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//
// gif.h
// by Charlie Tangora
// Public domain.
// Email me : ctangora -at- gmail -dot- com
//
// This file offers a simple, very limited way to create animated GIFs directly in code.
//
// Those looking for particular cleverness are likely to be disappointed; it's pretty
// much a straight-ahead implementation of the GIF format with optional Floyd-Steinberg
// dithering. (It does at least use delta encoding - only the changed portions of each
// frame are saved.)
//
// So resulting files are often quite large. The hope is that it will be handy nonetheless
// as a quick and easily-integrated way for programs to spit out animations.
//
// Only RGBA8 is currently supported as an input format. (The alpha is ignored.)
//
// If capturing a buffer with a bottom-left origin (such as OpenGL), define GIF_FLIP_VERT
// to automatically flip the buffer data when writing the image (the buffer itself is
// unchanged.
//
// USAGE:
// Create a GifWriter struct. Pass it to GifBegin() to initialize and write the header.
// Pass subsequent frames to GifWriteFrame().
// Finally, call GifEnd() to close the file handle and free memory.
//
#ifndef gif_h_
#define gif_h_
#include <stdio.h> // for FILE*
#include <string.h> // for memcpy and bzero
#include <stdint.h> // for integer typedefs
// Define these macros to hook into a custom memory allocator.
// TEMP_MALLOC and TEMP_FREE will only be called in stack fashion - frees in the reverse order of mallocs
// and any temp memory allocated by a function will be freed before it exits.
// MALLOC and FREE are used only by GifBegin and GifEnd respectively (to allocate a buffer the size of the image, which
// is used to find changed pixels for delta-encoding.)
#ifndef GIF_TEMP_MALLOC
#include <stdlib.h>
#define GIF_TEMP_MALLOC malloc
#endif
#ifndef GIF_TEMP_FREE
#include <stdlib.h>
#define GIF_TEMP_FREE free
#endif
#ifndef GIF_MALLOC
#include <stdlib.h>
#define GIF_MALLOC malloc
#endif
#ifndef GIF_FREE
#include <stdlib.h>
#define GIF_FREE free
#endif
const int kGifTransIndex = 0;
struct GifPalette
{
int bitDepth;
uint8_t r[256];
uint8_t g[256];
uint8_t b[256];
// k-d tree over RGB space, organized in heap fashion
// i.e. left child of node i is node i*2, right child is node i*2+1
// nodes 256-511 are implicitly the leaves, containing a color
uint8_t treeSplitElt[255];
uint8_t treeSplit[255];
};
// max, min, and abs functions
int GifIMax(int l, int r) { return l>r?l:r; }
int GifIMin(int l, int r) { return l<r?l:r; }
int GifIAbs(int i) { return i<0?-i:i; }
// walks the k-d tree to pick the palette entry for a desired color.
// Takes as in/out parameters the current best color and its error -
// only changes them if it finds a better color in its subtree.
// this is the major hotspot in the code at the moment.
void GifGetClosestPaletteColor(GifPalette* pPal, int r, int g, int b, int& bestInd, int& bestDiff, int treeRoot = 1)
{
// base case, reached the bottom of the tree
if(treeRoot > (1<<pPal->bitDepth)-1)
{
int ind = treeRoot-(1<<pPal->bitDepth);
if(ind == kGifTransIndex) return;
// check whether this color is better than the current winner
int r_err = r - ((int32_t)pPal->r[ind]);
int g_err = g - ((int32_t)pPal->g[ind]);
int b_err = b - ((int32_t)pPal->b[ind]);
int diff = GifIAbs(r_err)+GifIAbs(g_err)+GifIAbs(b_err);
if(diff < bestDiff)
{
bestInd = ind;
bestDiff = diff;
}
return;
}
// take the appropriate color (r, g, or b) for this node of the k-d tree
int comps[3]; comps[0] = r; comps[1] = g; comps[2] = b;
int splitComp = comps[pPal->treeSplitElt[treeRoot]];
int splitPos = pPal->treeSplit[treeRoot];
if(splitPos > splitComp)
{
// check the left subtree
GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2);
if( bestDiff > splitPos - splitComp )
{
// cannot prove there's not a better value in the right subtree, check that too
GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2+1);
}
}
else
{
GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2+1);
if( bestDiff > splitComp - splitPos )
{
GifGetClosestPaletteColor(pPal, r, g, b, bestInd, bestDiff, treeRoot*2);
}
}
}
void GifSwapPixels(uint8_t* image, int pixA, int pixB)
{
uint8_t rA = image[pixA*4];
uint8_t gA = image[pixA*4+1];
uint8_t bA = image[pixA*4+2];
uint8_t aA = image[pixA*4+3];
uint8_t rB = image[pixB*4];
uint8_t gB = image[pixB*4+1];
uint8_t bB = image[pixB*4+2];
uint8_t aB = image[pixA*4+3];
image[pixA*4] = rB;
image[pixA*4+1] = gB;
image[pixA*4+2] = bB;
image[pixA*4+3] = aB;
image[pixB*4] = rA;
image[pixB*4+1] = gA;
image[pixB*4+2] = bA;
image[pixB*4+3] = aA;
}
// just the partition operation from quicksort
int GifPartition(uint8_t* image, const int left, const int right, const int elt, int pivotIndex)
{
const int pivotValue = image[(pivotIndex)*4+elt];
GifSwapPixels(image, pivotIndex, right-1);
int storeIndex = left;
bool split = 0;
for(int ii=left; ii<right-1; ++ii)
{
int arrayVal = image[ii*4+elt];
if( arrayVal < pivotValue )
{
GifSwapPixels(image, ii, storeIndex);
++storeIndex;
}
else if( arrayVal == pivotValue )
{
if(split)
{
GifSwapPixels(image, ii, storeIndex);
++storeIndex;
}
split = !split;
}
}
GifSwapPixels(image, storeIndex, right-1);
return storeIndex;
}
// Perform an incomplete sort, finding all elements above and below the desired median
void GifPartitionByMedian(uint8_t* image, int left, int right, int com, int neededCenter)
{
if(left < right-1)
{
int pivotIndex = left + (right-left)/2;
pivotIndex = GifPartition(image, left, right, com, pivotIndex);
// Only "sort" the section of the array that contains the median
if(pivotIndex > neededCenter)
GifPartitionByMedian(image, left, pivotIndex, com, neededCenter);
if(pivotIndex < neededCenter)
GifPartitionByMedian(image, pivotIndex+1, right, com, neededCenter);
}
}
// Builds a palette by creating a balanced k-d tree of all pixels in the image
void GifSplitPalette(uint8_t* image, int numPixels, int firstElt, int lastElt, int splitElt, int splitDist, int treeNode, bool buildForDither, GifPalette* pal)
{
if(lastElt <= firstElt || numPixels == 0)
return;
// base case, bottom of the tree
if(lastElt == firstElt+1)
{
if(buildForDither)
{
// Dithering needs at least one color as dark as anything
// in the image and at least one brightest color -
// otherwise it builds up error and produces strange artifacts
if( firstElt == 1 )
{
// special case: the darkest color in the image
uint32_t r=255, g=255, b=255;
for(int ii=0; ii<numPixels; ++ii)
{
r = (uint32_t)GifIMin((int32_t)r, image[ii * 4 + 0]);
g = (uint32_t)GifIMin((int32_t)g, image[ii * 4 + 1]);
b = (uint32_t)GifIMin((int32_t)b, image[ii * 4 + 2]);
}
pal->r[firstElt] = (uint8_t)r;
pal->g[firstElt] = (uint8_t)g;
pal->b[firstElt] = (uint8_t)b;
return;
}
if( firstElt == (1 << pal->bitDepth)-1 )
{
// special case: the lightest color in the image
uint32_t r=0, g=0, b=0;
for(int ii=0; ii<numPixels; ++ii)
{
r = (uint32_t)GifIMax((int32_t)r, image[ii * 4 + 0]);
g = (uint32_t)GifIMax((int32_t)g, image[ii * 4 + 1]);
b = (uint32_t)GifIMax((int32_t)b, image[ii * 4 + 2]);
}
pal->r[firstElt] = (uint8_t)r;
pal->g[firstElt] = (uint8_t)g;
pal->b[firstElt] = (uint8_t)b;
return;
}
}
// otherwise, take the average of all colors in this subcube
uint64_t r=0, g=0, b=0;
for(int ii=0; ii<numPixels; ++ii)
{
r += image[ii*4+0];
g += image[ii*4+1];
b += image[ii*4+2];
}
r += (uint64_t)numPixels / 2; // round to nearest
g += (uint64_t)numPixels / 2;
b += (uint64_t)numPixels / 2;
r /= (uint64_t)numPixels;
g /= (uint64_t)numPixels;
b /= (uint64_t)numPixels;
pal->r[firstElt] = (uint8_t)r;
pal->g[firstElt] = (uint8_t)g;
pal->b[firstElt] = (uint8_t)b;
return;
}
// Find the axis with the largest range
int minR = 255, maxR = 0;
int minG = 255, maxG = 0;
int minB = 255, maxB = 0;
for(int ii=0; ii<numPixels; ++ii)
{
int r = image[ii*4+0];
int g = image[ii*4+1];
int b = image[ii*4+2];
if(r > maxR) maxR = r;
if(r < minR) minR = r;
if(g > maxG) maxG = g;
if(g < minG) minG = g;
if(b > maxB) maxB = b;
if(b < minB) minB = b;
}
int rRange = maxR - minR;
int gRange = maxG - minG;
int bRange = maxB - minB;
// and split along that axis. (incidentally, this means this isn't a "proper" k-d tree but I don't know what else to call it)
int splitCom = 1;
if(bRange > gRange) splitCom = 2;
if(rRange > bRange && rRange > gRange) splitCom = 0;
int subPixelsA = numPixels * (splitElt - firstElt) / (lastElt - firstElt);
int subPixelsB = numPixels-subPixelsA;
GifPartitionByMedian(image, 0, numPixels, splitCom, subPixelsA);
pal->treeSplitElt[treeNode] = (uint8_t)splitCom;
pal->treeSplit[treeNode] = image[subPixelsA*4+splitCom];
GifSplitPalette(image, subPixelsA, firstElt, splitElt, splitElt-splitDist, splitDist/2, treeNode*2, buildForDither, pal);
GifSplitPalette(image+subPixelsA*4, subPixelsB, splitElt, lastElt, splitElt+splitDist, splitDist/2, treeNode*2+1, buildForDither, pal);
}
// Finds all pixels that have changed from the previous image and
// moves them to the fromt of th buffer.
// This allows us to build a palette optimized for the colors of the
// changed pixels only.
int GifPickChangedPixels( const uint8_t* lastFrame, uint8_t* frame, int numPixels )
{
int numChanged = 0;
uint8_t* writeIter = frame;
for (int ii=0; ii<numPixels; ++ii)
{
if(lastFrame[0] != frame[0] ||
lastFrame[1] != frame[1] ||
lastFrame[2] != frame[2])
{
writeIter[0] = frame[0];
writeIter[1] = frame[1];
writeIter[2] = frame[2];
++numChanged;
writeIter += 4;
}
lastFrame += 4;
frame += 4;
}
return numChanged;
}
// Creates a palette by placing all the image pixels in a k-d tree and then averaging the blocks at the bottom.
// This is known as the "modified median split" technique
void GifMakePalette( const uint8_t* lastFrame, const uint8_t* nextFrame, uint32_t width, uint32_t height, int bitDepth, bool buildForDither, GifPalette* pPal )
{
pPal->bitDepth = bitDepth;
// SplitPalette is destructive (it sorts the pixels by color) so
// we must create a copy of the image for it to destroy
size_t imageSize = (size_t)(width * height * 4 * sizeof(uint8_t));
uint8_t* destroyableImage = (uint8_t*)GIF_TEMP_MALLOC(imageSize);
memcpy(destroyableImage, nextFrame, imageSize);
int numPixels = (int)(width * height);
if(lastFrame)
numPixels = GifPickChangedPixels(lastFrame, destroyableImage, numPixels);
const int lastElt = 1 << bitDepth;
const int splitElt = lastElt/2;
const int splitDist = splitElt/2;
GifSplitPalette(destroyableImage, numPixels, 1, lastElt, splitElt, splitDist, 1, buildForDither, pPal);
GIF_TEMP_FREE(destroyableImage);
// add the bottom node for the transparency index
pPal->treeSplit[1 << (bitDepth-1)] = 0;
pPal->treeSplitElt[1 << (bitDepth-1)] = 0;
pPal->r[0] = pPal->g[0] = pPal->b[0] = 0;
}
// Implements Floyd-Steinberg dithering, writes palette value to alpha
void GifDitherImage( const uint8_t* lastFrame, const uint8_t* nextFrame, uint8_t* outFrame, uint32_t width, uint32_t height, GifPalette* pPal )
{
int numPixels = (int)(width * height);
// quantPixels initially holds color*256 for all pixels
// The extra 8 bits of precision allow for sub-single-color error values
// to be propagated
int32_t *quantPixels = (int32_t *)GIF_TEMP_MALLOC(sizeof(int32_t) * (size_t)numPixels * 4);
for( int ii=0; ii<numPixels*4; ++ii )
{
uint8_t pix = nextFrame[ii];
int32_t pix16 = int32_t(pix) * 256;
quantPixels[ii] = pix16;
}
for( uint32_t yy=0; yy<height; ++yy )
{
for( uint32_t xx=0; xx<width; ++xx )
{
int32_t* nextPix = quantPixels + 4*(yy*width+xx);
const uint8_t* lastPix = lastFrame? lastFrame + 4*(yy*width+xx) : NULL;
// Compute the colors we want (rounding to nearest)
int32_t rr = (nextPix[0] + 127) / 256;
int32_t gg = (nextPix[1] + 127) / 256;
int32_t bb = (nextPix[2] + 127) / 256;
// if it happens that we want the color from last frame, then just write out
// a transparent pixel
if( lastFrame &&
lastPix[0] == rr &&
lastPix[1] == gg &&
lastPix[2] == bb )
{
nextPix[0] = rr;
nextPix[1] = gg;
nextPix[2] = bb;
nextPix[3] = kGifTransIndex;
continue;
}
int32_t bestDiff = 1000000;
int32_t bestInd = kGifTransIndex;
// Search the palete
GifGetClosestPaletteColor(pPal, rr, gg, bb, bestInd, bestDiff);
// Write the result to the temp buffer
int32_t r_err = nextPix[0] - int32_t(pPal->r[bestInd]) * 256;
int32_t g_err = nextPix[1] - int32_t(pPal->g[bestInd]) * 256;
int32_t b_err = nextPix[2] - int32_t(pPal->b[bestInd]) * 256;
nextPix[0] = pPal->r[bestInd];
nextPix[1] = pPal->g[bestInd];
nextPix[2] = pPal->b[bestInd];
nextPix[3] = bestInd;
// Propagate the error to the four adjacent locations
// that we haven't touched yet
int quantloc_7 = (int)(yy * width + xx + 1);
int quantloc_3 = (int)(yy * width + width + xx - 1);
int quantloc_5 = (int)(yy * width + width + xx);
int quantloc_1 = (int)(yy * width + width + xx + 1);
if(quantloc_7 < numPixels)
{
int32_t* pix7 = quantPixels+4*quantloc_7;
pix7[0] += GifIMax( -pix7[0], r_err * 7 / 16 );
pix7[1] += GifIMax( -pix7[1], g_err * 7 / 16 );
pix7[2] += GifIMax( -pix7[2], b_err * 7 / 16 );
}
if(quantloc_3 < numPixels)
{
int32_t* pix3 = quantPixels+4*quantloc_3;
pix3[0] += GifIMax( -pix3[0], r_err * 3 / 16 );
pix3[1] += GifIMax( -pix3[1], g_err * 3 / 16 );
pix3[2] += GifIMax( -pix3[2], b_err * 3 / 16 );
}
if(quantloc_5 < numPixels)
{
int32_t* pix5 = quantPixels+4*quantloc_5;
pix5[0] += GifIMax( -pix5[0], r_err * 5 / 16 );
pix5[1] += GifIMax( -pix5[1], g_err * 5 / 16 );
pix5[2] += GifIMax( -pix5[2], b_err * 5 / 16 );
}
if(quantloc_1 < numPixels)
{
int32_t* pix1 = quantPixels+4*quantloc_1;
pix1[0] += GifIMax( -pix1[0], r_err / 16 );
pix1[1] += GifIMax( -pix1[1], g_err / 16 );
pix1[2] += GifIMax( -pix1[2], b_err / 16 );
}
}
}
// Copy the palettized result to the output buffer
for( int ii=0; ii<numPixels*4; ++ii )
{
outFrame[ii] = (uint8_t)quantPixels[ii];
}
GIF_TEMP_FREE(quantPixels);
}
// Picks palette colors for the image using simple thresholding, no dithering
void GifThresholdImage( const uint8_t* lastFrame, const uint8_t* nextFrame, uint8_t* outFrame, uint32_t width, uint32_t height, GifPalette* pPal )
{
uint32_t numPixels = width*height;
for( uint32_t ii=0; ii<numPixels; ++ii )
{
// if a previous color is available, and it matches the current color,
// set the pixel to transparent
if(lastFrame &&
lastFrame[0] == nextFrame[0] &&
lastFrame[1] == nextFrame[1] &&
lastFrame[2] == nextFrame[2])
{
outFrame[0] = lastFrame[0];
outFrame[1] = lastFrame[1];
outFrame[2] = lastFrame[2];
outFrame[3] = kGifTransIndex;
}
else
{
// palettize the pixel
int32_t bestDiff = 1000000;
int32_t bestInd = 1;
GifGetClosestPaletteColor(pPal, nextFrame[0], nextFrame[1], nextFrame[2], bestInd, bestDiff);
// Write the resulting color to the output buffer
outFrame[0] = pPal->r[bestInd];
outFrame[1] = pPal->g[bestInd];
outFrame[2] = pPal->b[bestInd];
outFrame[3] = (uint8_t)bestInd;
}
if(lastFrame) lastFrame += 4;
outFrame += 4;
nextFrame += 4;
}
}
// Simple structure to write out the LZW-compressed portion of the image
// one bit at a time
struct GifBitStatus
{
uint8_t bitIndex; // how many bits in the partial byte written so far
uint8_t byte; // current partial byte
uint32_t chunkIndex;
uint8_t chunk[256]; // bytes are written in here until we have 256 of them, then written to the file
};
// insert a single bit
void GifWriteBit( GifBitStatus& stat, uint32_t bit )
{
bit = bit & 1;
bit = bit << stat.bitIndex;
stat.byte |= bit;
++stat.bitIndex;
if( stat.bitIndex > 7 )
{
// move the newly-finished byte to the chunk buffer
stat.chunk[stat.chunkIndex++] = stat.byte;
// and start a new byte
stat.bitIndex = 0;
stat.byte = 0;
}
}
// write all bytes so far to the file
void GifWriteChunk( FILE* f, GifBitStatus& stat )
{
fputc((int)stat.chunkIndex, f);
fwrite(stat.chunk, 1, stat.chunkIndex, f);
stat.bitIndex = 0;
stat.byte = 0;
stat.chunkIndex = 0;
}
void GifWriteCode( FILE* f, GifBitStatus& stat, uint32_t code, uint32_t length )
{
for( uint32_t ii=0; ii<length; ++ii )
{
GifWriteBit(stat, code);
code = code >> 1;
if( stat.chunkIndex == 255 )
{
GifWriteChunk(f, stat);
}
}
}
// The LZW dictionary is a 256-ary tree constructed as the file is encoded,
// this is one node
struct GifLzwNode
{
uint16_t m_next[256];
};
// write a 256-color (8-bit) image palette to the file
void GifWritePalette( const GifPalette* pPal, FILE* f )
{
fputc(0, f); // first color: transparency
fputc(0, f);
fputc(0, f);
for(int ii=1; ii<(1 << pPal->bitDepth); ++ii)
{
uint32_t r = pPal->r[ii];
uint32_t g = pPal->g[ii];
uint32_t b = pPal->b[ii];
fputc((int)r, f);
fputc((int)g, f);
fputc((int)b, f);
}
}
// write the image header, LZW-compress and write out the image
void GifWriteLzwImage(FILE* f, uint8_t* image, uint32_t left, uint32_t top, uint32_t width, uint32_t height, uint32_t delay, GifPalette* pPal)
{
// graphics control extension
fputc(0x21, f);
fputc(0xf9, f);
fputc(0x04, f);
fputc(0x05, f); // leave prev frame in place, this frame has transparency
fputc(delay & 0xff, f);
fputc((delay >> 8) & 0xff, f);
fputc(kGifTransIndex, f); // transparent color index
fputc(0, f);
fputc(0x2c, f); // image descriptor block
fputc(left & 0xff, f); // corner of image in canvas space
fputc((left >> 8) & 0xff, f);
fputc(top & 0xff, f);
fputc((top >> 8) & 0xff, f);
fputc(width & 0xff, f); // width and height of image
fputc((width >> 8) & 0xff, f);
fputc(height & 0xff, f);
fputc((height >> 8) & 0xff, f);
//fputc(0, f); // no local color table, no transparency
//fputc(0x80, f); // no local color table, but transparency
fputc(0x80 + pPal->bitDepth-1, f); // local color table present, 2 ^ bitDepth entries
GifWritePalette(pPal, f);
const int minCodeSize = pPal->bitDepth;
const uint32_t clearCode = 1 << pPal->bitDepth;
fputc(minCodeSize, f); // min code size 8 bits
GifLzwNode* codetree = (GifLzwNode*)GIF_TEMP_MALLOC(sizeof(GifLzwNode)*4096);
memset(codetree, 0, sizeof(GifLzwNode)*4096);
int32_t curCode = -1;
uint32_t codeSize = (uint32_t)minCodeSize + 1;
uint32_t maxCode = clearCode+1;
GifBitStatus stat;
stat.byte = 0;
stat.bitIndex = 0;
stat.chunkIndex = 0;
GifWriteCode(f, stat, clearCode, codeSize); // start with a fresh LZW dictionary
for(uint32_t yy=0; yy<height; ++yy)
{
for(uint32_t xx=0; xx<width; ++xx)
{
#ifdef GIF_FLIP_VERT
// bottom-left origin image (such as an OpenGL capture)
uint8_t nextValue = image[((height-1-yy)*width+xx)*4+3];
#else
// top-left origin
uint8_t nextValue = image[(yy*width+xx)*4+3];
#endif
// "loser mode" - no compression, every single code is followed immediately by a clear
//WriteCode( f, stat, nextValue, codeSize );
//WriteCode( f, stat, 256, codeSize );
if( curCode < 0 )
{
// first value in a new run
curCode = nextValue;
}
else if( codetree[curCode].m_next[nextValue] )
{
// current run already in the dictionary
curCode = codetree[curCode].m_next[nextValue];
}
else
{
// finish the current run, write a code
GifWriteCode(f, stat, (uint32_t)curCode, codeSize);
// insert the new run into the dictionary
codetree[curCode].m_next[nextValue] = (uint16_t)++maxCode;
if( maxCode >= (1ul << codeSize) )
{
// dictionary entry count has broken a size barrier,
// we need more bits for codes
codeSize++;
}
if( maxCode == 4095 )
{
// the dictionary is full, clear it out and begin anew
GifWriteCode(f, stat, clearCode, codeSize); // clear tree
memset(codetree, 0, sizeof(GifLzwNode)*4096);
codeSize = (uint32_t)(minCodeSize + 1);
maxCode = clearCode+1;
}
curCode = nextValue;
}
}
}
// compression footer
GifWriteCode(f, stat, (uint32_t)curCode, codeSize);
GifWriteCode(f, stat, clearCode, codeSize);
GifWriteCode(f, stat, clearCode + 1, (uint32_t)minCodeSize + 1);
// write out the last partial chunk
while( stat.bitIndex ) GifWriteBit(stat, 0);
if( stat.chunkIndex ) GifWriteChunk(f, stat);
fputc(0, f); // image block terminator
GIF_TEMP_FREE(codetree);
}
struct GifWriter
{
FILE* f;
uint8_t* oldImage;
bool firstFrame;
};
// Creates a gif file.
// The input GIFWriter is assumed to be uninitialized.
// The delay value is the time between frames in hundredths of a second - note that not all viewers pay much attention to this value.
bool GifBegin( GifWriter* writer, const char* filename, uint32_t width, uint32_t height, uint32_t delay, int32_t bitDepth = 8, bool dither = false )
{
(void)bitDepth; (void)dither; // Mute "Unused argument" warnings
#if defined(_MSC_VER) && (_MSC_VER >= 1400)
writer->f = 0;
fopen_s(&writer->f, filename, "wb");
#else
writer->f = fopen(filename, "wb");
#endif
if(!writer->f) return false;
writer->firstFrame = true;
// allocate
writer->oldImage = (uint8_t*)GIF_MALLOC(width*height*4);
fputs("GIF89a", writer->f);
// screen descriptor
fputc(width & 0xff, writer->f);
fputc((width >> 8) & 0xff, writer->f);
fputc(height & 0xff, writer->f);
fputc((height >> 8) & 0xff, writer->f);
fputc(0xf0, writer->f); // there is an unsorted global color table of 2 entries
fputc(0, writer->f); // background color
fputc(0, writer->f); // pixels are square (we need to specify this because it's 1989)
// now the "global" palette (really just a dummy palette)
// color 0: black
fputc(0, writer->f);
fputc(0, writer->f);
fputc(0, writer->f);
// color 1: also black
fputc(0, writer->f);
fputc(0, writer->f);
fputc(0, writer->f);
if( delay != 0 )
{
// animation header
fputc(0x21, writer->f); // extension
fputc(0xff, writer->f); // application specific
fputc(11, writer->f); // length 11
fputs("NETSCAPE2.0", writer->f); // yes, really
fputc(3, writer->f); // 3 bytes of NETSCAPE2.0 data
fputc(1, writer->f); // JUST BECAUSE
fputc(0, writer->f); // loop infinitely (byte 0)
fputc(0, writer->f); // loop infinitely (byte 1)
fputc(0, writer->f); // block terminator
}
return true;
}
// Writes out a new frame to a GIF in progress.
// The GIFWriter should have been created by GIFBegin.
// AFAIK, it is legal to use different bit depths for different frames of an image -
// this may be handy to save bits in animations that don't change much.
bool GifWriteFrame( GifWriter* writer, const uint8_t* image, uint32_t width, uint32_t height, uint32_t delay, int bitDepth = 8, bool dither = false )
{
if(!writer->f) return false;
const uint8_t* oldImage = writer->firstFrame? NULL : writer->oldImage;
writer->firstFrame = false;
GifPalette pal;
GifMakePalette((dither? NULL : oldImage), image, width, height, bitDepth, dither, &pal);
if(dither)
GifDitherImage(oldImage, image, writer->oldImage, width, height, &pal);
else
GifThresholdImage(oldImage, image, writer->oldImage, width, height, &pal);
GifWriteLzwImage(writer->f, writer->oldImage, 0, 0, width, height, delay, &pal);
return true;
}
// Writes the EOF code, closes the file handle, and frees temp memory used by a GIF.
// Many if not most viewers will still display a GIF properly if the EOF code is missing,
// but it's still a good idea to write it out.
bool GifEnd( GifWriter* writer )
{
if(!writer->f) return false;
fputc(0x3b, writer->f); // end of file
fclose(writer->f);
GIF_FREE(writer->oldImage);
writer->f = NULL;
writer->oldImage = NULL;
return true;
}
#endif
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