25 Sep
2002
25 Sep
'02
1:20 p.m.
Hi,
Steve wrote:
I'm hacking together a VU meter app for jack,
using FLTK, and it works OK,
except that when the update rate falls out of sync with the video refresh
rate the window flickers. I'm pasting a bigass image as the background,
see screenshot http://inanna.ecs.soton.ac.uk/~swh/vu-ss.png (apologies
for the tacky brushed steel background, its a placholder, honest).
I seem to remeber that on the Amiga and in GL I could issue a call to wait
for the next vertical blank, forcing the redraw to be in sync with the
video hardware. Is there an equivalent in FLTK or X?
How do other people get round this?
I am not sure how exactly you are doing this, but my first guess would
be to ask if you are rendering into an off-screen pixmap (until
everything in there is finished) and then do one quick Blt() to bring
this to your on-screen window. That should at least keep the flickering
low.
I am not sure if there are still ways to wait for vertical retrace
nowadays, but even if there are, I imagine it would not make sense,
given the overhead/latency the X protocol will put between the beginning
of the VBL and your attempt to draw things onto the screen "right at
that moment".
Hope that helps,
Frank
--
Frank Neumann (Frank.Neumann(a)st.com), VIONA Development Center
STMicroelectronics, Karlstraße 27, 76133 Karlsruhe
