Collisions between kinematic and dynamic objects

[Pierre]

Hi,

I have a problem with dynamic objects that should collide with kinematic objects (think kinematic platforms), but they don't. The dynamic objects go right through the kinematics.

Any idea what I'm doing wrong?

The setup for the objects is the same as in PEEL's Newton3.13 plugin.

Thanks.

[JoeJ]

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body = NewtonCreateKinematicBody (this->world, shape, &trans[0][0]);
NewtonBodySetMassProperties (body, mass, shape); //some mass recommended to avoid infinite collision forces
NewtonBodySetCollidable (body, true); // <-


Note that if you animate them, you also need to set their velocity yourself.

[Pierre]

Thanks, I will try your suggestion ASAP.

Note that if you animate them, you also need to set their velocity yourself.

This is more surprising, I would have expected the engine to take care of that automatically (as in Havok, etc).

Is there a helper function that I can use to derive the velocities from a source & destination matrices? (I need both linear & angular velocities).

[JoeJ]

I found that surprising too, but by setting velocity and not changing position, it's very easy to create a conveyor belt for example.
So it's more a cool than a missing feature

Is there a helper function that I can use to derive the velocities from a source & destination matrices? (I need both linear & angular velocities).

Three is at least a utility to do it the other way:
void NewtonBodyIntegrateVelocity (const NewtonBody* const bodyPtr, dFloat timestep)

[Julio Jerez]

the reasoning is the by not having them animated automatically the app gets best of both.
the application can always move the body in various ways:
1-It can place then on its own app container and loop over the bodies an update the before the newton update
2-it can moves then in a dedicate transform call back.
3-It can make a engine listener to group then to collect and update them in the listener call back

to animate the body you call the procedure stated by Joe, but you need to calculate velocity and omega from the delta position and delta orientation, this is very simple.

for the position:

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let dt be the time step
Let p1 be the target position;
let  p0 b the current position
veloc = (p1 - p0) / dt

for the angular velocity is more complex but there is function in the math library for assistance.

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dQuaterion::CalcAverageOmega

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let q0 be the current orination
let q1 be the target orientation
then
omega = q0.CalcAverageOmega (q1, dt);

with veloc and omega you set those in the body, (any body with no zero mass)
and you can call

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NewtonBodySetVelocity(body, &velocity[0]);
NewtonBodySetOmega(body, &omega[0]);
NewtonBodyIntegrateVelocity (body, dt);

if the body was kinematic will only move when you call the function.
if the body is dynamics it moves and continue moving by its inertia as long as the velocity is not changed again.

[Pierre]

Thanks, I will give it a try this evening

[Pierre]

I think I have a first version kind of working (only linear velocity for now). I had a lot of performance issues for a while but it all went away when I figured I had to update the "OnAABBOverlap" function (in PEEL's Newton plugin) to ignore kinematic pairs myself. There's still a one frame delay somewhere but I can work it out tomorrow or another day.