Prevent implicit framebuffer clear from clobbering alpha in emulated RGB

third_party/WebKit/Source/modules/webgl/WebGL2RenderingContextBase.cpp

 // Copyright 2015 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 "modules/webgl/WebGL2RenderingContextBase.h"
 
 #include "bindings/modules/v8/WebGLAny.h"
 #include "core/dom/DOMException.h"
 #include "core/frame/ImageBitmap.h"
 #include "core/html/HTMLCanvasElement.h"
@@ skipping 2558 matching lines @@
                                                      GLsizei instanceCount) {
   if (!validateDrawArrays("drawArraysInstanced"))
     return;
 
   if (!m_boundVertexArrayObject->isAllEnabledAttribBufferBound()) {
     synthesizeGLError(GL_INVALID_OPERATION, "drawArraysInstanced",
                       "no buffer is bound to enabled attribute");
     return;
   }
 
-  ScopedRGBEmulationColorMask emulationColorMask(contextGL(), m_colorMask,
+  ScopedRGBEmulationColorMask emulationColorMask(this, m_colorMask,
                                                  m_drawingBuffer.get());
   clearIfComposited();
   contextGL()->DrawArraysInstancedANGLE(mode, first, count, instanceCount);
   markContextChanged(CanvasChanged);
 }
 
 void WebGL2RenderingContextBase::drawElementsInstanced(GLenum mode,
                                                        GLsizei count,
                                                        GLenum type,
                                                        long long offset,
                                                        GLsizei instanceCount) {
   if (!validateDrawElements("drawElementsInstanced", type, offset))
     return;
 
   if (!m_boundVertexArrayObject->isAllEnabledAttribBufferBound()) {
     synthesizeGLError(GL_INVALID_OPERATION, "drawElementsInstanced",
                       "no buffer is bound to enabled attribute");
     return;
   }
 
-  ScopedRGBEmulationColorMask emulationColorMask(contextGL(), m_colorMask,
+  ScopedRGBEmulationColorMask emulationColorMask(this, m_colorMask,
                                                  m_drawingBuffer.get());
   clearIfComposited();
   contextGL()->DrawElementsInstancedANGLE(
       mode, count, type, reinterpret_cast<void*>(static_cast<intptr_t>(offset)),
       instanceCount);
   markContextChanged(CanvasChanged);
 }
 
 void WebGL2RenderingContextBase::drawRangeElements(GLenum mode,
                                                    GLuint start,
                                                    GLuint end,
                                                    GLsizei count,
                                                    GLenum type,
                                                    long long offset) {
   if (!validateDrawElements("drawRangeElements", type, offset))
     return;
 
   if (!m_boundVertexArrayObject->isAllEnabledAttribBufferBound()) {
     synthesizeGLError(GL_INVALID_OPERATION, "drawRangeElements",
                       "no buffer is bound to enabled attribute");
     return;
   }
 
-  ScopedRGBEmulationColorMask emulationColorMask(contextGL(), m_colorMask,
+  ScopedRGBEmulationColorMask emulationColorMask(this, m_colorMask,
                                                  m_drawingBuffer.get());
   clearIfComposited();
   contextGL()->DrawRangeElements(
       mode, start, end, count, type,
       reinterpret_cast<void*>(static_cast<intptr_t>(offset)));
   markContextChanged(CanvasChanged);
 }
 
 void WebGL2RenderingContextBase::drawBuffers(const Vector<GLenum>& buffers) {
   if (isContextLost())
     return;
 
-  ScopedRGBEmulationColorMask emulationColorMask(contextGL(), m_colorMask,
+  ScopedRGBEmulationColorMask emulationColorMask(this, m_colorMask,
                                                  m_drawingBuffer.get());
   GLsizei n = buffers.size();
   const GLenum* bufs = buffers.data();
   for (GLsizei i = 0; i < n; ++i) {
     switch (bufs[i]) {
       case GL_NONE:
       case GL_BACK:
       case GL_COLOR_ATTACHMENT0:
         break;
       default:
@@ skipping 2317 matching lines @@
 
 void WebGL2RenderingContextBase::
     DrawingBufferClientRestorePixelUnpackBufferBinding() {
   if (!contextGL())
     return;
   contextGL()->BindBuffer(GL_PIXEL_UNPACK_BUFFER,
                           objectOrZero(m_boundPixelUnpackBuffer.get()));
 }
 
 }  // namespace blink