// Copyright 2023 The PDFium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com

#include "core/fxge/dib/blend.h"

#include <algorithm>

#include "core/fxge/dib/fx_dib.h"
#include "third_party/base/check_op.h"
#include "third_party/base/notreached.h"

namespace fxge {

namespace {

constexpr uint8_t kColorSqrt[256] = {
    0x00, 0x03, 0x07, 0x0B, 0x0F, 0x12, 0x16, 0x19, 0x1D, 0x20, 0x23, 0x26,
    0x29, 0x2C, 0x2F, 0x32, 0x35, 0x37, 0x3A, 0x3C, 0x3F, 0x41, 0x43, 0x46,
    0x48, 0x4A, 0x4C, 0x4E, 0x50, 0x52, 0x54, 0x56, 0x57, 0x59, 0x5B, 0x5C,
    0x5E, 0x60, 0x61, 0x63, 0x64, 0x65, 0x67, 0x68, 0x69, 0x6B, 0x6C, 0x6D,
    0x6E, 0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A,
    0x7B, 0x7C, 0x7D, 0x7E, 0x80, 0x81, 0x82, 0x83, 0x84, 0x85, 0x86, 0x87,
    0x87, 0x88, 0x89, 0x8A, 0x8B, 0x8C, 0x8D, 0x8E, 0x8F, 0x90, 0x91, 0x91,
    0x92, 0x93, 0x94, 0x95, 0x96, 0x97, 0x97, 0x98, 0x99, 0x9A, 0x9B, 0x9C,
    0x9C, 0x9D, 0x9E, 0x9F, 0xA0, 0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA4, 0xA5,
    0xA6, 0xA7, 0xA7, 0xA8, 0xA9, 0xAA, 0xAA, 0xAB, 0xAC, 0xAD, 0xAD, 0xAE,
    0xAF, 0xB0, 0xB0, 0xB1, 0xB2, 0xB3, 0xB3, 0xB4, 0xB5, 0xB5, 0xB6, 0xB7,
    0xB7, 0xB8, 0xB9, 0xBA, 0xBA, 0xBB, 0xBC, 0xBC, 0xBD, 0xBE, 0xBE, 0xBF,
    0xC0, 0xC0, 0xC1, 0xC2, 0xC2, 0xC3, 0xC4, 0xC4, 0xC5, 0xC6, 0xC6, 0xC7,
    0xC7, 0xC8, 0xC9, 0xC9, 0xCA, 0xCB, 0xCB, 0xCC, 0xCC, 0xCD, 0xCE, 0xCE,
    0xCF, 0xD0, 0xD0, 0xD1, 0xD1, 0xD2, 0xD3, 0xD3, 0xD4, 0xD4, 0xD5, 0xD6,
    0xD6, 0xD7, 0xD7, 0xD8, 0xD9, 0xD9, 0xDA, 0xDA, 0xDB, 0xDC, 0xDC, 0xDD,
    0xDD, 0xDE, 0xDE, 0xDF, 0xE0, 0xE0, 0xE1, 0xE1, 0xE2, 0xE2, 0xE3, 0xE4,
    0xE4, 0xE5, 0xE5, 0xE6, 0xE6, 0xE7, 0xE7, 0xE8, 0xE9, 0xE9, 0xEA, 0xEA,
    0xEB, 0xEB, 0xEC, 0xEC, 0xED, 0xED, 0xEE, 0xEE, 0xEF, 0xF0, 0xF0, 0xF1,
    0xF1, 0xF2, 0xF2, 0xF3, 0xF3, 0xF4, 0xF4, 0xF5, 0xF5, 0xF6, 0xF6, 0xF7,
    0xF7, 0xF8, 0xF8, 0xF9, 0xF9, 0xFA, 0xFA, 0xFB, 0xFB, 0xFC, 0xFC, 0xFD,
    0xFD, 0xFE, 0xFE, 0xFF};

}  // namespace

int Blend(BlendMode blend_mode, int back_color, int src_color) {
  // Intentionally using DCHECKs, as Blend() is oftentimes called 3 times per
  // pixel.
  DCHECK_GE(back_color, 0);
  DCHECK_LE(back_color, 255);
  DCHECK_GE(src_color, 0);
  DCHECK_LE(src_color, 255);

  switch (blend_mode) {
    case BlendMode::kNormal:
      return src_color;
    case BlendMode::kMultiply:
      return src_color * back_color / 255;
    case BlendMode::kScreen:
      return src_color + back_color - src_color * back_color / 255;
    case BlendMode::kOverlay:
      return Blend(BlendMode::kHardLight, src_color, back_color);
    case BlendMode::kDarken:
      return std::min(src_color, back_color);
    case BlendMode::kLighten:
      return std::max(src_color, back_color);
    case BlendMode::kColorDodge: {
      if (src_color == 255) {
        return 255;
      }
      return std::min(back_color * 255 / (255 - src_color), 255);
    }
    case BlendMode::kColorBurn: {
      if (src_color == 0) {
        return 0;
      }
      return 255 - std::min((255 - back_color) * 255 / src_color, 255);
    }
    case BlendMode::kHardLight:
      if (src_color < 128) {
        return (src_color * back_color * 2) / 255;
      }
      return Blend(BlendMode::kScreen, back_color, 2 * src_color - 255);
    case BlendMode::kSoftLight: {
      if (src_color < 128) {
        return back_color - (255 - 2 * src_color) * back_color *
                                (255 - back_color) / 255 / 255;
      }
      return back_color + (2 * src_color - 255) *
                              (kColorSqrt[back_color] - back_color) / 255;
    }
    case BlendMode::kDifference:
      return std::abs(back_color - src_color);
    case BlendMode::kExclusion:
      return back_color + src_color - 2 * back_color * src_color / 255;
    default:
      // This function does not handle non-separable blend modes.
      NOTREACHED_NORETURN();
  }
}

}  // namespace fxge
