Add m-esr52 at 52.6.0

1 files changed, 1256 insertions, 0 deletions

diff --git a/dom/canvas/WebGLContextDraw.cpp b/dom/canvas/WebGLContextDraw.cpp
new file mode 100644
index 000000000..66fca7689
--- /dev/null
+++ b/dom/canvas/WebGLContextDraw.cpp
@@ -0,0 +1,1256 @@
+/* -*- 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 "mozilla/CheckedInt.h"
+#include "mozilla/UniquePtrExtensions.h"
+#include "nsPrintfCString.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"
+#include "WebGLVertexAttribData.h"
+
+#include <algorithm>
+
+namespace mozilla {
+
+// For a Tegra workaround.
+static const int MAX_DRAW_CALLS_SINCE_FLUSH = 100;
+
+////////////////////////////////////////
+
+class ScopedResolveTexturesForDraw
+{
+    struct TexRebindRequest
+    {
+        uint32_t texUnit;
+        WebGLTexture* tex;
+    };
+
+    WebGLContext* const mWebGL;
+    std::vector<TexRebindRequest> mRebindRequests;
+
+public:
+    ScopedResolveTexturesForDraw(WebGLContext* webgl, const char* funcName,
+                                 bool* const out_error);
+    ~ScopedResolveTexturesForDraw();
+};
+
+bool
+WebGLTexture::IsFeedback(WebGLContext* webgl, const char* funcName, uint32_t texUnit,
+                         const std::vector<const WebGLFBAttachPoint*>& fbAttachments) const
+{
+    auto itr = fbAttachments.cbegin();
+    for (; itr != fbAttachments.cend(); ++itr) {
+        const auto& attach = *itr;
+        if (attach->Texture() == this)
+            break;
+    }
+
+    if (itr == fbAttachments.cend())
+        return false;
+
+    ////
+
+    const auto minLevel = mBaseMipmapLevel;
+    uint32_t maxLevel;
+    if (!MaxEffectiveMipmapLevel(texUnit, &maxLevel)) {
+        // No valid mips. Will need fake-black.
+        return false;
+    }
+
+    ////
+
+    for (; itr != fbAttachments.cend(); ++itr) {
+        const auto& attach = *itr;
+        if (attach->Texture() != this)
+            continue;
+
+        const auto dstLevel = attach->MipLevel();
+
+        if (minLevel <= dstLevel && dstLevel <= maxLevel) {
+            webgl->ErrorInvalidOperation("%s: Feedback loop detected between tex target"
+                                         " 0x%04x, tex unit %u, levels %u-%u; and"
+                                         " framebuffer attachment 0x%04x, level %u.",
+                                         funcName, mTarget.get(), texUnit, minLevel,
+                                         maxLevel, attach->mAttachmentPoint, dstLevel);
+            return true;
+        }
+    }
+
+    return false;
+}
+
+ScopedResolveTexturesForDraw::ScopedResolveTexturesForDraw(WebGLContext* webgl,
+                                                           const char* funcName,
+                                                           bool* const out_error)
+    : mWebGL(webgl)
+{
+    MOZ_ASSERT(mWebGL->gl->IsCurrent());
+
+    if (!mWebGL->mActiveProgramLinkInfo) {
+        mWebGL->ErrorInvalidOperation("%s: The current program is not linked.", funcName);
+        *out_error = true;
+        return;
+    }
+
+    const std::vector<const WebGLFBAttachPoint*>* attachList = nullptr;
+    const auto& fb = mWebGL->mBoundDrawFramebuffer;
+    if (fb) {
+        if (!fb->ValidateAndInitAttachments(funcName)) {
+            *out_error = true;
+            return;
+        }
+
+        attachList = &(fb->ResolvedCompleteData()->texDrawBuffers);
+    } else {
+        webgl->ClearBackbufferIfNeeded();
+    }
+
+    MOZ_ASSERT(mWebGL->mActiveProgramLinkInfo);
+    const auto& uniformSamplers = mWebGL->mActiveProgramLinkInfo->uniformSamplers;
+    for (const auto& uniform : uniformSamplers) {
+        const auto& texList = *(uniform->mSamplerTexList);
+
+        for (const auto& texUnit : uniform->mSamplerValues) {
+            if (texUnit >= texList.Length())
+                continue;
+
+            const auto& tex = texList[texUnit];
+            if (!tex)
+                continue;
+
+            if (attachList &&
+                tex->IsFeedback(mWebGL, funcName, texUnit, *attachList))
+            {
+                *out_error = true;
+                return;
+            }
+
+            FakeBlackType fakeBlack;
+            if (!tex->ResolveForDraw(funcName, texUnit, &fakeBlack)) {
+                mWebGL->ErrorOutOfMemory("%s: Failed to resolve textures for draw.",
+                                         funcName);
+                *out_error = true;
+                return;
+            }
+
+            if (fakeBlack == FakeBlackType::None)
+                continue;
+
+            if (!mWebGL->BindFakeBlack(texUnit, tex->Target(), fakeBlack)) {
+                mWebGL->ErrorOutOfMemory("%s: Failed to create fake black texture.",
+                                         funcName);
+                *out_error = true;
+                return;
+            }
+
+            mRebindRequests.push_back({texUnit, tex});
+        }
+    }
+
+    *out_error = false;
+}
+
+ScopedResolveTexturesForDraw::~ScopedResolveTexturesForDraw()
+{
+    if (!mRebindRequests.size())
+        return;
+
+    gl::GLContext* gl = mWebGL->gl;
+
+    for (const auto& itr : mRebindRequests) {
+        gl->fActiveTexture(LOCAL_GL_TEXTURE0 + itr.texUnit);
+        gl->fBindTexture(itr.tex->Target().get(), itr.tex->mGLName);
+    }
+
+    gl->fActiveTexture(LOCAL_GL_TEXTURE0 + mWebGL->mActiveTexture);
+}
+
+bool
+WebGLContext::BindFakeBlack(uint32_t texUnit, TexTarget target, FakeBlackType fakeBlack)
+{
+    MOZ_ASSERT(fakeBlack == FakeBlackType::RGBA0000 ||
+               fakeBlack == FakeBlackType::RGBA0001);
+
+    const auto fnGetSlot = [this, target, fakeBlack]() -> UniquePtr<FakeBlackTexture>*
+    {
+        switch (fakeBlack) {
+        case FakeBlackType::RGBA0000:
+            switch (target.get()) {
+            case LOCAL_GL_TEXTURE_2D      : return &mFakeBlack_2D_0000;
+            case LOCAL_GL_TEXTURE_CUBE_MAP: return &mFakeBlack_CubeMap_0000;
+            case LOCAL_GL_TEXTURE_3D      : return &mFakeBlack_3D_0000;
+            case LOCAL_GL_TEXTURE_2D_ARRAY: return &mFakeBlack_2D_Array_0000;
+            default: return nullptr;
+            }
+
+        case FakeBlackType::RGBA0001:
+            switch (target.get()) {
+            case LOCAL_GL_TEXTURE_2D      : return &mFakeBlack_2D_0001;
+            case LOCAL_GL_TEXTURE_CUBE_MAP: return &mFakeBlack_CubeMap_0001;
+            case LOCAL_GL_TEXTURE_3D      : return &mFakeBlack_3D_0001;
+            case LOCAL_GL_TEXTURE_2D_ARRAY: return &mFakeBlack_2D_Array_0001;
+            default: return nullptr;
+            }
+
+        default:
+            return nullptr;
+        }
+    };
+
+    UniquePtr<FakeBlackTexture>* slot = fnGetSlot();
+    if (!slot) {
+        MOZ_CRASH("GFX: fnGetSlot failed.");
+    }
+    UniquePtr<FakeBlackTexture>& fakeBlackTex = *slot;
+
+    if (!fakeBlackTex) {
+        fakeBlackTex = FakeBlackTexture::Create(gl, target, fakeBlack);
+        if (!fakeBlackTex) {
+            return false;
+        }
+    }
+
+    gl->fActiveTexture(LOCAL_GL_TEXTURE0 + texUnit);
+    gl->fBindTexture(target.get(), fakeBlackTex->mGLName);
+    gl->fActiveTexture(LOCAL_GL_TEXTURE0 + mActiveTexture);
+    return true;
+}
+
+////////////////////////////////////////
+
+bool
+WebGLContext::DrawInstanced_check(const char* info)
+{
+    MOZ_ASSERT(IsWebGL2() ||
+               IsExtensionEnabled(WebGLExtensionID::ANGLE_instanced_arrays));
+    if (!mBufferFetchingHasPerVertex) {
+        /* http://www.khronos.org/registry/gles/extensions/ANGLE/ANGLE_instanced_arrays.txt
+         *  If all of the enabled vertex attribute arrays that are bound to active
+         *  generic attributes in the program have a non-zero divisor, the draw
+         *  call should return INVALID_OPERATION.
+         *
+         * NB: This also appears to apply to NV_instanced_arrays, though the
+         * INVALID_OPERATION emission is not explicitly stated.
+         * ARB_instanced_arrays does not have this restriction.
+         */
+        ErrorInvalidOperation("%s: at least one vertex attribute divisor should be 0", info);
+        return false;
+    }
+
+    return true;
+}
+
+bool
+WebGLContext::DrawArrays_check(const char* funcName, GLenum mode, GLint first,
+                               GLsizei vertCount, GLsizei instanceCount)
+{
+    if (!ValidateDrawModeEnum(mode, funcName))
+        return false;
+
+    if (!ValidateNonNegative(funcName, "first", first) ||
+        !ValidateNonNegative(funcName, "vertCount", vertCount) ||
+        !ValidateNonNegative(funcName, "instanceCount", instanceCount))
+    {
+        return false;
+    }
+
+    if (!ValidateStencilParamsForDrawCall())
+        return false;
+
+    if (IsWebGL2() && !gl->IsSupported(gl::GLFeature::prim_restart_fixed)) {
+        MOZ_ASSERT(gl->IsSupported(gl::GLFeature::prim_restart));
+        if (mPrimRestartTypeBytes != 0) {
+            mPrimRestartTypeBytes = 0;
+
+            // OSX appears to have severe perf issues with leaving this enabled.
+            gl->fDisable(LOCAL_GL_PRIMITIVE_RESTART);
+        }
+    }
+
+    if (!vertCount || !instanceCount)
+        return false; // No error, just early out.
+
+    if (!ValidateBufferFetching(funcName))
+        return false;
+
+    const auto checked_firstPlusCount = CheckedInt<GLsizei>(first) + vertCount;
+    if (!checked_firstPlusCount.isValid()) {
+        ErrorInvalidOperation("%s: overflow in first+vertCount", funcName);
+        return false;
+    }
+
+    if (uint32_t(checked_firstPlusCount.value()) > mMaxFetchedVertices) {
+        ErrorInvalidOperation("%s: Bound vertex attribute buffers do not have sufficient"
+                              " size for given first and count.",
+                              funcName);
+        return false;
+    }
+
+    return true;
+}
+
+////////////////////////////////////////
+
+template<typename T>
+static bool
+DoSetsIntersect(const std::set<T>& a, const std::set<T>& b)
+{
+    std::vector<T> intersection;
+    std::set_intersection(a.begin(), a.end(), b.begin(), b.end(),
+                          std::back_inserter(intersection));
+    return bool(intersection.size());
+}
+
+class ScopedDrawHelper final
+{
+    WebGLContext* const mWebGL;
+    bool mDidFake;
+
+public:
+    ScopedDrawHelper(WebGLContext* webgl, const char* funcName, uint32_t firstVertex,
+                     uint32_t vertCount, uint32_t instanceCount, bool* const out_error)
+        : mWebGL(webgl)
+        , mDidFake(false)
+    {
+        if (instanceCount > mWebGL->mMaxFetchedInstances) {
+            mWebGL->ErrorInvalidOperation("%s: Bound instance attribute buffers do not"
+                                          " have sufficient size for given"
+                                          " `instanceCount`.",
+                                          funcName);
+            *out_error = true;
+            return;
+        }
+
+        MOZ_ASSERT(mWebGL->gl->IsCurrent());
+
+        if (mWebGL->mBoundDrawFramebuffer) {
+            if (!mWebGL->mBoundDrawFramebuffer->ValidateAndInitAttachments(funcName)) {
+                *out_error = true;
+                return;
+            }
+        } else {
+            mWebGL->ClearBackbufferIfNeeded();
+        }
+
+        ////
+
+        const size_t requiredVerts = firstVertex + vertCount;
+        if (!mWebGL->DoFakeVertexAttrib0(funcName, requiredVerts)) {
+            *out_error = true;
+            return;
+        }
+        mDidFake = true;
+
+        ////
+        // Check UBO sizes.
+
+        const auto& linkInfo = mWebGL->mActiveProgramLinkInfo;
+
+        for (const auto& cur : linkInfo->uniformBlocks) {
+            const auto& dataSize = cur->mDataSize;
+            const auto& binding = cur->mBinding;
+            if (!binding) {
+                mWebGL->ErrorInvalidOperation("%s: Buffer for uniform block is null.",
+                                              funcName);
+                *out_error = true;
+                return;
+            }
+
+            const auto availByteCount = binding->ByteCount();
+            if (dataSize > availByteCount) {
+                mWebGL->ErrorInvalidOperation("%s: Buffer for uniform block is smaller"
+                                              " than UNIFORM_BLOCK_DATA_SIZE.",
+                                              funcName);
+                *out_error = true;
+                return;
+            }
+
+            if (binding->mBufferBinding->IsBoundForTF()) {
+                mWebGL->ErrorInvalidOperation("%s: Buffer for uniform block is bound or"
+                                              " in use for transform feedback.",
+                                              funcName);
+                *out_error = true;
+                return;
+            }
+        }
+
+        ////
+
+        const auto& tfo = mWebGL->mBoundTransformFeedback;
+        if (tfo && tfo->IsActiveAndNotPaused()) {
+            uint32_t numUsed;
+            switch (linkInfo->transformFeedbackBufferMode) {
+            case LOCAL_GL_INTERLEAVED_ATTRIBS:
+                numUsed = 1;
+                break;
+
+            case LOCAL_GL_SEPARATE_ATTRIBS:
+                numUsed = linkInfo->transformFeedbackVaryings.size();
+                break;
+
+            default:
+                MOZ_CRASH();
+            }
+
+            for (uint32_t i = 0; i < numUsed; ++i) {
+                const auto& buffer = tfo->mIndexedBindings[i].mBufferBinding;
+                if (buffer->IsBoundForNonTF()) {
+                    mWebGL->ErrorInvalidOperation("%s: Transform feedback varying %u's"
+                                                  " buffer is bound for"
+                                                  " non-transform-feedback.",
+                                                  funcName, i);
+                    *out_error = true;
+                    return;
+                }
+            }
+        }
+
+        ////
+
+        for (const auto& progAttrib : linkInfo->attribs) {
+            const auto& loc = progAttrib.mLoc;
+            if (loc == -1)
+                continue;
+
+            const auto& attribData = mWebGL->mBoundVertexArray->mAttribs[loc];
+
+            GLenum attribDataBaseType;
+            if (attribData.mEnabled) {
+                attribDataBaseType = attribData.BaseType();
+
+                if (attribData.mBuf->IsBoundForTF()) {
+                    mWebGL->ErrorInvalidOperation("%s: Vertex attrib %u's buffer is bound"
+                                                  " or in use for transform feedback.",
+                                                  funcName, loc);
+                    *out_error = true;
+                    return;
+                }
+            } else {
+                attribDataBaseType = mWebGL->mGenericVertexAttribTypes[loc];
+            }
+
+            if (attribDataBaseType != progAttrib.mBaseType) {
+                nsCString progType, dataType;
+                WebGLContext::EnumName(progAttrib.mBaseType, &progType);
+                WebGLContext::EnumName(attribDataBaseType, &dataType);
+                mWebGL->ErrorInvalidOperation("%s: Vertex attrib %u requires data of type"
+                                              " %s, but is being supplied with type %s.",
+                                              funcName, loc, progType.BeginReading(),
+                                              dataType.BeginReading());
+                *out_error = true;
+                return;
+            }
+        }
+
+        ////
+
+        mWebGL->RunContextLossTimer();
+    }
+
+    ~ScopedDrawHelper() {
+        if (mDidFake) {
+            mWebGL->UndoFakeVertexAttrib0();
+        }
+    }
+};
+
+////////////////////////////////////////
+
+static uint32_t
+UsedVertsForTFDraw(GLenum mode, uint32_t vertCount)
+{
+    uint8_t vertsPerPrim;
+
+    switch (mode) {
+    case LOCAL_GL_POINTS:
+        vertsPerPrim = 1;
+        break;
+    case LOCAL_GL_LINES:
+        vertsPerPrim = 2;
+        break;
+    case LOCAL_GL_TRIANGLES:
+        vertsPerPrim = 3;
+        break;
+    default:
+        MOZ_CRASH("`mode`");
+    }
+
+    return vertCount / vertsPerPrim * vertsPerPrim;
+}
+
+class ScopedDrawWithTransformFeedback final
+{
+    WebGLContext* const mWebGL;
+    WebGLTransformFeedback* const mTFO;
+    const bool mWithTF;
+    uint32_t mUsedVerts;
+
+public:
+    ScopedDrawWithTransformFeedback(WebGLContext* webgl, const char* funcName,
+                                    GLenum mode, uint32_t vertCount,
+                                    uint32_t instanceCount, bool* const out_error)
+        : mWebGL(webgl)
+        , mTFO(mWebGL->mBoundTransformFeedback)
+        , mWithTF(mTFO &&
+                  mTFO->mIsActive &&
+                  !mTFO->mIsPaused)
+        , mUsedVerts(0)
+    {
+        *out_error = false;
+        if (!mWithTF)
+            return;
+
+        if (mode != mTFO->mActive_PrimMode) {
+            mWebGL->ErrorInvalidOperation("%s: Drawing with transform feedback requires"
+                                          " `mode` to match BeginTransformFeedback's"
+                                          " `primitiveMode`.",
+                                          funcName);
+            *out_error = true;
+            return;
+        }
+
+        const auto usedVertsPerInstance = UsedVertsForTFDraw(mode, vertCount);
+        const auto usedVerts = CheckedInt<uint32_t>(usedVertsPerInstance) * instanceCount;
+
+        const auto remainingCapacity = mTFO->mActive_VertCapacity - mTFO->mActive_VertPosition;
+        if (!usedVerts.isValid() ||
+            usedVerts.value() > remainingCapacity)
+        {
+            mWebGL->ErrorInvalidOperation("%s: Insufficient buffer capacity remaining for"
+                                          " transform feedback.",
+                                          funcName);
+            *out_error = true;
+            return;
+        }
+
+        mUsedVerts = usedVerts.value();
+    }
+
+    void Advance() const {
+        if (!mWithTF)
+            return;
+
+        mTFO->mActive_VertPosition += mUsedVerts;
+    }
+};
+
+////////////////////////////////////////
+
+void
+WebGLContext::DrawArrays(GLenum mode, GLint first, GLsizei vertCount)
+{
+    const char funcName[] = "drawArrays";
+    if (IsContextLost())
+        return;
+
+    MakeContextCurrent();
+
+    bool error = false;
+    ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
+    if (error)
+        return;
+
+    const GLsizei instanceCount = 1;
+    if (!DrawArrays_check(funcName, mode, first, vertCount, instanceCount))
+        return;
+
+    const ScopedDrawHelper scopedHelper(this, funcName, first, vertCount, instanceCount, &error);
+    if (error)
+        return;
+
+    const ScopedDrawWithTransformFeedback scopedTF(this, funcName, mode, vertCount,
+                                                   instanceCount, &error);
+    if (error)
+        return;
+
+    {
+        ScopedDrawCallWrapper wrapper(*this);
+        gl->fDrawArrays(mode, first, vertCount);
+    }
+
+    Draw_cleanup(funcName);
+    scopedTF.Advance();
+}
+
+void
+WebGLContext::DrawArraysInstanced(GLenum mode, GLint first, GLsizei vertCount,
+                                  GLsizei instanceCount)
+{
+    const char funcName[] = "drawArraysInstanced";
+    if (IsContextLost())
+        return;
+
+    MakeContextCurrent();
+
+    bool error = false;
+    ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
+    if (error)
+        return;
+
+    if (!DrawArrays_check(funcName, mode, first, vertCount, instanceCount))
+        return;
+
+    if (!DrawInstanced_check(funcName))
+        return;
+
+    const ScopedDrawHelper scopedHelper(this, funcName, first, vertCount, instanceCount, &error);
+    if (error)
+        return;
+
+    const ScopedDrawWithTransformFeedback scopedTF(this, funcName, mode, vertCount,
+                                                   instanceCount, &error);
+    if (error)
+        return;
+
+    {
+        ScopedDrawCallWrapper wrapper(*this);
+        gl->fDrawArraysInstanced(mode, first, vertCount, instanceCount);
+    }
+
+    Draw_cleanup(funcName);
+    scopedTF.Advance();
+}
+
+////////////////////////////////////////
+
+bool
+WebGLContext::DrawElements_check(const char* funcName, GLenum mode, GLsizei vertCount,
+                                 GLenum type, WebGLintptr byteOffset,
+                                 GLsizei instanceCount)
+{
+    if (!ValidateDrawModeEnum(mode, funcName))
+        return false;
+
+    if (mBoundTransformFeedback &&
+        mBoundTransformFeedback->mIsActive &&
+        !mBoundTransformFeedback->mIsPaused)
+    {
+        ErrorInvalidOperation("%s: DrawElements* functions are incompatible with"
+                              " transform feedback.",
+                              funcName);
+        return false;
+    }
+
+    if (!ValidateNonNegative(funcName, "vertCount", vertCount) ||
+        !ValidateNonNegative(funcName, "byteOffset", byteOffset) ||
+        !ValidateNonNegative(funcName, "instanceCount", instanceCount))
+    {
+        return false;
+    }
+
+    if (!ValidateStencilParamsForDrawCall())
+        return false;
+
+    if (!vertCount || !instanceCount)
+        return false; // No error, just early out.
+
+    uint8_t bytesPerElem = 0;
+    switch (type) {
+    case LOCAL_GL_UNSIGNED_BYTE:
+        bytesPerElem = 1;
+        break;
+
+    case LOCAL_GL_UNSIGNED_SHORT:
+        bytesPerElem = 2;
+        break;
+
+    case LOCAL_GL_UNSIGNED_INT:
+        if (IsWebGL2() || IsExtensionEnabled(WebGLExtensionID::OES_element_index_uint)) {
+            bytesPerElem = 4;
+        }
+        break;
+    }
+
+    if (!bytesPerElem) {
+        ErrorInvalidEnum("%s: Invalid `type`: 0x%04x", funcName, type);
+        return false;
+    }
+
+    if (byteOffset % bytesPerElem != 0) {
+        ErrorInvalidOperation("%s: `byteOffset` must be a multiple of the size of `type`",
+                              funcName);
+        return false;
+    }
+
+    ////
+
+    if (IsWebGL2() && !gl->IsSupported(gl::GLFeature::prim_restart_fixed)) {
+        MOZ_ASSERT(gl->IsSupported(gl::GLFeature::prim_restart));
+        if (mPrimRestartTypeBytes != bytesPerElem) {
+            mPrimRestartTypeBytes = bytesPerElem;
+
+            const uint32_t ones = UINT32_MAX >> (32 - 8*mPrimRestartTypeBytes);
+            gl->fEnable(LOCAL_GL_PRIMITIVE_RESTART);
+            gl->fPrimitiveRestartIndex(ones);
+        }
+    }
+
+    ////
+
+    const GLsizei first = byteOffset / bytesPerElem;
+    const CheckedUint32 checked_byteCount = bytesPerElem * CheckedUint32(vertCount);
+
+    if (!checked_byteCount.isValid()) {
+        ErrorInvalidValue("%s: Overflow in byteCount.", funcName);
+        return false;
+    }
+
+    if (!mBoundVertexArray->mElementArrayBuffer) {
+        ErrorInvalidOperation("%s: Must have element array buffer binding.", funcName);
+        return false;
+    }
+
+    WebGLBuffer& elemArrayBuffer = *mBoundVertexArray->mElementArrayBuffer;
+
+    if (!elemArrayBuffer.ByteLength()) {
+        ErrorInvalidOperation("%s: Bound element array buffer doesn't have any data.",
+                              funcName);
+        return false;
+    }
+
+    CheckedInt<GLsizei> checked_neededByteCount = checked_byteCount.toChecked<GLsizei>() + byteOffset;
+
+    if (!checked_neededByteCount.isValid()) {
+        ErrorInvalidOperation("%s: Overflow in byteOffset+byteCount.", funcName);
+        return false;
+    }
+
+    if (uint32_t(checked_neededByteCount.value()) > elemArrayBuffer.ByteLength()) {
+        ErrorInvalidOperation("%s: Bound element array buffer is too small for given"
+                              " count and offset.",
+                              funcName);
+        return false;
+    }
+
+    if (!ValidateBufferFetching(funcName))
+        return false;
+
+    if (!mMaxFetchedVertices ||
+        !elemArrayBuffer.Validate(type, mMaxFetchedVertices - 1, first, vertCount))
+    {
+        ErrorInvalidOperation("%s: bound vertex attribute buffers do not have sufficient "
+                              "size for given indices from the bound element array",
+                              funcName);
+        return false;
+    }
+
+    // Bug 1008310 - Check if buffer has been used with a different previous type
+    if (elemArrayBuffer.IsElementArrayUsedWithMultipleTypes()) {
+        nsCString typeName;
+        WebGLContext::EnumName(type, &typeName);
+        GenerateWarning("%s: bound element array buffer previously used with a type other than "
+                        "%s, this will affect performance.",
+                        funcName, typeName.BeginReading());
+    }
+
+    return true;
+}
+
+static void
+HandleDrawElementsErrors(WebGLContext* webgl, const char* funcName,
+                         gl::GLContext::LocalErrorScope& errorScope)
+{
+    const auto err = errorScope.GetError();
+    if (err == LOCAL_GL_INVALID_OPERATION) {
+        webgl->ErrorInvalidOperation("%s: Driver rejected indexed draw call, possibly"
+                                     " due to out-of-bounds indices.", funcName);
+        return;
+    }
+
+    MOZ_ASSERT(!err);
+    if (err) {
+        webgl->ErrorImplementationBug("%s: Unexpected driver error during indexed draw"
+                                      " call. Please file a bug.",
+                                      funcName);
+        return;
+    }
+}
+
+void
+WebGLContext::DrawElements(GLenum mode, GLsizei vertCount, GLenum type,
+                           WebGLintptr byteOffset, const char* funcName)
+{
+    if (!funcName) {
+        funcName = "drawElements";
+    }
+
+    if (IsContextLost())
+        return;
+
+    MakeContextCurrent();
+
+    bool error = false;
+    ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
+    if (error)
+        return;
+
+    const GLsizei instanceCount = 1;
+    if (!DrawElements_check(funcName, mode, vertCount, type, byteOffset, instanceCount))
+        return;
+
+    const ScopedDrawHelper scopedHelper(this, funcName, 0, mMaxFetchedVertices, instanceCount,
+                                        &error);
+    if (error)
+        return;
+
+    {
+        ScopedDrawCallWrapper wrapper(*this);
+        {
+            UniquePtr<gl::GLContext::LocalErrorScope> errorScope;
+
+            if (gl->IsANGLE()) {
+                errorScope.reset(new gl::GLContext::LocalErrorScope(*gl));
+            }
+
+            gl->fDrawElements(mode, vertCount, type,
+                              reinterpret_cast<GLvoid*>(byteOffset));
+
+            if (errorScope) {
+                HandleDrawElementsErrors(this, funcName, *errorScope);
+            }
+        }
+    }
+
+    Draw_cleanup(funcName);
+}
+
+void
+WebGLContext::DrawElementsInstanced(GLenum mode, GLsizei vertCount, GLenum type,
+                                    WebGLintptr byteOffset, GLsizei instanceCount)
+{
+    const char funcName[] = "drawElementsInstanced";
+    if (IsContextLost())
+        return;
+
+    MakeContextCurrent();
+
+    bool error = false;
+    ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
+    if (error)
+        return;
+
+    if (!DrawElements_check(funcName, mode, vertCount, type, byteOffset, instanceCount))
+        return;
+
+    if (!DrawInstanced_check(funcName))
+        return;
+
+    const ScopedDrawHelper scopedHelper(this, funcName, 0, mMaxFetchedVertices, instanceCount,
+                                        &error);
+    if (error)
+        return;
+
+    {
+        ScopedDrawCallWrapper wrapper(*this);
+        {
+            UniquePtr<gl::GLContext::LocalErrorScope> errorScope;
+
+            if (gl->IsANGLE()) {
+                errorScope.reset(new gl::GLContext::LocalErrorScope(*gl));
+            }
+
+            gl->fDrawElementsInstanced(mode, vertCount, type,
+                                       reinterpret_cast<GLvoid*>(byteOffset),
+                                       instanceCount);
+            if (errorScope) {
+                HandleDrawElementsErrors(this, funcName, *errorScope);
+            }
+        }
+    }
+
+    Draw_cleanup(funcName);
+}
+
+////////////////////////////////////////
+
+void
+WebGLContext::Draw_cleanup(const char* funcName)
+{
+    if (gl->WorkAroundDriverBugs()) {
+        if (gl->Renderer() == gl::GLRenderer::Tegra) {
+            mDrawCallsSinceLastFlush++;
+
+            if (mDrawCallsSinceLastFlush >= MAX_DRAW_CALLS_SINCE_FLUSH) {
+                gl->fFlush();
+                mDrawCallsSinceLastFlush = 0;
+            }
+        }
+    }
+
+    // Let's check for a really common error: Viewport is larger than the actual
+    // destination framebuffer.
+    uint32_t destWidth = mViewportWidth;
+    uint32_t destHeight = mViewportHeight;
+
+    if (mBoundDrawFramebuffer) {
+        const auto& drawBuffers = mBoundDrawFramebuffer->ColorDrawBuffers();
+        for (const auto& cur : drawBuffers) {
+            if (!cur->IsDefined())
+                continue;
+            cur->Size(&destWidth, &destHeight);
+            break;
+        }
+    } else {
+        destWidth = mWidth;
+        destHeight = mHeight;
+    }
+
+    if (mViewportWidth > int32_t(destWidth) ||
+        mViewportHeight > int32_t(destHeight))
+    {
+        if (!mAlreadyWarnedAboutViewportLargerThanDest) {
+            GenerateWarning("%s: Drawing to a destination rect smaller than the viewport"
+                            " rect. (This warning will only be given once)",
+                            funcName);
+            mAlreadyWarnedAboutViewportLargerThanDest = true;
+        }
+    }
+}
+
+/*
+ * Verify that state is consistent for drawing, and compute max number of elements (maxAllowedCount)
+ * that will be legal to be read from bound VBOs.
+ */
+
+bool
+WebGLContext::ValidateBufferFetching(const char* info)
+{
+    MOZ_ASSERT(mCurrentProgram);
+    // Note that mCurrentProgram->IsLinked() is NOT GUARANTEED.
+    MOZ_ASSERT(mActiveProgramLinkInfo);
+
+#ifdef DEBUG
+    GLint currentProgram = 0;
+    MakeContextCurrent();
+    gl->fGetIntegerv(LOCAL_GL_CURRENT_PROGRAM, &currentProgram);
+    MOZ_ASSERT(GLuint(currentProgram) == mCurrentProgram->mGLName,
+               "WebGL: current program doesn't agree with GL state");
+#endif
+
+    if (mBufferFetchingIsVerified)
+        return true;
+
+    bool hasPerVertex = false;
+    uint32_t maxVertices = UINT32_MAX;
+    uint32_t maxInstances = UINT32_MAX;
+    const uint32_t attribCount = mBoundVertexArray->mAttribs.Length();
+
+    uint32_t i = 0;
+    for (const auto& vd : mBoundVertexArray->mAttribs) {
+        // If the attrib array isn't enabled, there's nothing to check;
+        // it's a static value.
+        if (!vd.mEnabled)
+            continue;
+
+        if (!vd.mBuf) {
+            ErrorInvalidOperation("%s: no VBO bound to enabled vertex attrib index %du!",
+                                  info, i);
+            return false;
+        }
+
+        ++i;
+    }
+
+    mBufferFetch_IsAttrib0Active = false;
+
+    for (const auto& attrib : mActiveProgramLinkInfo->attribs) {
+        if (attrib.mLoc == -1)
+            continue;
+
+        const uint32_t attribLoc(attrib.mLoc);
+        if (attribLoc >= attribCount)
+            continue;
+
+        if (attribLoc == 0) {
+            mBufferFetch_IsAttrib0Active = true;
+        }
+
+        const auto& vd = mBoundVertexArray->mAttribs[attribLoc];
+        if (!vd.mEnabled)
+            continue;
+
+        const auto& bufByteLen = vd.mBuf->ByteLength();
+        if (vd.ByteOffset() > bufByteLen) {
+            maxVertices = 0;
+            maxInstances = 0;
+            break;
+        }
+
+        size_t availBytes = bufByteLen - vd.ByteOffset();
+        if (vd.BytesPerVertex() > availBytes) {
+            maxVertices = 0;
+            maxInstances = 0;
+            break;
+        }
+        availBytes -= vd.BytesPerVertex();
+        const size_t vertCapacity = 1 + availBytes / vd.ExplicitStride();
+
+        if (vd.mDivisor == 0) {
+            if (vertCapacity < maxVertices) {
+                maxVertices = vertCapacity;
+            }
+            hasPerVertex = true;
+        } else {
+            const auto curMaxInstances = CheckedInt<size_t>(vertCapacity) * vd.mDivisor;
+            // If this isn't valid, it's because we overflowed, which means we can support
+            // *too much*. Don't update maxInstances in this case.
+            if (curMaxInstances.isValid() &&
+                curMaxInstances.value() < maxInstances)
+            {
+                maxInstances = curMaxInstances.value();
+            }
+        }
+    }
+
+    mBufferFetchingIsVerified = true;
+    mBufferFetchingHasPerVertex = hasPerVertex;
+    mMaxFetchedVertices = maxVertices;
+    mMaxFetchedInstances = maxInstances;
+
+    return true;
+}
+
+WebGLVertexAttrib0Status
+WebGLContext::WhatDoesVertexAttrib0Need() const
+{
+    MOZ_ASSERT(mCurrentProgram);
+    MOZ_ASSERT(mActiveProgramLinkInfo);
+
+    const auto& isAttribArray0Enabled = mBoundVertexArray->mAttribs[0].mEnabled;
+
+    bool legacyAttrib0 = gl->IsCompatibilityProfile();
+#ifdef XP_MACOSX
+    if (gl->WorkAroundDriverBugs()) {
+        // Failures in conformance/attribs/gl-disabled-vertex-attrib.
+        // Even in Core profiles on NV. Sigh.
+        legacyAttrib0 |= (gl->Vendor() == gl::GLVendor::NVIDIA);
+    }
+#endif
+
+    if (!legacyAttrib0)
+        return WebGLVertexAttrib0Status::Default;
+
+    if (isAttribArray0Enabled && mBufferFetch_IsAttrib0Active)
+        return WebGLVertexAttrib0Status::Default;
+
+    if (mBufferFetch_IsAttrib0Active)
+        return WebGLVertexAttrib0Status::EmulatedInitializedArray;
+
+    // Ensure that the legacy code has enough buffer.
+    return WebGLVertexAttrib0Status::EmulatedUninitializedArray;
+}
+
+bool
+WebGLContext::DoFakeVertexAttrib0(const char* funcName, GLuint vertexCount)
+{
+    if (!vertexCount) {
+        vertexCount = 1;
+    }
+
+    const auto whatDoesAttrib0Need = WhatDoesVertexAttrib0Need();
+    if (MOZ_LIKELY(whatDoesAttrib0Need == WebGLVertexAttrib0Status::Default))
+        return true;
+
+    if (!mAlreadyWarnedAboutFakeVertexAttrib0) {
+        GenerateWarning("Drawing without vertex attrib 0 array enabled forces the browser "
+                        "to do expensive emulation work when running on desktop OpenGL "
+                        "platforms, for example on Mac. It is preferable to always draw "
+                        "with vertex attrib 0 array enabled, by using bindAttribLocation "
+                        "to bind some always-used attribute to location 0.");
+        mAlreadyWarnedAboutFakeVertexAttrib0 = true;
+    }
+
+    gl->fEnableVertexAttribArray(0);
+
+    if (!mFakeVertexAttrib0BufferObject) {
+        gl->fGenBuffers(1, &mFakeVertexAttrib0BufferObject);
+        mFakeVertexAttrib0BufferObjectSize = 0;
+    }
+    gl->fBindBuffer(LOCAL_GL_ARRAY_BUFFER, mFakeVertexAttrib0BufferObject);
+
+    ////
+
+    switch (mGenericVertexAttribTypes[0]) {
+    case LOCAL_GL_FLOAT:
+        gl->fVertexAttribPointer(0, 4, LOCAL_GL_FLOAT, false, 0, 0);
+        break;
+
+    case LOCAL_GL_INT:
+        gl->fVertexAttribIPointer(0, 4, LOCAL_GL_INT, 0, 0);
+        break;
+
+    case LOCAL_GL_UNSIGNED_INT:
+        gl->fVertexAttribIPointer(0, 4, LOCAL_GL_UNSIGNED_INT, 0, 0);
+        break;
+
+    default:
+        MOZ_CRASH();
+    }
+
+    ////
+
+    const auto bytesPerVert = sizeof(mFakeVertexAttrib0Data);
+    const auto checked_dataSize = CheckedUint32(vertexCount) * bytesPerVert;
+    if (!checked_dataSize.isValid()) {
+        ErrorOutOfMemory("Integer overflow trying to construct a fake vertex attrib 0 array for a draw-operation "
+                         "with %d vertices. Try reducing the number of vertices.", vertexCount);
+        return false;
+    }
+    const auto dataSize = checked_dataSize.value();
+
+    if (mFakeVertexAttrib0BufferObjectSize < dataSize) {
+        gl->fBufferData(LOCAL_GL_ARRAY_BUFFER, dataSize, nullptr, LOCAL_GL_DYNAMIC_DRAW);
+        mFakeVertexAttrib0BufferObjectSize = dataSize;
+        mFakeVertexAttrib0DataDefined = false;
+    }
+
+    if (whatDoesAttrib0Need == WebGLVertexAttrib0Status::EmulatedUninitializedArray)
+        return true;
+
+    ////
+
+    if (mFakeVertexAttrib0DataDefined &&
+        memcmp(mFakeVertexAttrib0Data, mGenericVertexAttrib0Data, bytesPerVert) == 0)
+    {
+        return true;
+    }
+
+    ////
+
+    const UniqueBuffer data(malloc(dataSize));
+    if (!data) {
+        ErrorOutOfMemory("%s: Failed to allocate fake vertex attrib 0 array.",
+                         funcName);
+        return false;
+    }
+    auto itr = (uint8_t*)data.get();
+    const auto itrEnd = itr + dataSize;
+    while (itr != itrEnd) {
+        memcpy(itr, mGenericVertexAttrib0Data, bytesPerVert);
+        itr += bytesPerVert;
+    }
+
+    {
+        gl::GLContext::LocalErrorScope errorScope(*gl);
+
+        gl->fBufferSubData(LOCAL_GL_ARRAY_BUFFER, 0, dataSize, data.get());
+
+        const auto err = errorScope.GetError();
+        if (err) {
+            ErrorOutOfMemory("%s: Failed to upload fake vertex attrib 0 data.", funcName);
+            return false;
+        }
+    }
+
+    ////
+
+    memcpy(mFakeVertexAttrib0Data, mGenericVertexAttrib0Data, bytesPerVert);
+    mFakeVertexAttrib0DataDefined = true;
+    return true;
+}
+
+void
+WebGLContext::UndoFakeVertexAttrib0()
+{
+    const auto whatDoesAttrib0Need = WhatDoesVertexAttrib0Need();
+    if (MOZ_LIKELY(whatDoesAttrib0Need == WebGLVertexAttrib0Status::Default))
+        return;
+
+    if (mBoundVertexArray->mAttribs[0].mBuf) {
+        const WebGLVertexAttribData& attrib0 = mBoundVertexArray->mAttribs[0];
+        gl->fBindBuffer(LOCAL_GL_ARRAY_BUFFER, attrib0.mBuf->mGLName);
+        attrib0.DoVertexAttribPointer(gl, 0);
+    } else {
+        gl->fBindBuffer(LOCAL_GL_ARRAY_BUFFER, 0);
+    }
+
+    gl->fBindBuffer(LOCAL_GL_ARRAY_BUFFER, mBoundArrayBuffer ? mBoundArrayBuffer->mGLName : 0);
+}
+
+static GLuint
+CreateGLTexture(gl::GLContext* gl)
+{
+    MOZ_ASSERT(gl->IsCurrent());
+    GLuint ret = 0;
+    gl->fGenTextures(1, &ret);
+    return ret;
+}
+
+UniquePtr<WebGLContext::FakeBlackTexture>
+WebGLContext::FakeBlackTexture::Create(gl::GLContext* gl, TexTarget target,
+                                       FakeBlackType type)
+{
+    GLenum texFormat;
+    switch (type) {
+    case FakeBlackType::RGBA0000:
+        texFormat = LOCAL_GL_RGBA;
+        break;
+
+    case FakeBlackType::RGBA0001:
+        texFormat = LOCAL_GL_RGB;
+        break;
+
+    default:
+        MOZ_CRASH("GFX: bad type");
+    }
+
+    UniquePtr<FakeBlackTexture> result(new FakeBlackTexture(gl));
+    gl::ScopedBindTexture scopedBind(gl, result->mGLName, target.get());
+
+    gl->fTexParameteri(target.get(), LOCAL_GL_TEXTURE_MIN_FILTER, LOCAL_GL_NEAREST);
+    gl->fTexParameteri(target.get(), LOCAL_GL_TEXTURE_MAG_FILTER, LOCAL_GL_NEAREST);
+
+    // We allocate our zeros on the heap, and we overallocate (16 bytes instead of 4) to
+    // minimize the risk of running into a driver bug in texImage2D, as it is a bit
+    // unusual maybe to create 1x1 textures, and the stack may not have the alignment that
+    // TexImage2D expects.
+
+    const webgl::DriverUnpackInfo dui = {texFormat, texFormat, LOCAL_GL_UNSIGNED_BYTE};
+    UniqueBuffer zeros = moz_xcalloc(1, 16); // Infallible allocation.
+
+    MOZ_ASSERT(gl->IsCurrent());
+
+    if (target == LOCAL_GL_TEXTURE_CUBE_MAP) {
+        for (int i = 0; i < 6; ++i) {
+            const TexImageTarget curTarget = LOCAL_GL_TEXTURE_CUBE_MAP_POSITIVE_X + i;
+            const GLenum error = DoTexImage(gl, curTarget.get(), 0, &dui, 1, 1, 1,
+                                            zeros.get());
+            if (error) {
+                return nullptr;
+            }
+        }
+    } else {
+        const GLenum error = DoTexImage(gl, target.get(), 0, &dui, 1, 1, 1,
+                                        zeros.get());
+        if (error) {
+            return nullptr;
+        }
+    }
+
+    return result;
+}
+
+WebGLContext::FakeBlackTexture::FakeBlackTexture(gl::GLContext* gl)
+    : mGL(gl)
+    , mGLName(CreateGLTexture(gl))
+{
+}
+
+WebGLContext::FakeBlackTexture::~FakeBlackTexture()
+{
+    mGL->MakeCurrent();
+    mGL->fDeleteTextures(1, &mGLName);
+}
+
+} // namespace mozilla