path: root/dom/canvas/WebGLContextState.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "WebGLContext.h"

#include "GLContext.h"
#include "GLScreenBuffer.h"
#include "mozilla/dom/ToJSValue.h"
#include "mozilla/Preferences.h"
#include "nsString.h"
#include "WebGLBuffer.h"
#include "WebGLContextUtils.h"
#include "WebGLFramebuffer.h"
#include "WebGLProgram.h"
#include "WebGLRenderbuffer.h"
#include "WebGLShader.h"
#include "WebGLTexture.h"
#include "WebGLVertexArray.h"

namespace mozilla {

void
WebGLContext::Disable(GLenum cap)
{
    if (IsContextLost())
        return;

    if (!ValidateCapabilityEnum(cap, "disable"))
        return;

    realGLboolean* trackingSlot = GetStateTrackingSlot(cap);

    if (trackingSlot)
    {
        *trackingSlot = 0;
    }

    MakeContextCurrent();
    gl->fDisable(cap);
}

void
WebGLContext::Enable(GLenum cap)
{
    if (IsContextLost())
        return;

    if (!ValidateCapabilityEnum(cap, "enable"))
        return;

    realGLboolean* trackingSlot = GetStateTrackingSlot(cap);

    if (trackingSlot)
    {
        *trackingSlot = 1;
    }

    MakeContextCurrent();
    gl->fEnable(cap);
}

static JS::Value
StringValue(JSContext* cx, const nsAString& str, ErrorResult& rv)
{
    JSString* jsStr = JS_NewUCStringCopyN(cx, str.BeginReading(), str.Length());
    if (!jsStr) {
        rv.Throw(NS_ERROR_OUT_OF_MEMORY);
        return JS::NullValue();
    }

    return JS::StringValue(jsStr);
}

bool
WebGLContext::GetStencilBits(GLint* const out_stencilBits)
{
    *out_stencilBits = 0;
    if (mBoundDrawFramebuffer) {
        if (mBoundDrawFramebuffer->StencilAttachment().IsDefined() &&
            mBoundDrawFramebuffer->DepthStencilAttachment().IsDefined())
        {
            // Error, we don't know which stencil buffer's bits to use
            ErrorInvalidFramebufferOperation("getParameter: framebuffer has two stencil buffers bound");
            return false;
        }

        if (mBoundDrawFramebuffer->StencilAttachment().IsDefined() ||
            mBoundDrawFramebuffer->DepthStencilAttachment().IsDefined())
        {
            *out_stencilBits = 8;
        }
    } else if (mOptions.stencil) {
        *out_stencilBits = 8;
    }

    return true;
}

bool
WebGLContext::GetChannelBits(const char* funcName, GLenum pname, GLint* const out_val)
{
    if (mBoundDrawFramebuffer) {
        if (!mBoundDrawFramebuffer->ValidateAndInitAttachments(funcName))
            return false;
    }

    if (!mBoundDrawFramebuffer) {
        switch (pname) {
        case LOCAL_GL_RED_BITS:
        case LOCAL_GL_GREEN_BITS:
        case LOCAL_GL_BLUE_BITS:
            *out_val = 8;
            break;

        case LOCAL_GL_ALPHA_BITS:
            *out_val = (mOptions.alpha ? 8 : 0);
            break;

        case LOCAL_GL_DEPTH_BITS:
            if (mOptions.depth) {
                *out_val = gl->Screen()->DepthBits();
            } else {
                *out_val = 0;
            }
            break;

        case LOCAL_GL_STENCIL_BITS:
            *out_val = (mOptions.stencil ? 8 : 0);
            break;

        default:
            MOZ_CRASH("GFX: bad pname");
        }
        return true;
    }

    if (!gl->IsCoreProfile()) {
        gl->fGetIntegerv(pname, out_val);
        return true;
    }

    GLenum fbAttachment = 0;
    GLenum fbPName = 0;
    switch (pname) {
    case LOCAL_GL_RED_BITS:
        fbAttachment = LOCAL_GL_COLOR_ATTACHMENT0;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_RED_SIZE;
        break;

    case LOCAL_GL_GREEN_BITS:
        fbAttachment = LOCAL_GL_COLOR_ATTACHMENT0;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_GREEN_SIZE;
        break;

    case LOCAL_GL_BLUE_BITS:
        fbAttachment = LOCAL_GL_COLOR_ATTACHMENT0;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_BLUE_SIZE;
        break;

    case LOCAL_GL_ALPHA_BITS:
        fbAttachment = LOCAL_GL_COLOR_ATTACHMENT0;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_ALPHA_SIZE;
        break;

    case LOCAL_GL_DEPTH_BITS:
        fbAttachment = LOCAL_GL_DEPTH_ATTACHMENT;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_DEPTH_SIZE;
        break;

    case LOCAL_GL_STENCIL_BITS:
        fbAttachment = LOCAL_GL_STENCIL_ATTACHMENT;
        fbPName = LOCAL_GL_FRAMEBUFFER_ATTACHMENT_STENCIL_SIZE;
        break;

    default:
        MOZ_CRASH("GFX: bad pname");
    }

    gl->fGetFramebufferAttachmentParameteriv(LOCAL_GL_DRAW_FRAMEBUFFER, fbAttachment,
                                             fbPName, out_val);
    return true;
}

JS::Value
WebGLContext::GetParameter(JSContext* cx, GLenum pname, ErrorResult& rv)
{
    const char funcName[] = "getParameter";

    if (IsContextLost())
        return JS::NullValue();

    MakeContextCurrent();

    if (MinCapabilityMode()) {
        switch(pname) {
            ////////////////////////////
            // Single-value params

            // int
            case LOCAL_GL_MAX_VERTEX_ATTRIBS:
                return JS::Int32Value(MINVALUE_GL_MAX_VERTEX_ATTRIBS);

            case LOCAL_GL_MAX_FRAGMENT_UNIFORM_VECTORS:
                return JS::Int32Value(MINVALUE_GL_MAX_FRAGMENT_UNIFORM_VECTORS);

            case LOCAL_GL_MAX_VERTEX_UNIFORM_VECTORS:
                return JS::Int32Value(MINVALUE_GL_MAX_VERTEX_UNIFORM_VECTORS);

            case LOCAL_GL_MAX_VARYING_VECTORS:
                return JS::Int32Value(MINVALUE_GL_MAX_VARYING_VECTORS);

            case LOCAL_GL_MAX_TEXTURE_SIZE:
                return JS::Int32Value(MINVALUE_GL_MAX_TEXTURE_SIZE);

            case LOCAL_GL_MAX_CUBE_MAP_TEXTURE_SIZE:
                return JS::Int32Value(MINVALUE_GL_MAX_CUBE_MAP_TEXTURE_SIZE);

            case LOCAL_GL_MAX_TEXTURE_IMAGE_UNITS:
                return JS::Int32Value(MINVALUE_GL_MAX_TEXTURE_IMAGE_UNITS);

            case LOCAL_GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS:
                return JS::Int32Value(MINVALUE_GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS);

            case LOCAL_GL_MAX_RENDERBUFFER_SIZE:
                return JS::Int32Value(MINVALUE_GL_MAX_RENDERBUFFER_SIZE);

            default:
                // Return the real value; we're not overriding this one
                break;
        }
    }

    if (IsWebGL2() || IsExtensionEnabled(WebGLExtensionID::WEBGL_draw_buffers)) {
        if (pname == LOCAL_GL_MAX_COLOR_ATTACHMENTS) {
            return JS::Int32Value(mImplMaxColorAttachments);

        } else if (pname == LOCAL_GL_MAX_DRAW_BUFFERS) {
            return JS::Int32Value(mImplMaxDrawBuffers);

        } else if (pname >= LOCAL_GL_DRAW_BUFFER0 &&
                   pname < GLenum(LOCAL_GL_DRAW_BUFFER0 + mImplMaxDrawBuffers))
        {
            GLint ret = LOCAL_GL_NONE;
            if (!mBoundDrawFramebuffer) {
                if (pname == LOCAL_GL_DRAW_BUFFER0) {
                    ret = gl->Screen()->GetDrawBufferMode();
                }
            } else {
                gl->fGetIntegerv(pname, &ret);
            }
            return JS::Int32Value(ret);
        }
    }

    if (IsWebGL2() || IsExtensionEnabled(WebGLExtensionID::OES_vertex_array_object)) {
        if (pname == LOCAL_GL_VERTEX_ARRAY_BINDING) {
            WebGLVertexArray* vao =
                (mBoundVertexArray != mDefaultVertexArray) ? mBoundVertexArray.get() : nullptr;
            return WebGLObjectAsJSValue(cx, vao, rv);
        }
    }

    if (IsExtensionEnabled(WebGLExtensionID::EXT_disjoint_timer_query)) {
        switch (pname) {
        case LOCAL_GL_TIMESTAMP_EXT:
            {
                uint64_t val = 0;
                if (Has64BitTimestamps()) {
                    gl->fGetInteger64v(pname, (GLint64*)&val);
                } else {
                    gl->fGetIntegerv(pname, (GLint*)&val);
                }
                // TODO: JS doesn't support 64-bit integers. Be lossy and
                // cast to double (53 bits)
                return JS::NumberValue(val);
            }

        case LOCAL_GL_GPU_DISJOINT_EXT:
            {
                realGLboolean val = false; // Not disjoint by default.
                if (gl->IsExtensionSupported(gl::GLContext::EXT_disjoint_timer_query)) {
                    gl->fGetBooleanv(pname, &val);
                }
                return JS::BooleanValue(val);
            }

        default:
            break;
        }
    }

    // Privileged string params exposed by WEBGL_debug_renderer_info.
    // The privilege check is done in WebGLContext::IsExtensionSupported.
    // So here we just have to check that the extension is enabled.
    if (IsExtensionEnabled(WebGLExtensionID::WEBGL_debug_renderer_info)) {
        switch (pname) {
        case UNMASKED_VENDOR_WEBGL:
        case UNMASKED_RENDERER_WEBGL:
            {
                const char* overridePref = nullptr;
                GLenum driverEnum = LOCAL_GL_NONE;

                switch (pname) {
                case UNMASKED_RENDERER_WEBGL:
                    overridePref = "webgl.renderer-string-override";
                    driverEnum = LOCAL_GL_RENDERER;
                    break;
                case UNMASKED_VENDOR_WEBGL:
                    overridePref = "webgl.vendor-string-override";
                    driverEnum = LOCAL_GL_VENDOR;
                    break;
                default:
                    MOZ_CRASH("GFX: bad `pname`");
                }

                bool hasRetVal = false;

                nsAutoString ret;
                if (overridePref) {
                    nsresult res = Preferences::GetString(overridePref, &ret);
                    if (NS_SUCCEEDED(res) && ret.Length() > 0)
                        hasRetVal = true;
                }

                if (!hasRetVal) {
                    const char* chars = reinterpret_cast<const char*>(gl->fGetString(driverEnum));
                    ret = NS_ConvertASCIItoUTF16(chars);
                    hasRetVal = true;
                }

                return StringValue(cx, ret, rv);
            }
        }
    }

    if (IsWebGL2() || IsExtensionEnabled(WebGLExtensionID::OES_standard_derivatives)) {
        if (pname == LOCAL_GL_FRAGMENT_SHADER_DERIVATIVE_HINT) {
            GLint i = 0;
            gl->fGetIntegerv(pname, &i);
            return JS::Int32Value(i);
        }
    }

    if (IsExtensionEnabled(WebGLExtensionID::EXT_texture_filter_anisotropic)) {
        if (pname == LOCAL_GL_MAX_TEXTURE_MAX_ANISOTROPY_EXT) {
            GLfloat f = 0.f;
            gl->fGetFloatv(pname, &f);
            return JS::NumberValue(f);
        }
    }

    switch (pname) {
        //
        // String params
        //
        case LOCAL_GL_VENDOR:
        case LOCAL_GL_RENDERER:
            return StringValue(cx, "Mozilla", rv);
        case LOCAL_GL_VERSION:
            return StringValue(cx, "WebGL 1.0", rv);
        case LOCAL_GL_SHADING_LANGUAGE_VERSION:
            return StringValue(cx, "WebGL GLSL ES 1.0", rv);

        ////////////////////////////////
        // Single-value params

        // unsigned int
        case LOCAL_GL_CULL_FACE_MODE:
        case LOCAL_GL_FRONT_FACE:
        case LOCAL_GL_ACTIVE_TEXTURE:
        case LOCAL_GL_STENCIL_FUNC:
        case LOCAL_GL_STENCIL_FAIL:
        case LOCAL_GL_STENCIL_PASS_DEPTH_FAIL:
        case LOCAL_GL_STENCIL_PASS_DEPTH_PASS:
        case LOCAL_GL_STENCIL_BACK_FUNC:
        case LOCAL_GL_STENCIL_BACK_FAIL:
        case LOCAL_GL_STENCIL_BACK_PASS_DEPTH_FAIL:
        case LOCAL_GL_STENCIL_BACK_PASS_DEPTH_PASS:
        case LOCAL_GL_DEPTH_FUNC:
        case LOCAL_GL_BLEND_SRC_RGB:
        case LOCAL_GL_BLEND_SRC_ALPHA:
        case LOCAL_GL_BLEND_DST_RGB:
        case LOCAL_GL_BLEND_DST_ALPHA:
        case LOCAL_GL_BLEND_EQUATION_RGB:
        case LOCAL_GL_BLEND_EQUATION_ALPHA: {
            GLint i = 0;
            gl->fGetIntegerv(pname, &i);
            return JS::NumberValue(uint32_t(i));
        }

        case LOCAL_GL_GENERATE_MIPMAP_HINT:
            return JS::NumberValue(mGenerateMipmapHint);

        case LOCAL_GL_IMPLEMENTATION_COLOR_READ_FORMAT:
        case LOCAL_GL_IMPLEMENTATION_COLOR_READ_TYPE: {
            const webgl::FormatUsageInfo* usage;
            uint32_t width, height;
            if (!ValidateCurFBForRead(funcName, &usage, &width, &height))
                return JS::NullValue();

            const auto implPI = ValidImplementationColorReadPI(usage);

            GLenum ret;
            if (pname == LOCAL_GL_IMPLEMENTATION_COLOR_READ_FORMAT) {
                ret = implPI.format;
            } else {
                ret = implPI.type;
            }
            return JS::NumberValue(uint32_t(ret));
        }

        // int
        case LOCAL_GL_STENCIL_REF:
        case LOCAL_GL_STENCIL_BACK_REF: {
            GLint stencilBits = 0;
            if (!GetStencilBits(&stencilBits))
                return JS::NullValue();

            // Assuming stencils have 8 bits
            const GLint stencilMask = (1 << stencilBits) - 1;

            GLint refValue = 0;
            gl->fGetIntegerv(pname, &refValue);

            return JS::Int32Value(refValue & stencilMask);
        }

        case LOCAL_GL_STENCIL_CLEAR_VALUE:
        case LOCAL_GL_UNPACK_ALIGNMENT:
        case LOCAL_GL_PACK_ALIGNMENT:
        case LOCAL_GL_SUBPIXEL_BITS:
        case LOCAL_GL_SAMPLE_BUFFERS:
        case LOCAL_GL_SAMPLES:
        case LOCAL_GL_MAX_VERTEX_ATTRIBS:
        case LOCAL_GL_MAX_COMBINED_TEXTURE_IMAGE_UNITS:
        case LOCAL_GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS:
        case LOCAL_GL_MAX_TEXTURE_IMAGE_UNITS: {
            GLint i = 0;
            gl->fGetIntegerv(pname, &i);
            return JS::Int32Value(i);
        }

        case LOCAL_GL_RED_BITS:
        case LOCAL_GL_GREEN_BITS:
        case LOCAL_GL_BLUE_BITS:
        case LOCAL_GL_ALPHA_BITS:
        case LOCAL_GL_DEPTH_BITS:
        case LOCAL_GL_STENCIL_BITS: {
            // Deprecated and removed in GL Core profiles, so special handling required.
            GLint val;
            if (!GetChannelBits(funcName, pname, &val))
                return JS::NullValue();

            return JS::Int32Value(val);
        }

        case LOCAL_GL_MAX_TEXTURE_SIZE:
            return JS::Int32Value(mImplMaxTextureSize);

        case LOCAL_GL_MAX_CUBE_MAP_TEXTURE_SIZE:
            return JS::Int32Value(mImplMaxCubeMapTextureSize);

        case LOCAL_GL_MAX_RENDERBUFFER_SIZE:
            return JS::Int32Value(mImplMaxRenderbufferSize);

        case LOCAL_GL_MAX_VERTEX_UNIFORM_VECTORS:
            return JS::Int32Value(mGLMaxVertexUniformVectors);

        case LOCAL_GL_MAX_FRAGMENT_UNIFORM_VECTORS:
            return JS::Int32Value(mGLMaxFragmentUniformVectors);

        case LOCAL_GL_MAX_VARYING_VECTORS:
            return JS::Int32Value(mGLMaxVaryingVectors);

        case LOCAL_GL_COMPRESSED_TEXTURE_FORMATS: {
            uint32_t length = mCompressedTextureFormats.Length();
            JSObject* obj = dom::Uint32Array::Create(cx, this, length,
                                                     mCompressedTextureFormats.Elements());
            if (!obj) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return JS::ObjectOrNullValue(obj);
        }

        // unsigned int. here we may have to return very large values like 2^32-1 that can't be represented as
        // javascript integer values. We just return them as doubles and javascript doesn't care.
        case LOCAL_GL_STENCIL_BACK_VALUE_MASK:
            return JS::DoubleValue(mStencilValueMaskBack); // pass as FP value to allow large values such as 2^32-1.

        case LOCAL_GL_STENCIL_BACK_WRITEMASK:
            return JS::DoubleValue(mStencilWriteMaskBack);

        case LOCAL_GL_STENCIL_VALUE_MASK:
            return JS::DoubleValue(mStencilValueMaskFront);

        case LOCAL_GL_STENCIL_WRITEMASK:
            return JS::DoubleValue(mStencilWriteMaskFront);

        // float
        case LOCAL_GL_LINE_WIDTH:
            return JS::DoubleValue(mLineWidth);

        case LOCAL_GL_DEPTH_CLEAR_VALUE:
        case LOCAL_GL_POLYGON_OFFSET_FACTOR:
        case LOCAL_GL_POLYGON_OFFSET_UNITS:
        case LOCAL_GL_SAMPLE_COVERAGE_VALUE: {
            GLfloat f = 0.f;
            gl->fGetFloatv(pname, &f);
            return JS::DoubleValue(f);
        }

        // bool
        case LOCAL_GL_BLEND:
        case LOCAL_GL_DEPTH_TEST:
        case LOCAL_GL_STENCIL_TEST:
        case LOCAL_GL_CULL_FACE:
        case LOCAL_GL_DITHER:
        case LOCAL_GL_POLYGON_OFFSET_FILL:
        case LOCAL_GL_SCISSOR_TEST:
        case LOCAL_GL_SAMPLE_COVERAGE_INVERT:
        case LOCAL_GL_DEPTH_WRITEMASK: {
            realGLboolean b = 0;
            gl->fGetBooleanv(pname, &b);
            return JS::BooleanValue(bool(b));
        }

        // bool, WebGL-specific
        case UNPACK_FLIP_Y_WEBGL:
            return JS::BooleanValue(mPixelStore_FlipY);
        case UNPACK_PREMULTIPLY_ALPHA_WEBGL:
            return JS::BooleanValue(mPixelStore_PremultiplyAlpha);

        // uint, WebGL-specific
        case UNPACK_COLORSPACE_CONVERSION_WEBGL:
            return JS::NumberValue(uint32_t(mPixelStore_ColorspaceConversion));

        ////////////////////////////////
        // Complex values

        // 2 floats
        case LOCAL_GL_DEPTH_RANGE:
        case LOCAL_GL_ALIASED_POINT_SIZE_RANGE:
        case LOCAL_GL_ALIASED_LINE_WIDTH_RANGE: {
            GLenum driverPName = pname;
            if (gl->IsCoreProfile() &&
                driverPName == LOCAL_GL_ALIASED_POINT_SIZE_RANGE)
            {
                driverPName = LOCAL_GL_POINT_SIZE_RANGE;
            }

            GLfloat fv[2] = { 0 };
            gl->fGetFloatv(driverPName, fv);
            JSObject* obj = dom::Float32Array::Create(cx, this, 2, fv);
            if (!obj) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return JS::ObjectOrNullValue(obj);
        }

        // 4 floats
        case LOCAL_GL_COLOR_CLEAR_VALUE:
        case LOCAL_GL_BLEND_COLOR: {
            GLfloat fv[4] = { 0 };
            gl->fGetFloatv(pname, fv);
            JSObject* obj = dom::Float32Array::Create(cx, this, 4, fv);
            if (!obj) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return JS::ObjectOrNullValue(obj);
        }

        // 2 ints
        case LOCAL_GL_MAX_VIEWPORT_DIMS: {
            GLint iv[2] = { 0 };
            gl->fGetIntegerv(pname, iv);
            JSObject* obj = dom::Int32Array::Create(cx, this, 2, iv);
            if (!obj) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return JS::ObjectOrNullValue(obj);
        }

        // 4 ints
        case LOCAL_GL_SCISSOR_BOX:
        case LOCAL_GL_VIEWPORT: {
            GLint iv[4] = { 0 };
            gl->fGetIntegerv(pname, iv);
            JSObject* obj = dom::Int32Array::Create(cx, this, 4, iv);
            if (!obj) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return JS::ObjectOrNullValue(obj);
        }

        // 4 bools
        case LOCAL_GL_COLOR_WRITEMASK: {
            realGLboolean gl_bv[4] = { 0 };
            gl->fGetBooleanv(pname, gl_bv);
            bool vals[4] = { bool(gl_bv[0]), bool(gl_bv[1]),
                             bool(gl_bv[2]), bool(gl_bv[3]) };
            JS::Rooted<JS::Value> arr(cx);
            if (!dom::ToJSValue(cx, vals, &arr)) {
                rv = NS_ERROR_OUT_OF_MEMORY;
            }
            return arr;
        }

        case LOCAL_GL_ARRAY_BUFFER_BINDING: {
            return WebGLObjectAsJSValue(cx, mBoundArrayBuffer.get(), rv);
        }

        case LOCAL_GL_ELEMENT_ARRAY_BUFFER_BINDING: {
            return WebGLObjectAsJSValue(cx, mBoundVertexArray->mElementArrayBuffer.get(), rv);
        }

        case LOCAL_GL_RENDERBUFFER_BINDING: {
            return WebGLObjectAsJSValue(cx, mBoundRenderbuffer.get(), rv);
        }

        // DRAW_FRAMEBUFFER_BINDING is the same as FRAMEBUFFER_BINDING.
        case LOCAL_GL_FRAMEBUFFER_BINDING: {
            return WebGLObjectAsJSValue(cx, mBoundDrawFramebuffer.get(), rv);
        }

        case LOCAL_GL_CURRENT_PROGRAM: {
            return WebGLObjectAsJSValue(cx, mCurrentProgram.get(), rv);
        }

        case LOCAL_GL_TEXTURE_BINDING_2D: {
            return WebGLObjectAsJSValue(cx, mBound2DTextures[mActiveTexture].get(), rv);
        }

        case LOCAL_GL_TEXTURE_BINDING_CUBE_MAP: {
            return WebGLObjectAsJSValue(cx, mBoundCubeMapTextures[mActiveTexture].get(), rv);
        }

        default:
            break;
    }

    ErrorInvalidEnumInfo("getParameter: parameter", pname);
    return JS::NullValue();
}

void
WebGLContext::GetParameterIndexed(JSContext* cx, GLenum pname, GLuint index,
                                  JS::MutableHandle<JS::Value> retval)
{
    if (IsContextLost()) {
        retval.setNull();
        return;
    }

    MakeContextCurrent();

    switch (pname) {
        case LOCAL_GL_TRANSFORM_FEEDBACK_BUFFER_BINDING:
        {
            if (index >= mGLMaxTransformFeedbackSeparateAttribs) {
                ErrorInvalidValue("getParameterIndexed: index should be less than MAX_TRANSFORM_FEEDBACK_SEPARATE_ATTRIBS", index);
                retval.setNull();
                return;
            }
            retval.setNull(); // See bug 903594
            return;
        }

        default:
            break;
    }

    ErrorInvalidEnumInfo("getParameterIndexed: parameter", pname);
    retval.setNull();
}

bool
WebGLContext::IsEnabled(GLenum cap)
{
    if (IsContextLost())
        return false;

    if (!ValidateCapabilityEnum(cap, "isEnabled"))
        return false;

    MakeContextCurrent();
    return gl->fIsEnabled(cap);
}

bool
WebGLContext::ValidateCapabilityEnum(GLenum cap, const char* info)
{
    switch (cap) {
        case LOCAL_GL_BLEND:
        case LOCAL_GL_CULL_FACE:
        case LOCAL_GL_DEPTH_TEST:
        case LOCAL_GL_DITHER:
        case LOCAL_GL_POLYGON_OFFSET_FILL:
        case LOCAL_GL_SAMPLE_ALPHA_TO_COVERAGE:
        case LOCAL_GL_SAMPLE_COVERAGE:
        case LOCAL_GL_SCISSOR_TEST:
        case LOCAL_GL_STENCIL_TEST:
            return true;
        case LOCAL_GL_RASTERIZER_DISCARD:
            return IsWebGL2();
        default:
            ErrorInvalidEnumInfo(info, cap);
            return false;
    }
}

realGLboolean*
WebGLContext::GetStateTrackingSlot(GLenum cap)
{
    switch (cap) {
        case LOCAL_GL_DEPTH_TEST:
            return &mDepthTestEnabled;
        case LOCAL_GL_DITHER:
            return &mDitherEnabled;
        case LOCAL_GL_RASTERIZER_DISCARD:
            return &mRasterizerDiscardEnabled;
        case LOCAL_GL_SCISSOR_TEST:
            return &mScissorTestEnabled;
        case LOCAL_GL_STENCIL_TEST:
            return &mStencilTestEnabled;
    }

    return nullptr;
}

} // namespace mozilla