Make GrGLShaderBuilder::fragmentPosition() return a vec4, with 1.0 as the zw components when in the…

src/gpu/GrAARectRenderer.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrAARectRenderer.h"
 #include "GrGpu.h"
 #include "gl/GrGLEffect.h"
@@ skipping 182 matching lines @@
             // < 1 pixel wide or tall they serve to normalize the < 1 ramp to a 0 .. 1 range.
             builder->fsCodeAppend("\tfloat spanW = insetW + outset;\n");
             builder->fsCodeAppend("\tfloat spanH = insetH + outset;\n");
             // For rects < 1 pixel wide or tall, these scale factors are used to cap the maximum
             // value of coverage that is used. In other words it is the coverage that is
             // used in the interior of the rect after the ramp.
             builder->fsCodeAppend("\tfloat scaleW = min(1.0, 2.0*insetW/spanW);\n");
             builder->fsCodeAppend("\tfloat scaleH = min(1.0, 2.0*insetH/spanH);\n");
 
             // Compute the coverage for the rect's width
-            builder->fsCodeAppendf("\tvec2 offset = %s - %s.xy;\n",
+            builder->fsCodeAppendf("\tvec2 offset = %s.xy - %s.xy;\n",
                                    builder->fragmentPosition(), fsRectEdgeName);
             builder->fsCodeAppendf("\tfloat perpDot = abs(offset.x * %s.w - offset.y * %s.z);\n",
                                    fsRectEdgeName, fsRectEdgeName);
             builder->fsCodeAppendf(
                 "\tfloat coverage = scaleW*clamp((%s.x-perpDot)/spanW, 0.0, 1.0);\n",
                 fsWidthHeightName);
 
             // Compute the coverage for the rect's height and merge with the width
             builder->fsCodeAppendf("\tperpDot = abs(dot(offset, %s.zw));\n",
                                    fsRectEdgeName);
@@ skipping 709 matching lines @@
     combinedMatrix.mapPoints((SkPoint*)&devInside, (const SkPoint*)&rects[1], 2);
 
     if (devInside.isEmpty()) {
         this->fillAARect(gpu, target, devOutside, SkMatrix::I(), devOutside, useVertexCoverage);
         return;
     }
 
     this->geometryStrokeAARect(gpu, target, devOutside, devOutsideAssist,
                                devInside, useVertexCoverage, true);
 }