Re: Is Alpha Channel support in next release plan?

[Christof Petig <christof petig-baender de>]

Owen Taylor schrieb:
> It's not that translucency isn't considered interesting, but
> addressing it in GTK+ when it's not in the windowing system isn't
> particularly interesting, or, for that matter, feasible.

That translucency is interesting is exactly what I wanted to hear from 
the core team. [But this might not be news at all.]

I'll try to summarize some easy uses of transparency and try to outline 
what is needed to get some parts quickly. Perhaps there's something 
which can be done while waiting for X11 support.

IIRC semi transparent images within a container with a background image 
are already fully working with 2.2.

- event boxes with fully transparent background (IIRC an event box 
mandantes an X window which occludes background images of the containing 
widget). This is what I'm interested in most, now. Or to be more 
specific I want tooltips on labels/frames without occluding the 
background image.

- somewhat transparent entry background (background image lightly shines 
through)

- semi transparent dialogs and menus (like in the Qt hack)

- rarely semi transparent and mostly transparent status windows atop of 
other windows (e.g. clocks, volume meters etc.) Very eye candy, 
difficult to realize without X11 support.

I clearly see that the fact that Gtk realizes non NO_WINDOW widgets as X 
subwindows (which can't be semitransparent yet) results in the first two 
non-transparencies. Perhaps a hack would be to use the corresponding 
part of the background of the container as a background for the image 
[that's what I planned when I first met this side effect of eventbox]. 
Offering this as a feature of the widget set might be more interesting 
since the code would be shared between different projects. (And the task 
seems difficult to achive).

This would also be interesting once transparency becomes part of some X 
servers but not all.

As for task 3: Grabbing the area and using it as a background might be a 
fallback here (the hack used by Qt). It works 50%. But it clearly needs 
1+2 resolved first.

Task 4: A combination of 3 and shape extension might emulate this on 
traditional X servers.

----- gdk API issues -----------------

IIRC gdk does not allow to specify different alpha values for different 
pixels. Neither does it allow to specify alpha values for 
background/foreground colors. IMHO nice thing to have.

This would result in alpha enriched window contents which gdk-pixbuf can 
handle but X11 can't. (see task 1+2)

I'd love to have the API and gdk support solved when X11 support comes. 
We might already implement half hearted fallbacks for traditional X servers.

>  A) Despite claims to the contrary, windows with alpha transparency
>     is not a feature of X currently; it's also not really a 
>     feature of current versions of Win32 in any general form.
>     (Longhorn probably will have it.) These are our primary 
>     platforms. The only current GDK target with alpha-transparent
>     windows is DirectFB, and that's not even integrated into
>     the GTK+ distribution.

>  B) Some limited hacks are possible on X, and, I believe, also
>     on Win32, but emphasize both "limited" and "hacks"

Agreed. But perhaps something can be done now (the limited hacks).

>  C) Given infinite time, I might try to dust off my fade-in menus
>     and tooltips hack patch and integrate it properly into GDK, but
>     my time is very far from infinite these days. I wouldn't be
>     at all suprised if X *does* have transparent windows before 
>     it hits the top of my TODO pile.

is it still available online?

>     
>  D) Once our primary platforms have support for windows with alpha
>     transparency, I'm sure we'll support it into GDK.

without fallback methods for non capable servers? Which might serve as 
expermintal ground now? I don't think so.

Yours
  Christof