[haiku-appserver] Re: user needs to know about the clipping region?

  • From: mmlr@xxxxxxxx
  • To: haiku-appserver@xxxxxxxxxxxxx
  • Date: Fri, 25 Nov 2005 11:09:58 +0100 (CET)

> Stick with the clipping based approach, but how about an offscreen
> buffer  in main memory for just the parts in the frame buffer
> with transparency?

Not that I understand every aspect here, but I think that this is not as
easy as it sounds. As far as I understand it, you need to have the
current background to draw something transparent over it. If this is
the case, this would either require to keep the whole frambuffer in
main memory (reducing this approach to a double buffer), redrawing all
parts below the new transparent area to build up the backgroud (which
would take a long time for bigger areas) or to fetch the background
from the graphics card (which is terribly slow).
You can only keep the "parts with transparency" in a main memory buffer
if you know beforehand what parts will have transparency. With the
example of dragging a transparent bitmap this is certainly not the
case. And getting or redrawing the background everytime when a user
starts dragging that transparent bitmap around is a bit overkill I
think. Just imagine the situation where you select something in
ShowImage and drag it out to make a bitmap clip. The background changes
with every move.
Just my concerns about this. Or do I just miss something?


Other related posts: