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// Copyright 2025 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef SKIA_EXT_PMCOLOR_UTILS_H_
#define SKIA_EXT_PMCOLOR_UTILS_H_
#include <cstdint>
#include "third_party/skia/include/core/SkColor.h"
#include "third_party/skia/include/private/chromium/SkPMColor.h"
namespace skia {
// Interpret c as 4 x 8 bit channels and scale each of them by alpha/255
// (approximately).
inline uint32_t ScaleChannelsByAlpha(uint32_t c, unsigned alpha) {
// approximate rgb * alpha / 255 with
// rgb * (alpha + 1) / 256
// because >> 8 is faster than / 255
const unsigned scale = alpha + 1;
static constexpr uint32_t kMask = 0x00FF00FF;
// These variables imply that the passed in color is RGBA, but because
// each channel is independent, it also works for BGRA.
uint32_t rb = ((c & kMask) * scale) >> 8;
uint32_t ag = ((c >> 8) & kMask) * scale;
return (rb & kMask) | (ag & ~kMask);
}
// Blend two premultiplied colors together
inline SkPMColor BlendSrcOver(SkPMColor src, SkPMColor dst) {
uint32_t scale = 256 - SkPMColorGetA(src);
static constexpr uint32_t kMask = 0x00FF00FF;
uint32_t rb = (((dst & kMask) * scale) >> 8) & kMask;
uint32_t ag = (((dst >> 8) & kMask) * scale) & ~kMask;
rb += (src & kMask);
ag += (src & ~kMask);
// Color channels (but not alpha) can overflow, so we have to saturate to 0xFF
// in each lane.
return std::min(rb & 0x000001FF, 0x000000FFU) |
std::min(ag & 0x0001FF00, 0x0000FF00U) |
std::min(rb & 0x01FF0000, 0x00FF0000U) | (ag & 0xFF000000);
}
} // namespace skia
#endif // SKIA_EXT_PMCOLOR_UTILS_H_
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