[SOLVED] Slider constraint attached to world have limit?

[emersonmx]

I'm playing with slider constraint and I found something strange.

I create a slider contraint attached to world

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btTransform 
axis.setIdentity();
axis.setRotation(btQuaternion(0, 0, 1, 1));

btSliderConstraint* constraint =
    new btSliderConstraint(*rigid_body, axis, true);
constraint->setLowerLinLimit(-200);
constraint->setUpperLinLimit(200);
dynamic_world_->addConstraint(constraint, true);

The rigidbox have a box collision shape (btBoxShape) and have this configuration

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rigid_body->setLinearFactor(btVector3(0, 1, 0));
rigid_body->setAngularFactor(btVector3(0, 0, 0));
rigid_body->setDamping(0.999f, 1);
rigid_body->setActivationState(DISABLE_DEACTIVATION);

The rigidbody is moved with UP and DOWN keys. Like

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btScalar velocity = 250;
if (keyboard->isKeyDown(OIS::KC_UP)) {
    btVector3 position(0, velocity, 0);
    rigid_body->setLinearVelocity(position);
} else if (keyboard->isKeyDown(OIS::KC_DOWN)) {
    btVector3 position(0, -velocity, 0);
    rigid_body->setLinearVelocity(position);
}

And to hold the DOWN key, the rigidbody reaches the limit of the constraint(=-200).
If the key remains pressed, the rigidbody will exceed the limit of the constraint(>-200) and
after a while will go back to the limit of the constraint(=-200).

This does not occur if the limit is set to

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constraint->setLowerLinLimit(-100);
constraint->setUpperLinLimit(100);

I really can not explain why this occurs.
Does anyone have any idea why this happens?

[emersonmx]

Somehow, I managed to solve (luck) this by reducing the value of fixedTimeStep to 1 / 256.f

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dynamic_world_->stepSimulation(clock_->time() / 1000.f, 10, 1 / 256.f);

I assume from now on, when I have trouble, I'll increase the value of fixedTimeStep and see what happens.

[Rikus]

Hey,
Here is all the information you need regarding timeStep: http://www.bulletphysics.org/mediawiki- ... _The_World
What you just did (I think) is set the maxSubSteps to "0" (1/256.f)

By that you are setting to use a variable tick rate (it will use delta time for simulating the physics).

As the wiki says:

maxSubSteps == 0 ?
If you pass maxSubSteps=0 to the function, then it will assume a variable tick rate. Every tick, it will move the simulation along by exactly the timeStep you pass, in a single tick, instead of a number of ticks equal to fixedTimeStep.
This is not officially supported, and the death of determinism and framerate independence. Don't do it.

[emersonmx]

Hey,
Here is all the information you need regarding timeStep: http://www.bulletphysics.org/mediawiki- ... _The_World
What you just did (I think) is set the maxSubSteps to "0" (1/256.f)

By that you are setting to use a variable tick rate (it will use delta time for simulating the physics).

As the wiki says:

maxSubSteps == 0 ?
If you pass maxSubSteps=0 to the function, then it will assume a variable tick rate. Every tick, it will move the simulation along by exactly the timeStep you pass, in a single tick, instead of a number of ticks equal to fixedTimeStep.
This is not officially supported, and the death of determinism and framerate independence. Don't do it.

I use maxSubSteps = 10 and not maxSubSteps = 0
The real problem with decreasing the size of fixedTimeStep is the CPU usage (In my simulation I am using 1% ).