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Unified Diff: third_party/etc1/etc1.cpp

Issue 292663011: Simple PKM image decoder. (Closed) Base URL: https://skia.googlesource.com/skia.git@master
Patch Set: Resync Created 6 years, 7 months ago
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Index: third_party/etc1/etc1.cpp
diff --git a/third_party/etc1/etc1.cpp b/third_party/etc1/etc1.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..421ebfebc5a4aca71cc6c78fca2f131e00b4ad70
--- /dev/null
+++ b/third_party/etc1/etc1.cpp
@@ -0,0 +1,678 @@
+// 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.
+
+//////////////////////////////////////////////////////////////////////////////////////////
+
+// This is a fork of the AOSP project ETC1 codec. The original code can be found
+// at the following web site:
+// https://android.googlesource.com/platform/frameworks/native/+/master/opengl/include/ETC1/
+
+//////////////////////////////////////////////////////////////////////////////////////////
+
+#include "etc1.h"
+
+#include <cstring>
+
+/* 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;
+ }
+ }
+
+ 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);
+}
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