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// Copyright 2017 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 "ui/gfx/skia_color_space_util.h"
#include <algorithm>
#include <cmath>
#include <vector>
#include "base/logging.h"
namespace gfx {
float SkTransferFnEvalUnclamped(const SkColorSpaceTransferFn& fn, float x) {
if (x < fn.fD)
return fn.fC * x + fn.fF;
return std::pow(fn.fA * x + fn.fB, fn.fG) + fn.fE;
}
float SkTransferFnEval(const SkColorSpaceTransferFn& fn, float x) {
float fn_at_x_unclamped = SkTransferFnEvalUnclamped(fn, x);
return std::min(std::max(fn_at_x_unclamped, 0.f), 1.f);
}
SkColorSpaceTransferFn SkTransferFnInverse(const SkColorSpaceTransferFn& fn) {
SkColorSpaceTransferFn fn_inv = {0};
if (fn.fA > 0 && fn.fG > 0) {
double a_to_the_g = std::pow(fn.fA, fn.fG);
fn_inv.fA = 1.f / a_to_the_g;
fn_inv.fB = -fn.fE / a_to_the_g;
fn_inv.fG = 1.f / fn.fG;
}
fn_inv.fD = fn.fC * fn.fD + fn.fF;
fn_inv.fE = -fn.fB / fn.fA;
if (fn.fC != 0) {
fn_inv.fC = 1.f / fn.fC;
fn_inv.fF = -fn.fF / fn.fC;
}
return fn_inv;
}
bool SkTransferFnsApproximatelyCancel(const SkColorSpaceTransferFn& a,
const SkColorSpaceTransferFn& b) {
const float kStep = 1.f / 8.f;
const float kEpsilon = 2.5f / 256.f;
for (float x = 0; x <= 1.f; x += kStep) {
float a_of_x = SkTransferFnEval(a, x);
float b_of_a_of_x = SkTransferFnEval(b, a_of_x);
if (std::abs(b_of_a_of_x - x) > kEpsilon)
return false;
}
return true;
}
bool SkTransferFnIsApproximatelyIdentity(const SkColorSpaceTransferFn& a) {
const float kStep = 1.f / 8.f;
const float kEpsilon = 2.5f / 256.f;
for (float x = 0; x <= 1.f; x += kStep) {
float a_of_x = SkTransferFnEval(a, x);
if (std::abs(a_of_x - x) > kEpsilon)
return false;
}
return true;
}
bool SkMatrixIsApproximatelyIdentity(const SkMatrix44& m) {
const float kEpsilon = 1.f / 256.f;
for (int i = 0; i < 4; ++i) {
for (int j = 0; j < 4; ++j) {
float identity_value = i == j ? 1 : 0;
float value = m.get(i, j);
if (std::abs(identity_value - value) > kEpsilon)
return false;
}
}
return true;
}
} // namespace gfx
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