66 lines
2.3 KiB
C++
66 lines
2.3 KiB
C++
// Copyright (c) the JPEG XL Project Authors. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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#ifndef LIB_JXL_ALPHA_H_
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#define LIB_JXL_ALPHA_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <limits>
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#include "lib/jxl/base/compiler_specific.h"
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namespace jxl {
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// A very small value to avoid divisions by zero when converting to
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// unpremultiplied alpha. Page 21 of the technical introduction to OpenEXR
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// (https://www.openexr.com/documentation/TechnicalIntroduction.pdf) recommends
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// "a power of two" that is "less than half of the smallest positive 16-bit
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// floating-point value". That smallest value happens to be the denormal number
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// 2^-24, so 2^-26 should be a good choice.
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static constexpr float kSmallAlpha = 1.f / (1u << 26u);
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struct AlphaBlendingInputLayer {
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const float* r;
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const float* g;
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const float* b;
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const float* a;
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};
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struct AlphaBlendingOutput {
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float* r;
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float* g;
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float* b;
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float* a;
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};
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// Note: The pointers in `out` are allowed to alias those in `bg` or `fg`.
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// No pointer shall be null.
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void PerformAlphaBlending(const AlphaBlendingInputLayer& bg,
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const AlphaBlendingInputLayer& fg,
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const AlphaBlendingOutput& out, size_t num_pixels,
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bool alpha_is_premultiplied, bool clamp);
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// Single plane alpha blending
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void PerformAlphaBlending(const float* bg, const float* bga, const float* fg,
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const float* fga, float* out, size_t num_pixels,
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bool alpha_is_premultiplied, bool clamp);
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void PerformAlphaWeightedAdd(const float* bg, const float* fg, const float* fga,
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float* out, size_t num_pixels, bool clamp);
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void PerformMulBlending(const float* bg, const float* fg, float* out,
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size_t num_pixels, bool clamp);
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void PremultiplyAlpha(float* JXL_RESTRICT r, float* JXL_RESTRICT g,
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float* JXL_RESTRICT b, const float* JXL_RESTRICT a,
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size_t num_pixels);
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void UnpremultiplyAlpha(float* JXL_RESTRICT r, float* JXL_RESTRICT g,
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float* JXL_RESTRICT b, const float* JXL_RESTRICT a,
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size_t num_pixels);
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} // namespace jxl
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#endif // LIB_JXL_ALPHA_H_
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