Comments on: libPNG Tutorial: Loading PNG files from streams

By: Wracky

Wracky — Mon, 19 Dec 2011 12:36:27 +0000

Hi Benson, and thanks for posting!

The pUInt is actually one of our own typedefs. It guarantees a 32 bit int, same as the PNG one.
I thought I’d removed all our own types for the sake of this tutorial, but I guess this one slipped by, so thanks!

Regards,
Wracky.

By: Benson

Benson — Sun, 18 Dec 2011 01:33:19 +0000

Out of curiosity, should

pUInt q = (imgHeight- i – 1) * stride;

actually be:

png_uint_32 q = (imgHeight- i – 1) * stride;

By: Chris Arena

Chris Arena — Sat, 03 Sep 2011 16:26:26 +0000

Thanks for the tutorial!!

BTW, you don’t have to check for non-NULL before doing:

delete [] rowPtrs;
or
delete ptr;

The delete operator accepts NULL gracefully.

Cheers!!

By: Ash McConnell

Ash McConnell — Mon, 25 Apr 2011 19:52:24 +0000

Thanks for the tutorial, it helped a lot. I had a problem with mirrored and flipped images.

By: Paul

Paul — Wed, 09 Feb 2011 16:09:48 +0000

Very nice, thank you very much. Saved me at least a week of tinkering!

By: Dave

Dave — Tue, 25 Jan 2011 11:33:20 +0000

Awesome tutorial… thanks for the effort. Much appreciated.

By: Wracky

Wracky — Wed, 05 Jan 2011 17:36:58 +0000

Cool, thanks I’ve added your explanation to the tutorial.

By: Mario

Mario — Tue, 04 Jan 2011 23:08:29 +0000

Old image file formats (tga, bmp…) by default stores the data bottom up because of very old displays of the time, that raster bottom up.
As Guest saids, OpenGL uses bottom up to be consistent with 3d coordinates (small UV coordinate, small axis position)

By: Wracky

Wracky — Wed, 13 Oct 2010 07:53:54 +0000

Hi Ferneu!

Thanks for Commenting. As you already concluded, there are no reset functions.
I haven’t looked into the libPNG code itself though… but the functions provided indeed suggest that the infoPtr etc are only to be used once.

You could look into the LibPNG source to find out what’s exactly in the infoPtr.
See if it is safe to just reset it and find out what values would be appropriate.

That’s all I know really

By: Ferneu

Ferneu — Mon, 11 Oct 2010 21:06:10 +0000

by the way, the PNG docs are not clear so I’ll ask here: is it possible/safe to reuse the pngPtr and the infoPtr? A certain png API that was used to “initialize” the infoPtr is deprecated (and I don’t really know if it was safe using it on the first place). And I have not found how to “reset” the requested transformations eighter. Perhaps they are not supposed to be reused, that is why there is no API for reseting them…

Oh well…