On Tue, 11 Dec 2001, Jonathan Walther wrote:

> I have a square area, lets say 400x400.  I frequently re-paint the
> whole area with different sections of a larger drawable.  However
> I have another little image that I draw on top, 30x30 in size.
> When I draw this little box, I have no problem doing the masking such
> that the little arrow symbol is drawn on top of the larger area without
> disturbing the image underneath.  But the location of the little box
> also frequently changes, so making a static clipmask the size of the
> 400x400 area isn't the way.  I'd like to be able to repaint the whole
> 400x400 area, without disturbing the little arrow symbol.

Others have described the general solution, but a significant minority of
current hardware has a trick which would help this particular case;
Put the little box in a 400x400 overlay visual.
I'm talking about traditional 2D X overlays - I don't know
whether video overlays are the same.

Unfortunately, while overlay visuals are common in mid/high end graphics 
"workstations" (whether traditional X/unix or PC) they are not common
on "consumer" PC graphics cards - Matrox seem to be the only manufacturer
to support them in this market segment.

-- 
Dr. Andrew C. Aitchison         Computer Officer, DPMMS, Cambridge
[EMAIL PROTECTED]   http://www.dpmms.cam.ac.uk/~werdna

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