Make non-AA hairline stroke rects snap to pixels centers so they close.

src/gpu/gl/builders/GrGLVertexShaderBuilder.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrGLVertexShaderBuilder.h"
 #include "GrGLProgramBuilder.h"
 #include "../GrGLGpu.h"
@@ skipping 24 matching lines @@
 
 void GrGLVertexBuilder::transformToNormalizedDeviceSpace(const GrShaderVar& posVar) {
     SkASSERT(!fRtAdjustName);
 
     // setup RT Uniform
     fProgramBuilder->fUniformHandles.fRTAdjustmentUni =
             fProgramBuilder->addUniform(GrGLProgramBuilder::kVertex_Visibility,
                                         kVec4f_GrSLType, kDefault_GrSLPrecision,
                                         fProgramBuilder->rtAdjustment(),
                                         &fRtAdjustName);
-
-    // Transform from Skia's device coords to GL's normalized device coords. Note that
-    // because we want to "nudge" the device space positions we are converting to 
-    // non-homogeneous NDC.
-    if (kVec3f_GrSLType == posVar.getType()) {
+    if (this->getProgramBuilder()->desc().header().fSnapVerticesToPixelCenters) {
+        if (kVec3f_GrSLType == posVar.getType()) {
+            const char* p = posVar.c_str();
+            this->codeAppendf("{vec2 _posTmp = vec2(%s.x/%s.z, %s.y/%s.z);", p, p, p, p);
+        } else {
+            SkASSERT(kVec2f_GrSLType == posVar.getType());
+            this->codeAppendf("{vec2 _posTmp = %s;", posVar.c_str());
+        }
+        this->codeAppendf("_posTmp = floor(_posTmp) + vec2(0.5, 0.5);"
+                          "gl_Position = vec4(_posTmp.x * %s.x + %s.y, _posTmp.y * %s.z + %s.w, 0, 1);}",
+                          fRtAdjustName, fRtAdjustName, fRtAdjustName, fRtAdjustName);
+    } else if (kVec3f_GrSLType == posVar.getType()) {
         this->codeAppendf("gl_Position = vec4(dot(%s.xz, %s.xy)/%s.z, dot(%s.yz, %s.zw)/%s.z, 0, 1);",
                           posVar.c_str(), fRtAdjustName, posVar.c_str(),
                           posVar.c_str(), fRtAdjustName, posVar.c_str());
     } else {
         SkASSERT(kVec2f_GrSLType == posVar.getType());
         this->codeAppendf("gl_Position = vec4(%s.x * %s.x + %s.y, %s.y * %s.z + %s.w, 0, 1);",
                           posVar.c_str(), fRtAdjustName, fRtAdjustName,
                           posVar.c_str(), fRtAdjustName, fRtAdjustName);
     }
-
-    // We could have the GrGeometryProcessor do this, but its just easier to have it performed here.
-    // If we ever need to set variable pointsize, then we can reinvestigate
+    // We could have the GrGeometryProcessor do this, but its just easier to have it performed
+    // here. If we ever need to set variable pointsize, then we can reinvestigate
     this->codeAppend("gl_PointSize = 1.0;");
 }
 
 void GrGLVertexBuilder::bindVertexAttributes(GrGLuint programID) {
     const GrPrimitiveProcessor& primProc = fProgramBuilder->primitiveProcessor();
 
     int vaCount = primProc.numAttribs();
     for (int i = 0; i < vaCount; i++) {
         GL_CALL(BindAttribLocation(programID, i, primProc.getAttrib(i).fName));
     }
@@ skipping 14 matching lines @@
     for (int i = 0; i < fInputs.count(); ++i) {
         const GrGLShaderVar& attr = fInputs[i];
         // if attribute already added, don't add it again
         if (attr.getName().equals(var.getName())) {
             return false;
         }
     }
     fInputs.push_back(var);
     return true;
 }