zlib is easy once you grok it (isn't anything tho?) Its usage is completely
obfuscated in libpng too.
Basically, to decompress...
z_stream zdata;
memset(&zdata, 0, sizeof(z_stream));
inflateInit(&zdata);
zdata.next_in = (byte *)compressed_data;
zdata.avail_in = compressed_data_size;
while(zdata.avail_in)
{
zdata.next_out = (byte *)uncompressed_dest;
zdata.avail_out = number_of_bytes_you_want;
inflate(&zdata, Z_SYNC_FLUSH);
}
inflateEnd(&zdata);
So, for PNG, you'd decompress a byte for the filter type, then row bytes for
the line of data, and repeat for the number of lines. Everything returns
Z_OK normally, or Z_STREAM_END when you have decompressed all the data
(normally when avail_in is 0).
To compress, do the same, but deflate rather than inflate.
I've no need to remind you gents to sprinkle liberal amounts of error
checking in there =)
Cheers
John
-----Original Message-----
From: Bass, Garrett T. [mailto:gt...@ut...]
I'm also interested in this information. Zlib breaks my noggin.
-----Original Message-----
I've read a lot here about loading png's with and without using
the libraries (pnglib & zlib) both pros and cons. I was wondering
if anyone had any sample code for just loading pngs. I've read
through the src for both libraries and there's a LOT of stuff
I can't get my head around. (most of which I think is for saving
and such which I don't want) I can parse through the chunks and
all but the zlib stuff for decoding each line is stumping me
anyone out there that can give me a hand?
Jeremy Bake
RtroActiv
RAMetal
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