// 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_utils.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); | |
} |