[cc] Fix zebra-stripe compositor checkerboarding

cc/CCRendererGL.cpp

 // Copyright 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 #include "config.h"
 
 #if USE(ACCELERATED_COMPOSITING)
 #include "CCRendererGL.h"
 
@@ skipping 269 matching lines @@
 
 void CCRendererGL::drawCheckerboardQuad(const DrawingFrame& frame, const CCCheckerboardDrawQuad* quad)
 {
     const TileCheckerboardProgram* program = tileCheckerboardProgram();
     ASSERT(program && program->initialized());
     GLC(context(), context()->useProgram(program->program()));
 
     SkColor color = quad->color();
     GLC(context(), context()->uniform4f(program->fragmentShader().colorLocation(), SkColorGetR(color) / 255.0, SkColorGetG(color) / 255.0, SkColorGetB(color) / 255.0, 1));
 
+    const int checkerboardWidth = 16;
+    float frequency = 1.0 / checkerboardWidth;
+
     IntRect tileRect = quad->quadRect();
-    float texOffsetX = tileRect.x();
-    float texOffsetY = tileRect.y();
+    float texOffsetX = tileRect.x() % checkerboardWidth;
+    float texOffsetY = tileRect.y() % checkerboardWidth;
     float texScaleX = tileRect.width();
     float texScaleY = tileRect.height();
     GLC(context(), context()->uniform4f(program->fragmentShader().texTransformLocation(), texOffsetX, texOffsetY, texScaleX, texScaleY));
 
-    const int checkerboardWidth = 16;
-    float frequency = 1.0 / checkerboardWidth;
-
     GLC(context(), context()->uniform1f(program->fragmentShader().frequencyLocation(), frequency));
 
     setShaderOpacity(quad->opacity(), program->fragmentShader().alphaLocation());
     drawQuadGeometry(frame, quad->quadTransform(), quad->quadRect(), program->vertexShader().matrixLocation());
 }
 
 void CCRendererGL::drawDebugBorderQuad(const DrawingFrame& frame, const CCDebugBorderDrawQuad* quad)
 {
     static float glMatrix[16];
     const SolidColorProgram* program = solidColorProgram();
@@ skipping 1211 matching lines @@
 }
 
 bool CCRendererGL::isContextLost()
 {
     return (m_context->getGraphicsResetStatusARB() != GraphicsContext3D::NO_ERROR);
 }
 
 } // namespace cc
 
 #endif // USE(ACCELERATED_COMPOSITING)