//
// 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 <stdbool.h> // for bool macros
#include <stdint.h>  // for integer typedefs
#include <stdio.h>   // for FILE*
#include <string.h>  // for memcpy and bzero

// 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;

typedef struct {
	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[256];
	uint8_t treeSplit[256];
} GifPalette;

// 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) {
	// 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, 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 = (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, 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] = (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
typedef struct {
	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;

// 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
typedef struct {
	uint16_t m_next[256];
} GifLzwNode;

// 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);
}

typedef struct {
	FILE * f;
	uint8_t * oldImage;
	bool firstFrame;
} GifWriter;

// 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
