Re: Pixmap question

[Paul Barton-Davis <pbd Op Net>]

>I need to develop Display window which can a number of coloured layers.
>( the various layers used in IC design).
>
>Where each layer overlaps another, I want to see the correct ANDING of
>the colours.
>
>I need to be able to repaint with an odd layer removed from display.
>
>I can see that if I have multiple pixmaps (one for each layer to be
>displayed), but just sending the desired pixmaps to the screen I should 
>be able to achieve this.

1) I believe that no part of X (or GDK) current supports such
   things. This generally goes by the name "alpha channel", and X
   doesn't support it. A pixel in a Drawable is either completely
   transparent or completely opaque (with its own particular color).

2) the GNOME canvas will probably allow this. someone on this
   indicated that there is a standalone GTK version of the canvas floating
   around.

3) basically, you have to compute the pixmap "in client space" using
   you own chosen specific algorithms for the transparency computation,
   then shunt it to the server. of course, thats what the Canvas widget
   *might* take care of for you. I'm sure others will comment further.

Hope i got this right :)

--p