text: // Copyright 2015 Google Inc. All Rights Reserved.
  //
  // Use of this source code is governed by a BSD-style license
  // that can be found in the COPYING file in the root of the source
  // tree. An additional intellectual property rights grant can be found
  // in the file PATENTS. All contributing project authors may
  // be found in the AUTHORS file in the root of the source tree.
  // -----------------------------------------------------------------------------
  //
  // Author: Mislav Bradac (mislavm@google.com)
  //
  
  #include "./delta_palettization.h"
  
  #ifdef WEBP_EXPERIMENTAL_FEATURES
  #include "../webp/types.h"
  #include "../dsp/lossless.h"
  
  #define MK_COL(r, g, b) (((r) << 16) + ((g) << 8) + (b))
  
  // Format allows palette up to 256 entries, but more palette entries produce
  // bigger entropy. In the future it will probably be useful to add more entries
  // that are far from the origin of the palette or choose remaining entries
  // dynamically.
  #define DELTA_PALETTE_SIZE 226
  
  // Palette used for delta_palettization. Entries are roughly sorted by distance
  // of their signed equivalents from the origin.
  static const uint32_t kDeltaPalette[DELTA_PALETTE_SIZE] = {
    MK_COL(0u, 0u, 0u),
    MK_COL(255u, 255u, 255u),
    MK_COL(1u, 1u, 1u),
    MK_COL(254u, 254u, 254u),
    MK_COL(2u, 2u, 2u),
    MK_COL(4u, 4u, 4u),
    MK_COL(252u, 252u, 252u),
    MK_COL(250u, 0u, 0u),
    MK_COL(0u, 250u, 0u),
    MK_COL(0u, 0u, 250u),
    MK_COL(6u, 0u, 0u),
    MK_COL(0u, 6u, 0u),
    MK_COL(0u, 0u, 6u),
    MK_COL(0u, 0u, 248u),
    MK_COL(0u, 0u, 8u),
    MK_COL(0u, 248u, 0u),
    MK_COL(0u, 248u, 248u),
    MK_COL(0u, 248u, 8u),
    MK_COL(0u, 8u, 0u),
    MK_COL(0u, 8u, 248u),
    MK_COL(0u, 8u, 8u),
    MK_COL(8u, 8u, 8u),
    MK_COL(248u, 0u, 0u),
    MK_COL(248u, 0u, 248u),
    MK_COL(248u, 0u, 8u),
    MK_COL(248u, 248u, 0u),
    MK_COL(248u, 8u, 0u),
    MK_COL(8u, 0u, 0u),
    MK_COL(8u, 0u, 248u),
    MK_COL(8u, 0u, 8u),
    MK_COL(8u, 248u, 0u),
    MK_COL(8u, 8u, 0u),
    MK_COL(23u, 23u, 23u),
    MK_COL(13u, 13u, 13u),
    MK_COL(232u, 232u, 232u),
    MK_COL(244u, 244u, 244u),
    MK_COL(245u, 245u, 250u),
    MK_COL(50u, 50u, 50u),
    MK_COL(204u, 204u, 204u),
    MK_COL(236u, 236u, 236u),
    MK_COL(16u, 16u, 16u),
    MK_COL(240u, 16u, 16u),
    MK_COL(16u, 240u, 16u),
    MK_COL(240u, 240u, 16u),
    MK_COL(16u, 16u, 240u),
    MK_COL(240u, 16u, 240u),
    MK_COL(16u, 240u, 240u),
    MK_COL(240u, 240u, 240u),
    MK_COL(0u, 0u, 232u),
    MK_COL(0u, 232u, 0u),
    MK_COL(232u, 0u, 0u),
    MK_COL(0u, 0u, 24u),
    MK_COL(0u, 24u, 0u),
    MK_COL(24u, 0u, 0u),
    MK_COL(32u, 32u, 32u),
    MK_COL(224u, 32u, 32u),
    MK_COL(32u, 224u, 32u),
    MK_COL(224u, 224u, 32u),
    MK_COL(32u, 32u, 224u),
    MK_COL(224u, 32u, 224u),
    MK_COL(32u, 224u, 224u),
    MK_COL(224u, 224u, 224u),
    MK_COL(0u, 0u, 176u),
    MK_COL(0u, 0u, 80u),
    MK_COL(0u, 176u, 0u),
    MK_COL(0u, 176u, 176u),
    MK_COL(0u, 176u, 80u),
    MK_COL(0u, 80u, 0u),
    MK_COL(0u, 80u, 176u),
    MK_COL(0u, 80u, 80u),
    MK_COL(176u, 0u, 0u),
    MK_COL(176u, 0u, 176u),
    MK_COL(176u, 0u, 80u),
    MK_COL(176u, 176u, 0u),
    MK_COL(176u, 80u, 0u),
    MK_COL(80u, 0u, 0u),
    MK_COL(80u, 0u, 176u),
    MK_COL(80u, 0u, 80u),
    MK_COL(80u, 176u, 0u),
    MK_COL(80u, 80u, 0u),
    MK_COL(0u, 0u, 152u),
    MK_COL(0u, 0u, 104u),
    MK_COL(0u, 152u, 0u),
    MK_COL(0u, 152u, 152u),
    MK_COL(0u, 152u, 104u),
    MK_COL(0u, 104u, 0u),
    MK_COL(0u, 104u, 152u),
    MK_COL(0u, 104u, 104u),
    MK_COL(152u, 0u, 0u),
    MK_COL(152u, 0u, 152u),
    MK_COL(152u, 0u, 104u),
    MK_COL(152u, 152u, 0u),
    MK_COL(152u, 104u, 0u),
    MK_COL(104u, 0u, 0u),
    MK_COL(104u, 0u, 152u),
    MK_COL(104u, 0u, 104u),
    MK_COL(104u, 152u, 0u),
    MK_COL(104u, 104u, 0u),
    MK_COL(216u, 216u, 216u),
    MK_COL(216u, 216u, 40u),
    MK_COL(216u, 216u, 176u),
    MK_COL(216u, 216u, 80u),
    MK_COL(216u, 40u, 216u),
    MK_COL(216u, 40u, 40u),
    MK_COL(216u, 40u, 176u),
    MK_COL(216u, 40u, 80u),
    MK_COL(216u, 176u, 216u),
    MK_COL(216u, 176u, 40u),
    MK_COL(216u, 176u, 176u),
    MK_COL(216u, 176u, 80u),
    MK_COL(216u, 80u, 216u),
    MK_COL(216u, 80u, 40u),
    MK_COL(216u, 80u, 176u),
    MK_COL(216u, 80u, 80u),
    MK_COL(40u, 216u, 216u),
    MK_COL(40u, 216u, 40u),
    MK_COL(40u, 216u, 176u),
    MK_COL(40u, 216u, 80u),
    MK_COL(40u, 40u, 216u),
    MK_COL(40u, 40u, 40u),
    MK_COL(40u, 40u, 176u),
    MK_COL(40u, 40u, 80u),
    MK_COL(40u, 176u, 216u),
    MK_COL(40u, 176u, 40u),
    MK_COL(40u, 176u, 176u),
    MK_COL(40u, 176u, 80u),
    MK_COL(40u, 80u, 216u),
    MK_COL(40u, 80u, 40u),
    MK_COL(40u, 80u, 176u),
    MK_COL(40u, 80u, 80u),
    MK_COL(80u, 216u, 216u),
    MK_COL(80u, 216u, 40u),
    MK_COL(80u, 216u, 176u),
    MK_COL(80u, 216u, 80u),
    MK_COL(80u, 40u, 216u),
    MK_COL(80u, 40u, 40u),
    MK_COL(80u, 40u, 176u),
    MK_COL(80u, 40u, 80u),
    MK_COL(80u, 176u, 216u),
    MK_COL(80u, 176u, 40u),
    MK_COL(80u, 176u, 176u),
    MK_COL(80u, 176u, 80u),
    MK_COL(80u, 80u, 216u),
    MK_COL(80u, 80u, 40u),
    MK_COL(80u, 80u, 176u),
    MK_COL(80u, 80u, 80u),
    MK_COL(0u, 0u, 192u),
    MK_COL(0u, 0u, 64u),
    MK_COL(0u, 0u, 128u),
    MK_COL(0u, 192u, 0u),
    MK_COL(0u, 192u, 192u),
    MK_COL(0u, 192u, 64u),
    MK_COL(0u, 192u, 128u),
    MK_COL(0u, 64u, 0u),
    MK_COL(0u, 64u, 192u),
    MK_COL(0u, 64u, 64u),
    MK_COL(0u, 64u, 128u),
    MK_COL(0u, 128u, 0u),
    MK_COL(0u, 128u, 192u),
    MK_COL(0u, 128u, 64u),
    MK_COL(0u, 128u, 128u),
    MK_COL(176u, 216u, 216u),
    MK_COL(176u, 216u, 40u),
    MK_COL(176u, 216u, 176u),
    MK_COL(176u, 216u, 80u),
    MK_COL(176u, 40u, 216u),
    MK_COL(176u, 40u, 40u),
    MK_COL(176u, 40u, 176u),
    MK_COL(176u, 40u, 80u),
    MK_COL(176u, 176u, 216u),
    MK_COL(176u, 176u, 40u),
    MK_COL(176u, 176u, 176u),
    MK_COL(176u, 176u, 80u),
    MK_COL(176u, 80u, 216u),
    MK_COL(176u, 80u, 40u),
    MK_COL(176u, 80u, 176u),
    MK_COL(176u, 80u, 80u),
    MK_COL(192u, 0u, 0u),
    MK_COL(192u, 0u, 192u),
    MK_COL(192u, 0u, 64u),
    MK_COL(192u, 0u, 128u),
    MK_COL(192u, 192u, 0u),
    MK_COL(192u, 192u, 192u),
    MK_COL(192u, 192u, 64u),
    MK_COL(192u, 192u, 128u),
    MK_COL(192u, 64u, 0u),
    MK_COL(192u, 64u, 192u),
    MK_COL(192u, 64u, 64u),
    MK_COL(192u, 64u, 128u),
    MK_COL(192u, 128u, 0u),
    MK_COL(192u, 128u, 192u),
    MK_COL(192u, 128u, 64u),
    MK_COL(192u, 128u, 128u),
    MK_COL(64u, 0u, 0u),
    MK_COL(64u, 0u, 192u),
    MK_COL(64u, 0u, 64u),
    MK_COL(64u, 0u, 128u),
    MK_COL(64u, 192u, 0u),
    MK_COL(64u, 192u, 192u),
    MK_COL(64u, 192u, 64u),
    MK_COL(64u, 192u, 128u),
    MK_COL(64u, 64u, 0u),
    MK_COL(64u, 64u, 192u),
    MK_COL(64u, 64u, 64u),
    MK_COL(64u, 64u, 128u),
    MK_COL(64u, 128u, 0u),
    MK_COL(64u, 128u, 192u),
    MK_COL(64u, 128u, 64u),
    MK_COL(64u, 128u, 128u),
    MK_COL(128u, 0u, 0u),
    MK_COL(128u, 0u, 192u),
    MK_COL(128u, 0u, 64u),
    MK_COL(128u, 0u, 128u),
    MK_COL(128u, 192u, 0u),
    MK_COL(128u, 192u, 192u),
    MK_COL(128u, 192u, 64u),
    MK_COL(128u, 192u, 128u),
    MK_COL(128u, 64u, 0u),
    MK_COL(128u, 64u, 192u),
    MK_COL(128u, 64u, 64u),
    MK_COL(128u, 64u, 128u),
    MK_COL(128u, 128u, 0u),
    MK_COL(128u, 128u, 192u),
    MK_COL(128u, 128u, 64u),
    MK_COL(128u, 128u, 128u),
  };
  
  #undef MK_COL
  
  //------------------------------------------------------------------------------
  // TODO(skal): move the functions to dsp/lossless.c when the correct
  // granularity is found. For now, we'll just copy-paste some useful bits
  // here instead.
  
  // In-place sum of each component with mod 256.
  static WEBP_INLINE void AddPixelsEq(uint32_t* a, uint32_t b) {
    const uint32_t alpha_and_green = (*a & 0xff00ff00u) + (b & 0xff00ff00u);
    const uint32_t red_and_blue = (*a & 0x00ff00ffu) + (b & 0x00ff00ffu);
    *a = (alpha_and_green & 0xff00ff00u) | (red_and_blue & 0x00ff00ffu);
  }
  
  static WEBP_INLINE uint32_t Clip255(uint32_t a) {
    if (a < 256) {
      return a;
    }
    // return 0, when a is a negative integer.
    // return 255, when a is positive.
    return ~a >> 24;
  }
  
  // Delta palettization functions.
  static WEBP_INLINE int Square(int x) {
    return x * x;
  }
  
  static WEBP_INLINE uint32_t Intensity(uint32_t a) {
    return
        30 * ((a >> 16) & 0xff) +
        59 * ((a >>  8) & 0xff) +
        11 * ((a >>  0) & 0xff);
  }
  
  static uint32_t CalcDist(uint32_t predicted_value, uint32_t actual_value,
                           uint32_t palette_entry) {
    int i;
    uint32_t distance = 0;
    AddPixelsEq(&predicted_value, palette_entry);
    for (i = 0; i < 32; i += 8) {
      const int32_t av = (actual_value >> i) & 0xff;
      const int32_t pv = (predicted_value >> i) & 0xff;
      distance += Square(pv - av);
    }
    // We sum square of intensity difference with factor 10, but because Intensity
    // returns 100 times real intensity we need to multiply differences of colors
    // by 1000.
    distance *= 1000u;
    distance += Square(Intensity(predicted_value)
                       - Intensity(actual_value));
    return distance;
  }
  
  static uint32_t Predict(int x, int y, uint32_t* image) {
    const uint32_t t = (y == 0) ? ARGB_BLACK : image[x];
    const uint32_t l = (x == 0) ? ARGB_BLACK : image[x - 1];
    const uint32_t p =
        (((((t >> 24) & 0xff) + ((l >> 24) & 0xff)) / 2) << 24) +
        (((((t >> 16) & 0xff) + ((l >> 16) & 0xff)) / 2) << 16) +
        (((((t >>  8) & 0xff) + ((l >>  8) & 0xff)) / 2) <<  8) +
        (((((t >>  0) & 0xff) + ((l >>  0) & 0xff)) / 2) <<  0);
    if (x == 0 && y == 0) return ARGB_BLACK;
    if (x == 0) return t;
    if (y == 0) return l;
    return p;
  }
  
  static WEBP_INLINE int AddSubtractComponentFullWithCoefficient(
      int a, int b, int c) {
    return Clip255(a + ((b - c) >> 2));
  }
  
  static WEBP_INLINE uint32_t ClampedAddSubtractFullWithCoefficient(
      uint32_t c0, uint32_t c1, uint32_t c2) {
    const int a = AddSubtractComponentFullWithCoefficient(
        c0 >> 24, c1 >> 24, c2 >> 24);
    const int r = AddSubtractComponentFullWithCoefficient((c0 >> 16) & 0xff,
                                                         (c1 >> 16) & 0xff,
                                                         (c2 >> 16) & 0xff);
    const int g = AddSubtractComponentFullWithCoefficient((c0 >> 8) & 0xff,
                                                         (c1 >> 8) & 0xff,
                                                         (c2 >> 8) & 0xff);
    const int b = AddSubtractComponentFullWithCoefficient(
        c0 & 0xff, c1 & 0xff, c2 & 0xff);
    return ((uint32_t)a << 24) | (r << 16) | (g << 8) | b;
  }
  
  //------------------------------------------------------------------------------
  
  // Find palette entry with minimum error from difference of actual pixel value
  // and predicted pixel value. Propagate error of pixel to its top and left pixel
  // in src array. Write predicted_value + palette_entry to new_image. Return
  // index of best palette entry.
  static int FindBestPaletteEntry(uint32_t src, uint32_t predicted_value,
                                  const uint32_t palette[], int palette_size) {
    int i;
    int idx = 0;
    uint32_t best_distance = CalcDist(predicted_value, src, palette[0]);
    for (i = 1; i < palette_size; ++i) {
      const uint32_t distance = CalcDist(predicted_value, src, palette[i]);
      if (distance < best_distance) {
        best_distance = distance;
        idx = i;
      }
    }
    return idx;
  }
  
  static void ApplyBestPaletteEntry(int x, int y,
                                    uint32_t new_value, uint32_t palette_value,
                                    uint32_t* src, int src_stride,
                                    uint32_t* new_image) {
    AddPixelsEq(&new_value, palette_value);
    if (x > 0) {
      src[x - 1] = ClampedAddSubtractFullWithCoefficient(src[x - 1],
                                                         new_value, src[x]);
    }
    if (y > 0) {
      src[x - src_stride] =
          ClampedAddSubtractFullWithCoefficient(src[x - src_stride],
                                                new_value, src[x]);
    }
    new_image[x] = new_value;
  }
  
  //------------------------------------------------------------------------------
  // Main entry point
  
  static WebPEncodingError ApplyDeltaPalette(uint32_t* src, uint32_t* dst,
                                             uint32_t src_stride,
                                             uint32_t dst_stride,
                                             const uint32_t* palette,
                                             int palette_size,
                                             int width, int height,
                                             int num_passes) {
    int x, y;
    WebPEncodingError err = VP8_ENC_OK;
    uint32_t* new_image = (uint32_t*)WebPSafeMalloc(width, sizeof(*new_image));
    uint8_t* const tmp_row = (uint8_t*)WebPSafeMalloc(width, sizeof(*tmp_row));
    if (new_image == NULL || tmp_row == NULL) {
      err = VP8_ENC_ERROR_OUT_OF_MEMORY;
      goto Error;
    }
  
    while (num_passes--) {
      uint32_t* cur_src = src;
      uint32_t* cur_dst = dst;
      for (y = 0; y < height; ++y) {
        for (x = 0; x < width; ++x) {
          const uint32_t predicted_value = Predict(x, y, new_image);
          tmp_row[x] = FindBestPaletteEntry(cur_src[x], predicted_value,
                                            palette, palette_size);
          ApplyBestPaletteEntry(x, y, predicted_value, palette[tmp_row[x]],
                                cur_src, src_stride, new_image);
        }
        for (x = 0; x < width; ++x) {
          cur_dst[x] = palette[tmp_row[x]];
        }
        cur_src += src_stride;
        cur_dst += dst_stride;
      }
    }
   Error:
    WebPSafeFree(new_image);
    WebPSafeFree(tmp_row);
    return err;
  }
  
  // replaces enc->argb_ by a palettizable approximation of it,
  // and generates optimal enc->palette_[]
  WebPEncodingError WebPSearchOptimalDeltaPalette(VP8LEncoder* const enc) {
    const WebPPicture* const pic = enc->pic_;
    uint32_t* src = pic->argb;
    uint32_t* dst = enc->argb_;
    const int width = pic->width;
    const int height = pic->height;
  
    WebPEncodingError err = VP8_ENC_OK;
    memcpy(enc->palette_, kDeltaPalette, sizeof(kDeltaPalette));
    enc->palette_[DELTA_PALETTE_SIZE - 1] = src[0] - 0xff000000u;
    enc->palette_size_ = DELTA_PALETTE_SIZE;
    err = ApplyDeltaPalette(src, dst, pic->argb_stride, enc->current_width_,
                            enc->palette_, enc->palette_size_,
                            width, height, 2);
    if (err != VP8_ENC_OK) goto Error;
  
   Error:
    return err;
  }
  
  #else  // !WEBP_EXPERIMENTAL_FEATURES
  
  WebPEncodingError WebPSearchOptimalDeltaPalette(VP8LEncoder* const enc) {
    (void)enc;
    return VP8_ENC_ERROR_INVALID_CONFIGURATION;
  }
  
  #endif  // WEBP_EXPERIMENTAL_FEATURES
  