RE: [Algorithms] PNG w/ no libs

[Scott, J. <JS...@ra...>]

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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