Re: GDK-Pixbuf question, creating and reading private data-chunk for png

[David NeÄas <yeti physics muni cz>]

On Fri, Dec 03, 2010 at 08:35:22AM +0100, Arne Pagel wrote:
> I am using gdk_pixbuf_save to store a gdk_drawable into a PNG File.
>
> Now I want to add a private data-chunk to PNG to store some additional Information.
>
> Is it possible to add a private data-chunk with GDK functions?

You can add custom data using text chunks, pass "tEXT::somekey" as the
option name and the value in text form as the value.  This is often
sufficient for simple auxiliary data.

> If not, what do you think would be the best way to create this file?
>
> Using libpng with png_set_unknown_chunks() ?

Yes.

> Is there any examplke of how I get GDK-IMAGE-DATA to libpng?

Definitely, but I can't offer any particularly clear one.  But
generally, GdkPixbuf stores data as R, G, B (,A) bytes that corresponds
to PNG's PNG_COLOR_TYPE_RGB (PNG_COLOR_TYPE_RGB_ALPHA) with 8bit depth
so you just have to set the PNG row pointers to the pixbuf rows.

Yeti