[osg-users] Rendering performance issues

Robert Osfield robert.osfield at gmail.com
Tue Jul 8 01:29:22 PDT 2008


Hi Guys,

The gap between draw dispatch (the yellow bar) and draw GPU (the
orange bar) is by its nature variable.  The reason is it so variable
is that I have to estimate the begining of the draw GPU as the OpenGL
GPU stats extension only provide elapsed time, they don't provide any
details on absolutely time, while the CPU code is all in absolute
timings.   As GPU stats are really useful the best I could do is take
the time that the GPU stats were collected (on the next frame),  which
gives us a time that we know it was complete by, then estimate that
GPU work was, I can't recall the exact maths off hand.  The bottom
line is that it's position is an estimate, but it's length is measure.

As for the frame rate being awful when running with two GPU, this is
likely to be a driver/OS issue.

W.r.t whether you should use vsynv when you are using
projectors/LCD's, yes vysn is still required, they still read their
data via a scan line, so if swap buffer happens during the scan then
some of the screen will be from the previous frame, and some from the
next, or it can even be several frames worth on a single frame if your
frame rate is high.  What you'll see if a tearing across the screen,
especially visible when you are turning the eye point quickly.

Robert.



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