pngpalstrip.c

神龙卡开发原代码

/*
 * gif2png : Extract palette from a PNG file
 * Jasper DVD player utility
 * 
 * Fabrice Gautier, (c) 2002 Sigma Designs, Inc
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>

unsigned long swapl(unsigned long l)
{
	char *p;
	p=(char *)&l;
	return (p[0]<<24)+(p[1]<<16)+(p[2]<<8)+p[3];
}

#define BUFSIZE 64*1024

int main(int argc, char *argv[])
{
	char *buf;
	int fd,r;
	unsigned long cl;
	unsigned long ct;
	off_t chunkstart;

	if(argc<2) {
		fprintf(stderr,"usage %s filename.png\n",argv[0]);
		return 1;
	}

	fprintf(stderr,"%s %s\n",argv[0],argv[1]);

	buf=(char *)malloc(BUFSIZE);

	if(buf==NULL)
		return 1;

	fd=open(argv[1], O_RDWR);

	if(fd==-1){
		perror("Cannot open file");
		return 1;
	}
	//skip PNG signature;
	chunkstart=lseek(fd, 8, SEEK_SET);
	do {
		// get chunk
		read(fd, &cl, 4);
		cl=swapl(cl);
		r=read(fd, &ct, 4);
		ct=swapl(ct);
		
		if(r==-1) {
			perror("Cannot read file");
			return -1;
		}
		if(r==0) {
			printf("End of file, PLTE not found\n");
			break;
		}
		if(ct==(('P'<<24) + ('L'<<16) + ('T'<<8) +'E')) {
			fprintf(stderr,"PLTE found\n");
			
			// Seek to next Chunk
			// (skip cl data bytes +4 bytes for crc)	
			lseek(fd, cl+4, SEEK_CUR);
			r=read(fd, buf, BUFSIZE);
			if(r==BUFSIZE) {
				printf("Error: file size after Palette "
				       "larger than BUFSIZE (%d Bytes)\n",
				       BUFSIZE);
			} else {
				ftruncate(fd, chunkstart);
				lseek(fd, 0, SEEK_END);
				write(fd, buf, r);			       
			}
			break;
		}
		fprintf(stderr,"Chunk is %c%c%c%c len=%lx\n",
		       (char)ct>>24, (char)ct>>16, (char)ct>>8, (char)ct, cl);
		chunkstart=lseek(fd, cl+4, SEEK_CUR);		
	} while(1);
	
	
	close(fd);
	return 0;
}