SSG uses a frame counter for a couple of jobs.
ssgGetFrameCounter();
...the counter is incremented in ssgCullAndDraw() - but if you use
multiple calls to ssgCullAndDraw each frame (eg to do multipass
rendering - or to render some objects in a separate rendering pass)
then the counter is incremented too many times.
This is rather nasty to fix.
SSG has no way to know when you call Swapbuffers - so it can't tell
the difference between true multipass rendering and two consecutive
legitimate frames.
In retrospect, we should probably have an SSG call that you're
required to make before each swapbuffers - but we don't have it
and if I add one and use it to increment the frame counter then
I'll break existing applications.
I suspect this problem will affect FlightGear...it explains a couple
of odd things I've seen in some of my work.
The only way I can think to fix this in a backwards compatible
way is to write:
ssgFrameUpdate () { ssgSetFrameCounter( ssgGetFrameCounter() + 1 ) ; }
ssgImprovedCullAndDraw ( ssgEntity *e )
{
int x = ssgGetFrameCounter() ;
ssgCullAndDraw( something ) ;
ssgSetFrameCounter ( x ) ;
}
...and to tell people:
1) Call ssgFrameUpdate() at the end of every frame - just before
Swapbuffers.
2) Use ssgImprovedCullAndDraw instead of ssgCullAndDraw - which is
now deprecated.
We'd need a better name than ssgImprovedCullAndDraw.
Can anyone think of a cleaner way to fix this?
---------------------------- Steve Baker -------------------------
HomeEmail: <sjb...@ai...> WorkEmail: <sj...@li...>
HomePage : http://web2.airmail.net/sjbaker1
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