The builtin stbi_zlib_compress does not compress as well as zlib or
miniz (which is not too surprising as it's <200 LOC), thus PNGs created
by stb_image_write are about 20-50% bigger than PNGs compressed with
libpng.
This change lets the user supply a custom deflate/zlib-style compress
function, which improves compression a lot. This was requested in #113.
Example for zlib:
#include <zlib.h>
unsigned char* compress_for_stbiw(unsigned char *data, int data_len,
int *out_len, int quality)
{
uLongf bufSize = compressBound(data_len);
// note that buf will be free'd by stb_image_write.h
// with STBIW_FREE() (plain free() by default)
unsigned char* buf = malloc(bufSize);
if(buf == NULL) return NULL;
if(compress2(buf, &bufSize, data, data_len, quality) != Z_OK)
{
free(buf);
return NULL;
}
*out_len = bufSize;
return buf;
}
#define STBIW_ZLIB_COMPRESS compress_for_stbiw
#define STB_IMAGE_WRITE_IMPLEMENTATION
#include "stb_image_write.h"
// ...
My guideline for the rules is the PNG loader (which I consider
"canonical"). In the _load functions, x and y are required but
comp is optional; in the _info functions, all three are optional.
Fixes issue #411 (and other related, unreported issues).
We tried but it was nothing but trouble. New rule: with
GCC/Clang, if you're compiling with -msse2, you get always-on
SSE2 code, otherwise you don't get any. Trying to ship
anything with proper runtime dispatch requires both working
around certain bugs and some fiddling with build settings,
which runs contrary to the intent of a one-file library,
so bail on it entirely.
Fixes issue #280.
Fixes issue #410.
