[Opensim-dev] Questions about Vehicle scripting calls

[Mike Higgins]

On 6/6/12 12:48 AM, Bengt Falke wrote:
> I am also interested in physics for vehicles mainly for creating 
> working yacht and for making my free moving scripted animals to work 
> in a smooth way.
> If there is a way I can contribute I will try to do so.
>
     Also at the recent OpenSim developers meeting, Andrew Hellershanks 
said (about llSetTImerEvent minimum time limits) "Not sure why you would 
want to use something other [less] than 1.0". I think the developers 
need to know that there are 1000's of scripters in SL DESPERATELY trying 
to find ANY WAY to make simple things like a fish move smoothly through 
the water at a constant velocity. In SL you can usually get timer() 
events as often as once every 0.2 seconds, which is not quite often 
enough for smooth looking motion. timer events more often would be one 
way to get smoother looking motion. I've seen people write scripts that 
had abominations like: while (1) { moveit(); llSleep(0.05); }  The 
OpenSim developers need to throw these guys a bone so they will NOT DO 
THAT HERE!

     Of course, LL only recently threw them the llSetKeyframedMotion() 
bone. Before that, people tried to use physics and llMoveToTarget() 
which was NEVER DESIGNED TO GENERATE LINEAR MOTION (it is always 
damped). Although you can play games with it and find reasonably linear 
portions of the curve. But that requires accurate llSetTimerEvent 
durations to stop the llMoveToTarget part way through a damped move. And 
in OpenSim, llMoveToTarget is damped 9 times faster than SL (mantis 
issue 5968) which requires pushing it nine times harder to try to 
capture a linear section and even more accurate llSetTimerEvent times to 
prevent the object from running away from you...

      The only other way in SL (before llSetKeframedMotion) to get 
something to move smoothly at a constant velocity is to make it a 
vehicle. Which is sort of like using a 4 ton hydrolic press to insert 
thumbtacks in a cork board.  And even in SL, the vehicle functions are 
really squirrely.

     So the major reason I am testing the OpenSim vehicle routines is to 
see if I can find a reliable subset of them, or a set of workarounds, 
that will allow me to move a fish smoothly through the water at a 
constant velocity.

     So far I have found a few problems and some workarounds:
1) Vehicles crash and burn at the sim boundary, the workaround is to add 
code to detect the sim boundary before the vehicle gets there and 
prevent it from even getting close. But if llSetTimerEvent is not 
accurate, if your timer() event is not called regularly to do this 
check, the vehicle runs into the sim boundary and goes crazy.
2)  The angular motor rotates around the wrong axes, but you can 
workaround that by multiplying your vectors by llGetRot (mantis issue 
6039). I'm guessing that nobody noticed this before because cars and 
boats and helicopters are usually horizontal and their local Z axis is 
aligned with the region Z axis.
3) The linear motor vector is clamped or projected onto the region XY 
plane. (mantis issue 6040) A car or a boat or a helicopter might never 
notice this, but with no Z values allowed in linear motors, how can 
airplanes glide up or down? Someone please tell me how to get this to work!


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