Well as we have noted before System.currentTimeMillis() is operating
system dependent (and becomes rather sloppy on Win9x).
We implemented this type of movement via capturing keypresses directly
without using a behavior. Our movement behavior then uses the
acceleration, speed, etc information to update the scene correctly.
- John Wright
Starfire Research
Georg Rehfeld wrote:
>
> Hello group members,
>
> has anybody of you successfully extended ViewPlatformAWTBehavior
> to handle KeyEvents and is willing to share hints or code?
>
> I'm trying to implement a simple Quake style behavior, where the
> mouse controls the view direction and some keys (say CURSOR UP/DOWN
> and LEFT/RIGHT) move the ViewPlatform forward/reverse and left/right
> (called 'strafing' in Quake) with respect to the current view
> direction. Needless to say, that the horizon shall remain
> horizontally, ever :-).
>
> This works, in principal.
>
> The problem is: since I started to respect deltaTime (via
> System.currentTimeMillis() as in KeyNavigatorBehavior) my
> Behavior became really worse:
>
> most notably, instead of accelerating smoothly to the desired
> maximum speed ever, it shows 3 different real behaviors randomly:
>
> - sometimes it only moves the VP in much too small steps, not
> accelerating at all, while the accelerating key is held down.
> When it is released, the VP suddenly has the maximum speed
> (decelerating then, as wanted, immediately).
>
> - most times it almost accelerates just fine to the desired
> speed, but in all the motion, when the framerate drops (i.e.
> due to new objects coming into view) the motion TOO is affected.
> Which should not be the case at all, as I'm respecting
> deltaTime from the last frame and that should compensate by
> moving the VP farther, when deltaTime is high. Besides, my
> deltaTimes are almost ever 10, 20, 30 ... milli seconds, due
> to the bad PC time resolution, possibly I should integrate
> that, but then, how does the KeyNavigatorBehavior class
> deal with that, I couldn't find any special code?
>
> - sometimes the final speed seems to be about double of the
> desired speed, then the movement seems to be smooth.
>
> My Pseudo-Code is as follows:
>
> protected synchronized void
> processAWTEvents(final AWTEvent[] events)
> {
> motion = false;
> // set motion = true, if some acc/decelerating
> // or movement is in progress
> if ... motion = true;
> // handle all AWT events
> ...
> processKeyEvent(event)
> ...
> }
>
> protected void processKeyEvent(final KeyEvent evt) {
> // record key states into instance variable(s)
> // and set motion = true on any recognized key event
> ...
> }
>
> protected synchronized void integrateTransforms() {
> // Check if the transform has been changed by another behavior
> targetTG.getTransform(currentTransform) ;
> if (! targetTransform.equals(currentTransform)) {
> resetView();
> }
>
> calcSpeed();
>
> // modify the target transform, this simply works
> ...
> }
>
> private void calcSpeed() {
> long now = System.currentTimeMillis();
> long deltaTime = now - lastTime;
> lastTime = now;
>
> // check for too old time sample
> if (deltaTime > 2000) deltaTime = 1;
>
> // protect against 0 deltaTime, this happens sometimes
> if (deltaTime < 1) deltaTime = 1;
>
> float dt = (float)deltaTime / 1000f;
>
> // exploit key states and then
> // integrate acceleration/drag over dt
> ...
> // integrate velocity over dt
> ...
> // set instance members for integrateTransforms()
> ...
> }
>
> Any hints are VERY welcome
>
> thanks
>
> Georg
> ___ ___
> | + | |__ Georg Rehfeld Woltmanstr. 12 20097 Hamburg
> |_|_\ |___ [EMAIL PROTECTED] +49 (40) 23 53 27 10
>
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