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 1339 matching lines @@
     case GL_DYNAMIC_DRAW:
         break;
     default:
         synthesizeGLError(GL_INVALID_ENUM, "bufferData", "invalid usage");
         return;
     }
 
     if (!validateValueFitNonNegInt32("bufferData", "size", size))
         return;
 
+    buffer->setSize(size);
+
     webContext()->bufferData(target, static_cast<GLsizeiptr>(size), data, usage);
 }
 
 void WebGLRenderingContextBase::bufferData(GLenum target, long long size, GLenum usage)
 {
     if (isContextLost())
         return;
     if (!size) {
         synthesizeGLError(GL_INVALID_VALUE, "bufferData", "size == 0");
         return;
@@ skipping 2101 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, long long bufferSize)
 {
-    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;
+    WebGLFramebuffer* readFramebufferBinding = nullptr;
     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 (bufferSize < static_cast<long long>(totalBytesRequired)) {
+        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "buffer is 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, long long bufferSize)
+{
+    // Due to WebGL's same-origin restrictions, it is not possible to
+    // taint the origin using the WebGL API.
+    ASSERT(canvas()->originClean());
+
+    if (!validateReadPixelsFuncParameters(width, height, format, type, bufferSize))
         return;
-    }
-    if (pixels->byteLength() < totalBytesRequired) {
-        synthesizeGLError(GL_INVALID_OPERATION, "readPixels", "ArrayBufferView not large enough for dimensions");
-        return;
-    }
 
     clearIfComposited();
-    void* data = pixels->baseAddress();
 
+    GLenum target = isWebGL2OrHigher() ? GL_READ_FRAMEBUFFER : GL_FRAMEBUFFER;
+    WebGLFramebuffer* readFramebufferBinding = getFramebufferBinding(target);

[Zhenyao Mo, 2015/08/19 17:20:23]

nit: ASSERT(readFramebufferBinding) here?

[yunchao, 2015/08/20 08:16:39]

Seems that we can't add this assertion. In my opinion, readFramebufferBinding
can be nullptr, when readPixels reads from WebGL default framebuffer (an
internal fbo). WDYT?

[Zhenyao Mo, 2015/08/20 17:27:34]

You are right.

     {
         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(), static_cast<long long>(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