Tim Nikias v2.0 wrote:
>>Now my particle system handles damping properly: the balls end up
>>sliding (looks like rolling...). I was afraid that I need some
>>conditionals to distinguish between slide/bounce state but "luckily" the
>>same piece of code handles both cases.
>>
>>There is no friction at all. The speed along the surface normal is
>>dampened by 30% every time a ball bounces off the floor.
> 
> 
> Nice one! How do you do it to keep particles out of the objects?
> 
> And what's your "lucky" code which keeps particles sliding nicely?

I won't show the code (it is still very ugly) but here is what I'm 
basically doing:

1. My approach is a "refined" Euler method -  I guess :) When the 
position of a particle is updated the gravity is also taken directly 
into account - not only speed. So gravity affects both the speed and the 
position during every step. Without it I see my particles bounce for too 
long with damping. This also gives 100% accuracy (when particles are not 
colliding) no matter how big time steps between frames.

2. If the new position indicates a collision, the previous position is 
restored (so basically particles _can't_ intersect with an object). The 
next happens:

a) speed is directed away from the surface taking the damping into 
account: this gives basic bounces.
b) particle is moved along the surface: this allows rolling and the 
bounces are also more accurate, still not perfect though. If I want them 
perfect I would have to find the _exact_ moment of collision.
c) gravity affects the speed along the surface: this allows the increase 
in speed when rolling - also the accuracy of bounces increase.

I might have forgotten something but basically it works like that.

By "lucky" I mean that there seems to be no bugs and everything seems to 
work as expected after I implemented 2.b and 2.c. BTW, have you tried 
how Cristophs particle system/MegaPov handles rolling/sliding? Just 
curious. At least it is a lot faster as it is hard coded.

Now I have only planes as environment and I check collisions by shooting 
a ray towards every plane. This obviously is accurate but a bad thing to 
do when there are many objects. Next I have to make the environment as a 
one single union and shoot proper rays towards it. Accuracy decreases 
but I can use as complex environment as I want.

Severi

Post a reply to this message