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Using listeners and signals with Nasal: Difference between revisions
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Using listeners and signals with Nasal (view source)
Revision as of 19:51, 19 May 2013
, 19 May 2013→Nasal code coupled to the autopilot system: http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg13029.html
m (→Nasal code coupled to the autopilot system: http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg13025.html) |
m (→Nasal code coupled to the autopilot system: http://www.mail-archive.com/flightgear-devel@lists.sourceforge.net/msg13029.html) |
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=== Nasal code coupled to the autopilot system === | === Nasal code coupled to the autopilot system === | ||
The FDM doesn't run at a fixed rate, either. It runs 120 times per second (if so configured), but it runs all iterations for a frame one after the other, then waits until the next frame. | The FDM doesn't run at a fixed rate, either. It runs 120 times per second (if so configured), but it runs all iterations for a frame one after the other, then waits until the next frame. The FDM runs at 120 hertz and with a fixed time step. | ||
However, we play one small trick to make that happen. We take the time that has elapsed since the last frame, compute how many whole iterations of the | |||
FDM will fit in that time slice (at 1/120th of a second per iteration.) Then we invoke the FDM that many times with a time step of 1/120th of a | |||
second. Finally we save out the remainder and add that into the next time slice. | |||
This can produce a small amount of temporal jitter between the graphics and the fdm if the graphics frame rates are not a diviser of 120. In the best | |||
case scenario, you've locked your graphics frame rate to 60 hz so the FDM runs exactly 2 iterations every time it is invoked and there is no temporal | |||
jitter at all, ever. | |||
One thing to keep in mind is that handing a different size time slice to the FDM every frame (and sometimes that time slice could be 1 second or more?) | |||
can lead to instabilities in the math. So our approach is intended to avoid that potential problem. As far as the FDM is concerned, it *is* running | |||
asyncronously, at a fixed time step. But, we are playing a little trick on the FDM (it doesn't care) in order to handle the unfortunate possibility of | |||
non-fixed and highly variable frame rates on PC hardware running consumer grade operating systems. | |||
Some people have a need to run Nasal code at the same rate as the simulation. Currently, without modifying the source code for FlightGear, the only way | Some people have a need to run Nasal code at the same rate as the simulation. Currently, without modifying the source code for FlightGear, the only way | ||