cc/raster/texture_compressor_etc1.h

// Copyright 2015 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.

#ifndef CC_RASTER_TEXTURE_COMPRESSOR_ETC1_H_
#define CC_RASTER_TEXTURE_COMPRESSOR_ETC1_H_

#include "cc/raster/texture_compressor.h"

#include <stdint.h>

#include "base/compiler_specific.h"
#include "base/logging.h"
#include "base/macros.h"

namespace cc {

template <typename T>
inline T clamp(T val, T min, T max) {
  return val < min ? min : (val > max ? max : val);
}

inline uint8_t round_to_5_bits(float val) {
  return clamp<uint8_t>(val * 31.0f / 255.0f + 0.5f, 0, 31);
}

inline uint8_t round_to_4_bits(float val) {
  return clamp<uint8_t>(val * 15.0f / 255.0f + 0.5f, 0, 15);
}

union Color {
  struct BgraColorType {
    uint8_t b;
    uint8_t g;
    uint8_t r;
    uint8_t a;
  } channels;
  uint8_t components[4];
  uint32_t bits;
};

// Codeword tables.
// See: Table 3.17.2
alignas(16) static const int16_t g_codeword_tables[8][4] = {
    {-8, -2, 2, 8},       {-17, -5, 5, 17},    {-29, -9, 9, 29},
    {-42, -13, 13, 42},   {-60, -18, 18, 60},  {-80, -24, 24, 80},
    {-106, -33, 33, 106}, {-183, -47, 47, 183}};

// Maps modifier indices to pixel index values.
// See: Table 3.17.3
static const uint8_t g_mod_to_pix[4] = {3, 2, 0, 1};

// The ETC1 specification index texels as follows:
// [a][e][i][m]     [ 0][ 4][ 8][12]
// [b][f][j][n] <-> [ 1][ 5][ 9][13]
// [c][g][k][o]     [ 2][ 6][10][14]
// [d][h][l][p]     [ 3][ 7][11][15]

// [ 0][ 1][ 2][ 3]     [ 0][ 1][ 4][ 5]
// [ 4][ 5][ 6][ 7] <-> [ 8][ 9][12][13]
// [ 8][ 9][10][11]     [ 2][ 3][ 6][ 7]
// [12][13][14][15]     [10][11][14][15]

// However, when extracting sub blocks from BGRA data the natural array
// indexing order ends up different:
// vertical0: [a][e][b][f]  horizontal0: [a][e][i][m]
//            [c][g][d][h]               [b][f][j][n]
// vertical1: [i][m][j][n]  horizontal1: [c][g][k][o]
//            [k][o][l][p]               [d][h][l][p]

// In order to translate from the natural array indices in a sub block to the
// indices (number) used by specification and hardware we use this table.
static const uint8_t g_idx_to_num[4][8] = {
    {0, 4, 1, 5, 2, 6, 3, 7},        // Vertical block 0.
    {8, 12, 9, 13, 10, 14, 11, 15},  // Vertical block 1.
    {0, 4, 8, 12, 1, 5, 9, 13},      // Horizontal block 0.
    {2, 6, 10, 14, 3, 7, 11, 15}     // Horizontal block 1.
};

inline void WriteColors444(uint8_t* block,
                           const Color& color0,
                           const Color& color1) {
  // Write output color for BGRA textures.
  block[0] = (color0.channels.r & 0xf0) | (color1.channels.r >> 4);
  block[1] = (color0.channels.g & 0xf0) | (color1.channels.g >> 4);
  block[2] = (color0.channels.b & 0xf0) | (color1.channels.b >> 4);
}

inline void WriteColors555(uint8_t* block,
                           const Color& color0,
                           const Color& color1) {
  // Table for conversion to 3-bit two complement format.
  static const uint8_t two_compl_trans_table[8] = {
      4,  // -4 (100b)
      5,  // -3 (101b)
      6,  // -2 (110b)
      7,  // -1 (111b)
      0,  //  0 (000b)
      1,  //  1 (001b)
      2,  //  2 (010b)
      3,  //  3 (011b)
  };

  int16_t delta_r =
      static_cast<int16_t>(color1.channels.r >> 3) - (color0.channels.r >> 3);
  int16_t delta_g =
      static_cast<int16_t>(color1.channels.g >> 3) - (color0.channels.g >> 3);
  int16_t delta_b =
      static_cast<int16_t>(color1.channels.b >> 3) - (color0.channels.b >> 3);
  DCHECK_GE(delta_r, -4);
  DCHECK_LE(delta_r, 3);
  DCHECK_GE(delta_g, -4);
  DCHECK_LE(delta_g, 3);
  DCHECK_GE(delta_b, -4);
  DCHECK_LE(delta_b, 3);

  // Write output color for BGRA textures.
  block[0] = (color0.channels.r & 0xf8) | two_compl_trans_table[delta_r + 4];
  block[1] = (color0.channels.g & 0xf8) | two_compl_trans_table[delta_g + 4];
  block[2] = (color0.channels.b & 0xf8) | two_compl_trans_table[delta_b + 4];
}

inline void WriteCodewordTable(uint8_t* block,
                               uint8_t sub_block_id,
                               uint8_t table) {
  DCHECK_LT(sub_block_id, 2);
  DCHECK_LT(table, 8);

  uint8_t shift = (2 + (3 - sub_block_id * 3));
  block[3] &= ~(0x07 << shift);
  block[3] |= table << shift;
}

inline void WritePixelData(uint8_t* block, uint32_t pixel_data) {
  block[4] |= pixel_data >> 24;
  block[5] |= (pixel_data >> 16) & 0xff;
  block[6] |= (pixel_data >> 8) & 0xff;
  block[7] |= pixel_data & 0xff;
}

inline void WriteFlip(uint8_t* block, bool flip) {
  block[3] &= ~0x01;
  block[3] |= static_cast<uint8_t>(flip);
}

inline void WriteDiff(uint8_t* block, bool diff) {
  block[3] &= ~0x02;
  block[3] |= static_cast<uint8_t>(diff) << 1;
}

// Compress and rounds BGR888 into BGR444. The resulting BGR444 color is
// expanded to BGR888 as it would be in hardware after decompression. The
// actual 444-bit data is available in the four most significant bits of each
// channel.
inline Color MakeColor444(const float* bgr) {
  uint8_t b4 = round_to_4_bits(bgr[0]);
  uint8_t g4 = round_to_4_bits(bgr[1]);
  uint8_t r4 = round_to_4_bits(bgr[2]);
  Color bgr444;
  bgr444.channels.b = (b4 << 4) | b4;
  bgr444.channels.g = (g4 << 4) | g4;
  bgr444.channels.r = (r4 << 4) | r4;
  // Added to distinguish between expanded 555 and 444 colors.
  bgr444.channels.a = 0x44;
  return bgr444;
}

// Compress and rounds BGR888 into BGR555. The resulting BGR555 color is
// expanded to BGR888 as it would be in hardware after decompression. The
// actual 555-bit data is available in the five most significant bits of each
// channel.
inline Color MakeColor555(const float* bgr) {
  uint8_t b5 = round_to_5_bits(bgr[0]);
  uint8_t g5 = round_to_5_bits(bgr[1]);
  uint8_t r5 = round_to_5_bits(bgr[2]);
  Color bgr555;
  bgr555.channels.b = (b5 << 3) | (b5 >> 2);
  bgr555.channels.g = (g5 << 3) | (g5 >> 2);
  bgr555.channels.r = (r5 << 3) | (r5 >> 2);
  // Added to distinguish between expanded 555 and 444 colors.
  bgr555.channels.a = 0x55;
  return bgr555;
}

class CC_EXPORT TextureCompressorETC1 : public TextureCompressor {
 public:
  TextureCompressorETC1() {}

  // Compress a texture using ETC1. Note that the |quality| parameter is
  // ignored. The current implementation does not support different quality
  // settings.
  void Compress(const uint8_t* src,
                uint8_t* dst,
                int width,
                int height,
                Quality quality) override;

 private:
  DISALLOW_COPY_AND_ASSIGN(TextureCompressorETC1);
};

}  // namespace cc

#endif  // CC_RASTER_TEXTURE_COMPRESSOR_ETC1_H_