ui/gfx/skia_color_space_util.cc

// 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"
#include "base/numerics/ranges.h"

namespace gfx {

float SkTransferFnEvalUnclamped(const skcms_TransferFunction& fn, float x) {
  if (x < fn.d)
    return fn.c * x + fn.f;
  return std::pow(fn.a * x + fn.b, fn.g) + fn.e;
}

float SkTransferFnEval(const skcms_TransferFunction& fn, float x) {
  float fn_at_x_unclamped = SkTransferFnEvalUnclamped(fn, x);
  return base::ClampToRange(fn_at_x_unclamped, 0.0f, 1.0f);
}

skcms_TransferFunction SkTransferFnInverse(const skcms_TransferFunction& fn) {
  skcms_TransferFunction fn_inv = {0};
  if (fn.a > 0 && fn.g > 0) {
    double a_to_the_g = std::pow(fn.a, fn.g);
    fn_inv.a = 1.f / a_to_the_g;
    fn_inv.b = -fn.e / a_to_the_g;
    fn_inv.g = 1.f / fn.g;
  }
  fn_inv.d = fn.c * fn.d + fn.f;
  fn_inv.e = -fn.b / fn.a;
  if (fn.c != 0) {
    fn_inv.c = 1.f / fn.c;
    fn_inv.f = -fn.f / fn.c;
  }
  return fn_inv;
}

bool SkTransferFnsApproximatelyCancel(const skcms_TransferFunction& a,
                                      const skcms_TransferFunction& 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 skcms_TransferFunction& 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