WebGL 2: add readPixels API to read pixels into pixel pack buffer

Source/modules/webgl/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 204 matching lines @@
         if (!desiredSize.isEmpty()) {
             forciblyEvictedContexts().remove(0);
             evictedContext->forceRestoreContext();
         }
         break;
     }
 }
 
 namespace {
 
-// ScopedDrawingBufferBinder is used for ReadPixels/CopyTexImage2D/CopySubImage2D to read from
-// a multisampled DrawingBuffer. In this situation, we need to blit to a single sampled buffer
-// for reading, during which the bindings could be changed and need to be recovered.
-class ScopedDrawingBufferBinder {
-    STACK_ALLOCATED();
-public:
-    ScopedDrawingBufferBinder(DrawingBuffer* drawingBuffer, WebGLFramebuffer* framebufferBinding)
-        : m_drawingBuffer(drawingBuffer)
-        , m_readFramebufferBinding(framebufferBinding)
-    {
-        // Commit DrawingBuffer if needed (e.g., for multisampling)
-        if (!m_readFramebufferBinding && m_drawingBuffer)
-            m_drawingBuffer->commit();
-    }
-
-    ~ScopedDrawingBufferBinder()
-    {
-        // Restore DrawingBuffer if needed
-        if (!m_readFramebufferBinding && m_drawingBuffer)
-            m_drawingBuffer->restoreFramebufferBindings();
-    }
-
-private:
-    DrawingBuffer* m_drawingBuffer;
-    Member<WebGLFramebuffer> m_readFramebufferBinding;
-};
-
 GLint clamp(GLint value, GLint min, GLint max)
 {
     if (value < min)
         value = min;
     if (value > max)
         value = max;
     return value;
 }
 
 // Return true if a character belongs to the ASCII subset as defined in
@@ skipping 3460 matching lines @@
     case GL_FLOAT:
         return DOMArrayBufferView::TypeFloat32;
     case GL_HALF_FLOAT_OES:
         return DOMArrayBufferView::TypeUint16;
     default:
         ASSERT_NOT_REACHED();
         return DOMArrayBufferView::TypeUint8;
     }
 }
 
-void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels)
+bool WebGLRenderingContextBase::validateReadPixelsFuncParameters(GLsizei width, GLsizei height, GLenum format, GLenum type, unsigned domArrayBufferLength, WebGLFramebuffer*& readFramebufferBinding)

[Zhenyao Mo, 2015/08/18 21:48:39]

I prefer not to return the readFramebufferBinding here because the function name
doesn't indicate that. You can remove readFramebufferBinding from the argument
in this function, and add another helper function getBoundReadFramebuffer(). 
It's a trivia operation, so you can call this whenever you need it. It's clearer
this way.

[yunchao, 2015/08/19 09:33:39]

Make sense. Done.

 {
-    if (isContextLost())
-        return;
-    // Due to WebGL's same-origin restrictions, it is not possible to
-    // taint the origin using the WebGL API.
-    ASSERT(canvas()->originClean());
-    // Validate input parameters.
-    if (!pixels) {
-        synthesizeGLError(GL_INVALID_VALUE, "readPixels", "no destination ArrayBufferView");
-        return;
-    }
     if (!validateReadPixelsFormatAndType(format, type))
-        return;
+        return false;
     GLenum readBufferInternalFormat = 0, readBufferType = 0;
-    WebGLFramebuffer* readFramebufferBinding = nullptr;
     if (!validateReadBufferAndGetInfo("readPixels", readFramebufferBinding, &readBufferInternalFormat, &readBufferType))
-        return;
+        return false;
     if (!validateReadPixelsFormatTypeCombination(format, type, readBufferInternalFormat, readBufferType))
-        return;
-
-    DOMArrayBufferView::ViewType expectedViewType = readPixelsExpectedArrayBufferViewType(type);
-    // Validate array type against pixel type.
-    if (pixels->type() != expectedViewType) {
-        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView was the wrong type for the pixel format");
-        return;
-    }
+        return false;
 
     // Calculate array size, taking into consideration of PACK_ALIGNMENT.
     unsigned totalBytesRequired = 0;
     unsigned padding = 0;
     GLenum error = WebGLImageConversion::computeImageSizeInBytes(format, type, width, height, m_packAlignment, &totalBytesRequired, &padding);
     if (error != GL_NO_ERROR) {
         synthesizeGLError(error, "readPixels", "invalid dimensions");
+        return false;
+    }
+    if (domArrayBufferLength && domArrayBufferLength < totalBytesRequired) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView not large enough for dimensions");
+        return false;
+    }
+    return true;
+}
+
+void WebGLRenderingContextBase::readPixelsImpl(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, void* data, unsigned domArrayBufferLength)
+{
+    // Due to WebGL's same-origin restrictions, it is not possible to
+    // taint the origin using the WebGL API.
+    ASSERT(canvas()->originClean());
+
+    WebGLFramebuffer* readFramebufferBinding = nullptr;
+    if (!validateReadPixelsFuncParameters(format, type, width, height, domArrayBufferLength, readFramebufferBinding))
         return;
-    }
-    if (pixels->byteLength() < totalBytesRequired) {
-        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView not large enough for dimensions");
-        return;
-    }
 
     clearIfComposited();
-    void* data = pixels->baseAddress();
 
     {
         ScopedDrawingBufferBinder binder(drawingBuffer(), readFramebufferBinding);
         webContext()->readPixels(x, y, width, height, format, type, data);
     }
 }
 
+void WebGLRenderingContextBase::readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels)
+{
+    if (isContextLost())
+        return;
+    // Validate input parameters.
+    if (!pixels) {
+        synthesizeGLError(GL_INVALID_VALUE, "readPixels", "no destination ArrayBufferView");
+        return;
+    }
+
+    DOMArrayBufferView::ViewType expectedViewType = readPixelsExpectedArrayBufferViewType(type);
+    // Validate array type against pixel type.
+    if (pixels->type() != expectedViewType) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView was the wrong type for the pixel format");
+        return;
+    }
+
+    readPixelsImpl(x, y, width, height, format, type, pixels->baseAddress(), pixels->byteLength());
+}
+
 void WebGLRenderingContextBase::renderbufferStorageImpl(
     GLenum target, GLsizei samples, GLenum internalformat, GLsizei width, GLsizei height,
     const char* functionName)
 {
     ASSERT(!samples); // |samples| > 0 is only valid in WebGL2's renderbufferStorageMultisample().
     ASSERT(!isWebGL2OrHigher()); // Make sure this is overridden in WebGL 2.
     switch (internalformat) {
     case GL_DEPTH_COMPONENT16:
     case GL_RGBA4:
     case GL_RGB5_A1:
@@ skipping 2835 matching lines @@
 
     return totalBytesPerPixel;
 }
 
 DrawingBuffer* WebGLRenderingContextBase::drawingBuffer() const
 {
     return m_drawingBuffer.get();
 }
 
 } // namespace blink