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# 2 Triangle Meshes in Bullet Physics with btGImpact problem

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### #1Tomsoner34521  Members   -  Reputation: 124

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Posted 05 June 2012 - 09:35 AM

So this was my simple test to drop 2 tetrahedron that is not working

I get the translation (but not the rotation)
And there is a lot of jittering and bouncing on impact

And they seem to collide and not actually bounce off each other as well.

Any Suggestions?

#include <iostream>
#include <vector>
#include <time.h>
#include <glut.h>
#include "btBulletDynamicsCommon.h"
#include "BulletCollision/Gimpact/btGImpactShape.h"
#include "BulletCollision/Gimpact/btGImpactCollisionAlgorithm.h"
using namespace std;

btDefaultCollisionConfiguration* collisionConfiguration = new btDefaultCollisionConfiguration();
btCollisionDispatcher* dispatcher = new   btCollisionDispatcher(collisionConfiguration);
btSequentialImpulseConstraintSolver* solver = new btSequentialImpulseConstraintSolver;
btDiscreteDynamicsWorld* dynamicsWorld = new btDiscreteDynamicsWorld(dispatcher,overlappingPairCache,solver,collisionConfiguration);

float zoom = 15.0f;
float rotx = 0;
float roty = 0.001f;
float tx = 0;
float ty = 0;
int lastx=0;
int lasty=0;
unsigned char Buttons[3] = {0};

void Init()
{
glEnable(GL_DEPTH_TEST);
glEnable (GL_BLEND);
glBlendFunc (GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

}
//-------------------------------------------------------------------------------
/// \brief   Called when the screen gets resized
/// \param   w   -   the new width
/// \param   h   -   the new height
///
void reshape(int w, int h)
{
// prevent divide by 0 error when minimised
if(w==0)
h = 1;
glViewport(0,0,w,h);
glMatrixMode(GL_PROJECTION);
gluPerspective(45,(float)w/h,0.1,100);
glMatrixMode(GL_MODELVIEW);
}

//-------------------------------------------------------------------------------
//
void Motion(int x,int y)
{
int diffx=x-lastx;
int diffy=y-lasty;
lastx=x;
lasty=y;
if( Buttons[2] )
{
zoom -= (float) 0.05f * diffx*2;
}
else
if( Buttons[0] )
{
rotx += (float) 0.5f * diffy;
roty += (float) 0.5f * diffx;
}
else
if( Buttons[1] )
{
tx += (float) 0.05f * diffx;
ty -= (float) 0.05f * diffy;
}
glutPostRedisplay();
}
//-------------------------------------------------------------------------------
//
void Mouse(int b,int s,int x,int y)
{
lastx=x;
lasty=y;
switch(b)
{
case GLUT_LEFT_BUTTON:
Buttons[0] = ((GLUT_DOWN==s)?1:0);
break;
case GLUT_MIDDLE_BUTTON:
Buttons[1] = ((GLUT_DOWN==s)?1:0);
break;
case GLUT_RIGHT_BUTTON:
Buttons[2] = ((GLUT_DOWN==s)?1:0);
break;
default:
break;
}
glutPostRedisplay();
}

//-------------------------------------------------------------------------------
///
void display()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glTranslatef(0,0,-zoom);
glTranslatef(tx,ty,0);
glRotatef(rotx,1,0,0);
glRotatef(roty,0,1,0);
glColor3f(1.0f,1.0f,1.0f);
// draw grid
glBegin(GL_LINES);
for(int i=-10;i<=10;++i) {
glVertex3f(i,0,-10);
glVertex3f(i,0,10);
glVertex3f(10,0,i);
glVertex3f(-10,0,i);
}
glEnd();

dynamicsWorld->stepSimulation(1.f/60.f,10);
dynamicsWorld->applyGravity();

//print positions of all objects
for (int j=dynamicsWorld->getNumCollisionObjects()-1; j>=0 ;j--)
{
btCollisionObject* obj = dynamicsWorld->getCollisionObjectArray()[j];
btRigidBody* body = btRigidBody::upcast(obj);
if (body && body->getMotionState())
{
btTransform trans;
body->getMotionState()->getWorldTransform(trans);
printf("world pos = %f,%f,%f\n",float(trans.getOrigin().getX()),float(trans.getOrigin().getY()),float(trans.getOrigin().getZ()));

btScalar m[16];
trans.getOpenGLMatrix(m);

glPushMatrix();
glColor4f(1,1,1,1);

glMultMatrixf((GLfloat*)m);

//    glTranslatef(trans.getOrigin().getX(),trans.getOrigin().getY(), float(trans.getOrigin().getZ()));
//glutSolidSphere(1.0f,20,20);

glBegin(GL_TRIANGLES);
glVertex3f(0,1,0);glVertex3f(1,0,0);glVertex3f(0,0,0);
glVertex3f(0,1,0);glVertex3f(0,0,1);glVertex3f(1,0,0);
glVertex3f(1,0,0);glVertex3f(0,0,1);glVertex3f(0,0,0);
glVertex3f(0,1,0);glVertex3f(0,0,0);glVertex3f(0,0,1);
glEnd();
glPopMatrix();

}

}

glutPostRedisplay();
glutSwapBuffers();
}

int main(int argc,char** argv) {
dynamicsWorld->setGravity(btVector3(0,-10,0));
///create a few basic rigid bodies
btCollisionShape* groundShape = new btBoxShape(btVector3(btScalar(50.),btScalar(55.),btScalar(50.)));
//keep track of the shapes, we release memory at exit.
//make sure to re-use collision shapes among rigid bodies whenever possible!
btAlignedObjectArray<btCollisionShape*> collisionShapes;
collisionShapes.push_back(groundShape);
btTransform groundTransform;
groundTransform.setIdentity();
groundTransform.setOrigin(btVector3(0,-55,0));
{
btScalar mass(0.);
//rigidbody is dynamic if and only if mass is non zero, otherwise static
bool isDynamic = (mass != 0.f);
btVector3 localInertia(0,0,0);
if (isDynamic)
groundShape->calculateLocalInertia(mass,localInertia);
//using motionstate is recommended, it provides interpolation capabilities, and only synchronizes 'active' objects
btDefaultMotionState* myMotionState = new btDefaultMotionState(groundTransform);
btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,groundShape,localInertia);
btRigidBody* body = new btRigidBody(rbInfo);
//add the body to the dynamics world
}

btTriangleMesh* mesh = new btTriangleMesh(false);
mesh->addTriangle( btVector3( 0, 1, 0 ), btVector3( 0, 0, 0 ), btVector3( 0, 1, 0 ) );
mesh->addTriangle( btVector3( 0, 1, 0 ), btVector3( 0, 0, 1 ), btVector3( 1, 0, 0 ) );
mesh->addTriangle( btVector3( 1, 0, 0 ), btVector3( 0, 0, 1 ), btVector3( 0, 0, 0 ) );
mesh->addTriangle( btVector3( 0, 1, 0 ), btVector3( 0, 0, 0 ), btVector3( 0, 0, 1 ) );

vector <int> indices;
indices.push_back(2);indices.push_back(1);indices.push_back(0);
indices.push_back(2);indices.push_back(3);indices.push_back(1);
indices.push_back(1);indices.push_back(3);indices.push_back(0);
indices.push_back(2);indices.push_back(0);indices.push_back(3);
std::vector <float> positions;
positions.push_back(0);positions.push_back(0);positions.push_back(0);
positions.push_back(1);positions.push_back(0);positions.push_back(0);
positions.push_back(0);positions.push_back(1);positions.push_back(0);
positions.push_back(0);positions.push_back(0);positions.push_back(1);
btCollisionDispatcher * dispatcher = static_cast<btCollisionDispatcher *>(dynamicsWorld ->getDispatcher());
btGImpactCollisionAlgorithm::registerAlgorithm(dispatcher);
btTriangleIndexVertexArray * vert = new btTriangleIndexVertexArray
( 4,
&indices[0],
3*sizeof(int),
4,
&positions[0],
sizeof(float)  );

btGImpactMeshShape * impact_shape = new btGImpactMeshShape(vert);
impact_shape->setLocalScaling(btVector3(1.,1.,1.));
impact_shape->setMargin(0.04f);
impact_shape->updateBound();
collisionShapes.push_back(impact_shape);
btVector3 localInertia2(0,0,0);
btScalar mass(3.0f);
btTransform startTransform2;
startTransform2.setIdentity();
startTransform2.setOrigin( btVector3(2,10,0) ); //center is myShape's center
impact_shape->calculateLocalInertia(mass,localInertia2);
btDefaultMotionState* motionState = new btDefaultMotionState(startTransform2);
btRigidBody * rig = new btRigidBody(mass,motionState,impact_shape,localInertia2);

btGImpactMeshShape * impact_shape2 = new btGImpactMeshShape(vert);
impact_shape2->setLocalScaling(btVector3(1.,1.,1.));
impact_shape2->setMargin(0.04f);
impact_shape2->updateBound();
collisionShapes.push_back(impact_shape2);
startTransform2.setIdentity();
startTransform2.setOrigin( btVector3(3,14,0) ); //center is myShape's center
impact_shape2->calculateLocalInertia(mass,localInertia2);
btDefaultMotionState* motionState2 = new btDefaultMotionState(startTransform2);
btRigidBody * rig2 = new btRigidBody(mass,motionState2,impact_shape2,localInertia2);

glutInit(&argc,argv);
glutInitDisplayMode(GLUT_DOUBLE|GLUT_RGBA|GLUT_DEPTH);
glutInitWindowSize(900,900);
glutInitWindowPosition(200,100);
glutCreateWindow("TestBed Framework");
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMouseFunc(Mouse);
glutMotionFunc(Motion);
Init();
glutMainLoop();
return 0;
}


Edited by Tomsoner34521, 05 June 2012 - 11:01 AM.

### #2Krohm  Crossbones+   -  Reputation: 3261

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Posted 05 June 2012 - 11:41 PM

For quick test, try changing them to convex hulls. Just to rule out some issues with the algorithm or not.

Not related but occasions for cleanup:
I see a lot of redudant code: no need to call applyGravity (it's called in the simulation loop). You don't need to use btAlignedObjectArray to store btCollisionShape* as you are not storing objects there. It is my understanding it is a non-owning container (just as std::vector is), it will destroy the array itself by using its internal allocator without releasing the pointers. btAlignedObjectArray is intended to be used with btVector3 or stuff like that for hi-perf SIMD processing, not as a generic container.

To be completely honest, I think I missed the code where you cleanup your memory.

Regardless of what the documentation writes, a rigid body is NOT dynamic just because mass is nonzero. Kinematics can also have 0 mass. The implication is: if mass is zero and object is not marked as kinematic then object is static.
You don't need to compute local inertia if that is zero, it's done for you in the ctor.

Edited by Krohm, 05 June 2012 - 11:42 PM.

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