animate light to dark

[Michael J. Lew]

Dear all,

I am trying to get a smooth animation of a background going from 
light to dark (and vice versa), but I'm having trouble making it fast 
enough, smooth enough and flicker-free. I think it is something to do 
with screen redraws in OS X (see Jim Hurley's BZ entry 2639), but 
maybe it's more general.

What I need is to have a large dark region behind some images get 
light over about half a second so that the transition doesn't look 
too amateurish. I also need to be able to respond to messages while 
the change in darkness is occurring. I've tried playing with fill 
colors of buttons and fields and with blendlevels of an image. I also 
tried the straightforward approach of simply stacking a sequence of 
buttons with different fill colors and hiding or showing them in 
sequence. For every approach I've tried the transitions are good 
enough with small areas, but when the objects are made large enough 
for my purposes they are slow and yukky.

I've tried fiddling with unlock screen commands and with wait 
commands, and while they are necessary for intermediate stages to be 
visible, they don't fix the problems. Does anyone have a suggestion 
that might help?

I've experimented with timing screen redraws and found that when only 
a small area is changed they occur almost instantly, but when a large 
area is changed they take much longer (I don't want to say how long 
because it will make me want a new Mac ;-) Does it seem strange that 
the time needed for a screen redraw scales with the area of the 
control that has changed its appearance? I would have thought a 
redraw would be a redraw of the whole screen and so it wouldn't make 
any difference whether the alteration was of a small area or large.

Thanks for any help.

Michael

-- 
Michael J. Lew

Senior Lecturer
Department of Pharmacology
The University of Melbourne
Parkville 3010
Victoria
Australia

Phone +613 8344 8304

**
New email address: michaell at unimelb.edu.au
**