Fix bug where ovals' AA exceed bounds by .5 pixel

src/gpu/GrOvalRenderer.cpp

Index: src/gpu/GrOvalRenderer.cpp
diff --git a/src/gpu/GrOvalRenderer.cpp b/src/gpu/GrOvalRenderer.cpp
index cef08f431e3a4f047737d6d845c66e58b8f2cf3a..c0957b7079babcda390c6a44d380001b082e2e3f 100644
--- a/src/gpu/GrOvalRenderer.cpp
+++ b/src/gpu/GrOvalRenderer.cpp
@@ -820,27 +820,28 @@ private:
             const SkRect& bounds = geom.fDevBounds;
 
             // The inner radius in the vertex data must be specified in normalized space.
+            // fOffsets are expanded from xxRadii to include the half-pixel antialiasing width.
             verts[0].fPos = SkPoint::Make(bounds.fLeft,  bounds.fTop);
             verts[0].fColor = color;
-            verts[0].fOffset = SkPoint::Make(-xRadius, -yRadius);
+            verts[0].fOffset = SkPoint::Make(-xRadius - SK_ScalarHalf, -yRadius - SK_ScalarHalf);

[jvanverth1, 2016/06/30 18:00:06]

I suggest creating two variables, like xMaxOffset and yMaxOffset, set them to
xRadius + 0.5 and yRadius + 0.5, and use those here instead. I think that'd be a
little clearer.

[vjiaoblack, 2016/06/30 18:41:17]

Done.

             verts[0].fOuterRadii = SkPoint::Make(xRadRecip, yRadRecip);
             verts[0].fInnerRadii = SkPoint::Make(xInnerRadRecip, yInnerRadRecip);
 
             verts[1].fPos = SkPoint::Make(bounds.fLeft,  bounds.fBottom);
             verts[1].fColor = color;
-            verts[1].fOffset = SkPoint::Make(-xRadius, yRadius);
+            verts[1].fOffset = SkPoint::Make(-xRadius - SK_ScalarHalf, yRadius + SK_ScalarHalf);
             verts[1].fOuterRadii = SkPoint::Make(xRadRecip, yRadRecip);
             verts[1].fInnerRadii = SkPoint::Make(xInnerRadRecip, yInnerRadRecip);
 
             verts[2].fPos = SkPoint::Make(bounds.fRight, bounds.fBottom);
             verts[2].fColor = color;
-            verts[2].fOffset = SkPoint::Make(xRadius, yRadius);
+            verts[2].fOffset = SkPoint::Make(xRadius + SK_ScalarHalf, yRadius + SK_ScalarHalf);
             verts[2].fOuterRadii = SkPoint::Make(xRadRecip, yRadRecip);
             verts[2].fInnerRadii = SkPoint::Make(xInnerRadRecip, yInnerRadRecip);
 
             verts[3].fPos = SkPoint::Make(bounds.fRight, bounds.fTop);
             verts[3].fColor = color;
-            verts[3].fOffset = SkPoint::Make(xRadius, -yRadius);
+            verts[3].fOffset = SkPoint::Make(xRadius + SK_ScalarHalf, -yRadius - SK_ScalarHalf);
             verts[3].fOuterRadii = SkPoint::Make(xRadRecip, yRadRecip);
             verts[3].fInnerRadii = SkPoint::Make(xInnerRadRecip, yInnerRadRecip);
 
@@ -938,11 +939,11 @@ static GrDrawBatch* create_ellipse_batch(GrColor color,
         yRadius += scaledStroke.fY;
     }
 
-    // We've extended the outer x radius out half a pixel to antialias.
-    // This will also expand the rect so all the pixels will be captured.
-    // TODO: Consider if we should use sqrt(2)/2 instead
-    xRadius += SK_ScalarHalf;
-    yRadius += SK_ScalarHalf;
+    // We've extended the outer x radius out half a pixel to antialias. 

[jvanverth1, 2016/06/30 18:00:06]

I would delete all these lines.

[vjiaoblack, 2016/06/30 18:41:17]

Done.

+    // This will also expand the rect so all the pixels will be captured. 
+    // TODO: Consider if we should use sqrt(2)/2 instead  
+    // xRadius += SK_ScalarHalf; 
+    // yRadius += SK_ScalarHalf;
 
     EllipseBatch::Geometry geometry;
     geometry.fColor = color;
@@ -953,6 +954,9 @@ static GrDrawBatch* create_ellipse_batch(GrColor color,
     geometry.fDevBounds = SkRect::MakeLTRB(center.fX - xRadius, center.fY - yRadius,
                                            center.fX + xRadius, center.fY + yRadius);
 
+    // outset bounds to include half-pixel width antialiasing. 
+    geometry.fDevBounds.outset(SK_ScalarHalf, SK_ScalarHalf);
+
     return new EllipseBatch(geometry, viewMatrix,
                             isStrokeOnly && innerXRadius > 0 && innerYRadius > 0);
 }