Huns Valen
I spent days trying to find the bug in my flight physics code that was causing this, only to discover that it was the viewer camera all along. The problem is that sometimes the aircraft flies "visually" smoothly at any speed up to 100 meters/sec; and other times it's visibly jerky, appearing to "vibrate" (change in apparent size many times/sec) as though the camera was acting like a spring instead of being fixed in place behind the vehicle.
I'm using the eye/offset calls:
llSetCameraEyeOffset(eye);
llSetCameraAtOffset(offset);
This is because the "newer" (21 years old instead of 23) follow cam is missing features that would be necessary to produce the same behavior, and I find it unsatisfying and confusing to use for aircraft.
I instrumented my vehicle with code that captures llGetVel() and llGetOmega() 20 times/sec (rotated into the local reference frame), then uses llSetText() to display mean, standard deviation, and range once per second. What I discovered:
  • Sigma (standard deviation) for local X can be very low (0.0 to 0.02) in level, unaccelerated flight regardless of whether the visual apperance is jerky or not. There is no difference.
  • When it's visually smooth, sigma can actually be quite a lot higher, closer to 1, and it still looks totally smooth. This happens during accelerating and turning.
  • Local Y's sigma is typically very close to 0 in either case.
  • Local Z's sigma is typically very close to 0 in either case.
  • All three axes of llGetOmega() are always zero unless the aircraft is turning, climbing, descending, or yawing.
If the statistical analysis is not enough of a smoking gun, here's another:
  • When the aircraft is flying smooth, and I refocus the camera on my avatar, it starts getting jerky, like the camera is damping at some wild speed. Single-frame jumps of tens to hundreds of pixels along the axis of motion.
The attached screenshot is the llSetText() stats output when the camera was jerky. Zero standard deviation in this regime + jerky visuals, vs. standard deviation WAY higher during maneuvers when the camera is smooth, provides strong evidence that this is a viewer bug.
My code is invariant either way. My stats are invariant either way. When flying smoothly, refocusing the camera makes it do the jerky rendering thing. And sometimes it does the jerky rendering thing whether I do that or not.

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