work towards gif support

1 files changed, 103 insertions, 0 deletions

diff --git a/src/gif.c b/src/gif.c
index 0c1ebb3..6928dd2 100644
--- a/src/gif.c
+++ b/src/gif.c
@@ -1,9 +1,112 @@
 
 #include <stdio.h>
+#include <string.h>
 
 #include "gif.h"
 
+#define GIF87a 0
+#define GIF89a 1
+
 unsigned char *loadgif(FILE *infile, int *bufwidth, int *bufheight){
+	int version;
+	unsigned char *palette;
+	int pallen;
+	unsigned char *buf;
+	unsigned int bpp;
+
+	{
+		/* Read header*/
+		unsigned char packed;
+		unsigned char header[13];
+		
+		if(fread(header, 1, 13, infile) != 13)
+			return NULL;
+		if(!memcmp("GIF89a", header, 6))
+			version = GIF89a;
+		else if(!memcmp("GIF87a", header, 6))
+			version = GIF87a;
+		else
+			return NULL;
+		
+		*bufwidth = header[6] | header[7] << 8;
+		*bufheight = header[8] | header[9] << 8;
+		packed = header[10];
+		bpp = (packed & 7) + 1;
+
+		/* Read colormap */
+		if(packed & 0x80){
+			printf("Reading palette\n");
+			pallen = 1 << bpp;
+			printf("pallen: %i\n", pallen);
+			palette = malloc(3 * pallen);
+			fread(palette, 1, 3 * pallen, infile);
+		}
+	}
+
+	{
+		int blocktype;
+		while((blocktype = fgetc(infile)) != EOF){
+			if(blocktype == ';'){
+				printf("end of file\n");
+				break;
+			}else if(blocktype == '!'){
+				int bytecount, fncode;
+				if((fncode = fgetc(infile)) == EOF)
+					return NULL;
+				while(1){
+					bytecount = fgetc(infile);
+					printf("Skipping extblock 0x%x\n", fncode);
+					if(bytecount == EOF)
+						return NULL;
+					else if(bytecount > 0)
+						fseek(infile, bytecount, SEEK_CUR);
+					else
+						break;
+				}
+			}else if(blocktype == ','){
+				int imagex, imagey, imagew, imageh;
+				unsigned char imagedesc[9];
+				if(fread(imagedesc, 1, 9, infile) != 9)
+					return NULL;
+				if(imagedesc[8] & 0x80){
+					printf("ERROR: local palettes not supported\n");
+					return NULL;
+				}
+				if(imagedesc[8] & 0x40){
+					printf("ERROR: interlaced images\n");
+					return NULL;
+				}
+
+				imagex = imagedesc[0] | imagedesc[1] << 8;
+				imagey = imagedesc[2] | imagedesc[3] << 8;
+				imagew = imagedesc[4] | imagedesc[5] << 8;
+				imageh = imagedesc[6] | imagedesc[7] << 8;
+
+				if(imagex != 0 || imagey != 0 || imagew != *bufwidth || imageh != *bufheight){
+					printf("%ix%i %ix%i\n", imagex, imagey, imagew, imageh);
+					printf("TODO: allow this sort of thing\n");
+					return NULL;
+				}
+
+				{
+					int initcodesize, curcodesize;
+					initcodesize = fgetc(infile);
+					if(initcodesize < 1 || initcodesize > 9){
+						printf("bad code size %i\n", initcodesize);
+						return NULL;
+					}
+					curcodesize = initcodesize + 1;
+				}
+
+				break;
+			}else{
+				printf("Unknown block type %i\n", blocktype);
+				return NULL;
+			}
+		}
+	}
+
+	printf("end\n");
 	return NULL;
 }