexAndIndexSpace(fMaxVertices,
                                                                0,
                                                                GrTCast<void**>(&fVertices),
                                                                NULL);
         GrAlwaysAssert(success);
         SkASSERT(2*sizeof(SkPoint) == fDrawTarget->getDrawState().getVertexSize());
     }
 
-    SkScalar dx = SkIntToScalar(glyph->fBounds.fLeft);
-    SkScalar dy = SkIntToScalar(glyph->fBounds.fTop);
-    SkScalar width = SkIntToScalar(glyph->fBounds.width());
-    SkScalar height = SkIntToScalar(glyph->fBounds.height());
+    SkScalar dx = SkIntToScalar(glyph->fBounds.fLeft + SK_DistanceFieldInset);
+    SkScalar dy = SkIntToScalar(glyph->fBounds.fTop + SK_DistanceFieldInset);
+    SkScalar width = SkIntToScalar(glyph->fBounds.width() - 2*SK_DistanceFieldInset);
+    SkScalar height = SkIntToScalar(glyph->fBounds.height() - 2*SK_DistanceFieldInset);
 
     SkScalar scale = fTextRatio;
     dx *= scale;
     dy *= scale;
     sx += dx;
     sy += dy;
     width *= scale;
     height *= scale;
 
-    SkFixed tx = SkIntToFixed(glyph->fAtlasLocation.fX);
-    SkFixed ty = SkIntToFixed(glyph->fAtlasLocation.fY);
-    SkFixed tw = SkIntToFixed(glyph->fBounds.width());
-    SkFixed th = SkIntToFixed(glyph->fBounds.height());
+    SkFixed tx = SkIntToFixed(glyph->fAtlasLocation.fX + SK_DistanceFieldInset);
+    SkFixed ty = SkIntToFixed(glyph->fAtlasLocation.fY + SK_DistanceFieldInset);
+    SkFixed tw = SkIntToFixed(glyph->fBounds.width() - 2*SK_DistanceFieldInset);
+    SkFixed th = SkIntToFixed(glyph->fBounds.height() - 2*SK_DistanceFieldInset);
 
     static const size_t kVertexSize = 2 * sizeof(SkPoint);
     fVertices[2*fCurrVertex].setRectFan(sx,
                                         sy,
                                         sx + width,
                                         sy + height,
                                         kVertexSize);
     fVertices[2*fCurrVertex+1].setRectFan(SkFixedToFloat(texture->normalizeFixedX(tx)),
                                           SkFixedToFloat(texture->normalizeFixedY(ty)),
                                           SkFixedToFloat(texture->normalizeFixedX(tx + tw)),
@@ skipping 169 matching lines @@
                                       SkScalarToFixed(y) - (glyph.fAdvanceY >> alignShift)
                                         + SK_FixedHalf, //d1g.fHalfSampleY,
                                       fontScaler);
             }
             pos += scalarsPerPosition;
         }
     }
 
     this->finish();
 }