skia/ext/rgba_to_yuva.cc

// Copyright 2021 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "skia/ext/rgba_to_yuva.h"

#include "base/notreached.h"
#include "third_party/skia/include/core/SkCanvas.h"
#include "third_party/skia/include/core/SkColorFilter.h"
#include "third_party/skia/include/core/SkPaint.h"
#include "third_party/skia/include/effects/SkColorMatrix.h"

namespace skia {

void BlitRGBAToYUVA(sk_sp<SkImage> src_image,
                    const SkRect& src_rect,
                    sk_sp<SkSurface> dst_surfaces[SkYUVAInfo::kMaxPlanes],
                    const SkYUVAInfo& dst_yuva_info,
                    const SkRect& dst_rect) {
  // TODO(https://crbug.com/1206168): These color matrices are copied directly
  // from kRGBtoYColorWeights et al in the gpu::GLHelperScaling::
  // CreateI420Planerizer method this is code is replacing. This corresponds
  // to hard-coding kRec601_Limited_SkYUVColorSpace. This should look up the
  // matrix based on |dst_yuva_info|.
  SkColorMatrix rgb_to_yuv(0.257f, 0.504f, 0.098f, 0.000f, 0.0625f,    //
                           -0.148f, -0.291f, 0.439f, 0.000f, 0.5000f,  //
                           0.439f, -0.368f, -0.071f, 0.000f, 0.5000f,  //
                           0.000f, 0.000f, 0.000f, 0.000f, 1.0000f);

  // Permutation matrices to select the appropriate YUVA channels for each
  // output plane.
  const SkColorMatrix xxxY(0, 0, 0, 0, 0,  //
                           0, 0, 0, 0, 0,  //
                           0, 0, 0, 0, 0,  //
                           1, 0, 0, 0, 0);
  const SkColorMatrix UVx1(0, 1, 0, 0, 0,  //
                           0, 0, 1, 0, 0,  //
                           0, 0, 0, 0, 0,  //
                           0, 0, 0, 1, 0);

  // Only Y_UV has been tested.
  SkColorMatrix permutation_matrices[SkYUVAInfo::kMaxPlanes];
  switch (dst_yuva_info.planeConfig()) {
    case SkYUVAInfo::PlaneConfig::kY_UV:
      permutation_matrices[0] = xxxY;
      permutation_matrices[1] = UVx1;
      break;
    default:
      NOTREACHED();
      break;
  }

  // Blit each plane.
  for (int plane = 0; plane < dst_yuva_info.numPlanes(); ++plane) {
    SkColorMatrix color_matrix = rgb_to_yuv;
    color_matrix.postConcat(permutation_matrices[plane]);

    SkSamplingOptions sampling_options(SkFilterMode::kLinear);

    SkPaint paint;
    paint.setBlendMode(SkBlendMode::kSrc);
    paint.setColorFilter(SkColorFilters::Matrix(color_matrix));

    float subsampling_factors[2] = {
        static_cast<float>(dst_surfaces[plane]->width()) /
            dst_yuva_info.dimensions().width(),
        static_cast<float>(dst_surfaces[plane]->height()) /
            dst_yuva_info.dimensions().height(),
    };
    SkRect plane_dst_rect =
        SkRect::MakeXYWH(dst_rect.x() * subsampling_factors[0],
                         dst_rect.y() * subsampling_factors[1],
                         dst_rect.width() * subsampling_factors[0],
                         dst_rect.height() * subsampling_factors[1]);

    dst_surfaces[plane]->getCanvas()->drawImageRect(
        src_image, src_rect, plane_dst_rect, sampling_options, &paint,
        SkCanvas::kFast_SrcRectConstraint);
  }
}

}  // namespace skia