Maybe gif-lib wasn't too bright an idea...

host/gif.c

@@ -0,0 +1,134 @@
+
+#include "gif.h"
+#include <stdio.h>
+#include <stdlib.h>
+
+typedef struct {
+	uint8_t *data;
+	unsigned int index;
+	unsigned int length;
+} readBuffer_t;	
+
+int gifBufferInput (GifFileType *gif, GifByteType *dest, int n){
+	readBuffer_t *rb = gif->userData;
+	if(rb->index+n > rb->length)
+		n = rb->length - rb->index;
+	memcpy(dest, rb->data, n);
+	return n;
+}
+
+struct _gifAnimationState {
+	int idx;
+	GifFileType *gif;
+	framebuffer_t frame;
+};
+
+gifAnimationState_t *gif_read(uint8_t *buf, unsigned int buflength){
+	/* On first invocation, parse gif and store it in the state struct */
+	gifAnimationState_t *st = malloc(sizeof(*state));
+	if(!st){
+		fprintf(stderr, "Failed to allocate %d bytes\n", sizeof(*state));
+		return 0;
+	}
+
+	readBuffer_t readBuf = {buf, 0, buflength};
+	int err = 0;
+	GifFileType *gif = DGifOpen(readBuf, OutputFunc writeFunc, &err);
+	if(err){
+		fprintf(stderr, "Could not read GIF data: %s\n", GifErrorString(err));
+		goto error;
+	}
+
+	unsigned int framesize = gif->SWidth*gif->SHeight;
+	if(framesize == 0){ /* Can this actually happen? */
+		fprintf(stderr, "Invalid 0*0px gif\n");
+		goto error;
+	}
+	color_t *fb = calloc(framesize, sizeof(color_t));
+	if(!fb){
+		fprintf(stderr, "Failed to allocate framebuffer for GIF (%d bytes)\n", gif->SWidth*gif->SHeight);
+		goto error;
+	}
+	if(gif->SColorMap){ /* Initially fill framebuffer with background color */
+		GifColorType *col = gif->SColorMap[gif->SBackGroundColor]->Colors;
+		color_t c = {col->Red, col->Green, col->Blue, 255};
+		/* Some magic to reduce the amount of calls to small-block memcpys */
+		fb[0] = c;
+		int i = 1;
+		int j = 2;
+		while(j < framesize){
+			memcpy(fb+i*sizeof(color_t), fb, i*sizeof(color_t));
+			i = j;
+			j *= 2;
+		}
+		memcpy(fb+i*sizeof(color_t), fb, (framesize-i)*sizeof(color_t))
+	}else{
+		/* Set all pixels to a transparent black */
+		memset(fb, 0, framesize*sizeof(color_t));
+	}
+
+	st->gif = gif;
+	st->idx = 0;
+	st->frame->data = fb;
+	st->frame->w = gif->SWidth;
+	st->frame->h = gif->SHeight;
+	return st;
+error:
+	free(fb);
+	free(st);
+	return 0;
+}
+
+/* buf ⇜ input data
+ * state ⇜ internal state, initialize as NULL */
+framebuffer_t* gif_render(uint8_t *buf, unsigned int buflength, gifAnimationState_t **state){
+	gifAnimationState_t *st;
+	if(*state == NULL){
+		st = gif_read(buf, buflength, state);
+		if(!st)
+			goto error;
+		*state = st;
+	}else{
+		st = *state;
+	}
+
+	GifFileType *gif = st->gif;
+
+	SavedImage *img = gif->images[st->idx];
+	cmo = img->ImageDesc->ColorMap;
+	if(!cmo){
+		ColorMapObject *cmo = gif->SColorMap;
+		if(!cmo){
+			fprintf(stderr, "Missing color table for GIF frame %d\n", st->idx);
+			goto error;
+		}
+	}
+	unsigned int ix = img->ImageDesc->Left;
+	unsigned int iy = img->ImageDesc->Top;
+	unsigned int iw = img->ImageDesc->Width;
+	unsigned int ih = img->ImageDesc->Height;
+	if((iy+ih)*gif->SWidth + ix+iw > st->frame->w*st->frame->h;){
+		fprintf(stderr, "Invalid gif: Image %d (x %d y %d w %d h %d) out of bounds (w %d h %d)\n",
+				st->idx, ix, iy, iw, ih, gif->SWidth, gif->SHeight);
+		goto error;
+	}
+	uint8_t *p = img->RasterBits;
+	color_t *fb = st->frame->data;
+	for(unsigned int y = iy; y < iy+ih; y++){
+		for(unsigned int x = ix; x < ix+iw; x++){
+			GifColorType col = cmo[*p++]->Colors;
+			fb[y*st->frame->w + x] = {col.Red, col.Green, col.Blue, 255};
+		}
+	}
+
+	st->idx++;
+	if(st->idx >= gif->ImageCount)
+		st->idx = 0;
+	return fb;
+error:
+	if(st)
+		free(st->frame->data);
+	free(st);
+	return 0;
+}
+