[ODE] Question about variable step size and collision detection

[Jaroslav Sinecky]

Few months ago there was an interesting post here about implementing 
Stewart-Trinkle stepper to guarantee no penetration without using 
excesively small time steps. It seemed pretty interesting to me. What 
happened to that guys? Some more development done on that? Did you 
finally implemented it in ODE? Some more demos?

Jaroslav


Per Bull Holmen wrote:
> --- Christoph Beyer <boernerb at web.de> skrev:
>
>   
>> My first idea would be to use very small stepsize
>> like 0.0001 (fixed or
>> unfixed)
>> so that small and fast objects are collided
>> correctly.
>> Maybe using ODE with doubles instead of singles.
>> If you have no performance problems this seems to me
>> the easiest way.
>> But if you have problems with performance, this is
>> not very efficient.
>>     
>
> I don't have any performance problems, cause I haven't
> started implementing it yet... :) I just wanted to
> figure out the best tools in advance. I want the game
> to run on minimal configurations, because 2D games
> can. But I realize that 2D games have requirements
> that 3D games don't. You see more precisely what is
> happening, because things don't get obscured because
> of camera angles etc. This means that when colliding
> objects penetrate each others, it will be all too
> visible - 2D graphics must be pixel perfect.
>
> Calculating the next position and rotation for each
> object, taking into account a velocity vector, torque,
> forces applied to it etc, I probably can do on my own
> (at least satisfactory for my game). Precise,
> bulletproof collision detection I can too, though I'd
> like not having to, cause it will be complex.
> Collision response, taking into account rotation,
> uneven distribution of mass etc... especially when
> there are restrictions of freedom, hinges etc (which
> there will be much of), I can NOT do.
>
> I was wondering if any of you have an idea how the
> following two solutions might work:
>
> 1) Bullet physics engine, which has very sophisticated
> collision detection, can according to their developer
> be used together with ODE's dynamics. This sounds like
> a great solution, but I have a feeling it still won't
> let me avoid object penetration during impact. Any
> experience or knowledge about using the two together
> is welcome.
>
> 2) Is it possible to use ODE in a more low level kind
> of way? Then I could move the objects around myself
> according to speed, direction, torque etc. Whenever a
> collision is detected, I might call ODE to make it
> compute the collision response. I'm worried about that
> type of solution cause I think I've read that ODE
> discourages to manipulate the objects positions on
> your own (not sure though). Is this true? Also, if I
> just call ODE's dWorldQuickStep() function to have
> this done, I'm actually making guesses about how the
> engine is implemented (which isn't the proper OO way
> do to something): I'm guessing that it only takes the
> objects present position and collision info into
> account, and not for instance previous positions and
> previous calculations done by ODE's dWorldQuickStep()
> or similar functions. Is it possible, or not, to use
> ODE this way?
>
> Id like to avoid the very-small-timestep approach
> because it would be inefficient, and though it might
> work on my rather new IntelMac, it might not work on
> older machines.
>
> Per
>
>
> 	
> 	
> 		
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