dom/canvas/WebGLContextDraw.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 "GeckoProfiler.h"
#include "MozFramebuffer.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 "WebGLTransformFeedback.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());

  const std::vector<const WebGLFBAttachPoint*>* attachList = nullptr;
  const auto& fb = mWebGL->mBoundDrawFramebuffer;
  if (fb) {
    attachList = &(fb->ResolvedCompleteData()->texDrawBuffers);
  }

  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.empty()) 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) {
    gl->fPixelStorei(LOCAL_GL_UNPACK_ALIGNMENT, 1);
    if (IsWebGL2()) {
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_PIXELS, 0);
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_ROWS, 0);
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_IMAGES, 0);
    }

    fakeBlackTex = FakeBlackTexture::Create(gl, target, fakeBlack);

    gl->fPixelStorei(LOCAL_GL_UNPACK_ALIGNMENT, mPixelStore_UnpackAlignment);
    if (IsWebGL2()) {
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_PIXELS,
                       mPixelStore_UnpackSkipPixels);
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_ROWS, mPixelStore_UnpackSkipRows);
      gl->fPixelStorei(LOCAL_GL_UNPACK_SKIP_IMAGES,
                       mPixelStore_UnpackSkipImages);
    }
    if (!fakeBlackTex) {
      return false;
    }
  }

  gl->fActiveTexture(LOCAL_GL_TEXTURE0 + texUnit);
  gl->fBindTexture(target.get(), fakeBlackTex->mGLName);
  gl->fActiveTexture(LOCAL_GL_TEXTURE0 + mActiveTexture);
  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* const webgl, const char* const funcName,
                   const GLenum mode, const Maybe<uint32_t>& lastRequiredVertex,
                   const uint32_t instanceCount, bool* const out_error)
      : mWebGL(webgl), mDidFake(false) {
    MOZ_ASSERT(mWebGL->gl->IsCurrent());

    if (!mWebGL->BindCurFBForDraw(funcName)) {
      *out_error = true;
      return;
    }

    if (!mWebGL->ValidateDrawModeEnum(mode, funcName)) {
      *out_error = true;
      return;
    }

    if (!mWebGL->ValidateStencilParamsForDrawCall()) {
      *out_error = true;
      return;
    }

    if (!mWebGL->mActiveProgramLinkInfo) {
      mWebGL->ErrorInvalidOperation("%s: The current program is not linked.",
                                    funcName);
      *out_error = true;
      return;
    }
    const auto& linkInfo = mWebGL->mActiveProgramLinkInfo;

    ////
    // Check UBO sizes.

    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;
        }

        // Technically we don't know that this will be updated yet, but we can
        // speculatively mark it.
        buffer->ResetLastUpdateFenceId();
      }
    }

    ////

    const auto& fetchLimits = linkInfo->GetDrawFetchLimits(funcName);
    if (!fetchLimits) {
      *out_error = true;
      return;
    }

    if (lastRequiredVertex && instanceCount) {
      if (lastRequiredVertex.value() >= fetchLimits->maxVerts) {
        mWebGL->ErrorInvalidOperation(
            "%s: Vertex fetch requires vertex #%u, but"
            " attribs only supply %" PRIu64 ".",
            funcName, lastRequiredVertex.value(), fetchLimits->maxVerts);
        *out_error = true;
        return;
      }
      if (instanceCount > fetchLimits->maxInstances) {
        mWebGL->ErrorInvalidOperation(
            "%s: Instance fetch requires %u, but"
            " attribs only supply %" PRIu64 ".",
            funcName, instanceCount, fetchLimits->maxInstances);
        *out_error = true;
        return;
      }
    }

    ////

    if (lastRequiredVertex) {
      if (!mWebGL->DoFakeVertexAttrib0(funcName, lastRequiredVertex.value())) {
        *out_error = true;
        return;
      }
      mDidFake = true;
    }

    ////

    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;
  }
};

static bool HasInstancedDrawing(const WebGLContext& webgl) {
  return webgl.IsWebGL2() ||
         webgl.IsExtensionEnabled(WebGLExtensionID::ANGLE_instanced_arrays);
}

////////////////////////////////////////

bool WebGLContext::DrawArrays_check(const char* const funcName,
                                    const GLint first, const GLsizei vertCount,
                                    const GLsizei instanceCount,
                                    Maybe<uint32_t>* const out_lastVert) {
  if (!ValidateNonNegative(funcName, "first", first) ||
      !ValidateNonNegative(funcName, "vertCount", vertCount) ||
      !ValidateNonNegative(funcName, "instanceCount", instanceCount)) {
    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) {
    *out_lastVert = Nothing();
  } else {
    const auto lastVert_checked = CheckedInt<uint32_t>(first) + vertCount - 1;
    if (!lastVert_checked.isValid()) {
      ErrorOutOfMemory("%s: `first+vertCount` out of range.", funcName);
      return false;
    }
    *out_lastVert = Some(lastVert_checked.value());
  }
  return true;
}

void WebGLContext::DrawArraysInstanced(GLenum mode, GLint first,
                                       GLsizei vertCount, GLsizei instanceCount,
                                       const char* const funcName) {
  AUTO_PROFILER_LABEL("WebGLContext::DrawArraysInstanced", GRAPHICS);
  if (IsContextLost()) return;

  const gl::GLContext::TlsScope inTls(gl);

  Maybe<uint32_t> lastVert;
  if (!DrawArrays_check(funcName, first, vertCount, instanceCount, &lastVert))
    return;

  bool error = false;
  const ScopedDrawHelper scopedHelper(this, funcName, mode, lastVert,
                                      instanceCount, &error);
  if (error) return;

  const ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
  if (error) return;

  const ScopedDrawWithTransformFeedback scopedTF(
      this, funcName, mode, vertCount, instanceCount, &error);
  if (error) return;

  {
    ScopedDrawCallWrapper wrapper(*this);
    if (vertCount && instanceCount) {
      AUTO_PROFILER_LABEL("glDrawArraysInstanced", GRAPHICS);
      if (HasInstancedDrawing(*this)) {
        gl->fDrawArraysInstanced(mode, first, vertCount, instanceCount);
      } else {
        MOZ_ASSERT(instanceCount == 1);
        gl->fDrawArrays(mode, first, vertCount);
      }
    }
  }

  Draw_cleanup(funcName);
  scopedTF.Advance();
}

////////////////////////////////////////

bool WebGLContext::DrawElements_check(const char* const funcName,
                                      const GLsizei rawIndexCount,
                                      const GLenum type,
                                      const WebGLintptr byteOffset,
                                      const GLsizei instanceCount,
                                      Maybe<uint32_t>* const out_lastVert) {
  if (mBoundTransformFeedback && mBoundTransformFeedback->mIsActive &&
      !mBoundTransformFeedback->mIsPaused) {
    ErrorInvalidOperation(
        "%s: DrawElements* functions are incompatible with"
        " transform feedback.",
        funcName);
    return false;
  }

  if (!ValidateNonNegative(funcName, "vertCount", rawIndexCount) ||
      !ValidateNonNegative(funcName, "byteOffset", byteOffset) ||
      !ValidateNonNegative(funcName, "instanceCount", instanceCount)) {
    return false;
  }
  const auto indexCount = uint32_t(rawIndexCount);

  uint8_t bytesPerIndex = 0;
  switch (type) {
    case LOCAL_GL_UNSIGNED_BYTE:
      bytesPerIndex = 1;
      break;

    case LOCAL_GL_UNSIGNED_SHORT:
      bytesPerIndex = 2;
      break;

    case LOCAL_GL_UNSIGNED_INT:
      if (IsWebGL2() ||
          IsExtensionEnabled(WebGLExtensionID::OES_element_index_uint)) {
        bytesPerIndex = 4;
      }
      break;
  }
  if (!bytesPerIndex) {
    ErrorInvalidEnum("%s: Invalid `type`: 0x%04x", funcName, type);
    return false;
  }
  if (byteOffset % bytesPerIndex != 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 != bytesPerIndex) {
      mPrimRestartTypeBytes = bytesPerIndex;

      const uint32_t ones = UINT32_MAX >> (32 - 8 * mPrimRestartTypeBytes);
      gl->fEnable(LOCAL_GL_PRIMITIVE_RESTART);
      gl->fPrimitiveRestartIndex(ones);
    }
  }

  ////
  // Index fetching

  if (!indexCount || !instanceCount) {
    *out_lastVert = Nothing();
    return true;
  }

  const auto& indexBuffer = mBoundVertexArray->mElementArrayBuffer;

  size_t availBytes = 0;
  if (indexBuffer) {
    MOZ_ASSERT(!indexBuffer->IsBoundForTF(), "This should be impossible.");
    availBytes = indexBuffer->ByteLength();
  }
  const auto availIndices =
      AvailGroups(availBytes, byteOffset, bytesPerIndex, bytesPerIndex);
  if (indexCount > availIndices) {
    ErrorInvalidOperation("%s: Index buffer too small.", funcName);
    return false;
  }

  *out_lastVert =
      indexBuffer->GetIndexedFetchMaxVert(type, byteOffset, indexCount);
  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::DrawElementsInstanced(GLenum mode, GLsizei indexCount,
                                         GLenum type, WebGLintptr byteOffset,
                                         GLsizei instanceCount,
                                         const char* const funcName) {
  AUTO_PROFILER_LABEL("WebGLContext::DrawElementsInstanced", GRAPHICS);
  if (IsContextLost()) return;

  const gl::GLContext::TlsScope inTls(gl);

  Maybe<uint32_t> lastVert;
  if (!DrawElements_check(funcName, indexCount, type, byteOffset, instanceCount,
                          &lastVert)) {
    return;
  }

  bool error = false;
  const ScopedDrawHelper scopedHelper(this, funcName, mode, lastVert,
                                      instanceCount, &error);
  if (error) return;

  const ScopedResolveTexturesForDraw scopedResolve(this, funcName, &error);
  if (error) return;

  {
    ScopedDrawCallWrapper wrapper(*this);
    {
      UniquePtr<gl::GLContext::LocalErrorScope> errorScope;

      if (gl->IsANGLE()) {
        errorScope.reset(new gl::GLContext::LocalErrorScope(*gl));
      }

      if (indexCount && instanceCount) {
        AUTO_PROFILER_LABEL("glDrawElementsInstanced", GRAPHICS);
        if (HasInstancedDrawing(*this)) {
          gl->fDrawElementsInstanced(mode, indexCount, type,
                                     reinterpret_cast<GLvoid*>(byteOffset),
                                     instanceCount);
        } else {
          MOZ_ASSERT(instanceCount == 1);
          gl->fDrawElements(mode, indexCount, type,
                            reinterpret_cast<GLvoid*>(byteOffset));
        }
      }

      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 = mDefaultFB->mSize.width;
    destHeight = mDefaultFB->mSize.height;
  }

  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;
    }
  }
}

WebGLVertexAttrib0Status WebGLContext::WhatDoesVertexAttrib0Need() const {
  MOZ_ASSERT(mCurrentProgram);
  MOZ_ASSERT(mActiveProgramLinkInfo);

  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 (!mActiveProgramLinkInfo->attrib0Active) {
    // Ensure that the legacy code has enough buffer.
    return WebGLVertexAttrib0Status::EmulatedUninitializedArray;
  }

  const auto& isAttribArray0Enabled = mBoundVertexArray->mAttribs[0].mEnabled;
  return isAttribArray0Enabled
             ? WebGLVertexAttrib0Status::Default
             : WebGLVertexAttrib0Status::EmulatedInitializedArray;
}

bool WebGLContext::DoFakeVertexAttrib0(const char* const funcName,
                                       const uint32_t lastVert) {
  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(lastVert) + 1) * bytesPerVert;
  if (!checked_dataSize.isValid()) {
    ErrorOutOfMemory(
        "Integer overflow trying to construct a fake vertex attrib 0"
        " array for a draw-operation with %" PRIu64
        " vertices. Try"
        " reducing the number of vertices.",
        uint64_t(lastVert) + 1);
    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);

  const webgl::DriverUnpackInfo dui = {texFormat, texFormat,
                                       LOCAL_GL_UNSIGNED_BYTE};
  UniqueBuffer zeros = moz_xcalloc(1, 4);  // 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->fDeleteTextures(1, &mGLName);
}

}  // namespace mozilla