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Added gif file writter library 

Setup for a new amazing feature! ;)
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Ray 7 years ago
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/**********************************************************************************************
*
* gif.h by Charlie Tangora [ctangora -at- gmail -dot- com]
* adapted to C99 and reformatted by Ramon Santamaria (@raysan5)
*
* 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.)
*
* CONFIGURATION:
*
* #define GIF_IMPLEMENTATION
* Generates the implementation of the library into the included file.
* If not defined, the library is in header only mode and can be included in other headers
* or source files without problems. But only ONE file should hold the implementation.
*
* USAGE:
* 1) Create a GifWriter struct. Pass it to GifBegin() to initialize and write the header.
* 2) Pass subsequent frames to GifWriteFrame().
* 3) Finally, call GifEnd() to close the file handle and free memory.
*
*
* LICENSE: public domain (www.unlicense.org)
*
* This is free and unencumbered software released into the public domain.
* Anyone is free to copy, modify, publish, use, compile, sell, or distribute this
* software, either in source code form or as a compiled binary, for any purpose,
* commercial or non-commercial, and by any means.
*
* 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.
*
**********************************************************************************************/
#ifndef GIF_H
#define GIF_H
#include <stdio.h> // Required for: FILE
#include <stdint.h> // Required for for integer typedefs
//#define GIF_STATIC
#ifdef GIF_STATIC
#define GIFDEF static // Functions just visible to module including this file
#else
#ifdef __cplusplus
#define GIFDEF extern "C" // Functions visible from other files (no name mangling of functions in C++)
#else
#define GIFDEF extern // Functions visible from other files
#endif
#endif
//----------------------------------------------------------------------------------
// Defines and Macros
//----------------------------------------------------------------------------------
//#define MAX_RESOURCES_SUPPORTED 256
//----------------------------------------------------------------------------------
// Types and Structures Definition
//----------------------------------------------------------------------------------
typedef struct GifWriter {
FILE *f;
uint8_t *oldImage;
bool firstFrame;
} GifWriter;
//----------------------------------------------------------------------------------
// Global variables
//----------------------------------------------------------------------------------
//...
//----------------------------------------------------------------------------------
// Module Functions Declaration
//----------------------------------------------------------------------------------
// NOTE: By default use bitDepth = 8, dither = false
GIFDEF bool GifBegin(GifWriter *writer, const char *filename, uint32_t width, uint32_t height, uint32_t delay, int32_t bitDepth, bool dither);
GIFDEF bool GifWriteFrame(GifWriter *writer, const uint8_t *image, uint32_t width, uint32_t height, uint32_t delay, int bitDepth, bool dither);
GIFDEF bool GifEnd(GifWriter *writer);
#endif // GIF_H
/***********************************************************************************
*
* GIF IMPLEMENTATION
*
************************************************************************************/
#if defined(GIF_IMPLEMENTATION)
#include <stdio.h> // Required for: FILE, fopen(), fclose()
#include <string.h> // Required for: memcpy()
#include <stdint.h> // Required for for integer typedefs
// Define these macros to hook into a custom memory allocator.
// GIF_TEMP_MALLOC and GIF_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.
#if !defined(GIF_TEMP_MALLOC)
#include <stdlib.h>
#define GIF_TEMP_MALLOC malloc
#define GIF_TEMP_FREE free
#endif
// Check if custom malloc/free functions defined, if not, using standard ones
// GIF_MALLOC and GIF_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.
#if !defined(GIF_MALLOC)
#include <stdlib.h> // Required for: malloc(), free()
#define GIF_MALLOC(size) malloc(size)
#define GIF_FREE(ptr) free(ptr)
#endif
//----------------------------------------------------------------------------------
// Defines and Macros
//----------------------------------------------------------------------------------
#define GIFMIN(a, b) (((a)<(b))?(a):(b))
#define GIFMAX(a, b) (((a)>(b))?(a):(b))
#define GIFABS(x) ((x)<0?-(x):(x))
//----------------------------------------------------------------------------------
// Types and Structures Definition
//----------------------------------------------------------------------------------
//Gif palette structure
typedef 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];
} GifPalette;
// Simple structure to write out the LZW-compressed
// portion of the imageone bit at a time
typedef 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
} GifBitStatus;
// The LZW dictionary is a 256-ary tree constructed
// as the file is encoded, this is one node
typedef struct GifLzwNode {
uint16_t m_next[256];
} GifLzwNode;
//----------------------------------------------------------------------------------
// Global Variables Definition
//----------------------------------------------------------------------------------
const int kGifTransIndex = 0;
//----------------------------------------------------------------------------------
// Module specific Functions Declaration
//----------------------------------------------------------------------------------
static void GifGetClosestPaletteColor(GifPalette *pPal, int r, int g, int b, int *bestInd, int *bestDiff, int treeRoot);
static void GifSwapPixels(uint8_t *image, int pixA, int pixB);
static int GifPartition(uint8_t *image, const int left, const int right, const int elt, int pivotIndex);
static void GifPartitionByMedian(uint8_t *image, int left, int right, int com, int neededCenter);
static void GifSplitPalette(uint8_t *image, int numPixels, int firstElt, int lastElt, int splitElt, int splitDist, int treeNode, bool buildForDither, GifPalette *pal);
static int GifPickChangedPixels(const uint8_t *lastFrame, uint8_t *frame, int numPixels);
static void GifMakePalette(const uint8_t *lastFrame, const uint8_t *nextFrame, uint32_t width, uint32_t height, int bitDepth, bool buildForDither, GifPalette *pPal);
static void GifDitherImage(const uint8_t *lastFrame, const uint8_t *nextFrame, uint8_t *outFrame, uint32_t width, uint32_t height, GifPalette *pPal);
static void GifThresholdImage(const uint8_t *lastFrame, const uint8_t *nextFrame, uint8_t *outFrame, uint32_t width, uint32_t height, GifPalette *pPal);
static void GifWriteBit(GifBitStatus *stat, uint32_t bit);
static void GifWriteChunk(FILE *f, GifBitStatus *stat);
static void GifWriteCode(FILE *f, GifBitStatus *stat, uint32_t code, uint32_t length);
static void GifWritePalette(const GifPalette *pPal, FILE *f);
static void GifWriteLzwImage(FILE *f, uint8_t *image, uint32_t left, uint32_t top, uint32_t width, uint32_t height, uint32_t delay, GifPalette *pPal);
//----------------------------------------------------------------------------------
// Module Functions Definition
//----------------------------------------------------------------------------------
// 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.
GIFDEF bool GifBegin(GifWriter *writer, const char *filename, uint32_t width, uint32_t height, uint32_t delay, int32_t bitDepth, bool dither)
{
#if _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.
GIFDEF bool GifWriteFrame(GifWriter *writer, const uint8_t *image, uint32_t width, uint32_t height, uint32_t delay, int bitDepth, bool dither)
{
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.
GIFDEF 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;
}
//----------------------------------------------------------------------------------
// Module specific Functions Definition
//----------------------------------------------------------------------------------
// 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.
static void GifGetClosestPaletteColor(GifPalette *pPal, int r, int g, int b, int *bestInd, int *bestDiff, int treeRoot)
{
// 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 = GIFABS(r_err)+GIFABS(g_err)+GIFABS(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);
}
}
}
static 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
static 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
static 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
static 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 = GIFMIN(r, image[ii*4+0]);
g = GIFMIN(g, image[ii*4 + 1]);
b = GIFMIN(b, image[ii*4+2]);
}
pal->r[firstElt] = r;
pal->g[firstElt] = g;
pal->b[firstElt] = 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 = GIFMAX(r, image[ii*4+0]);
g = GIFMAX(g, image[ii*4 + 1]);
b = GIFMAX(b, image[ii*4+2]);
}
pal->r[firstElt] = r;
pal->g[firstElt] = g;
pal->b[firstElt] = 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 += numPixels / 2; // round to nearest
g += numPixels / 2;
b += numPixels / 2;
r /= numPixels;
g /= numPixels;
b /= 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] = 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.
static 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
static 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
int imageSize = width*height*4*sizeof(uint8_t);
uint8_t *destroyableImage = (uint8_t*)GIF_TEMP_MALLOC(imageSize);
memcpy(destroyableImage, nextFrame, imageSize);
int numPixels = 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
static void GifDitherImage(const uint8_t *lastFrame, const uint8_t *nextFrame, uint8_t *outFrame, uint32_t width, uint32_t height, GifPalette *pPal)
{
int numPixels = 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)*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, 1);
// 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 = (yy*width+xx + 1);
int quantloc_3 = (yy*width+width+xx-1);
int quantloc_5 = (yy*width+width+xx);
int quantloc_1 = (yy*width+width+xx + 1);
if (quantloc_7 < numPixels)
{
int32_t *pix7 = quantPixels+4*quantloc_7;
pix7[0] += GIFMAX(-pix7[0], r_err*7 / 16);
pix7[1] += GIFMAX(-pix7[1], g_err*7 / 16);
pix7[2] += GIFMAX(-pix7[2], b_err*7 / 16);
}
if (quantloc_3 < numPixels)
{
int32_t *pix3 = quantPixels+4*quantloc_3;
pix3[0] += GIFMAX(-pix3[0], r_err*3 / 16);
pix3[1] += GIFMAX(-pix3[1], g_err*3 / 16);
pix3[2] += GIFMAX(-pix3[2], b_err*3 / 16);
}
if (quantloc_5 < numPixels)
{
int32_t *pix5 = quantPixels+4*quantloc_5;
pix5[0] += GIFMAX(-pix5[0], r_err*5 / 16);
pix5[1] += GIFMAX(-pix5[1], g_err*5 / 16);
pix5[2] += GIFMAX(-pix5[2], b_err*5 / 16);
}
if (quantloc_1 < numPixels)
{
int32_t *pix1 = quantPixels+4*quantloc_1;
pix1[0] += GIFMAX(-pix1[0], r_err / 16);
pix1[1] += GIFMAX(-pix1[1], g_err / 16);
pix1[2] += GIFMAX(-pix1[2], b_err / 16);
}
}
}
// Copy the palettized result to the output buffer
for (int ii=0; ii<numPixels*4; ++ii)
{
outFrame[ii] = quantPixels[ii];
}
GIF_TEMP_FREE(quantPixels);
}
// Picks palette colors for the image using simple thresholding, no dithering
static 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, 1);
// 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] = bestInd;
}
if (lastFrame) lastFrame += 4;
outFrame += 4;
nextFrame += 4;
}
}
// insert a single bit
static 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
static void GifWriteChunk(FILE *f, GifBitStatus *stat)
{
fputc(stat->chunkIndex, f);
fwrite(stat->chunk, 1, stat->chunkIndex, f);
stat->bitIndex = 0;
stat->byte = 0;
stat->chunkIndex = 0;
}
static 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);
}
}
}
// write a 256-color (8-bit) image palette to the file
static 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(r, f);
fputc(g, f);
fputc(b, f);
}
}
// write the image header, LZW-compress and write out the image
static 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 = 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)
{
uint8_t nextValue = image[(yy*width+xx)*4+3];
// "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, curCode, codeSize);
// insert the new run into the dictionary
codetree[curCode].m_next[nextValue] = ++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);
curCode = -1;
codeSize = minCodeSize + 1;
maxCode = clearCode + 1;
}
curCode = nextValue;
}
}
}
// compression footer
GifWriteCode(f, &stat, curCode, codeSize);
GifWriteCode(f, &stat, clearCode, codeSize);
GifWriteCode(f, &stat, clearCode + 1, 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);
}
#endif // GIF_IMPLEMENTATION

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