loadpng deficiencies (was Re: [AD] GIF patent / support)

[Peter Wang <tjaden@xxxxxxxxxx>]

Chris wrote:

> Also, I'm not too fond of loadpng. When I last looked, it still did 
> some questionable things (reducing 16-bit down to 8-bit when loading, 


It doesn't.  I suppose you mean this:

   /* Convert 16-bit to 8-bit. */
   if (bit_depth == 16)
   png_set_strip_16(png_ptr);

This strips 16-bits _per colour component_ down to 8-bits per colour 
component, which is all that Allegro supports.

> saves 8-bit bitmaps by accessing bmp->line[0] and assuming linear memory, 


I will fix this in the next version.

> and saving 24-bit bitmaps as 32-bit PNGs,


It doesn't.

> even though 15/16-bit bitmaps save as 24-bit PNGs).


PNG doesn't support what Allegro calls 15/16-bit images.  From 
http://www.libpng.org/pub/png/book/chapter08.html : "RGB (truecolor) 
PNGs ... are supported in only two depths: 8 and 16 bits per sample, 
corresponding to 24 and 48 bits per pixel."

BTW, I wrote zlib/libpng installation instructions for mingw users here: 
http://members.ozadsl.com.au/~tjaden/loadpng/mingw.html .  I think 
that's pretty easy.

Peter