[gtkada] How to access the alpha channel in a Pixbuf

[Dmitry A. Kazakov]

On Tue, 6 Nov 2007 19:50:53 +0100, you wrote:

> So the questions are:
> 
> 1. How should I access the alpha channel data?
> Should I do unchecked_conversion to array of guchars? (Or packed record
> with R, G, B, and A members)

Yes, and the array should be flat. Alternatively you could use
Interfaces.C.Pointers instead of the array.

> 2. In case of RGBA data format, is the array of Rgb_Record consistent at
> all with the image data? (ie. does it not treat the alpha channel byte
> as a color byte of the next pixel?)

Looks like it is not, because Get_Pixels is imported directly from GDK:

   pragma Import (C, Get_Pixels, "gdk_pixbuf_get_pixels");

The bindings could be a bit thicker here, or maybe thinner, returning a
pointer to guchar, obtained from Interfaces.C.Pointers.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de