Repository: notnullnotvoid/msf_gif Branch: master Commit: e280bc2189ed Files: 3 Total size: 40.4 KB Directory structure: gitextract_9lu4txhx/ ├── .gitignore ├── README.md └── msf_gif.h ================================================ FILE CONTENTS ================================================ ================================================ FILE: .gitignore ================================================ .DS_Store test/ ================================================ FILE: README.md ================================================ A single-header animated GIF exporter, suitable for recording gifs in realtime. * **Easy to use**. Single-header C code compiles as C99 or C++98. The only dependency is the C standard library headers. Simple and minimal API. * **High-quality results**. Uses a straightforward palette selection and dithering algorithm that is guaranteed to provide equal fidelity for all areas of the image, thereby avoiding the artifacts that are typical of the kind of frequency-based adaptive color quantization algorithms used in most gif encoders. See the side-by-side comparison below for an example. * **Small file sizes**. Uses delta encoding between frames and a compression-friendly dithering kernel, resulting in significantly smaller files than most gif encoders, without sacrificing quality. * **Fast**. Designed for speed, and uses SSE where available to encode at hundreds of megabytes a second, several times faster than comparable gif libraries. * **Public domain**. Also available under MIT license. See the bottom of the source file for license text. * **Actively maintained**. This is not abandonware! If there is a problem or a feature you feel is missing, tell me and there's a good chance I can add it. Or submit a pull request if you're feeling generous - the code is relatively short and simple. ## Examples [![Example gif from Escher](examples/flip.gif)](https://eschergame.com/) [![Example gif from DIWide](examples/diwide.gif)](https://github.com/notnullnotvoid/DIWide) ![Side-by-side comparison: MSF half](examples/keyhole-msf-2x.gif) ![Side-by-side comparison: JO half](examples/keyhole-jo-2x.gif) Above: a side-by-side comparisons of different color quantization algorithms dealing with a difficult area of an animation. On the left is the constant-quality algorithm used by msf_gif. On the right is an adaptive algorithm with a random dither. The adaptive algorithm struggles to give sufficient quality to the tomato because it's a small portion of the image and therefore gets only a small portion of the color palette. The adaptive algorithm also takes longer to encode, and results in a larger file. ## How to use In **exactly one** translation unit (.c or .cpp file), `#define MSF_GIF_IMPL` before including the header, like so: ```cpp #define MSF_GIF_IMPL #include "msf_gif.h" ``` Everywhere else, just include the header like normal. ### Usage example ```cpp int width = 480, height = 320, centisecondsPerFrame = 5, quality = 16; MsfGifState gifState = {}; // msf_gif_bgra_flag = true; //optionally, set this flag if your pixels are in BGRA format instead of RGBA // msf_gif_alpha_threshold = 128; //optionally, enable transparency (see documentation in header for details) msf_gif_begin(&gifState, width, height); msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 1 msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 2 msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 3, etc... MsfGifResult result = msf_gif_end(&gifState); if (result.data) { FILE * fp = fopen("MyGif.gif", "wb"); fwrite(result.data, result.dataSize, 1, fp); fclose(fp); } msf_gif_free(result); ``` Detailed function documentation can be found in the header. ### A note on image resizing If the data source you're making a gif from is high-resolution, the resulting gif may be prohibitively large and take a long time to export. To make a gif with a smaller resolution, you have a few options: 1. A good option, if capturing a gif directly from a game or other application, is to render the scene a second time to a smaller-resolution texture. However, it can be tricky to set up, and could be expensive depending on the scene. 2. Another option is to render to a texture and downscale on the GPU. This can be tricky to get right, and quality may suffer. You can do your own higher-quality resampling in a compute shader or fragment shader, but that's more difficult. 3. The easiest option is to downscale on the CPU. For this you can use [stb_image_resize2.h](https://github.com/nothings/stb/blob/master/stb_image_resize2.h), which provides high-quality results, but can be slow. ### Contributing The code and data that I use for testing and benchmarking the library can be found in a separate repository at https://github.com/notnullnotvoid/msf_gif-testing. Feel free to use this if you want to test changes to the library. ================================================ FILE: msf_gif.h ================================================ /* HOW TO USE: In exactly one translation unit (.c or .cpp file), #define MSF_GIF_IMPL before including the header, like so: #define MSF_GIF_IMPL #include "msf_gif.h" Everywhere else, just include the header like normal. USAGE EXAMPLE: int width = 480, height = 320, centisecondsPerFrame = 5, quality = 16; MsfGifState gifState = {}; // msf_gif_bgra_flag = true; //optionally, set this flag if your pixels are in BGRA format instead of RGBA // msf_gif_alpha_threshold = 128; //optionally, enable transparency (see function documentation below for details) msf_gif_begin(&gifState, width, height); msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 1 msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 2 msf_gif_frame(&gifState, ..., centisecondsPerFrame, quality, width * 4); //frame 3, etc... MsfGifResult result = msf_gif_end(&gifState); if (result.data) { FILE * fp = fopen("MyGif.gif", "wb"); fwrite(result.data, result.dataSize, 1, fp); fclose(fp); } msf_gif_free(result); Detailed function documentation can be found in the header section below. ERROR HANDLING: If memory allocation fails, the functions will signal the error via their return values. If one function call fails, the library will free all of its allocations, and all subsequent calls will safely no-op and return 0 until the next call to `msf_gif_begin()`. Therefore, it's safe to check only the return value of `msf_gif_end()`. REPLACING MALLOC: This library uses malloc+realloc+free internally for memory allocation. To facilitate integration with custom memory allocators, these calls go through macros, which can be redefined. The expected function signature equivalents of the macros are as follows: void * MSF_GIF_MALLOC(void * context, size_t newSize) void * MSF_GIF_REALLOC(void * context, void * oldMemory, size_t oldSize, size_t newSize) void MSF_GIF_FREE(void * context, void * oldMemory, size_t oldSize) If your allocator needs a context pointer, you can set the `customAllocatorContext` field of the MsfGifState struct before calling msf_gif_begin(), and it will be passed to all subsequent allocator macro calls. The maximum number of bytes the library will allocate to encode a single gif is bounded by the following formula: `(2 * 1024 * 1024) + (128 * 1024) + (width * height * 8) + ((2048 + width * height * 1.5) * 2 * frameCount)` The peak heap memory usage in bytes, if using a general-purpose heap allocator, is bounded by the following formula: `(2 * 1024 * 1024) + (128 * 1024) + (width * height * 11) + 2048 + (16 * frameCount) + (2 * sizeOfResultingGif) See end of file for license information. */ //version 2.4 //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// HEADER /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// #ifndef MSF_GIF_H #define MSF_GIF_H #include #include typedef struct { void * data; size_t dataSize; size_t allocSize; //internal use void * contextPointer; //internal use } MsfGifResult; typedef struct { //internal use uint32_t * pixels; int depth, count, rbits, gbits, bbits; } MsfCookedFrame; typedef struct MsfGifBuffer { //internal use struct MsfGifBuffer * next; size_t size; uint8_t data[1]; } MsfGifBuffer; typedef size_t (* MsfGifFileWriteFunc) (const void * buffer, size_t size, size_t count, void * stream); typedef struct { //internal use MsfGifFileWriteFunc fileWriteFunc; void * fileWriteData; MsfCookedFrame previousFrame; MsfCookedFrame currentFrame; int16_t * lzwMem; uint8_t * tlbMem; uint8_t * usedMem; MsfGifBuffer * listHead; MsfGifBuffer * listTail; int width, height; void * customAllocatorContext; int framesSubmitted; //needed for transparency to work correctly (because we reach into the previous frame) } MsfGifState; #ifdef __cplusplus extern "C" { #endif //__cplusplus /** * @param width Image width in pixels. * @param height Image height in pixels. * @return Non-zero on success, 0 on error. */ int msf_gif_begin(MsfGifState * handle, int width, int height); /** * @param pixelData Pointer to raw framebuffer data. Rows must be contiguous in memory, in RGBA8 format * (or BGRA8 if you have set `msf_gif_bgra_flag = true`). * Note: This function does NOT free `pixelData`. You must free it yourself afterwards. * @param centiSecondsPerFrame How many hundredths of a second this frame should be displayed for. * Note: This being specified in centiseconds is a limitation of the GIF format. * @param quality This parameter limits the maximum color accuracy for quantization. * Actual color accuracy varies dynamically based on how many colors are used in the frame. * `quality` is clamped between 1 and 16. The recommended default is 16. * Lowering this value can result in smaller gifs and slightly faster exports, * but the resulting gifs may look noticeably worse with a more extreme dither pattern. * @param pitchInBytes The number of bytes from the beginning of one row of pixels to the beginning of the next. * If zero, the rows will be assumed to be contiguous (equivalent to `width * 4`). * If negative, the rows will be reversed, thus flipping the image vertically. * Regardless, `pixelData` should always point to the *first* row in memory, not the last. * @return Non-zero on success, 0 on error. */ int msf_gif_frame(MsfGifState * handle, uint8_t * pixelData, int centiSecondsPerFrame, int quality, int pitchInBytes); /** * @return A block of memory containing the gif file data, or NULL on error. * You are responsible for freeing this via `msf_gif_free()`. */ MsfGifResult msf_gif_end(MsfGifState * handle); /** * @param result The MsfGifResult struct, verbatim as it was returned from `msf_gif_end()`. */ void msf_gif_free(MsfGifResult result); //The gif format only supports 1-bit transparency, meaning a pixel will either be fully transparent or fully opaque. //Pixels with an alpha value less than the alpha threshold will be treated as transparent. //To enable exporting transparent gifs, set it to a value between 1 and 255 (inclusive) before calling msf_gif_frame(). //Setting it to 0 causes the alpha channel to be ignored. Its initial value is 0. extern int msf_gif_alpha_threshold; //Set `msf_gif_bgra_flag = true` before calling `msf_gif_frame()` if your pixels are in BGRA byte order instead of RBGA. extern int msf_gif_bgra_flag; //TO-FILE FUNCTIONS //These functions are equivalent to the ones above, but they write results to a file incrementally, //instead of building a buffer in memory. This can result in lower memory usage when saving large gifs, //because memory usage is bounded by only the size of a single frame, and is not dependent on the number of frames. //There is currently no reason to use these unless you are on a memory-constrained platform. //If in doubt about which API to use, for now you should use the normal (non-file) functions above. //The signature of MsfGifFileWriteFunc matches fwrite for convenience, so that you can use the C file API like so: // FILE * fp = fopen("MyGif.gif", "wb"); // msf_gif_begin_to_file(&handle, width, height, (MsfGifFileWriteFunc) fwrite, (void *) fp); // msf_gif_frame_to_file(...) // msf_gif_end_to_file(&handle); // fclose(fp); //If you use a custom file write function, you must take care to return the same values that fwrite() would return. //Note that all three functions will potentially write to the file. int msf_gif_begin_to_file(MsfGifState * handle, int width, int height, MsfGifFileWriteFunc func, void * filePointer); int msf_gif_frame_to_file(MsfGifState * handle, uint8_t * pixelData, int centiSecondsPerFrame, int quality, int pitchInBytes); int msf_gif_end_to_file(MsfGifState * handle); //returns 0 on error and non-zero on success #ifdef __cplusplus } #endif //__cplusplus #endif //MSF_GIF_H //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// IMPLEMENTATION /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// #ifdef MSF_GIF_IMPL #ifndef MSF_GIF_ALREADY_IMPLEMENTED_IN_THIS_TRANSLATION_UNIT #define MSF_GIF_ALREADY_IMPLEMENTED_IN_THIS_TRANSLATION_UNIT //ensure the library user has either defined all of malloc/realloc/free, or none #if defined(MSF_GIF_MALLOC) && defined(MSF_GIF_REALLOC) && defined(MSF_GIF_FREE) //ok #elif !defined(MSF_GIF_MALLOC) && !defined(MSF_GIF_REALLOC) && !defined(MSF_GIF_FREE) //ok #else #error "You must either define all of MSF_GIF_MALLOC, MSF_GIF_REALLOC, and MSF_GIF_FREE, or define none of them" #endif //provide default allocator definitions that redirect to the standard global allocator #if !defined(MSF_GIF_MALLOC) #include //malloc, etc. #define MSF_GIF_MALLOC(contextPointer, newSize) malloc(newSize) #define MSF_GIF_REALLOC(contextPointer, oldMemory, oldSize, newSize) realloc(oldMemory, newSize) #define MSF_GIF_FREE(contextPointer, oldMemory, oldSize) free(oldMemory) #endif //instrumentation for capturing profiling traces (useless for the library user, but useful for the library author) #ifdef MSF_GIF_ENABLE_TRACING #define MsfTimeFunc TimeFunc #define MsfTimeLoop TimeLoop #define msf_init_profiling_thread init_profiling_thread #else #define MsfTimeFunc #define MsfTimeLoop(name) #define msf_init_profiling_thread() #endif //MSF_GIF_ENABLE_TRACING #include //memcpy //TODO: use compiler-specific notation to force-inline functions currently marked inline #if defined(__GNUC__) //gcc, clang static inline int msf_bit_log(int i) { return 32 - __builtin_clz(i); } #elif defined(_MSC_VER) //msvc #include static inline int msf_bit_log(int i) { unsigned long idx; _BitScanReverse(&idx, i); return idx + 1; } #else //fallback implementation for other compilers //from https://stackoverflow.com/a/31718095/3064745 - thanks! static inline int msf_bit_log(int i) { static const int MultiplyDeBruijnBitPosition[32] = { 0, 9, 1, 10, 13, 21, 2, 29, 11, 14, 16, 18, 22, 25, 3, 30, 8, 12, 20, 28, 15, 17, 24, 7, 19, 27, 23, 6, 26, 5, 4, 31, }; i |= i >> 1; i |= i >> 2; i |= i >> 4; i |= i >> 8; i |= i >> 16; return MultiplyDeBruijnBitPosition[(uint32_t)(i * 0x07C4ACDDU) >> 27] + 1; } #endif static inline int msf_imin(int a, int b) { return a < b? a : b; } static inline int msf_imax(int a, int b) { return b < a? a : b; } //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// Frame Cooking /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// #if (defined (__SSE2__) || defined (_M_X64) || _M_IX86_FP == 2) && !defined(MSF_GIF_NO_SSE2) #include #endif int msf_gif_alpha_threshold = 0; int msf_gif_bgra_flag = 0; static void msf_cook_frame(MsfCookedFrame * frame, uint8_t * raw, uint8_t * used, int width, int height, int pitch, int depth) { MsfTimeFunc //bit depth for each channel const static int rdepthsArray[17] = { 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5 }; const static int gdepthsArray[17] = { 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5, 5, 6 }; const static int bdepthsArray[17] = { 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 4, 4, 4, 5, 5 }; //this extra level of indirection looks unnecessary but we need to explicitly decay the arrays to pointers //in order to be able to swap them because of C's annoying not-quite-pointers, not-quite-value-types stack arrays. const int * rdepths = msf_gif_bgra_flag? bdepthsArray : rdepthsArray; const int * gdepths = gdepthsArray; const int * bdepths = msf_gif_bgra_flag? rdepthsArray : bdepthsArray; const static int ditherKernel[16] = { 0 << 12, 8 << 12, 2 << 12, 10 << 12, 12 << 12, 4 << 12, 14 << 12, 6 << 12, 3 << 12, 11 << 12, 1 << 12, 9 << 12, 15 << 12, 7 << 12, 13 << 12, 5 << 12, }; uint32_t * cooked = frame->pixels; int count = 0; MsfTimeLoop("do") do { int rbits = rdepths[depth], gbits = gdepths[depth], bbits = bdepths[depth]; int paletteSize = (1 << (rbits + gbits + bbits)) + 1; memset(used, 0, paletteSize * sizeof(uint8_t)); //TODO: document what this math does and why it's correct int rdiff = (1 << (8 - rbits)) - 1; int gdiff = (1 << (8 - gbits)) - 1; int bdiff = (1 << (8 - bbits)) - 1; short rmul = (short) ((255.0f - rdiff) / 255.0f * 257); short gmul = (short) ((255.0f - gdiff) / 255.0f * 257); short bmul = (short) ((255.0f - bdiff) / 255.0f * 257); int gmask = ((1 << gbits) - 1) << rbits; int bmask = ((1 << bbits) - 1) << rbits << gbits; MsfTimeLoop("cook") for (int y = 0; y < height; ++y) { int x = 0; #if (defined (__SSE2__) || defined (_M_X64) || _M_IX86_FP == 2) && !defined(MSF_GIF_NO_SSE2) __m128i k = _mm_loadu_si128((__m128i *) &ditherKernel[(y & 3) * 4]); __m128i k2 = _mm_or_si128(_mm_srli_epi32(k, rbits), _mm_slli_epi32(_mm_srli_epi32(k, bbits), 16)); for (; x < width - 3; x += 4) { uint8_t * pixels = &raw[y * pitch + x * 4]; __m128i p = _mm_loadu_si128((__m128i *) pixels); __m128i rb = _mm_and_si128(p, _mm_set1_epi32(0x00FF00FF)); __m128i rb1 = _mm_mullo_epi16(rb, _mm_set_epi16(bmul, rmul, bmul, rmul, bmul, rmul, bmul, rmul)); __m128i rb2 = _mm_adds_epu16(rb1, k2); __m128i r3 = _mm_srli_epi32(_mm_and_si128(rb2, _mm_set1_epi32(0x0000FFFF)), 16 - rbits); __m128i b3 = _mm_and_si128(_mm_srli_epi32(rb2, 32 - rbits - gbits - bbits), _mm_set1_epi32(bmask)); __m128i g = _mm_and_si128(_mm_srli_epi32(p, 8), _mm_set1_epi32(0x000000FF)); __m128i g1 = _mm_mullo_epi16(g, _mm_set1_epi32(gmul)); __m128i g2 = _mm_adds_epu16(g1, _mm_srli_epi32(k, gbits)); __m128i g3 = _mm_and_si128(_mm_srli_epi32(g2, 16 - rbits - gbits), _mm_set1_epi32(gmask)); __m128i out = _mm_or_si128(_mm_or_si128(r3, g3), b3); //mask in transparency based on threshold //NOTE: we can theoretically do a sub instead of srli by doing an unsigned compare via bias // to maybe save a TINY amount of throughput? but lol who cares maybe I'll do it later -m __m128i invAlphaMask = _mm_cmplt_epi32(_mm_srli_epi32(p, 24), _mm_set1_epi32(msf_gif_alpha_threshold)); out = _mm_or_si128(_mm_and_si128(invAlphaMask, _mm_set1_epi32(paletteSize - 1)), _mm_andnot_si128(invAlphaMask, out)); //TODO: does storing this as a __m128i then reading it back as a uint32_t violate strict aliasing? uint32_t * c = &cooked[y * width + x]; _mm_storeu_si128((__m128i *) c, out); } #endif //scalar cleanup loop for (; x < width; ++x) { uint8_t * p = &raw[y * pitch + x * 4]; //transparent pixel if alpha is low if (p[3] < msf_gif_alpha_threshold) { cooked[y * width + x] = paletteSize - 1; continue; } int dx = x & 3, dy = y & 3; int k = ditherKernel[dy * 4 + dx]; cooked[y * width + x] = (msf_imin(65535, p[2] * bmul + (k >> bbits)) >> (16 - rbits - gbits - bbits) & bmask) | (msf_imin(65535, p[1] * gmul + (k >> gbits)) >> (16 - rbits - gbits ) & gmask) | msf_imin(65535, p[0] * rmul + (k >> rbits)) >> (16 - rbits ); } } count = 0; MsfTimeLoop("mark") for (int i = 0; i < width * height; ++i) { used[cooked[i]] = 1; } //count used colors, transparent is ignored MsfTimeLoop("count") for (int j = 0; j < paletteSize - 1; ++j) { count += used[j]; } } while (count >= 256 && --depth); MsfCookedFrame ret = { cooked, depth, count, rdepths[depth], gdepths[depth], bdepths[depth] }; *frame = ret; } //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// Frame Compression /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// static inline void msf_put_code(uint8_t * * writeHead, uint32_t * blockBits, int len, uint32_t code) { //insert new code into block buffer int idx = *blockBits / 8; int bit = *blockBits % 8; (*writeHead)[idx + 0] |= code << bit ; (*writeHead)[idx + 1] |= code >> ( 8 - bit); (*writeHead)[idx + 2] |= code >> (16 - bit); *blockBits += len; //prep the next block buffer if the current one is full if (*blockBits >= 256 * 8) { *blockBits -= 255 * 8; (*writeHead) += 256; (*writeHead)[2] = (*writeHead)[1]; (*writeHead)[1] = (*writeHead)[0]; (*writeHead)[0] = 255; memset((*writeHead) + 4, 0, 256); } } typedef struct { int16_t * data; int len; int stride; } MsfStridedList; static inline void msf_lzw_reset(MsfStridedList * lzw, int tableSize, int stride) { MsfTimeFunc memset(lzw->data, 0xFF, 4096 * stride * sizeof(int16_t)); lzw->len = tableSize + 2; lzw->stride = stride; } //PERF TODO: is it possible to use the same array for both `used` and `tlb`? static MsfGifBuffer * msf_compress_frame(void * allocContext, int width, int height, int centiSeconds, MsfCookedFrame frame, MsfGifState * handle, uint8_t * used, uint8_t * tlb, int16_t * lzwMem) { MsfTimeFunc //NOTE: We reserve enough memory for the theoretical worst case upfront because it's a reasonable amount, // and prevents us from ever having to check size or realloc during compression. //NOTE: headers + color table + 12 bits per pixel (since 12 bits is the maximum code size) // + space for at least one full Image Data block (needed for small images since we zero a whole block at a time) int maxBufSize = offsetof(MsfGifBuffer, data) + 32 + 256 * 3 + width * height * 3 / 2 + (256 + 4); MsfGifBuffer * buffer = (MsfGifBuffer *) MSF_GIF_MALLOC(allocContext, maxBufSize); if (!buffer) { return NULL; } uint8_t * writeHead = buffer->data; MsfStridedList lzw = { lzwMem }; //allocate tlb int totalBits = frame.rbits + frame.gbits + frame.bbits; int tlbSize = (1 << totalBits) + 1; //generate palette typedef struct { uint8_t r, g, b; } Color3; Color3 table[256] = { {0} }; int tableIdx = 1; //we start counting at 1 because 0 is the transparent color //transparent is always last in the table tlb[tlbSize-1] = 0; MsfTimeLoop("table") for (int i = 0; i < tlbSize-1; ++i) { if (used[i]) { tlb[i] = tableIdx; int rmask = (1 << frame.rbits) - 1; int gmask = (1 << frame.gbits) - 1; //isolate components int r = i & rmask; int g = i >> frame.rbits & gmask; int b = i >> (frame.rbits + frame.gbits); //shift into highest bits r <<= 8 - frame.rbits; g <<= 8 - frame.gbits; b <<= 8 - frame.bbits; table[tableIdx].r = r | r >> frame.rbits | r >> (frame.rbits * 2) | r >> (frame.rbits * 3); table[tableIdx].g = g | g >> frame.gbits | g >> (frame.gbits * 2) | g >> (frame.gbits * 3); table[tableIdx].b = b | b >> frame.bbits | b >> (frame.bbits * 2) | b >> (frame.bbits * 3); if (msf_gif_bgra_flag) { uint8_t temp = table[tableIdx].r; table[tableIdx].r = table[tableIdx].b; table[tableIdx].b = temp; } ++tableIdx; } } int hasTransparentPixels = used[tlbSize-1]; //SPEC: "Because of some algorithmic constraints however, black & white images which have one color bit // must be indicated as having a code size of 2." int tableBits = msf_imax(2, msf_bit_log(tableIdx - 1)); int tableSize = 1 << tableBits; //NOTE: we don't just compare `depth` field here because it will be wrong for the first frame and we will segfault MsfCookedFrame previous = handle->previousFrame; int hasSamePal = frame.rbits == previous.rbits && frame.gbits == previous.gbits && frame.bbits == previous.bbits; int framesCompatible = hasSamePal && !hasTransparentPixels; //write the Graphics `Control Extension` and `Image Descriptor` blocks //NOTE: because __attribute__((__packed__)) is annoyingly compiler-specific, we do this unreadable weirdness char headerBytes[19] = "\x21\xF9\x04\x05\0\0\0\0" "\x2C\0\0\0\0\0\0\0\0\x80"; //NOTE: we need to check the frame number because if we reach into the buffer prior to the first frame, // we'll just clobber the file header instead, which is a bug if (hasTransparentPixels && handle->framesSubmitted > 0) { handle->listTail->data[3] = 0x09; //set the previous frame's disposal to background, so transparency is possible } memcpy(&headerBytes[4], ¢iSeconds, 2); memcpy(&headerBytes[13], &width, 2); memcpy(&headerBytes[15], &height, 2); headerBytes[17] |= tableBits - 1; memcpy(writeHead, headerBytes, 18); writeHead += 18; //write Local Color Table memcpy(writeHead, table, tableSize * sizeof(Color3)); writeHead += tableSize * sizeof(Color3); *writeHead++ = tableBits; //prep first Image Data block (analogous to what we do at the end of msf_put_code()) memset(writeHead, 0, 256 + 4); //we write up to 4 bytes ahead of the end of the block - see msf_put_code() writeHead[0] = 255; uint32_t blockBits = 8; //relative to block.head //SPEC: "Encoders should output a Clear code as the first code of each image data stream." msf_lzw_reset(&lzw, tableSize, tableIdx); msf_put_code(&writeHead, &blockBits, msf_bit_log(lzw.len - 1), tableSize); int lastCode = framesCompatible && frame.pixels[0] == previous.pixels[0]? 0 : tlb[frame.pixels[0]]; MsfTimeLoop("compress") for (int i = 1; i < width * height; ++i) { //PERF: branching vs. branchless version of this line is observed to have no discernable impact on speed int color = framesCompatible && frame.pixels[i] == previous.pixels[i]? 0 : tlb[frame.pixels[i]]; int code = (&lzw.data[lastCode * lzw.stride])[color]; if (code < 0) { //write to code stream int codeBits = msf_bit_log(lzw.len - 1); msf_put_code(&writeHead, &blockBits, codeBits, lastCode); if (lzw.len > 4095) { //reset buffer code table msf_put_code(&writeHead, &blockBits, codeBits, tableSize); msf_lzw_reset(&lzw, tableSize, tableIdx); } else { (&lzw.data[lastCode * lzw.stride])[color] = lzw.len; ++lzw.len; } lastCode = color; } else { lastCode = code; } } //write code for leftover index buffer contents, then the end code msf_put_code(&writeHead, &blockBits, msf_imin(12, msf_bit_log(lzw.len - 1)), lastCode); msf_put_code(&writeHead, &blockBits, msf_imin(12, msf_bit_log(lzw.len)), tableSize + 1); //flush remaining data if (blockBits > 8) { int bytes = (blockBits + 7) / 8; //round up writeHead[0] = bytes - 1; writeHead += bytes; } *writeHead++ = 0; //terminating block //fill in buffer header and shrink buffer to fit data buffer->next = NULL; buffer->size = writeHead - buffer->data; MsfGifBuffer * moved = (MsfGifBuffer *) MSF_GIF_REALLOC(allocContext, buffer, maxBufSize, offsetof(MsfGifBuffer, data) + buffer->size); if (!moved) { MSF_GIF_FREE(allocContext, buffer, maxBufSize); return NULL; } return moved; } //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// To-memory API /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// static const int lzwAllocSize = 4096 * 256 * sizeof(int16_t); static const int tlbAllocSize = ((1 << 16) + 1) * sizeof(uint8_t); static const int usedAllocSize = ((1 << 16) + 1) * sizeof(uint8_t); //NOTE: by C standard library conventions, freeing NULL should be a no-op, // but just in case the user's custom free doesn't follow that rule, we do null checks on our end as well. static void msf_free_gif_state(MsfGifState * handle) { if (handle->previousFrame.pixels) MSF_GIF_FREE(handle->customAllocatorContext, handle->previousFrame.pixels, handle->width * handle->height * sizeof(uint32_t)); if (handle->currentFrame.pixels) MSF_GIF_FREE(handle->customAllocatorContext, handle->currentFrame.pixels, handle->width * handle->height * sizeof(uint32_t)); if (handle->lzwMem) MSF_GIF_FREE(handle->customAllocatorContext, handle->lzwMem, lzwAllocSize); if (handle->tlbMem) MSF_GIF_FREE(handle->customAllocatorContext, handle->tlbMem, tlbAllocSize); if (handle->usedMem) MSF_GIF_FREE(handle->customAllocatorContext, handle->usedMem, usedAllocSize); for (MsfGifBuffer * node = handle->listHead; node;) { MsfGifBuffer * next = node->next; //NOTE: we have to copy the `next` pointer BEFORE freeing the node holding it MSF_GIF_FREE(handle->customAllocatorContext, node, offsetof(MsfGifBuffer, data) + node->size); node = next; } handle->listHead = NULL; //this implicitly marks the handle as invalid until the next msf_gif_begin() call } int msf_gif_begin(MsfGifState * handle, int width, int height) { MsfTimeFunc //To help avoid potential overflow errors, let's just not even try to support images larger than 1GB in size. //And let's also reject images with width or height more or less than what the gif format itself supports. const int MAX_PIXELS = 268435456; //2^30 / 4 = 1GB / bytesPerPixel if (width < 1 || height < 1 || width > 65535 || height > 65535 || width >= MAX_PIXELS / height) { handle->listHead = NULL; //this implicitly marks the handle as invalid until the next msf_gif_begin() call return 0; } //NOTE: we cannot stomp the entire struct to zero because we must preserve `customAllocatorContext`. MsfCookedFrame empty = {0}; //god I hate MSVC... handle->previousFrame = empty; handle->currentFrame = empty; handle->width = width; handle->height = height; handle->framesSubmitted = 0; //NOTE: Default stack sizes for some platforms are very small. Emscripten in particular uses a 64k stack by default. // So anything that large or larger must be allocated on the heap, even if its maximum size is compile-time known. // The `lzw`, `tlb`, and `used` arrays are 2MB, 64KB, and 64KB respectively, so we allocate them here. // We could make them arrays at global scope, but that would create problems if the library is used from multiple threads. handle->lzwMem = (int16_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, lzwAllocSize); handle->tlbMem = (uint8_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, tlbAllocSize); handle->usedMem = (uint8_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, usedAllocSize); handle->previousFrame.pixels = (uint32_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, handle->width * handle->height * sizeof(uint32_t)); handle->currentFrame.pixels = (uint32_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, handle->width * handle->height * sizeof(uint32_t)); //setup header buffer header (lol) handle->listHead = (MsfGifBuffer *) MSF_GIF_MALLOC(handle->customAllocatorContext, offsetof(MsfGifBuffer, data) + 32); if (!handle->listHead || !handle->lzwMem || !handle->previousFrame.pixels || !handle->currentFrame.pixels) { msf_free_gif_state(handle); return 0; } handle->listTail = handle->listHead; handle->listHead->next = NULL; handle->listHead->size = 32; //NOTE: because __attribute__((__packed__)) is annoyingly compiler-specific, we do this unreadable weirdness char headerBytes[33] = "GIF89a\0\0\0\0\x70\0\0" "\x21\xFF\x0BNETSCAPE2.0\x03\x01\0\0\0"; memcpy(&headerBytes[6], &width, 2); memcpy(&headerBytes[8], &height, 2); memcpy(handle->listHead->data, headerBytes, 32); return 1; } int msf_gif_frame(MsfGifState * handle, uint8_t * pixelData, int centiSecondsPerFrame, int quality, int pitchInBytes) { MsfTimeFunc if (!handle->listHead) { return 0; } //TODO: sanity-check `pitchInBytes` quality = msf_imax(1, msf_imin(16, quality)); if (pitchInBytes == 0) pitchInBytes = handle->width * 4; if (pitchInBytes < 0) pixelData -= pitchInBytes * (handle->height - 1); msf_cook_frame(&handle->currentFrame, pixelData, handle->usedMem, handle->width, handle->height, pitchInBytes, msf_imin(quality, handle->previousFrame.depth + 160 / msf_imax(1, handle->previousFrame.count))); MsfGifBuffer * buffer = msf_compress_frame(handle->customAllocatorContext, handle->width, handle->height, centiSecondsPerFrame, handle->currentFrame, handle, handle->usedMem, handle->tlbMem, handle->lzwMem); if (!buffer) { msf_free_gif_state(handle); return 0; } handle->listTail->next = buffer; handle->listTail = buffer; //swap current and previous frames MsfCookedFrame tmp = handle->previousFrame; handle->previousFrame = handle->currentFrame; handle->currentFrame = tmp; handle->framesSubmitted += 1; return 1; } MsfGifResult msf_gif_end(MsfGifState * handle) { MsfTimeFunc if (!handle->listHead) { MsfGifResult empty = {0}; return empty; } //first pass: determine total size size_t total = 1; //1 byte for trailing marker for (MsfGifBuffer * node = handle->listHead; node; node = node->next) { total += node->size; } //second pass: write data uint8_t * buffer = (uint8_t *) MSF_GIF_MALLOC(handle->customAllocatorContext, total); if (buffer) { uint8_t * writeHead = buffer; for (MsfGifBuffer * node = handle->listHead; node; node = node->next) { memcpy(writeHead, node->data, node->size); writeHead += node->size; } *writeHead++ = 0x3B; } //third pass: free buffers msf_free_gif_state(handle); MsfGifResult ret = { buffer, total, total, handle->customAllocatorContext }; return ret; } void msf_gif_free(MsfGifResult result) { MsfTimeFunc if (result.data) { MSF_GIF_FREE(result.contextPointer, result.data, result.allocSize); } } //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// /// To-file API /// //////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// int msf_gif_begin_to_file(MsfGifState * handle, int width, int height, MsfGifFileWriteFunc func, void * filePointer) { handle->fileWriteFunc = func; handle->fileWriteData = filePointer; return msf_gif_begin(handle, width, height); } int msf_gif_frame_to_file(MsfGifState * handle, uint8_t * pixelData, int centiSecondsPerFrame, int quality, int pitchInBytes) { if (!msf_gif_frame(handle, pixelData, centiSecondsPerFrame, quality, pitchInBytes)) { return 0; } //NOTE: this is a somewhat hacky implementation which is not perfectly efficient, but it's good enough for now MsfGifBuffer * head = handle->listHead; if (!handle->fileWriteFunc(head->data, head->size, 1, handle->fileWriteData)) { msf_free_gif_state(handle); return 0; } handle->listHead = head->next; MSF_GIF_FREE(handle->customAllocatorContext, head, offsetof(MsfGifBuffer, data) + head->size); return 1; } int msf_gif_end_to_file(MsfGifState * handle) { //NOTE: this is a somewhat hacky implementation which is not perfectly efficient, but it's good enough for now MsfGifResult result = msf_gif_end(handle); int ret = (int) handle->fileWriteFunc(result.data, result.dataSize, 1, handle->fileWriteData); msf_gif_free(result); return ret; } #endif //MSF_GIF_ALREADY_IMPLEMENTED_IN_THIS_TRANSLATION_UNIT #endif //MSF_GIF_IMPL /* ------------------------------------------------------------------------------ This software is available under 2 licenses -- choose whichever you prefer. ------------------------------------------------------------------------------ ALTERNATIVE A - MIT License Copyright (c) 2025 Miles Fogle Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions: The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software. 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In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law. THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE. ------------------------------------------------------------------------------ */