Re: setting a transparent color on a pixbuf for Canvas layering

[muppet <scott asofyet org>]

On Jun 30, 2008, at 5:52 PM, zentara wrote:

> How do I take the non-transparent zzrgbwb.png , load it with Gtk2, and
> make green transparent without resorting to GD?


Short answer:  Just use GD.  There's no shame in it.


Long answer:  It sounds like what you really want is to create an  
alpha mask from certain areas of your source image.  The basic  
algorithm is:

1.  blow your 24-bit rgb data up to 32-bit rgba with a all set to 255
2.  walk through each pixel in the image, setting the alpha channel  
for that pixel where the rgb values match some criteria.
3.  done.

This is easily done with GdkPixbuf in C; you just get a pointer to the  
pixel data and go to town with a trivial loop.

In perl, it's a bit more difficult to manage a GdkPixbuf's image  
data.  You could write some XS to do it in C with speed and ease, but  
then you have XS code to deal with.  You could write it in perl and  
deal with a map-reduce and unpack and pack and all the fun stuff  
there, and hope you can get the speed reasonable.

Or, just use GD, which has already solved the problem for you.



--
The one difference between Dali and a crazy man is very simple: Dali  
is not crazy at all.
  -- Salvador Dali