Re: How does one overlay one image on top of another ?

[Bob Murphy <bob murphy access-company com>]

> I found gdk_draw_drawable(), but don't really understand GdkDrawables. I'd REALLY like to
> draw an image on a "different layer" such that I can move/remove it w/o having to redraw
> the original. Failing that, I'll settle for learning how to overlay one image on top of
> another.

I recently did a test hack that achieved images that overlay each other 
using GTK on Ubuntu:
1. Make a GtkWindow.
2. Make a GtkVBox and put it in the window.
3. Make a GtkFixed and put it at the upper left of the GtkVBox.
4. Make another GtkFixed and put it a little to the right of the other one.
5. Make a GtkImage from a PNG file, and put it in the GtkFixed from step 3.
6. Make another GtkImage from the same PNG file, and put it in the 
GtkFixed from step 4.
7. Show everything.

The result was that the GtkImage from step 6 was on top of the GtkImage 
from step 5, just shifted a little to the right, so that it covered most 
of the lower image but not all of it.

What's more, the PNG file I used had an alpha channel, and where the 
upper GtkImage where it was not opaque, it was color-composited, so I 
could see the lower image through it.

You could do this all with GDK directly, and you can also use GDK to 
composite multiple images into a single image and put that to the 
screen. But it's a bit more fooling around.

- Bob Murphy