After some time, my body becomes unmovable

[raphaelr]

I'm working on the physics for my game, but I can't seem to get started. Here's the relevant code that triggers the problem (actually my game uses Ammo.js, but Bullet, which Ammo is based on, exhibits this behaviour too):

Code: Select all

// Enter these commands, followed by <Return>, to control the player:
// "l" - Left
// "r" - Right
// "u" - Up

#include <btBulletDynamicsCommon.h>
#include <stdio.h>
#include <time.h>
#include <boost/timer/timer.hpp>
#include <boost/thread.hpp>

boost::mutex playerBodyLock;

void reader(btRigidBody *body);

int main() {
	btDefaultCollisionConfiguration config;
	btCollisionDispatcher dispatcher(&config);
	btDbvtBroadphase broadphase;
	btSequentialImpulseConstraintSolver solver;
	btDiscreteDynamicsWorld world(&dispatcher, &broadphase, &solver, &config);
	world.setGravity(btVector3(0, -10, 0));

	btStaticPlaneShape environmentShape(btVector3(0.0f, 1.0f, 0.0f), -3);
	btDefaultMotionState environmentMotionState;
	btCapsuleShape playerShape(1.0f, 2.0f);
	btDefaultMotionState playerMotionState;
	btVector3 playerInertia;
	playerShape.calculateLocalInertia(30, playerInertia);

	btRigidBody::btRigidBodyConstructionInfo environmentBodyCI(0.0f, &environmentMotionState, &environmentShape);
	btRigidBody environmentBody(environmentBodyCI);
	btRigidBody::btRigidBodyConstructionInfo playerBodyCI(30.0f, &playerMotionState, &playerShape, playerInertia);
	btRigidBody playerBody(playerBodyCI);

	playerBody.setAngularFactor(btVector3(0.0f, 0.0f, 0.0f));
	playerBody.setLinearFactor(btVector3(1.0f, 1.0f, 0.0f));
	world.addRigidBody(&environmentBody);
	world.addRigidBody(&playerBody);

	boost::thread readThread(reader, &playerBody);
	boost::timer::cpu_timer timer;
	timer.start();
	float lastUpdate = timer.elapsed().wall / 1e9;
	btTransform playerTransform;
	while(true) {
		{
			boost::lock_guard<boost::mutex> lock(playerBodyLock);
			float now = timer.elapsed().wall / 1e9;
			world.stepSimulation(now - lastUpdate, 5);

			playerBody.getMotionState()->getWorldTransform(playerTransform);
			printf("%f\t%f\t%f\n", playerTransform.getOrigin().x(), playerTransform.getOrigin().y(), playerTransform.getOrigin().z());
			lastUpdate = now;
		}
		boost::this_thread::sleep(boost::posix_time::millisec(40));
	}
}

void reader(btRigidBody *body)
{
	while(true) {
		char command[5];
		fgets(command, sizeof(command), stdin);
		switch(command[0]) {
		case 'l': {
			boost::lock_guard<boost::mutex> lock(playerBodyLock);
			body->applyCentralImpulse(btVector3(-30, 0, 0));
			break;
		}
		case 'r': {
			boost::lock_guard<boost::mutex> lock(playerBodyLock);
			body->applyCentralImpulse(btVector3(30, 0, 0));
			break;
		}
		case 'u': {
			boost::lock_guard<boost::mutex> lock(playerBodyLock);
			body->applyCentralImpulse(btVector3(0, 100, 0));
			break;
		}
		}
	}
}

First, the player capsule falls for a while. Then, if you enter "u<Return>" it moves up and comes down again. However, if you wait ~5 seconds after the body comes to a halt, it can't be moved again ever so slightly. Here's the code I've written using Ammo: https://gist.github.com/2481565. Both the C++ version and the JS version have the problem, and I can't figure out what I'm doing wrong.

My operating system is Windows 7 x64. I use Bullet 2.80-rev2531 in the "Release" configuration, compiled with Visual Studio 2010. My processor is an Intel Core i7 Q820 @ 1.73 GHz. As for the JS version, I've tested it with the latest Chrome (on the stable update channel) and Firefox 12 (Beta) on the same system.

- Raphael

[note173]

It's deactivation. After some time being inactive body goes to "sleep". Use body->activate(true) before applying any forces to make sure it's not sleeping.

[raphaelr]

Thanks, that was the problem.