-
-
Save AndreasOM/907764 to your computer and use it in GitHub Desktop.
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
// by alex evans, 2011. released into the public domain. | |
// based on a first ever reading of the png spec, it occurs to me that a minimal png encoder should be quite simple. | |
// this is a first stab - may be buggy! the only external dependency is zlib and some basic typedefs (u32, u8) | |
// | |
// more context at http://altdevblogaday.org/2011/04/06/a-smaller-jpg-encoder/. | |
// | |
// follow me on twitter @mmalex http://twitter.com/mmalex | |
// | |
// fixed a buffer overrun | |
u32 crc_table[256]={0}; | |
void make_crc_table(void) | |
{ | |
for (int n = 0; n < 256; n++) { | |
u32 c = n; | |
for (int k = 0; k < 8; k++) if (c & 1) c = 0xedb88320L ^ (c >> 1); else c = c >> 1; | |
crc_table[n] = c; | |
} | |
} | |
u32 update_crc(u32 c, unsigned char *buf, int len) | |
{ | |
if (!crc_table[0]) make_crc_table(); | |
for (int n = 0; n < len; n++) c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8); | |
return c; | |
} | |
u8* CompressPNG(void *img, int w, int h, int numchans, u32 &len_out) | |
{ int p=w*numchans; | |
z_stream z={0}; deflateInit(&z,-1); | |
u8 *zbuf=(u8*)malloc(53+(z.avail_out=deflateBound(&z,(1+p)*h))+1+w); // +w: ensure we can at least store when uncompressed line (w-53-X might be enough) | |
u8 *scanline=zbuf+53+z.avail_out; | |
z.next_out=zbuf+41; | |
for (int y=0;y<h;++y) | |
{ | |
u8 *dst=scanline; *dst++ = 0; | |
u8 *src=((u8*)img)+y*p; | |
for (int x=0;x<p;++x) *dst++ = *src++; // this line was overrunning the buffer in the original version | |
z.avail_in=1+p; z.next_in=scanline; | |
int err = deflate(&z,(y==h-1) ? Z_FINISH : Z_NO_FLUSH); | |
} | |
len_out=z.next_out-zbuf-41; | |
u8 pnghdr[41]={0x89,0x50,0x4e,0x47,0x0d,0x0a,0x1a,0x0a,0x00,0x00,0x00,0x0d,0x49,0x48,0x44,0x52, | |
0,0,w>>8,w,0,0,h>>8,h,8,"\0\0\04\02\06"[numchans],0,0,0,0,0,0,0, | |
len_out>>24,len_out>>16,len_out>>8,len_out,0x49,0x44,0x41,0x54}; | |
*(u32*)(pnghdr+29)=htonl(update_crc(0xffffffffL,pnghdr+12,17)^0xffffffffL); | |
memcpy(zbuf,pnghdr,41); // header | |
memcpy(z.next_out+4,"\x49\x45\x4e\x44\xae\x42\x60\x82",8); // footer | |
*(u32*)z.next_out =htonl(update_crc(0xffffffffL, zbuf+41-4, len_out+4)^0xffffffffL); | |
deflateEnd(&z); | |
len_out+=53; | |
return zbuf; | |
} | |
void PNGTest() | |
{ | |
u32 img[200][320]; | |
for (int y=0;y<200;++y) for (int x=0;x<320;++x) img[y][x]=x+(y<<8)+0xff000000; | |
u32 blen; u8*zbuf = CompressPNG(img,16,16,4,blen); | |
FILE *f=fopen("test.png","wb"); | |
fwrite(zbuf,1,blen,f); | |
fclose(f); | |
free(zbuf); | |
} |
Yep, youre right.
In "most" cases it fits anyway, but not in all...
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Hi Andreas! well spotted on the memory bug; however it's +p you want, not +w....
maybe I'll fork my original, I have some other edits...