Hi,
painting is not double buffered in vcl Windows (including
SmGraphicWindow) - and currently there is no method to have that
automatically. The notable excpetion is the Mac, where drawing is double
buffered just above the system level.
In places where you want to avoid flickering through constant redrawing
the usual solution is to draw to a VirtualDevice (see vcl/virdev.hxx)
created with the Window as reference (to get bit depth and other
properties right), then draw that using the DrawOutDev call on the
Window to copy the contents of said VirtualDevice. This will flicker the
least amount since it paints only once instead of first painting the
background, then content to the window.
This works easiest if your Window is fully opaque (no transparencies
involved), in which case you know your background. I assume this is the
case for the math window. If your Window is transparent, you need to
copy the window background before drawing on it - which is somewhat
cumbersome and can be error prone.
Kind regards, pl
P.S.: Yes, double buffering would be a very nice feature on a per window
basis and basically every other toolkit than creaky old vcl has that. Sorry.
On 6/14/10 11:23 PM, Jonas Finnemann Jensen wrote:
Hi,
I'm working on creating a visual formula editor in OO.o Math for
Go-OO as part of Google Summer of Code 2010. So far it's going pretty
good, but run into some minor flickering issues when redrawing often,
which is why I'm posting here...
In OO.o Math I need to redraw then entire formula whenever the the
caret moves or the formula is changed. The widget is drawn in
SmGraphicWindow::Paint. To redraw the widget I call Invalidate().
Now I would expect that some kind of double buffering to happen
around the call to SmGraphicWindow::Paint. But as far as I can see
the widget (SmGraphicWindow) is at times completely blank, this is
very brief, but enough to be visible and course flickering.
How is Window::Paint supposed to be implemented to avoid flickering?
Is the drawing in Window::Paint double buffered? If not why? And how
should I implement double buffering?
- I haven't found much in terms of documentation, so if there's any
please throw it at me...
If anybody wants to try it out (I doubt that's necessary) I've attached a
patch that makes it easy to reproduce the issue by clicking the formula
and hitting some keys.
The patch will make any key course the formula to be redrawn, so it's
easy to make it redraw as fast as it would if the user entered text...
The patch is against ooo320-m17 (with go-oo patches), but it's only
two lines show if it doesn't apply it's easy to copy-paste.
Anyway, I hope you can help me resolve this problem...
--
Regards Jonas Finnemann Jensen.
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