gecko-dev/dom/canvas/WebGLTexelConversions.cpp

/* 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 "WebGLTexelConversions.h"

namespace mozilla {

using namespace WebGLTexelConversions;

namespace {

/** @class WebGLImageConverter
 *
 * This class is just a helper to implement WebGLContext::ConvertImage below.
 *
 * Design comments:
 *
 * WebGLContext::ConvertImage has to handle hundreds of format conversion paths.
 * It is important to minimize executable code size here. Instead of passing
 * around a large number of function parameters hundreds of times, we create a
 * WebGLImageConverter object once, storing these parameters, and then we call
 * the run() method on it.
 */
class WebGLImageConverter {
  const size_t mWidth, mHeight;
  const void* const mSrcStart;
  void* const mDstStart;
  const ptrdiff_t mSrcStride, mDstStride;
  bool mAlreadyRun;
  bool mSuccess;

  /*
   * Returns sizeof(texel)/sizeof(type). The point is that we will iterate over
   * texels with typed pointers and this value will tell us by how much we need
   * to increment these pointers to advance to the next texel.
   */
  template <WebGLTexelFormat Format>
  static size_t NumElementsPerTexelForFormat() {
    switch (Format) {
      case WebGLTexelFormat::A8:
      case WebGLTexelFormat::A16F:
      case WebGLTexelFormat::A32F:
      case WebGLTexelFormat::R8:
      case WebGLTexelFormat::R16F:
      case WebGLTexelFormat::R32F:
      case WebGLTexelFormat::RGB565:
      case WebGLTexelFormat::RGB11F11F10F:
      case WebGLTexelFormat::RGBA4444:
      case WebGLTexelFormat::RGBA5551:
        return 1;
      case WebGLTexelFormat::RA8:
      case WebGLTexelFormat::RA16F:
      case WebGLTexelFormat::RA32F:
      case WebGLTexelFormat::RG8:
      case WebGLTexelFormat::RG16F:
      case WebGLTexelFormat::RG32F:
        return 2;
      case WebGLTexelFormat::RGB8:
      case WebGLTexelFormat::RGB16F:
      case WebGLTexelFormat::RGB32F:
        return 3;
      case WebGLTexelFormat::RGBA8:
      case WebGLTexelFormat::RGBA16F:
      case WebGLTexelFormat::RGBA32F:
      case WebGLTexelFormat::BGRX8:
      case WebGLTexelFormat::BGRA8:
        return 4;
      default:
        MOZ_ASSERT(false, "Unknown texel format. Coding mistake?");
        return 0;
    }
  }

  /*
   * This is the completely format-specific templatized conversion function,
   * that will be instantiated hundreds of times for all different combinations.
   * It is important to avoid generating useless code here. In particular, many
   * instantiations of this function template will never be called, so we try
   * to return immediately in these cases to allow the compiler to avoid
   * generating useless code.
   */
  template <WebGLTexelFormat SrcFormat, WebGLTexelFormat DstFormat,
            WebGLTexelPremultiplicationOp PremultiplicationOp>
  void run() {
    // check for never-called cases. We early-return to allow the compiler
    // to avoid generating this code. It would be tempting to abort() instead,
    // as returning early does leave the destination surface with uninitialized
    // data, but that would not allow the compiler to avoid generating this
    // code. So instead, we return early, so Success() will return false, and
    // the caller must check that and abort in that case. See
    // WebGLContext::ConvertImage.

    if (SrcFormat == DstFormat &&
        PremultiplicationOp == WebGLTexelPremultiplicationOp::None) {
      // Should have used a fast exit path earlier, rather than entering this
      // function. we explicitly return here to allow the compiler to avoid
      // generating this code
      return;
    }

    // Only textures uploaded from DOM elements or ImageData can allow DstFormat
    // != SrcFormat. DOM elements can only give BGRA8, BGRX8, A8, RGB565
    // formats. See DOMElementToImageSurface. ImageData is always RGBA8. So all
    // other SrcFormat will always satisfy DstFormat==SrcFormat, so we can avoid
    // compiling the code for all the unreachable paths.
    const bool CanSrcFormatComeFromDOMElementOrImageData =
        SrcFormat == WebGLTexelFormat::BGRA8 ||
        SrcFormat == WebGLTexelFormat::BGRX8 ||
        SrcFormat == WebGLTexelFormat::A8 ||
        SrcFormat == WebGLTexelFormat::RGB565 ||
        SrcFormat == WebGLTexelFormat::RGBA8;
    if (!CanSrcFormatComeFromDOMElementOrImageData && SrcFormat != DstFormat) {
      return;
    }

    // Likewise, only textures uploaded from DOM elements or ImageData can
    // possibly have to be unpremultiplied.
    if (!CanSrcFormatComeFromDOMElementOrImageData &&
        PremultiplicationOp == WebGLTexelPremultiplicationOp::Unpremultiply) {
      return;
    }

    // there is no point in premultiplication/unpremultiplication
    // in the following cases:
    //  - the source format has no alpha
    //  - the source format has no color
    //  - the destination format has no color
    if (!HasAlpha(SrcFormat) || !HasColor(SrcFormat) || !HasColor(DstFormat)) {
      if (PremultiplicationOp != WebGLTexelPremultiplicationOp::None) {
        return;
      }
    }

    // end of early return cases.

    MOZ_ASSERT(!mAlreadyRun, "converter should be run only once!");
    mAlreadyRun = true;

    // gather some compile-time meta-data about the formats at hand.

    using SrcType = typename DataTypeForFormat<SrcFormat>::Type;
    using DstType = typename DataTypeForFormat<DstFormat>::Type;

    const WebGLTexelFormat IntermediateSrcFormat =
        IntermediateFormat<SrcFormat>::Value;
    const WebGLTexelFormat IntermediateDstFormat =
        IntermediateFormat<DstFormat>::Value;
    using IntermediateSrcType =
        typename DataTypeForFormat<IntermediateSrcFormat>::Type;
    using IntermediateDstType =
        typename DataTypeForFormat<IntermediateDstFormat>::Type;

    const size_t NumElementsPerSrcTexel =
        NumElementsPerTexelForFormat<SrcFormat>();
    const size_t NumElementsPerDstTexel =
        NumElementsPerTexelForFormat<DstFormat>();
    const size_t MaxElementsPerTexel = 4;
    MOZ_ASSERT(NumElementsPerSrcTexel <= MaxElementsPerTexel,
               "unhandled format");
    MOZ_ASSERT(NumElementsPerDstTexel <= MaxElementsPerTexel,
               "unhandled format");

    // we assume that the strides are multiples of the sizeof of respective
    // types. this assumption will allow us to iterate over src and dst images
    // using typed pointers, e.g. uint8_t* or uint16_t* or float*, instead of
    // untyped pointers. So this assumption allows us to write cleaner and safer
    // code, but it might not be true forever and if it eventually becomes
    // wrong, we'll have to revert to always iterating using uint8_t* pointers
    // regardless of the types at hand.
    MOZ_ASSERT(
        mSrcStride % sizeof(SrcType) == 0 && mDstStride % sizeof(DstType) == 0,
        "Unsupported: texture stride is not a multiple of sizeof(type)");
    const ptrdiff_t srcStrideInElements =
        mSrcStride / static_cast<ptrdiff_t>(sizeof(SrcType));
    const ptrdiff_t dstStrideInElements =
        mDstStride / static_cast<ptrdiff_t>(sizeof(DstType));
    // Pop quiz: What's `ptrdiff_t(-16) / sizeof(int32_t)`?
    // Did you guess +4611686018427387900?
    MOZ_ASSERT(bool(srcStrideInElements < 0) == bool(mSrcStride < 0));
    MOZ_ASSERT(bool(dstStrideInElements < 0) == bool(mDstStride < 0));

    const SrcType* srcRowStart = static_cast<const SrcType*>(mSrcStart);
    DstType* dstRowStart = static_cast<DstType*>(mDstStart);

    // the loop performing the texture format conversion
    for (size_t i = 0; i < mHeight; ++i) {
      const SrcType* srcRowEnd = srcRowStart + mWidth * NumElementsPerSrcTexel;
      const SrcType* srcPtr = srcRowStart;
      DstType* dstPtr = dstRowStart;
      while (srcPtr != srcRowEnd) {
        // convert a single texel. We proceed in 3 steps: unpack the source
        // texel so the corresponding interchange format (e.g. unpack RGB565 to
        // RGBA8), convert the resulting data type to the destination type (e.g.
        // convert from RGBA8 to RGBA32F), and finally pack the destination
        // texel (e.g. pack RGBA32F to RGB32F).
        IntermediateSrcType unpackedSrc[MaxElementsPerTexel];
        IntermediateDstType unpackedDst[MaxElementsPerTexel];

        // unpack a src texel to corresponding intermediate src format.
        // for example, unpack RGB565 to RGBA8
        unpack<SrcFormat>(srcPtr, unpackedSrc);
        // convert the data type to the destination type, if needed.
        // for example, convert RGBA8 to RGBA32F
        convertType(unpackedSrc, unpackedDst);
        // pack the destination texel.
        // for example, pack RGBA32F to RGB32F
        pack<DstFormat, PremultiplicationOp>(unpackedDst, dstPtr);

        srcPtr += NumElementsPerSrcTexel;
        dstPtr += NumElementsPerDstTexel;
      }
      srcRowStart += srcStrideInElements;
      dstRowStart += dstStrideInElements;
    }

    mSuccess = true;
  }

  template <WebGLTexelFormat SrcFormat, WebGLTexelFormat DstFormat>
  void run(WebGLTexelPremultiplicationOp premultiplicationOp) {
#define WEBGLIMAGECONVERTER_CASE_PREMULTIPLICATIONOP(PremultiplicationOp) \
  case PremultiplicationOp:                                               \
    return run<SrcFormat, DstFormat, PremultiplicationOp>();

    switch (premultiplicationOp) {
      WEBGLIMAGECONVERTER_CASE_PREMULTIPLICATIONOP(
          WebGLTexelPremultiplicationOp::None)
      WEBGLIMAGECONVERTER_CASE_PREMULTIPLICATIONOP(
          WebGLTexelPremultiplicationOp::Premultiply)
      WEBGLIMAGECONVERTER_CASE_PREMULTIPLICATIONOP(
          WebGLTexelPremultiplicationOp::Unpremultiply)
      default:
        MOZ_ASSERT(false, "unhandled case. Coding mistake?");
    }

#undef WEBGLIMAGECONVERTER_CASE_PREMULTIPLICATIONOP
  }

  template <WebGLTexelFormat SrcFormat>
  void run(WebGLTexelFormat dstFormat,
           WebGLTexelPremultiplicationOp premultiplicationOp) {
#define WEBGLIMAGECONVERTER_CASE_DSTFORMAT(DstFormat) \
  case DstFormat:                                     \
    return run<SrcFormat, DstFormat>(premultiplicationOp);

    switch (dstFormat) {
      // 1-channel formats
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::A8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::A16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::A32F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::R8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::R16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::R32F)
      // 2-channel formats
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RA8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RA16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RA32F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RG8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RG16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RG32F)
      // 3-channel formats
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGB565)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGB8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGB11F11F10F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGB16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGB32F)
      // 4-channel formats
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGBA4444)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGBA5551)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGBA8)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGBA16F)
      WEBGLIMAGECONVERTER_CASE_DSTFORMAT(WebGLTexelFormat::RGBA32F)

      default:
        MOZ_ASSERT(false, "unhandled case. Coding mistake?");
    }

#undef WEBGLIMAGECONVERTER_CASE_DSTFORMAT
  }

 public:
  void run(WebGLTexelFormat srcFormat, WebGLTexelFormat dstFormat,
           WebGLTexelPremultiplicationOp premultiplicationOp) {
#define WEBGLIMAGECONVERTER_CASE_SRCFORMAT(SrcFormat) \
  case SrcFormat:                                     \
    return run<SrcFormat>(dstFormat, premultiplicationOp);

    switch (srcFormat) {
      // 1-channel formats
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::A8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::A16F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::A32F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::R8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::R16F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::R32F)
      // 2-channel formats
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RA8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RA16F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RA32F)
      // 3-channel formats
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGB565)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGB8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGB16F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGB32F)
      // 4-channel formats
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGBA4444)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGBA5551)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGBA8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGBA16F)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::RGBA32F)
      // DOM element source formats
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::BGRX8)
      WEBGLIMAGECONVERTER_CASE_SRCFORMAT(WebGLTexelFormat::BGRA8)

      default:
        MOZ_ASSERT(false, "unhandled case. Coding mistake?");
    }

#undef WEBGLIMAGECONVERTER_CASE_SRCFORMAT
  }

  WebGLImageConverter(size_t width, size_t height, const void* srcStart,
                      void* dstStart, ptrdiff_t srcStride, ptrdiff_t dstStride)
      : mWidth(width),
        mHeight(height),
        mSrcStart(srcStart),
        mDstStart(dstStart),
        mSrcStride(srcStride),
        mDstStride(dstStride),
        mAlreadyRun(false),
        mSuccess(false) {}

  bool Success() const { return mSuccess; }
};

}  // end anonymous namespace

bool ConvertImage(size_t width, size_t height, const void* srcBegin,
                  size_t srcStride, gl::OriginPos srcOrigin,
                  WebGLTexelFormat srcFormat, bool srcPremultiplied,
                  void* dstBegin, size_t dstStride, gl::OriginPos dstOrigin,
                  WebGLTexelFormat dstFormat, bool dstPremultiplied,
                  bool* const out_wasTrivial) {
  *out_wasTrivial = true;

  if (srcFormat == WebGLTexelFormat::FormatNotSupportingAnyConversion ||
      dstFormat == WebGLTexelFormat::FormatNotSupportingAnyConversion) {
    return false;
  }

  if (!width || !height) return true;

  const bool shouldYFlip = (srcOrigin != dstOrigin);

  const bool canSkipPremult =
      (!HasAlpha(srcFormat) || !HasColor(srcFormat) || !HasColor(dstFormat));

  WebGLTexelPremultiplicationOp premultOp;
  if (canSkipPremult) {
    premultOp = WebGLTexelPremultiplicationOp::None;
  } else if (!srcPremultiplied && dstPremultiplied) {
    premultOp = WebGLTexelPremultiplicationOp::Premultiply;
  } else if (srcPremultiplied && !dstPremultiplied) {
    premultOp = WebGLTexelPremultiplicationOp::Unpremultiply;
  } else {
    premultOp = WebGLTexelPremultiplicationOp::None;
  }

  const uint8_t* srcItr = (const uint8_t*)srcBegin;
  const uint8_t* const srcEnd = srcItr + srcStride * height;
  uint8_t* dstItr = (uint8_t*)dstBegin;
  ptrdiff_t dstItrStride = dstStride;
  if (shouldYFlip) {
    dstItr = dstItr + dstStride * (height - 1);
    dstItrStride = -dstItrStride;
  }

  if (srcFormat == dstFormat &&
      premultOp == WebGLTexelPremultiplicationOp::None) {
    // Fast exit path: we just have to memcpy all the rows.
    //
    // The case where absolutely nothing needs to be done is supposed to have
    // been handled earlier (in TexImage2D_base, etc).
    //
    // So the case we're handling here is when even though no format conversion
    // is needed, we still might have to flip vertically and/or to adjust to a
    // different stride.

    // We ignore canSkipPremult for this perf trap, since it's an avoidable perf
    // cliff under the WebGL API user's control.
    MOZ_ASSERT(
        (srcPremultiplied != dstPremultiplied || shouldYFlip ||
         srcStride != dstStride),
        "Performance trap -- should handle this case earlier to avoid memcpy");

    const auto bytesPerPixel = TexelBytesForFormat(srcFormat);
    const size_t bytesPerRow = bytesPerPixel * width;

    while (srcItr != srcEnd) {
      memcpy(dstItr, srcItr, bytesPerRow);
      srcItr += srcStride;
      dstItr += dstItrStride;
    }
    return true;
  }

  *out_wasTrivial = false;

  WebGLImageConverter converter(width, height, srcItr, dstItr, srcStride,
                                dstItrStride);
  converter.run(srcFormat, dstFormat, premultOp);

  if (!converter.Success()) {
    // the dst image may be left uninitialized, so we better not try to
    // continue even in release builds. This should never happen anyway,
    // and would be a bug in our code.
    MOZ_CRASH("programming mistake in WebGL texture conversions");
  }

  return true;
}

}  // end namespace mozilla