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/*
* Copyright 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#pragma once
#include <math/mat4.h>
#include <tonemap/tonemap.h>
#include <ui/GraphicTypes.h>
#include <cstddef>
namespace android::shaders {
/**
* Arguments for creating an effect that applies color transformations in linear XYZ space.
* A linear effect is decomposed into the following steps when operating on an image:
* 1. Electrical-Optical Transfer Function (EOTF) maps the input RGB signal into the intended
* relative display brightness of the scene in nits for each RGB channel
* 2. Transformation matrix from linear RGB brightness to linear XYZ, to operate on display
* luminance.
* 3. Opto-Optical Transfer Function (OOTF) applies a "rendering intent". This can include tone
* mapping to display SDR content alongside HDR content, or any number of subjective transformations
* 4. Transformation matrix from linear XYZ back to linear RGB brightness.
* 5. Opto-Electronic Transfer Function (OETF) maps the display brightness of the scene back to
* output RGB colors.
*
* For further reading, consult the recommendation in ITU-R BT.2390-4:
* https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2390-4-2018-PDF-E.pdf
*
* Skia normally attempts to do its own simple tone mapping, i.e., the working color space is
* intended to be the output surface. However, Skia does not support complex tone mapping such as
* polynomial interpolation. As such, this filter assumes that tone mapping has not yet been applied
* to the source colors. so that the tone mapping process is only applied once by this effect. Tone
* mapping is applied when presenting HDR content (content with HLG or PQ transfer functions)
* alongside other content, whereby maximum input luminance is mapped to maximum output luminance
* and intermediate values are interpolated.
*/
struct LinearEffect {
// Input dataspace of the source colors.
const ui::Dataspace inputDataspace = ui::Dataspace::SRGB;
// Working dataspace for the output surface.
const ui::Dataspace outputDataspace = ui::Dataspace::SRGB;
// Sets whether alpha premultiplication must be undone.
// This is required if the source colors use premultiplied alpha and is not opaque.
const bool undoPremultipliedAlpha = false;
// "Fake" dataspace of the destination colors. This is used for applying an OETF to compute
// non-linear RGB. This is used when Skia is expected to color manage the input image based on
// the dataspace of the provided source image and destination surface. Some use-cases in
// RenderEngine expect to apply a different OETF than what is expected by Skia. As in,
// RenderEngine will color manage to a custom destination and "cast" the result to Skia's
// working space.
ui::Dataspace fakeOutputDataspace = ui::Dataspace::UNKNOWN;
enum SkSLType { Shader, ColorFilter };
SkSLType type = Shader;
};
static inline bool operator==(const LinearEffect& lhs, const LinearEffect& rhs) {
return lhs.inputDataspace == rhs.inputDataspace && lhs.outputDataspace == rhs.outputDataspace &&
lhs.undoPremultipliedAlpha == rhs.undoPremultipliedAlpha &&
lhs.fakeOutputDataspace == rhs.fakeOutputDataspace;
}
struct LinearEffectHasher {
// Inspired by art/runtime/class_linker.cc
// Also this is what boost:hash_combine does
static size_t HashCombine(size_t seed, size_t val) {
return seed ^ (val + 0x9e3779b9 + (seed << 6) + (seed >> 2));
}
size_t operator()(const LinearEffect& le) const {
size_t result = std::hash<ui::Dataspace>{}(le.inputDataspace);
result = HashCombine(result, std::hash<ui::Dataspace>{}(le.outputDataspace));
result = HashCombine(result, std::hash<bool>{}(le.undoPremultipliedAlpha));
return HashCombine(result, std::hash<ui::Dataspace>{}(le.fakeOutputDataspace));
}
};
// Generates a shader string that applies color transforms in linear space.
// Typical use-cases supported:
// 1. Apply tone-mapping
// 2. Apply color transform matrices in linear space
std::string buildLinearEffectSkSL(const LinearEffect& linearEffect);
// Generates a list of uniforms to set on the LinearEffect shader above.
std::vector<tonemap::ShaderUniform> buildLinearEffectUniforms(
const LinearEffect& linearEffect, const mat4& colorTransform, float maxDisplayLuminance,
float currentDisplayLuminanceNits, float maxLuminance, AHardwareBuffer* buffer = nullptr,
aidl::android::hardware::graphics::composer3::RenderIntent renderIntent =
aidl::android::hardware::graphics::composer3::RenderIntent::TONE_MAP_COLORIMETRIC);
} // namespace android::shaders
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