// Copyright 2009 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#include <ETC1/etc1.h>
#include <string.h>
/* From http://www.khronos.org/registry/gles/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt
The number of bits that represent a 4x4 texel block is 64 bits if
<internalformat> is given by ETC1_RGB8_OES.
The data for a block is a number of bytes,
{q0, q1, q2, q3, q4, q5, q6, q7}
where byte q0 is located at the lowest memory address and q7 at
the highest. The 64 bits specifying the block is then represented
by the following 64 bit integer:
int64bit = 256*(256*(256*(256*(256*(256*(256*q0+q1)+q2)+q3)+q4)+q5)+q6)+q7;
ETC1_RGB8_OES:
a) bit layout in bits 63 through 32 if diffbit = 0
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48
-----------------------------------------------
| base col1 | base col2 | base col1 | base col2 |
| R1 (4bits)| R2 (4bits)| G1 (4bits)| G2 (4bits)|
-----------------------------------------------
47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
---------------------------------------------------
| base col1 | base col2 | table | table |diff|flip|
| B1 (4bits)| B2 (4bits)| cw 1 | cw 2 |bit |bit |
---------------------------------------------------
b) bit layout in bits 63 through 32 if diffbit = 1
63 62 61 60 59 58 57 56 55 54 53 52 51 50 49 48
-----------------------------------------------
| base col1 | dcol 2 | base col1 | dcol 2 |
| R1' (5 bits) | dR2 | G1' (5 bits) | dG2 |
-----------------------------------------------
47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 32
---------------------------------------------------
| base col 1 | dcol 2 | table | table |diff|flip|
| B1' (5 bits) | dB2 | cw 1 | cw 2 |bit |bit |
---------------------------------------------------
c) bit layout in bits 31 through 0 (in both cases)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
-----------------------------------------------
| most significant pixel index bits |
| p| o| n| m| l| k| j| i| h| g| f| e| d| c| b| a|
-----------------------------------------------
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
--------------------------------------------------
| least significant pixel index bits |
| p| o| n| m| l| k| j| i| h| g| f| e| d| c | b | a |
--------------------------------------------------
Add table 3.17.2: Intensity modifier sets for ETC1 compressed textures:
table codeword modifier table
------------------ ----------------------
0 -8 -2 2 8
1 -17 -5 5 17
2 -29 -9 9 29
3 -42 -13 13 42
4 -60 -18 18 60
5 -80 -24 24 80
6 -106 -33 33 106
7 -183 -47 47 183
Add table 3.17.3 Mapping from pixel index values to modifier values for
ETC1 compressed textures:
pixel index value
---------------
msb lsb resulting modifier value
----- ----- -------------------------
1 1 -b (large negative value)
1 0 -a (small negative value)
0 0 a (small positive value)
0 1 b (large positive value)
*/
static const int kModifierTable[] = {
/* 0 */2, 8, -2, -8,
/* 1 */5, 17, -5, -17,
/* 2 */9, 29, -9, -29,
/* 3 */13, 42, -13, -42,
/* 4 */18, 60, -18, -60,
/* 5 */24, 80, -24, -80,
/* 6 */33, 106, -33, -106,
/* 7 */47, 183, -47, -183 };
static const int kLookup[8] = { 0, 1, 2, 3, -4, -3, -2, -1 };
static inline etc1_byte clamp(int x) {
return (etc1_byte) (x >= 0 ? (x < 255 ? x : 255) : 0);
}
static
inline int convert4To8(int b) {
int c = b & 0xf;
return (c << 4) | c;
}
static
inline int convert5To8(int b) {
int c = b & 0x1f;
return (c << 3) | (c >> 2);
}
static
inline int convert6To8(int b) {
int c = b & 0x3f;
return (c << 2) | (c >> 4);
}
static
inline int divideBy255(int d) {
return (d + 128 + (d >> 8)) >> 8;
}
static
inline int convert8To4(int b) {
int c = b & 0xff;
return divideBy255(b * 15);
}
static
inline int convert8To5(int b) {
int c = b & 0xff;
return divideBy255(b * 31);
}
static
inline int convertDiff(int base, int diff) {
return convert5To8((0x1f & base) + kLookup[0x7 & diff]);
}
static
void decode_subblock(etc1_byte* pOut, int r, int g, int b, const int* table,
etc1_uint32 low, bool second, bool flipped) {
int baseX = 0;
int baseY = 0;
if (second) {
if (flipped) {
baseY = 2;
} else {
baseX = 2;
}
}
for (int i = 0; i < 8; i++) {
int x, y;
if (flipped) {
x = baseX + (i >> 1);
y = baseY + (i & 1);
} else {
x = baseX + (i >> 2);
y = baseY + (i & 3);
}
int k = y + (x * 4);
int offset = ((low >> k) & 1) | ((low >> (k + 15)) & 2);
int delta = table[offset];
etc1_byte* q = pOut + 3 * (x + 4 * y);
*q++ = clamp(r + delta);
*q++ = clamp(g + delta);
*q++ = clamp(b + delta);
}
}
// Input is an ETC1 compressed version of the data.
// Output is a 4 x 4 square of 3-byte pixels in form R, G, B
void etc1_decode_block(const etc1_byte* pIn, etc1_byte* pOut) {
etc1_uint32 high = (pIn[0] << 24) | (pIn[1] << 16) | (pIn[2] << 8) | pIn[3];
etc1_uint32 low = (pIn[4] << 24) | (pIn[5] << 16) | (pIn[6] << 8) | pIn[7];
int r1, r2, g1, g2, b1, b2;
if (high & 2) {
// differential
int rBase = high >> 27;
int gBase = high >> 19;
int bBase = high >> 11;
r1 = convert5To8(rBase);
r2 = convertDiff(rBase, high >> 24);
g1 = convert5To8(gBase);
g2 = convertDiff(gBase, high >> 16);
b1 = convert5To8(bBase);
b2 = convertDiff(bBase, high >> 8);
} else {
// not differential
r1 = convert4To8(high >> 28);
r2 = convert4To8(high >> 24);
g1 = convert4To8(high >> 20);
g2 = convert4To8(high >> 16);
b1 = convert4To8(high >> 12);
b2 = convert4To8(high >> 8);
}
int tableIndexA = 7 & (high >> 5);
int tableIndexB = 7 & (high >> 2);
const int* tableA = kModifierTable + tableIndexA * 4;
const int* tableB = kModifierTable + tableIndexB * 4;
bool flipped = (high & 1) != 0;
decode_subblock(pOut, r1, g1, b1, tableA, low, false, flipped);
decode_subblock(pOut, r2, g2, b2, tableB, low, true, flipped);
}
typedef struct {
etc1_uint32 high;
etc1_uint32 low;
etc1_uint32 score; // Lower is more accurate
} etc_compressed;
static
inline void take_best(etc_compressed* a, const etc_compressed* b) {
if (a->score > b->score) {
*a = *b;
}
}
static
void etc_average_colors_subblock(const etc1_byte* pIn, etc1_uint32 inMask,
etc1_byte* pColors, bool flipped, bool second) {
int r = 0;
int g = 0;
int b = 0;
if (flipped) {
int by = 0;
if (second) {
by = 2;
}
for (int y = 0; y < 2; y++) {
int yy = by + y;
for (int x = 0; x < 4; x++) {
int i = x + 4 * yy;
if (inMask & (1 << i)) {
const etc1_byte* p = pIn + i * 3;
r += *(p++);
g += *(p++);
b += *(p++);
}
}
}
} else {
int bx = 0;
if (second) {
bx = 2;
}
for (int y = 0; y < 4; y++) {
for (int x = 0; x < 2; x++) {
int xx = bx + x;
int i = xx + 4 * y;
if (inMask & (1 << i)) {
const etc1_byte* p = pIn + i * 3;
r += *(p++);
g += *(p++);
b += *(p++);
}
}
}
}
pColors[0] = (etc1_byte)((r + 4) >> 3);
pColors[1] = (etc1_byte)((g + 4) >> 3);
pColors[2] = (etc1_byte)((b + 4) >> 3);
}
static
inline int square(int x) {
return x * x;
}
static etc1_uint32 chooseModifier(const etc1_byte* pBaseColors,
const etc1_byte* pIn, etc1_uint32 *pLow, int bitIndex,
const int* pModifierTable) {
etc1_uint32 bestScore = ~0;
int bestIndex = 0;
int pixelR = pIn[0];
int pixelG = pIn[1];
int pixelB = pIn[2];
int r = pBaseColors[0];
int g = pBaseColors[1];
int b = pBaseColors[2];
for (int i = 0; i < 4; i++) {
int modifier = pModifierTable[i];
int decodedG = clamp(g + modifier);
etc1_uint32 score = (etc1_uint32) (6 * square(decodedG - pixelG));
if (score >= bestScore) {
continue;
}
int decodedR = clamp(r + modifier);
score += (etc1_uint32) (3 * square(decodedR - pixelR));
if (score >= bestScore) {
continue;
}
int decodedB = clamp(b + modifier);
score += (etc1_uint32) square(decodedB - pixelB);
if (score < bestScore) {
bestScore = score;
bestIndex = i;
}
}
etc1_uint32 lowMask = (((bestIndex >> 1) << 16) | (bestIndex & 1))
<< bitIndex;
*pLow |= lowMask;
return bestScore;
}
static
void etc_encode_subblock_helper(const etc1_byte* pIn, etc1_uint32 inMask,
etc_compressed* pCompressed, bool flipped, bool second,
const etc1_byte* pBaseColors, const int* pModifierTable) {
int score = pCompressed->score;
if (flipped) {
int by = 0;
if (second) {
by = 2;
}
for (int y = 0; y < 2; y++) {
int yy = by + y;
for (int x = 0; x < 4; x++) {
int i = x + 4 * yy;
if (inMask & (1 << i)) {
score += chooseModifier(pBaseColors, pIn + i * 3,
&pCompressed->low, yy + x * 4, pModifierTable);
}
}
}
} else {
int bx = 0;
if (second) {
bx = 2;
}
for (int y = 0; y < 4; y++) {
for (int x = 0; x < 2; x++) {
int xx = bx + x;
int i = xx + 4 * y;
if (inMask & (1 << i)) {
score += chooseModifier(pBaseColors, pIn + i * 3,
&pCompressed->low, y + xx * 4, pModifierTable);
}
}
}
}
pCompressed->score = score;
}
static bool inRange4bitSigned(int color) {
return color >= -4 && color <= 3;
}
static void etc_encodeBaseColors(etc1_byte* pBaseColors,
const etc1_byte* pColors, etc_compressed* pCompressed) {
int r1, g1, b1, r2, g2, b2; // 8 bit base colors for sub-blocks
bool differential;
{
int r51 = convert8To5(pColors[0]);
int g51 = convert8To5(pColors[1]);
int b51 = convert8To5(pColors[2]);
int r52 = convert8To5(pColors[3]);
int g52 = convert8To5(pColors[4]);
int b52 = convert8To5(pColors[5]);
r1 = convert5To8(r51);
g1 = convert5To8(g51);
b1 = convert5To8(b51);
int dr = r52 - r51;
int dg = g52 - g51;
int db = b52 - b51;
differential = inRange4bitSigned(dr) && inRange4bitSigned(dg)
&& inRange4bitSigned(db);
if (differential) {
r2 = convert5To8(r51 + dr);
g2 = convert5To8(g51 + dg);
b2 = convert5To8(b51 + db);
pCompressed->high |= (r51 << 27) | ((7 & dr) << 24) | (g51 << 19)
| ((7 & dg) << 16) | (b51 << 11) | ((7 & db) << 8) | 2;
}
}
if (!differential) {
int r41 = convert8To4(pColors[0]);
int g41 = convert8To4(pColors[1]);
int b41 = convert8To4(pColors[2]);
int r42 = convert8To4(pColors[3]);
int g42 = convert8To4(pColors[4]);
int b42 = convert8To4(pColors[5]);
r1 = convert4To8(r41);
g1 = convert4To8(g41);
b1 = convert4To8(b41);
r2 = convert4To8(r42);
g2 = convert4To8(g42);
b2 = convert4To8(b42);
pCompressed->high |= (r41 << 28) | (r42 << 24) | (g41 << 20) | (g42
<< 16) | (b41 << 12) | (b42 << 8);
}
pBaseColors[0] = r1;
pBaseColors[1] = g1;
pBaseColors[2] = b1;
pBaseColors[3] = r2;
pBaseColors[4] = g2;
pBaseColors[5] = b2;
}
static
void etc_encode_block_helper(const etc1_byte* pIn, etc1_uint32 inMask,
const etc1_byte* pColors, etc_compressed* pCompressed, bool flipped) {
pCompressed->score = ~0;
pCompressed->high = (flipped ? 1 : 0);
pCompressed->low = 0;
etc1_byte pBaseColors[6];
etc_encodeBaseColors(pBaseColors, pColors, pCompressed);
int originalHigh = pCompressed->high;
const int* pModifierTable = kModifierTable;
for (int i = 0; i < 8; i++, pModifierTable += 4) {
etc_compressed temp;
temp.score = 0;
temp.high = originalHigh | (i << 5);
temp.low = 0;
etc_encode_subblock_helper(pIn, inMask, &temp, flipped, false,
pBaseColors, pModifierTable);
take_best(pCompressed, &temp);
}
pModifierTable = kModifierTable;
etc_compressed firstHalf = *pCompressed;
for (int i = 0; i < 8; i++, pModifierTable += 4) {
etc_compressed temp;
temp.score = firstHalf.score;
temp.high = firstHalf.high | (i << 2);
temp.low = firstHalf.low;
etc_encode_subblock_helper(pIn, inMask, &temp, flipped, true,
pBaseColors + 3, pModifierTable);
if (i == 0) {
*pCompressed = temp;
} else {
take_best(pCompressed, &temp);
}
}
}
static void writeBigEndian(etc1_byte* pOut, etc1_uint32 d) {
pOut[0] = (etc1_byte)(d >> 24);
pOut[1] = (etc1_byte)(d >> 16);
pOut[2] = (etc1_byte)(d >> 8);
pOut[3] = (etc1_byte) d;
}
// Input is a 4 x 4 square of 3-byte pixels in form R, G, B
// inmask is a 16-bit mask where bit (1 << (x + y * 4)) tells whether the corresponding (x,y)
// pixel is valid or not. Invalid pixel color values are ignored when compressing.
// Output is an ETC1 compressed version of the data.
void etc1_encode_block(const etc1_byte* pIn, etc1_uint32 inMask,
etc1_byte* pOut) {
etc1_byte colors[6];
etc1_byte flippedColors[6];
etc_average_colors_subblock(pIn, inMask, colors, false, false);
etc_average_colors_subblock(pIn, inMask, colors + 3, false, true);
etc_average_colors_subblock(pIn, inMask, flippedColors, true, false);
etc_average_colors_subblock(pIn, inMask, flippedColors + 3, true, true);
etc_compressed a, b;
etc_encode_block_helper(pIn, inMask, colors, &a, false);
etc_encode_block_helper(pIn, inMask, flippedColors, &b, true);
take_best(&a, &b);
writeBigEndian(pOut, a.high);
writeBigEndian(pOut + 4, a.low);
}
// Return the size of the encoded image data (does not include size of PKM header).
etc1_uint32 etc1_get_encoded_data_size(etc1_uint32 width, etc1_uint32 height) {
return (((width + 3) & ~3) * ((height + 3) & ~3)) >> 1;
}
// Encode an entire image.
// pIn - pointer to the image data. Formatted such that the Red component of
// pixel (x,y) is at pIn + pixelSize * x + stride * y + redOffset;
// pOut - pointer to encoded data. Must be large enough to store entire encoded image.
int etc1_encode_image(const etc1_byte* pIn, etc1_uint32 width, etc1_uint32 height,
etc1_uint32 pixelSize, etc1_uint32 stride, etc1_byte* pOut) {
if (pixelSize < 2 || pixelSize > 3) {
return -1;
}
static const unsigned short kYMask[] = { 0x0, 0xf, 0xff, 0xfff, 0xffff };
static const unsigned short kXMask[] = { 0x0, 0x1111, 0x3333, 0x7777,
0xffff };
etc1_byte block[ETC1_DECODED_BLOCK_SIZE];
etc1_byte encoded[ETC1_ENCODED_BLOCK_SIZE];
etc1_uint32 encodedWidth = (width + 3) & ~3;
etc1_uint32 encodedHeight = (height + 3) & ~3;
for (etc1_uint32 y = 0; y < encodedHeight; y += 4) {
etc1_uint32 yEnd = height - y;
if (yEnd > 4) {
yEnd = 4;
}
int ymask = kYMask[yEnd];
for (etc1_uint32 x = 0; x < encodedWidth; x += 4) {
etc1_uint32 xEnd = width - x;
if (xEnd > 4) {
xEnd = 4;
}
int mask = ymask & kXMask[xEnd];
for (etc1_uint32 cy = 0; cy < yEnd; cy++) {
etc1_byte* q = block + (cy * 4) * 3;
const etc1_byte* p = pIn + pixelSize * x + stride * (y + cy);
if (pixelSize == 3) {
memcpy(q, p, xEnd * 3);
} else {
for (etc1_uint32 cx = 0; cx < xEnd; cx++) {
int pixel = (p[1] << 8) | p[0];
*q++ = convert5To8(pixel >> 11);
*q++ = convert6To8(pixel >> 5);
*q++ = convert5To8(pixel);
p += pixelSize;
}
}
}
etc1_encode_block(block, mask, encoded);
memcpy(pOut, encoded, sizeof(encoded));
pOut += sizeof(encoded);
}
}
return 0;
}
// Decode an entire image.
// pIn - pointer to encoded data.
// pOut - pointer to the image data. Will be written such that the Red component of
// pixel (x,y) is at pIn + pixelSize * x + stride * y + redOffset. Must be
// large enough to store entire image.
int etc1_decode_image(const etc1_byte* pIn, etc1_byte* pOut,
etc1_uint32 width, etc1_uint32 height,
etc1_uint32 pixelSize, etc1_uint32 stride) {
if (pixelSize < 2 || pixelSize > 3) {
return -1;
}
etc1_byte block[ETC1_DECODED_BLOCK_SIZE];
etc1_uint32 encodedWidth = (width + 3) & ~3;
etc1_uint32 encodedHeight = (height + 3) & ~3;
for (etc1_uint32 y = 0; y < encodedHeight; y += 4) {
etc1_uint32 yEnd = height - y;
if (yEnd > 4) {
yEnd = 4;
}
for (etc1_uint32 x = 0; x < encodedWidth; x += 4) {
etc1_uint32 xEnd = width - x;
if (xEnd > 4) {
xEnd = 4;
}
etc1_decode_block(pIn, block);
pIn += ETC1_ENCODED_BLOCK_SIZE;
for (etc1_uint32 cy = 0; cy < yEnd; cy++) {
const etc1_byte* q = block + (cy * 4) * 3;
etc1_byte* p = pOut + pixelSize * x + stride * (y + cy);
if (pixelSize == 3) {
memcpy(p, q, xEnd * 3);
} else {
for (etc1_uint32 cx = 0; cx < xEnd; cx++) {
etc1_byte r = *q++;
etc1_byte g = *q++;
etc1_byte b = *q++;
etc1_uint32 pixel = ((r >> 3) << 11) | ((g >> 2) << 5) | (b >> 3);
*p++ = (etc1_byte) pixel;
*p++ = (etc1_byte) (pixel >> 8);
}
}
}
}
}
return 0;
}
static const char kMagic[] = { 'P', 'K', 'M', ' ', '1', '0' };
static const etc1_uint32 ETC1_PKM_FORMAT_OFFSET = 6;
static const etc1_uint32 ETC1_PKM_ENCODED_WIDTH_OFFSET = 8;
static const etc1_uint32 ETC1_PKM_ENCODED_HEIGHT_OFFSET = 10;
static const etc1_uint32 ETC1_PKM_WIDTH_OFFSET = 12;
static const etc1_uint32 ETC1_PKM_HEIGHT_OFFSET = 14;
static const etc1_uint32 ETC1_RGB_NO_MIPMAPS = 0;
static void writeBEUint16(etc1_byte* pOut, etc1_uint32 data) {
pOut[0] = (etc1_byte) (data >> 8);
pOut[1] = (etc1_byte) data;
}
static etc1_uint32 readBEUint16(const etc1_byte* pIn) {
return (pIn[0] << 8) | pIn[1];
}
// Format a PKM header
void etc1_pkm_format_header(etc1_byte* pHeader, etc1_uint32 width, etc1_uint32 height) {
memcpy(pHeader, kMagic, sizeof(kMagic));
etc1_uint32 encodedWidth = (width + 3) & ~3;
etc1_uint32 encodedHeight = (height + 3) & ~3;
writeBEUint16(pHeader + ETC1_PKM_FORMAT_OFFSET, ETC1_RGB_NO_MIPMAPS);
writeBEUint16(pHeader + ETC1_PKM_ENCODED_WIDTH_OFFSET, encodedWidth);
writeBEUint16(pHeader + ETC1_PKM_ENCODED_HEIGHT_OFFSET, encodedHeight);
writeBEUint16(pHeader + ETC1_PKM_WIDTH_OFFSET, width);
writeBEUint16(pHeader + ETC1_PKM_HEIGHT_OFFSET, height);
}
// Check if a PKM header is correctly formatted.
etc1_bool etc1_pkm_is_valid(const etc1_byte* pHeader) {
if (memcmp(pHeader, kMagic, sizeof(kMagic))) {
return false;
}
etc1_uint32 format = readBEUint16(pHeader + ETC1_PKM_FORMAT_OFFSET);
etc1_uint32 encodedWidth = readBEUint16(pHeader + ETC1_PKM_ENCODED_WIDTH_OFFSET);
etc1_uint32 encodedHeight = readBEUint16(pHeader + ETC1_PKM_ENCODED_HEIGHT_OFFSET);
etc1_uint32 width = readBEUint16(pHeader + ETC1_PKM_WIDTH_OFFSET);
etc1_uint32 height = readBEUint16(pHeader + ETC1_PKM_HEIGHT_OFFSET);
return format == ETC1_RGB_NO_MIPMAPS &&
encodedWidth >= width && encodedWidth - width < 4 &&
encodedHeight >= height && encodedHeight - height < 4;
}
// Read the image width from a PKM header
etc1_uint32 etc1_pkm_get_width(const etc1_byte* pHeader) {
return readBEUint16(pHeader + ETC1_PKM_WIDTH_OFFSET);
}
// Read the image height from a PKM header
etc1_uint32 etc1_pkm_get_height(const etc1_byte* pHeader){
return readBEUint16(pHeader + ETC1_PKM_HEIGHT_OFFSET);
}