WebGL: clarify which Front or Back buffer is used by each API.

Source/core/html/canvas/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 897 matching lines @@
         if (canvas()->hasImageBuffer())
             drawingBuffer()->paintRenderingResultsToCanvas(canvas()->buffer());
     }
 
     if (m_framebufferBinding)
         webContext()->bindFramebuffer(GL_FRAMEBUFFER, objectOrZero(m_framebufferBinding.get()));
     else
         drawingBuffer()->bind();
 }
 
-PassRefPtrWillBeRawPtr<ImageData> WebGLRenderingContextBase::paintRenderingResultsToImageData()
-{
-    if (isContextLost())
-        return nullptr;
-
-    clearIfComposited();
-    drawingBuffer()->commit();
-    int width, height;
-    RefPtr<Uint8ClampedArray> imageDataPixels = drawingBuffer()->paintRenderingResultsToImageData(width, height);
-    if (!imageDataPixels)
-        return nullptr;
-
-    if (m_framebufferBinding)
-        webContext()->bindFramebuffer(GL_FRAMEBUFFER, objectOrZero(m_framebufferBinding.get()));
-    else
-        drawingBuffer()->bind();
-
-    return ImageData::create(IntSize(width, height), imageDataPixels);
-}
-
 void WebGLRenderingContextBase::reshape(int width, int height)
 {
     if (isContextLost())
         return;
 
     // This is an approximation because at WebGLRenderingContextBase level we don't
     // know if the underlying FBO uses textures or renderbuffers.
     GLint maxSize = std::min(m_maxTextureSize, m_maxRenderbufferSize);
     // Limit drawing buffer size to 4k to avoid memory exhaustion.
     const int sizeUpperLimit = 4096;
@@ skipping 2602 matching lines @@
             WebGLRenderingContextBase* gl = toWebGLRenderingContextBase(canvas->renderingContext());
             ScopedTexture2DRestorer restorer(gl);
             if (gl && gl->drawingBuffer()->copyToPlatformTexture(webContext(), texture->object(), internalformat, type,
                 level, m_unpackPremultiplyAlpha, !m_unpackFlipY, DrawingBuffer::Back)) {
                 texture->setLevelInfo(target, level, internalformat, canvas->width(), canvas->height(), type);
                 return;
             }
         }
     }
 
-    RefPtrWillBeRawPtr<ImageData> imageData = canvas->getImageData();
-    if (imageData)
-        texImage2D(target, level, internalformat, format, type, imageData.get(), exceptionState);
-    else
-        texImage2DImpl(target, level, internalformat, format, type, canvas->copiedImage(), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
+    texImage2DImpl(target, level, internalformat, format, type, canvas->copiedImage(HTMLCanvasElement::Back), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
 }
 
 PassRefPtr<Image> WebGLRenderingContextBase::videoFrameToImage(HTMLVideoElement* video, BackingStoreCopy backingStoreCopy)
 {
     IntSize size(video->videoWidth(), video->videoHeight());
     ImageBuffer* buf = m_generatedImageCache.imageBuffer(size);
     if (!buf) {
         synthesizeGLError(GL_OUT_OF_MEMORY, "texImage2D", "out of memory");
         return nullptr;
     }
@@ skipping 213 matching lines @@
     texSubImage2DImpl(target, level, xoffset, yoffset, format, type, imageForRender.get(), WebGLImageConversion::HtmlDomImage, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
 }
 
 void WebGLRenderingContextBase::texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
     GLenum format, GLenum type, HTMLCanvasElement* canvas, ExceptionState& exceptionState)
 {
     if (isContextLost() || !validateHTMLCanvasElement("texSubImage2D", canvas, exceptionState)
         || !validateTexFunc("texSubImage2D", TexSubImage2D, SourceHTMLCanvasElement, target, level, format, canvas->width(), canvas->height(), 0, format, type, xoffset, yoffset))
         return;
 
-    RefPtrWillBeRawPtr<ImageData> imageData = canvas->getImageData();
-    if (imageData)
-        texSubImage2D(target, level, xoffset, yoffset, format, type, imageData.get(), exceptionState);
-    else
-        texSubImage2DImpl(target, level, xoffset, yoffset, format, type, canvas->copiedImage(), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
+    texSubImage2DImpl(target, level, xoffset, yoffset, format, type, canvas->copiedImage(HTMLCanvasElement::Back), WebGLImageConversion::HtmlDomCanvas, m_unpackFlipY, m_unpackPremultiplyAlpha, exceptionState);
 }
 
 void WebGLRenderingContextBase::texSubImage2D(GLenum target, GLint level, GLint xoffset, GLint yoffset,
     GLenum format, GLenum type, HTMLVideoElement* video, ExceptionState& exceptionState)
 {
     if (isContextLost() || !validateHTMLVideoElement("texSubImage2D", video, exceptionState)
         || !validateTexFunc("texSubImage2D", TexSubImage2D, SourceHTMLVideoElement, target, level, format, video->videoWidth(), video->videoHeight(), 0, format, type, xoffset, yoffset))
         return;
 
     RefPtr<Image> image = videoFrameToImage(video, ImageBuffer::fastCopyImageMode());
@@ skipping 1993 matching lines @@
     return m_sharedWebGraphicsContext3D ? m_sharedWebGraphicsContext3D->drawingBuffer() : 0;
 }
 #else
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 #endif
 
 } // namespace blink