/*
 * Copyright (C) 2015-2017 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
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
 */

#pragma once

#if ENABLE(WEBGL)

#include "ActivityStateChangeObserver.h"
#include "ExceptionOr.h"
#include "GPUBasedCanvasRenderingContext.h"
#include "GraphicsContextGLOpenGL.h"
#include "ImageBuffer.h"
#include "SuspendableTimer.h"
#include "Timer.h"
#include "WebGLAny.h"
#include "WebGLBuffer.h"
#include "WebGLContextAttributes.h"
#include "WebGLFramebuffer.h"
#include "WebGLProgram.h"
#include "WebGLRenderbuffer.h"
#include "WebGLStateTracker.h"
#include "WebGLTexture.h"
#include "WebGLVertexArrayObjectOES.h"
#include <JavaScriptCore/ConsoleTypes.h>
#include <limits>
#include <memory>

#if ENABLE(WEBGL2)
#include "WebGLVertexArrayObject.h"
#endif

namespace WebCore {

class ANGLEInstancedArrays;
class EXTBlendMinMax;
class EXTTextureFilterAnisotropic;
class EXTShaderTextureLOD;
class EXTsRGB;
class EXTFragDepth;
class HTMLImageElement;
class ImageData;
class IntSize;
class OESStandardDerivatives;
class OESTextureFloat;
class OESTextureFloatLinear;
class OESTextureHalfFloat;
class OESTextureHalfFloatLinear;
class OESVertexArrayObject;
class OESElementIndexUint;
#if ENABLE(OFFSCREEN_CANVAS)
class OffscreenCanvas;
#endif
class WebGLActiveInfo;
class WebGLContextGroup;
class WebGLContextObject;
class WebGLCompressedTextureASTC;
class WebGLCompressedTextureATC;
class WebGLCompressedTextureETC;
class WebGLCompressedTextureETC1;
class WebGLCompressedTexturePVRTC;
class WebGLCompressedTextureS3TC;
class WebGLDebugRendererInfo;
class WebGLDebugShaders;
class WebGLDepthTexture;
class WebGLDrawBuffers;
class WebGLExtension;
class WebGLLoseContext;
class WebGLObject;
class WebGLShader;
class WebGLSharedObject;
class WebGLShaderPrecisionFormat;
class WebGLUniformLocation;

#if ENABLE(VIDEO)
class HTMLVideoElement;
#endif

#if ENABLE(OFFSCREEN_CANVAS)
using WebGLCanvas = WTF::Variant<RefPtr<HTMLCanvasElement>, RefPtr<OffscreenCanvas>>;
#else
using WebGLCanvas = WTF::Variant<RefPtr<HTMLCanvasElement>>;
#endif

class WebGLRenderingContextBase : public GraphicsContextGLOpenGL::Client, public GPUBasedCanvasRenderingContext, private ActivityStateChangeObserver {
    WTF_MAKE_ISO_ALLOCATED(WebGLRenderingContextBase);
public:
    static std::unique_ptr<WebGLRenderingContextBase> create(CanvasBase&, WebGLContextAttributes&, const String&);
    virtual ~WebGLRenderingContextBase();

    WebGLCanvas canvas();

    int drawingBufferWidth() const;
    int drawingBufferHeight() const;

    void activeTexture(GCGLenum texture);
    void attachShader(WebGLProgram*, WebGLShader*);
    void bindAttribLocation(WebGLProgram*, GCGLuint index, const String& name);
    void bindBuffer(GCGLenum target, WebGLBuffer*);
    void bindFramebuffer(GCGLenum target, WebGLFramebuffer*);
    void bindRenderbuffer(GCGLenum target, WebGLRenderbuffer*);
    void bindTexture(GCGLenum target, WebGLTexture*);
    void blendColor(GCGLfloat red, GCGLfloat green, GCGLfloat blue, GCGLfloat alpha);
    void blendEquation(GCGLenum mode);
    void blendEquationSeparate(GCGLenum modeRGB, GCGLenum modeAlpha);
    void blendFunc(GCGLenum sfactor, GCGLenum dfactor);
    void blendFuncSeparate(GCGLenum srcRGB, GCGLenum dstRGB, GCGLenum srcAlpha, GCGLenum dstAlpha);

    using BufferDataSource = WTF::Variant<RefPtr<ArrayBuffer>, RefPtr<ArrayBufferView>>;
    void bufferData(GCGLenum target, long long size, GCGLenum usage);
    void bufferData(GCGLenum target, Optional<BufferDataSource>&&, GCGLenum usage);
    void bufferSubData(GCGLenum target, long long offset, Optional<BufferDataSource>&&);

    GCGLenum checkFramebufferStatus(GCGLenum target);
    virtual void clear(GCGLbitfield mask) = 0;
    void clearColor(GCGLfloat red, GCGLfloat green, GCGLfloat blue, GCGLfloat alpha);
    void clearDepth(GCGLfloat);
    void clearStencil(GCGLint);
    void colorMask(GCGLboolean red, GCGLboolean green, GCGLboolean blue, GCGLboolean alpha);
    void compileShader(WebGLShader*);

    void compressedTexImage2D(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLsizei width, GCGLsizei height, GCGLint border, ArrayBufferView& data);
    void compressedTexSubImage2D(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLsizei width, GCGLsizei height, GCGLenum format, ArrayBufferView& data);

    void copyTexImage2D(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLint x, GCGLint y, GCGLsizei width, GCGLsizei height, GCGLint border);
    void copyTexSubImage2D(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLint x, GCGLint y, GCGLsizei width, GCGLsizei height);

    RefPtr<WebGLBuffer> createBuffer();
    RefPtr<WebGLFramebuffer> createFramebuffer();
    RefPtr<WebGLProgram> createProgram();
    RefPtr<WebGLRenderbuffer> createRenderbuffer();
    RefPtr<WebGLShader> createShader(GCGLenum type);
    RefPtr<WebGLTexture> createTexture();

    void cullFace(GCGLenum mode);

    void deleteBuffer(WebGLBuffer*);
    void deleteFramebuffer(WebGLFramebuffer*);
    void deleteProgram(WebGLProgram*);
    void deleteRenderbuffer(WebGLRenderbuffer*);
    void deleteShader(WebGLShader*);
    void deleteTexture(WebGLTexture*);

    void depthFunc(GCGLenum);
    void depthMask(GCGLboolean);
    void depthRange(GCGLfloat zNear, GCGLfloat zFar);
    void detachShader(WebGLProgram*, WebGLShader*);
    void disable(GCGLenum cap);
    void disableVertexAttribArray(GCGLuint index);
    void drawArrays(GCGLenum mode, GCGLint first, GCGLsizei count);
    void drawElements(GCGLenum mode, GCGLsizei count, GCGLenum type, long long offset);

    void enable(GCGLenum cap);
    void enableVertexAttribArray(GCGLuint index);
    void finish();
    void flush();
    void framebufferRenderbuffer(GCGLenum target, GCGLenum attachment, GCGLenum renderbuffertarget, WebGLRenderbuffer*);
    void framebufferTexture2D(GCGLenum target, GCGLenum attachment, GCGLenum textarget, WebGLTexture*, GCGLint level);
    void frontFace(GCGLenum mode);
    void generateMipmap(GCGLenum target);

    RefPtr<WebGLActiveInfo> getActiveAttrib(WebGLProgram*, GCGLuint index);
    RefPtr<WebGLActiveInfo> getActiveUniform(WebGLProgram*, GCGLuint index);
    Optional<Vector<RefPtr<WebGLShader>>> getAttachedShaders(WebGLProgram*);
    GCGLint getAttribLocation(WebGLProgram*, const String& name);
    WebGLAny getBufferParameter(GCGLenum target, GCGLenum pname);
    Optional<WebGLContextAttributes> getContextAttributes();
    GCGLenum getError();
    virtual WebGLExtension* getExtension(const String& name) = 0;
    virtual WebGLAny getFramebufferAttachmentParameter(GCGLenum target, GCGLenum attachment, GCGLenum pname) = 0;
    virtual WebGLAny getParameter(GCGLenum pname) = 0;
    WebGLAny getProgramParameter(WebGLProgram*, GCGLenum pname);
    String getProgramInfoLog(WebGLProgram*);
    WebGLAny getRenderbufferParameter(GCGLenum target, GCGLenum pname);
    WebGLAny getShaderParameter(WebGLShader*, GCGLenum pname);
    String getShaderInfoLog(WebGLShader*);
    RefPtr<WebGLShaderPrecisionFormat> getShaderPrecisionFormat(GCGLenum shaderType, GCGLenum precisionType);
    String getShaderSource(WebGLShader*);
    virtual Optional<Vector<String>> getSupportedExtensions() = 0;
    WebGLAny getTexParameter(GCGLenum target, GCGLenum pname);
    WebGLAny getUniform(WebGLProgram*, const WebGLUniformLocation*);
    RefPtr<WebGLUniformLocation> getUniformLocation(WebGLProgram*, const String&);
    WebGLAny getVertexAttrib(GCGLuint index, GCGLenum pname);
    long long getVertexAttribOffset(GCGLuint index, GCGLenum pname);

    bool extensionIsEnabled(const String&);

    bool isPreservingDrawingBuffer() const { return m_attributes.preserveDrawingBuffer; }
    void setPreserveDrawingBuffer(bool value) { m_attributes.preserveDrawingBuffer = value; }

    bool preventBufferClearForInspector() const { return m_preventBufferClearForInspector; }
    void setPreventBufferClearForInspector(bool value) { m_preventBufferClearForInspector = value; }

    virtual void hint(GCGLenum target, GCGLenum mode) = 0;
    GCGLboolean isBuffer(WebGLBuffer*);
    bool isContextLost() const;
    GCGLboolean isEnabled(GCGLenum cap);
    GCGLboolean isFramebuffer(WebGLFramebuffer*);
    GCGLboolean isProgram(WebGLProgram*);
    GCGLboolean isRenderbuffer(WebGLRenderbuffer*);
    GCGLboolean isShader(WebGLShader*);
    GCGLboolean isTexture(WebGLTexture*);

    void lineWidth(GCGLfloat);
    void linkProgram(WebGLProgram*);
    bool linkProgramWithoutInvalidatingAttribLocations(WebGLProgram*);
    void pixelStorei(GCGLenum pname, GCGLint param);
    void polygonOffset(GCGLfloat factor, GCGLfloat units);
    void readPixels(GCGLint x, GCGLint y, GCGLsizei width, GCGLsizei height, GCGLenum format, GCGLenum type, ArrayBufferView& pixels);
    void releaseShaderCompiler();
    virtual void renderbufferStorage(GCGLenum target, GCGLenum internalformat, GCGLsizei width, GCGLsizei height) = 0;
    void sampleCoverage(GCGLfloat value, GCGLboolean invert);
    void scissor(GCGLint x, GCGLint y, GCGLsizei width, GCGLsizei height);
    void shaderSource(WebGLShader*, const String&);
    void stencilFunc(GCGLenum func, GCGLint ref, GCGLuint mask);
    void stencilFuncSeparate(GCGLenum face, GCGLenum func, GCGLint ref, GCGLuint mask);
    void stencilMask(GCGLuint);
    void stencilMaskSeparate(GCGLenum face, GCGLuint mask);
    void stencilOp(GCGLenum fail, GCGLenum zfail, GCGLenum zpass);
    void stencilOpSeparate(GCGLenum face, GCGLenum fail, GCGLenum zfail, GCGLenum zpass);

    void texImage2D(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLsizei width, GCGLsizei height, GCGLint border, GCGLenum format, GCGLenum type, RefPtr<ArrayBufferView>&&);

#if ENABLE(VIDEO)
    using TexImageSource = WTF::Variant<RefPtr<ImageBitmap>, RefPtr<ImageData>, RefPtr<HTMLImageElement>, RefPtr<HTMLCanvasElement>, RefPtr<HTMLVideoElement>>;
#else
    using TexImageSource = WTF::Variant<RefPtr<ImageBitmap>, RefPtr<ImageData>, RefPtr<HTMLImageElement>, RefPtr<HTMLCanvasElement>>;
#endif

    ExceptionOr<void> texImage2D(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLenum format, GCGLenum type, Optional<TexImageSource>);

    void texParameterf(GCGLenum target, GCGLenum pname, GCGLfloat param);
    void texParameteri(GCGLenum target, GCGLenum pname, GCGLint param);

    void texSubImage2D(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLsizei width, GCGLsizei height, GCGLenum format, GCGLenum type, RefPtr<ArrayBufferView>&&);
    ExceptionOr<void> texSubImage2D(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLenum format, GCGLenum type, Optional<TexImageSource>&&);

    template <class TypedArray, class DataType>
    class TypedList {
    public:
        using VariantType = Variant<RefPtr<TypedArray>, Vector<DataType>>;

        TypedList(VariantType&& variant)
            : m_variant(WTFMove(variant))
        {
        }

        const DataType* data() const
        {
            return WTF::switchOn(m_variant,
                [] (const RefPtr<TypedArray>& typedArray) -> const DataType* { return typedArray->data(); },
                [] (const Vector<DataType>& vector) -> const DataType* { return vector.data(); }
            );
        }

        GCGLsizei length() const
        {
            return WTF::switchOn(m_variant,
                [] (const RefPtr<TypedArray>& typedArray) -> GCGLsizei { return typedArray->length(); },
                [] (const Vector<DataType>& vector) -> GCGLsizei { return vector.size(); }
            );
        }

    private:
        VariantType m_variant;
    };

    using Float32List = TypedList<Float32Array, float>;
    using Int32List = TypedList<Int32Array, int>;

    void uniform1f(const WebGLUniformLocation*, GCGLfloat x);
    void uniform2f(const WebGLUniformLocation*, GCGLfloat x, GCGLfloat y);
    void uniform3f(const WebGLUniformLocation*, GCGLfloat x, GCGLfloat y, GCGLfloat z);
    void uniform4f(const WebGLUniformLocation*, GCGLfloat x, GCGLfloat y, GCGLfloat z, GCGLfloat w);

    void uniform1i(const WebGLUniformLocation*, GCGLint x);
    void uniform2i(const WebGLUniformLocation*, GCGLint x, GCGLint y);
    void uniform3i(const WebGLUniformLocation*, GCGLint x, GCGLint y, GCGLint z);
    void uniform4i(const WebGLUniformLocation*, GCGLint x, GCGLint y, GCGLint z, GCGLint w);

    void uniform1fv(const WebGLUniformLocation*, Float32List&&);
    void uniform2fv(const WebGLUniformLocation*, Float32List&&);
    void uniform3fv(const WebGLUniformLocation*, Float32List&&);
    void uniform4fv(const WebGLUniformLocation*, Float32List&&);

    void uniform1iv(const WebGLUniformLocation*, Int32List&&);
    void uniform2iv(const WebGLUniformLocation*, Int32List&&);
    void uniform3iv(const WebGLUniformLocation*, Int32List&&);
    void uniform4iv(const WebGLUniformLocation*, Int32List&&);

    void uniformMatrix2fv(const WebGLUniformLocation*, GCGLboolean transpose, Float32List&&);
    void uniformMatrix3fv(const WebGLUniformLocation*, GCGLboolean transpose, Float32List&&);
    void uniformMatrix4fv(const WebGLUniformLocation*, GCGLboolean transpose, Float32List&&);

    void useProgram(WebGLProgram*);
    void validateProgram(WebGLProgram*);

    void vertexAttrib1f(GCGLuint index, GCGLfloat x);
    void vertexAttrib2f(GCGLuint index, GCGLfloat x, GCGLfloat y);
    void vertexAttrib3f(GCGLuint index, GCGLfloat x, GCGLfloat y, GCGLfloat z);
    void vertexAttrib4f(GCGLuint index, GCGLfloat x, GCGLfloat y, GCGLfloat z, GCGLfloat w);

    void vertexAttrib1fv(GCGLuint index, Float32List&&);
    void vertexAttrib2fv(GCGLuint index, Float32List&&);
    void vertexAttrib3fv(GCGLuint index, Float32List&&);
    void vertexAttrib4fv(GCGLuint index, Float32List&&);

    void vertexAttribPointer(GCGLuint index, GCGLint size, GCGLenum type, GCGLboolean normalized,
        GCGLsizei stride, long long offset);

    void viewport(GCGLint x, GCGLint y, GCGLsizei width, GCGLsizei height);

    // WEBKIT_lose_context support
    enum LostContextMode {
        // Lost context occurred at the graphics system level.
        RealLostContext,

        // Lost context provoked by WEBKIT_lose_context.
        SyntheticLostContext
    };
    void forceLostContext(LostContextMode);
    void forceRestoreContext();
    void loseContextImpl(LostContextMode);
    WEBCORE_EXPORT void simulateContextChanged();

    GraphicsContextGLOpenGL* graphicsContextGL() const { return m_context.get(); }
    WebGLContextGroup* contextGroup() const { return m_contextGroup.get(); }
    PlatformLayer* platformLayer() const override;

    void reshape(int width, int height) override;

    void markLayerComposited() final;
    void paintRenderingResultsToCanvas() override;
    RefPtr<ImageData> paintRenderingResultsToImageData();

    void removeSharedObject(WebGLSharedObject&);
    void removeContextObject(WebGLContextObject&);
    
    unsigned getMaxVertexAttribs() const { return m_maxVertexAttribs; }

    bool isContextUnrecoverablyLost() const;

    // Instanced Array helper functions.
    void drawArraysInstanced(GCGLenum mode, GCGLint first, GCGLsizei count, GCGLsizei primcount);
    void drawElementsInstanced(GCGLenum mode, GCGLsizei count, GCGLenum type, long long offset, GCGLsizei primcount);
    void vertexAttribDivisor(GCGLuint index, GCGLuint divisor);

    // Used for testing only, from Internals.
    WEBCORE_EXPORT void setFailNextGPUStatusCheck();

    // GraphicsContextGL::Client
    void didComposite() override;
    void forceContextLost() override;
    void recycleContext() override;
    void dispatchContextChangedNotification() override;

protected:
    WebGLRenderingContextBase(CanvasBase&, WebGLContextAttributes);
    WebGLRenderingContextBase(CanvasBase&, Ref<GraphicsContextGLOpenGL>&&, WebGLContextAttributes);

    friend class WebGLDrawBuffers;
    friend class WebGLFramebuffer;
    friend class WebGLObject;
    friend class OESVertexArrayObject;
    friend class WebGLDebugShaders;
    friend class WebGLCompressedTextureASTC;
    friend class WebGLCompressedTextureATC;
    friend class WebGLCompressedTextureETC;
    friend class WebGLCompressedTextureETC1;
    friend class WebGLCompressedTexturePVRTC;
    friend class WebGLCompressedTextureS3TC;
    friend class WebGLRenderingContextErrorMessageCallback;
    friend class WebGLVertexArrayObjectOES;
    friend class WebGLVertexArrayObject;
    friend class WebGLVertexArrayObjectBase;

    virtual void initializeNewContext();
    virtual void initializeVertexArrayObjects() = 0;
    void setupFlags();

    // ActiveDOMObject
    void stop() override;
    const char* activeDOMObjectName() const override;
    void suspend(ReasonForSuspension) override;
    void resume() override;

    void addSharedObject(WebGLSharedObject&);
    void addContextObject(WebGLContextObject&);
    void detachAndRemoveAllObjects();

    void destroyGraphicsContextGL();
    void markContextChanged();
    void markContextChangedAndNotifyCanvasObserver();

    void addActivityStateChangeObserverIfNecessary();
    void removeActivityStateChangeObserver();

    // Query whether it is built on top of compliant GLES2 implementation.
    bool isGLES2Compliant() { return m_isGLES2Compliant; }
    // Query if the GL implementation is NPOT strict.
    bool isGLES2NPOTStrict() { return m_isGLES2NPOTStrict; }
    // Query if depth_stencil buffer is supported.
    bool isDepthStencilSupported() { return m_isDepthStencilSupported; }

    // Helper to return the size in bytes of OpenGL data types
    // like GL_FLOAT, GL_INT, etc.
    unsigned sizeInBytes(GCGLenum type);

    // Basic validation of count and offset against number of elements in element array buffer
    bool validateElementArraySize(GCGLsizei count, GCGLenum type, GCGLintptr offset);

    // Conservative but quick index validation
    virtual bool validateIndexArrayConservative(GCGLenum type, unsigned& numElementsRequired) = 0;

    // Precise but slow index validation -- only done if conservative checks fail
    bool validateIndexArrayPrecise(GCGLsizei count, GCGLenum type, GCGLintptr offset, unsigned& numElementsRequired);
    bool validateVertexAttributes(unsigned elementCount, unsigned primitiveCount = 0);

    bool validateWebGLObject(const char*, WebGLObject*);

#if !USE(ANGLE)
    bool validateDrawArrays(const char* functionName, GCGLenum mode, GCGLint first, GCGLsizei count, GCGLsizei primcount);
    bool validateDrawElements(const char* functionName, GCGLenum mode, GCGLsizei count, GCGLenum type, long long offset, unsigned& numElements, GCGLsizei primcount);
    bool validateNPOTTextureLevel(GCGLsizei width, GCGLsizei height, GCGLint level, const char* functionName);
#endif

    // Adds a compressed texture format.
    void addCompressedTextureFormat(GCGLenum);

    RefPtr<Image> drawImageIntoBuffer(Image&, int width, int height, int deviceScaleFactor);

#if ENABLE(VIDEO)
    RefPtr<Image> videoFrameToImage(HTMLVideoElement*, BackingStoreCopy);
#endif

    WebGLTexture::TextureExtensionFlag textureExtensionFlags() const;

    bool enableSupportedExtension(ASCIILiteral extensionNameLiteral);

    virtual void uncacheDeletedBuffer(WebGLBuffer*);

    RefPtr<GraphicsContextGLOpenGL> m_context;
    RefPtr<WebGLContextGroup> m_contextGroup;

    bool m_restoreAllowed { false };
    SuspendableTimer m_restoreTimer;

    bool m_needsUpdate;
    bool m_markedCanvasDirty;
    HashSet<WebGLContextObject*> m_contextObjects;

    // List of bound VBO's. Used to maintain info about sizes for ARRAY_BUFFER and stored values for ELEMENT_ARRAY_BUFFER
    RefPtr<WebGLBuffer> m_boundArrayBuffer;
    RefPtr<WebGLBuffer> m_boundCopyReadBuffer;
    RefPtr<WebGLBuffer> m_boundCopyWriteBuffer;
    RefPtr<WebGLBuffer> m_boundPixelPackBuffer;
    RefPtr<WebGLBuffer> m_boundPixelUnpackBuffer;
    RefPtr<WebGLBuffer> m_boundTransformFeedbackBuffer;
    RefPtr<WebGLBuffer> m_boundUniformBuffer;

    RefPtr<WebGLVertexArrayObjectBase> m_defaultVertexArrayObject;
    RefPtr<WebGLVertexArrayObjectBase> m_boundVertexArrayObject;

    void setBoundVertexArrayObject(WebGLVertexArrayObjectBase* arrayObject)
    {
        m_boundVertexArrayObject = arrayObject ? arrayObject : m_defaultVertexArrayObject;
    }
    
    class VertexAttribValue {
    public:
        VertexAttribValue()
        {
            initValue();
        }
        
        void initValue()
        {
            value[0] = 0.0f;
            value[1] = 0.0f;
            value[2] = 0.0f;
            value[3] = 1.0f;
        }
        
        GCGLfloat value[4];
    };
    Vector<VertexAttribValue> m_vertexAttribValue;
    unsigned m_maxVertexAttribs;
#if !USE(ANGLE)
    RefPtr<WebGLBuffer> m_vertexAttrib0Buffer;
    long m_vertexAttrib0BufferSize { 0 };
    GCGLfloat m_vertexAttrib0BufferValue[4];
    bool m_forceAttrib0BufferRefill { true };
    bool m_vertexAttrib0UsedBefore { false };
#endif

    RefPtr<WebGLProgram> m_currentProgram;
    RefPtr<WebGLFramebuffer> m_framebufferBinding;
    RefPtr<WebGLFramebuffer> m_readFramebufferBinding;
    RefPtr<WebGLRenderbuffer> m_renderbufferBinding;
    struct TextureUnitState {
        RefPtr<WebGLTexture> texture2DBinding;
        RefPtr<WebGLTexture> textureCubeMapBinding;
    };
    Vector<TextureUnitState> m_textureUnits;
#if !USE(ANGLE)
    HashSet<unsigned, DefaultHash<unsigned>::Hash, WTF::UnsignedWithZeroKeyHashTraits<unsigned>> m_unrenderableTextureUnits;
#endif
    unsigned long m_activeTextureUnit;

    RefPtr<WebGLTexture> m_blackTexture2D;
    RefPtr<WebGLTexture> m_blackTextureCubeMap;

    Vector<GCGLenum> m_compressedTextureFormats;

    // Fixed-size cache of reusable image buffers for video texImage2D calls.
    class LRUImageBufferCache {
    public:
        LRUImageBufferCache(int capacity);
        // The pointer returned is owned by the image buffer map.
        ImageBuffer* imageBuffer(const IntSize& size);
    private:
        void bubbleToFront(size_t idx);
        Vector<std::unique_ptr<ImageBuffer>> m_buffers;
    };
    LRUImageBufferCache m_generatedImageCache { 0 };

    GCGLint m_maxTextureSize;
    GCGLint m_maxCubeMapTextureSize;
    GCGLint m_maxRenderbufferSize;
    GCGLint m_maxViewportDims[2] { 0, 0 };
    GCGLint m_maxTextureLevel;
    GCGLint m_maxCubeMapTextureLevel;

    GCGLint m_maxDrawBuffers;
    GCGLint m_maxColorAttachments;
    GCGLenum m_backDrawBuffer;
    bool m_drawBuffersWebGLRequirementsChecked;
    bool m_drawBuffersSupported;

    GCGLint m_packAlignment;
    GCGLint m_unpackAlignment;
    bool m_unpackFlipY;
    bool m_unpackPremultiplyAlpha;
    GCGLenum m_unpackColorspaceConversion;
    bool m_contextLost { false };
    LostContextMode m_contextLostMode { SyntheticLostContext };
    WebGLContextAttributes m_attributes;

    bool m_layerCleared;
    GCGLfloat m_clearColor[4];
    bool m_scissorEnabled;
    GCGLfloat m_clearDepth;
    GCGLint m_clearStencil;
    GCGLboolean m_colorMask[4];
    GCGLboolean m_depthMask;

    bool m_stencilEnabled;
    GCGLuint m_stencilMask, m_stencilMaskBack;
    GCGLint m_stencilFuncRef, m_stencilFuncRefBack; // Note that these are the user specified values, not the internal clamped value.
    GCGLuint m_stencilFuncMask, m_stencilFuncMaskBack;

    bool m_isGLES2Compliant;
    bool m_isGLES2NPOTStrict;
    bool m_isDepthStencilSupported;
    bool m_isRobustnessEXTSupported;

    bool m_synthesizedErrorsToConsole { true };
    int m_numGLErrorsToConsoleAllowed;

    bool m_preventBufferClearForInspector { false };

    // A WebGLRenderingContext can be created in a state where it appears as
    // a valid and active context, but will not execute any important operations
    // until its load policy is completely resolved.
    bool m_isPendingPolicyResolution { false };
    bool m_hasRequestedPolicyResolution { false };
    bool isContextLostOrPending();

    // Enabled extension objects.
    // FIXME: Move some of these to WebGLRenderingContext, the ones not needed for WebGL2
    std::unique_ptr<EXTFragDepth> m_extFragDepth;
    std::unique_ptr<EXTBlendMinMax> m_extBlendMinMax;
    std::unique_ptr<EXTsRGB> m_extsRGB;
    std::unique_ptr<EXTTextureFilterAnisotropic> m_extTextureFilterAnisotropic;
    std::unique_ptr<EXTShaderTextureLOD> m_extShaderTextureLOD;
    std::unique_ptr<OESTextureFloat> m_oesTextureFloat;
    std::unique_ptr<OESTextureFloatLinear> m_oesTextureFloatLinear;
    std::unique_ptr<OESTextureHalfFloat> m_oesTextureHalfFloat;
    std::unique_ptr<OESTextureHalfFloatLinear> m_oesTextureHalfFloatLinear;
    std::unique_ptr<OESStandardDerivatives> m_oesStandardDerivatives;
    std::unique_ptr<OESVertexArrayObject> m_oesVertexArrayObject;
    std::unique_ptr<OESElementIndexUint> m_oesElementIndexUint;
    std::unique_ptr<WebGLLoseContext> m_webglLoseContext;
    std::unique_ptr<WebGLDebugRendererInfo> m_webglDebugRendererInfo;
    std::unique_ptr<WebGLDebugShaders> m_webglDebugShaders;
    std::unique_ptr<WebGLCompressedTextureASTC> m_webglCompressedTextureASTC;
    std::unique_ptr<WebGLCompressedTextureATC> m_webglCompressedTextureATC;
    std::unique_ptr<WebGLCompressedTextureETC> m_webglCompressedTextureETC;
    std::unique_ptr<WebGLCompressedTextureETC1> m_webglCompressedTextureETC1;
    std::unique_ptr<WebGLCompressedTexturePVRTC> m_webglCompressedTexturePVRTC;
    std::unique_ptr<WebGLCompressedTextureS3TC> m_webglCompressedTextureS3TC;
    std::unique_ptr<WebGLDepthTexture> m_webglDepthTexture;
    std::unique_ptr<WebGLDrawBuffers> m_webglDrawBuffers;
    std::unique_ptr<ANGLEInstancedArrays> m_angleInstancedArrays;

    // Helpers for getParameter and other similar functions.
    bool getBooleanParameter(GCGLenum);
    Vector<bool> getBooleanArrayParameter(GCGLenum);
    float getFloatParameter(GCGLenum);
    int getIntParameter(GCGLenum);
    unsigned getUnsignedIntParameter(GCGLenum);
    long long getInt64Parameter(GCGLenum);
    RefPtr<Float32Array> getWebGLFloatArrayParameter(GCGLenum);
    RefPtr<Int32Array> getWebGLIntArrayParameter(GCGLenum);

    // Clear the backbuffer if it was composited since the last operation.
    // clearMask is set to the bitfield of any clear that would happen anyway at this time
    // and the function returns true if that clear is now unnecessary.
    bool clearIfComposited(GCGLbitfield clearMask = 0);

    // Helper to restore state that clearing the framebuffer may destroy.
    void restoreStateAfterClear();

    ExceptionOr<void> texImageSource2D(GCGLenum target, GCGLint level, GCGLint internalformat, GCGLsizei width, GCGLsizei height, GCGLint border, GCGLenum format, GCGLenum type, TexImageSource&&);
    void texImage2DBase(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLsizei width, GCGLsizei height, GCGLint border, GCGLenum format, GCGLenum type, GCGLsizei byteLength, const void* pixels);
    void texImage2DImpl(GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLsizei width, GCGLsizei height, GCGLenum format, GCGLenum type, Image*, GraphicsContextGL::DOMSource, bool flipY, bool premultiplyAlpha);
    void texSubImage2DBase(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLsizei width, GCGLsizei height, GCGLenum internalformat, GCGLenum format, GCGLenum type, GCGLsizei byteLength, const void* pixels);
    void texSubImage2DImpl(GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset, GCGLenum format, GCGLenum type, Image*, GraphicsContextGL::DOMSource, bool flipY, bool premultiplyAlpha);

#if !USE(ANGLE)
    bool checkTextureCompleteness(const char*, bool);

    void createFallbackBlackTextures1x1();

    // Helper function for copyTex{Sub}Image, check whether the internalformat
    // and the color buffer format of the current bound framebuffer combination
    // is valid.
    bool isTexInternalFormatColorBufferCombinationValid(GCGLenum texInternalFormat, GCGLenum colorBufferFormat);

    // Helper function to get the bound read framebuffer's color buffer format.
    GCGLenum getBoundReadFramebufferColorFormat();

    // Helper function to get the bound read framebuffer's width.
    int getBoundReadFramebufferWidth();

    // Helper function to get the bound read framebuffer's height.
    int getBoundReadFramebufferHeight();
#endif

    // Helper function to verify limits on the length of uniform and attribute locations.
    bool validateLocationLength(const char* functionName, const String&);

    // Helper function to check if size is non-negative.
    // Generate GL error and return false for negative inputs; otherwise, return true.
    bool validateSize(const char* functionName, GCGLint x, GCGLint y);

    // Helper function to check if all characters in the string belong to the
    // ASCII subset as defined in GLSL ES 1.0 spec section 3.1.
    bool validateString(const char* functionName, const String&);

    // Helper function to check target and texture bound to the target.
    // Generate GL errors and return 0 if target is invalid or texture bound is
    // null.  Otherwise, return the texture bound to the target.
    RefPtr<WebGLTexture> validateTextureBinding(const char* functionName, GCGLenum target, bool useSixEnumsForCubeMap);

    // Helper function to check input format/type for functions {copy}Tex{Sub}Image.
    // Generates GL error and returns false if parameters are invalid.
    bool validateTexFuncFormatAndType(const char* functionName, GCGLenum internalformat, GCGLenum format, GCGLenum type, GCGLint level);

    // 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, GCGLenum target, GCGLint level);

    enum TexFuncValidationFunctionType {
        TexImage,
        TexSubImage,
        CopyTexImage
    };

    enum TexFuncValidationSourceType {
        SourceArrayBufferView,
        SourceImageBitmap,
        SourceImageData,
        SourceHTMLImageElement,
        SourceHTMLCanvasElement,
#if ENABLE(VIDEO)
        SourceHTMLVideoElement,
#endif
    };

    // Helper function for tex{Sub}Image2D to check if the input format/type/level/target/width/height/border/xoffset/yoffset are valid.
    // Otherwise, it would return quickly without doing other work.
    bool validateTexFunc(const char* functionName, TexFuncValidationFunctionType, TexFuncValidationSourceType, GCGLenum target, GCGLint level, GCGLenum internalformat, GCGLsizei width,
        GCGLsizei height, GCGLint border, GCGLenum format, GCGLenum type, GCGLint xoffset, GCGLint yoffset);

    // Helper function to check input parameters for functions {copy}Tex{Sub}Image.
    // Generates GL error and returns false if parameters are invalid.
    bool validateTexFuncParameters(const char* functionName,
        TexFuncValidationFunctionType,
        GCGLenum target, GCGLint level,
        GCGLenum internalformat,
        GCGLsizei width, GCGLsizei height, GCGLint border,
        GCGLenum format, GCGLenum type);

    enum NullDisposition {
        NullAllowed,
        NullNotAllowed
    };

    // Helper function to validate that the given ArrayBufferView
    // is of the correct type and contains enough data for the texImage call.
    // Generates GL error and returns false if parameters are invalid.
    bool validateTexFuncData(const char* functionName, GCGLint level,
        GCGLsizei width, GCGLsizei height,
        GCGLenum internalformat, GCGLenum format, GCGLenum type,
        ArrayBufferView* pixels,
        NullDisposition);

    // Helper function to validate a given texture format is settable as in
    // you can supply data to texImage2D, or call texImage2D, copyTexImage2D and
    // copyTexSubImage2D.
    // Generates GL error and returns false if the format is not settable.
    bool validateSettableTexInternalFormat(const char* functionName, GCGLenum format);

#if !USE(ANGLE)
    // Helper function to validate compressed texture data is correct size
    // for the given format and dimensions.
    bool validateCompressedTexFuncData(const char* functionName, GCGLsizei width, GCGLsizei height, GCGLenum format, ArrayBufferView& pixels);

    // Helper function for validating compressed texture formats.
    bool validateCompressedTexFormat(GCGLenum format);

    // Helper function to validate compressed texture dimensions are valid for
    // the given format.
    bool validateCompressedTexDimensions(const char* functionName, GCGLenum target, GCGLint level, GCGLsizei width, GCGLsizei height, GCGLenum format);

    // Helper function to validate compressed texture dimensions are valid for
    // the given format.
    bool validateCompressedTexSubDimensions(const char* functionName, GCGLenum target, GCGLint level, GCGLint xoffset, GCGLint yoffset,
        GCGLsizei width, GCGLsizei height, GCGLenum format, WebGLTexture*);
#endif

    // Helper function to validate mode for draw{Arrays/Elements}.
    bool validateDrawMode(const char* functionName, GCGLenum);

    // Helper function to validate if front/back stencilMask and stencilFunc settings are the same.
    bool validateStencilSettings(const char* functionName);

    // Helper function to validate stencil func.
    bool validateStencilFunc(const char* functionName, GCGLenum);

    // Helper function for texParameterf and texParameteri.
    void texParameter(GCGLenum target, GCGLenum pname, GCGLfloat parami, GCGLint paramf, bool isFloat);

    // Helper function to print errors and warnings to console.
    void printToConsole(MessageLevel, const String&);

    // Helper function to validate input parameters for framebuffer functions.
    // Generate GL error if parameters are illegal.
    virtual bool validateFramebufferFuncParameters(const char* functionName, GCGLenum target, GCGLenum attachment) = 0;

    // Helper function to validate blend equation mode.
    virtual bool validateBlendEquation(const char* functionName, GCGLenum) = 0;

    // Helper function to validate blend func factors.
    bool validateBlendFuncFactors(const char* functionName, GCGLenum src, GCGLenum dst);

    // Helper function to validate a GL capability.
    virtual bool validateCapability(const char* functionName, GCGLenum) = 0;

    // Helper function to validate input parameters for uniform functions.
    bool validateUniformParameters(const char* functionName, const WebGLUniformLocation*, const Float32List&, GCGLsizei mod);
    bool validateUniformParameters(const char* functionName, const WebGLUniformLocation*, const Int32List&, GCGLsizei mod);
    bool validateUniformParameters(const char* functionName, const WebGLUniformLocation*, void*, GCGLsizei, GCGLsizei mod);
    bool validateUniformMatrixParameters(const char* functionName, const WebGLUniformLocation*, GCGLboolean transpose, const Float32List&, GCGLsizei mod);
    bool validateUniformMatrixParameters(const char* functionName, const WebGLUniformLocation*, GCGLboolean transpose, const void*, GCGLsizei, GCGLsizei mod);

    // Helper function to validate parameters for bufferData.
    // Return the current bound buffer to target, or 0 if parameters are invalid.
    WebGLBuffer* validateBufferDataParameters(const char* functionName, GCGLenum target, GCGLenum usage);

    // Helper function for tex{Sub}Image2D to make sure image is ready.
    ExceptionOr<bool> validateHTMLImageElement(const char* functionName, HTMLImageElement*);
    ExceptionOr<bool> validateHTMLCanvasElement(const char* functionName, HTMLCanvasElement*);
#if ENABLE(VIDEO)
    ExceptionOr<bool> validateHTMLVideoElement(const char* functionName, HTMLVideoElement*);
#endif

    // Helper functions for vertexAttribNf{v}.
    void vertexAttribfImpl(const char* functionName, GCGLuint index, GCGLsizei expectedSize, GCGLfloat, GCGLfloat, GCGLfloat, GCGLfloat);
    void vertexAttribfvImpl(const char* functionName, GCGLuint index, Float32List&&, GCGLsizei expectedSize);

    // Helper function for delete* (deleteBuffer, deleteProgram, etc) functions.
    // Return false if caller should return without further processing.
    bool deleteObject(WebGLObject*);

    // Helper function for bind* (bindBuffer, bindTexture, etc) and useProgram.
    // Return false if caller should return without further processing.
    bool checkObjectToBeBound(const char* functionName, WebGLObject*);

    bool validateAndCacheBufferBinding(const char* functionName, GCGLenum target, WebGLBuffer*);

#if !USE(ANGLE)
    // Helpers for simulating vertexAttrib0.
    void initVertexAttrib0();
    Optional<bool> simulateVertexAttrib0(GCGLuint numVertex);
    bool validateSimulatedVertexAttrib0(GCGLuint numVertex);
    void restoreStatesAfterVertexAttrib0Simulation();
#endif

    // Wrapper for GraphicsContextGLOpenGL::synthesizeGLError that sends a message to the JavaScript console.
    enum ConsoleDisplayPreference { DisplayInConsole, DontDisplayInConsole };
    void synthesizeGLError(GCGLenum, const char* functionName, const char* description, ConsoleDisplayPreference = DisplayInConsole);

    String ensureNotNull(const String&) const;

    // Enable or disable stencil test based on user setting and whether the current FBO has a stencil buffer.
    void applyStencilTest();

    // Helper for enabling or disabling a capability.
    void enableOrDisable(GCGLenum capability, bool enable);

    // Clamp the width and height to GL_MAX_VIEWPORT_DIMS.
    IntSize clampedCanvasSize();

    virtual GCGLint getMaxDrawBuffers() = 0;
    virtual GCGLint getMaxColorAttachments() = 0;

    void setBackDrawBuffer(GCGLenum);

    void restoreCurrentFramebuffer();
    void restoreCurrentTexture2D();

    // Check if EXT_draw_buffers extension is supported and if it satisfies the WebGL requirements.
    bool supportsDrawBuffers();

#if ENABLE(OFFSCREEN_CANVAS)
    OffscreenCanvas* offscreenCanvas();
#endif

    template <typename T> inline Optional<T> checkedAddAndMultiply(T value, T add, T multiply);
    template <typename T> unsigned getMaxIndex(const RefPtr<JSC::ArrayBuffer> elementArrayBuffer, GCGLintptr uoffset, GCGLsizei n);

private:
    void scheduleTaskToDispatchContextLostEvent();
    // Helper for restoration after context lost.
    void maybeRestoreContext();

    bool validateArrayBufferType(const char* functionName, GCGLenum type, Optional<JSC::TypedArrayType>);
    void registerWithWebGLStateTracker();
    void checkForContextLossHandling();

    void activityStateDidChange(OptionSet<ActivityState::Flag> oldActivityState, OptionSet<ActivityState::Flag> newActivityState) override;

    WebGLStateTracker::Token m_trackerToken;
    Timer m_checkForContextLossHandlingTimer;
    bool m_isSuspended { false };
};

template <typename T>
inline Optional<T> WebGLRenderingContextBase::checkedAddAndMultiply(T value, T add, T multiply)
{
    Checked<T, RecordOverflow> checkedResult = Checked<T>(value);
    checkedResult += Checked<T>(add);
    checkedResult *= Checked<T>(multiply);
    if (checkedResult.hasOverflowed())
        return WTF::nullopt;

    return checkedResult.unsafeGet();
}

template<typename T>
inline unsigned WebGLRenderingContextBase::getMaxIndex(const RefPtr<JSC::ArrayBuffer> elementArrayBuffer, GCGLintptr uoffset, GCGLsizei n)
{
    unsigned maxIndex = 0;
    T restartIndex = 0;

#if ENABLE(WEBGL2)
    // WebGL 2 spec enforces that GL_PRIMITIVE_RESTART_FIXED_INDEX is always enabled, so ignore the restart index.
    if (isWebGL2())
        restartIndex = std::numeric_limits<T>::max();
#endif

    // Make uoffset an element offset.
    uoffset /= sizeof(T);
    const T* p = static_cast<const T*>(elementArrayBuffer->data()) + uoffset;
    while (n-- > 0) {
        if (*p != restartIndex && *p > maxIndex)
            maxIndex = *p;
        ++p;
    }

    return maxIndex;
}

} // namespace WebCore

SPECIALIZE_TYPE_TRAITS_CANVASRENDERINGCONTEXT(WebCore::WebGLRenderingContextBase, isWebGL())

#endif