| // 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(c * 15); |
| } |
| |
| static |
| inline int convert8To5(int b) { |
| int c = b & 0xff; |
| return divideBy255(c * 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; |
| } else { |
| 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); |
| } |