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

Source/modules/webgl/WebGLRenderingContextBase.h

 /*
  * 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 104 matching lines @@
 
 struct FormatTypeCompare {
     bool operator() (const FormatType& lhs, const FormatType& rhs) const
     {
         return (lhs.internalformat < rhs.internalformat
             || ((lhs.internalformat == rhs.internalformat) && (lhs.format < rhs.format))
             || ((lhs.internalformat == rhs.internalformat) && (lhs.format == rhs.format) && (lhs.type < rhs.type)));
     }
 };
 
+// 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;
+};
+
 class MODULES_EXPORT WebGLRenderingContextBase : public CanvasRenderingContext, public Page::MultisamplingChangedObserver {
     WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(WebGLRenderingContextBase);
 public:
     ~WebGLRenderingContextBase() override;
 
     virtual unsigned version() const = 0;
     virtual String contextName() const = 0;
     virtual void registerContextExtensions() = 0;
 
     virtual void initializeNewContext();
@@ skipping 108 matching lines @@
     GLboolean isFramebuffer(WebGLFramebuffer*);
     GLboolean isProgram(WebGLProgram*);
     GLboolean isRenderbuffer(WebGLRenderbuffer*);
     GLboolean isShader(WebGLShader*);
     GLboolean isTexture(WebGLTexture*);
 
     void lineWidth(GLfloat);
     void linkProgram(WebGLProgram*);
     void pixelStorei(GLenum pname, GLint param);
     void polygonOffset(GLfloat factor, GLfloat units);
-    void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels);
+    virtual void readPixels(GLint x, GLint y, GLsizei width, GLsizei height, GLenum format, GLenum type, DOMArrayBufferView* pixels);
     void renderbufferStorage(GLenum target, GLenum internalformat, GLsizei width, GLsizei height);
     void sampleCoverage(GLfloat value, GLboolean invert);
     void scissor(GLint x, GLint y, GLsizei width, GLsizei height);
     void shaderSource(WebGLShader*, const String&);
     void stencilFunc(GLenum func, GLint ref, GLuint mask);
     void stencilFuncSeparate(GLenum face, GLenum func, GLint ref, GLuint mask);
     void stencilMask(GLuint);
     void stencilMaskSeparate(GLenum face, GLuint mask);
     void stencilOp(GLenum fail, GLenum zfail, GLenum zpass);
     void stencilOpSeparate(GLenum face, GLenum fail, GLenum zfail, GLenum zpass);
@@ skipping 579 matching lines @@
     // Generates INVALID_ENUM and returns false if parameters are invalid.
     virtual bool validateReadPixelsFormatAndType(GLenum format, GLenum type);
 
     // Helper function to get expected ArrayBuffer view type for readPixels.
     virtual DOMArrayBufferView::ViewType readPixelsExpectedArrayBufferViewType(GLenum type);
 
     // Helper function to check format/type combination for readPixels.
     // Generates INVALID_OPERATION and returns false if the combination is unsupported.
     bool validateReadPixelsFormatTypeCombination(GLenum format, GLenum type, GLenum readBufferInternalFormat, GLenum readBufferType);
 
+    // Helper function to check parameters of readPixels. Returns true if all parameters
+    // are valid. Otherwise, generates appropriate error and returns false.
+    bool validateReadPixelsFuncParameters(GLsizei width, GLsizei height, GLenum format, GLenum type, long long bufferSize);
+
     virtual GLint getMaxTextureLevelForTarget(GLenum target);
 
     // Helper function to check input level for functions {copy}Tex{Sub}Image.
     // Generates GL error and returns false if level is invalid.
     bool validateTexFuncLevel(const char* functionName, GLenum target, GLint level);
 
     // Helper function to check if a 64-bit value is non-negative and can fit into a 32-bit integer.
     // Generates GL error and returns false if not.
     bool validateValueFitNonNegInt32(const char* functionName, const char* paramName, long long value);
 
@@ skipping 208 matching lines @@
     static IntSize oldestContextSize();
 };
 
 DEFINE_TYPE_CASTS(WebGLRenderingContextBase, CanvasRenderingContext, context, context->is3d(), context.is3d());
 
 } // namespace blink
 
 WTF_ALLOW_MOVE_INIT_AND_COMPARE_WITH_MEM_FUNCTIONS(blink::WebGLRenderingContextBase::TextureUnitState);
 
 #endif // WebGLRenderingContextBase_h