Jeff Molofee - NeHe's OpenGL Tutorials

OldPos[i]=ArrayPos[i];

TVector::unit(ArrayVel[i],uveloc);

ArrayPos[i]=ArrayPos[i]+ArrayVel[i]*RestTime;

rt2=OldPos[i].dist(ArrayPos[i]);

// Test If Collision Occured Between Ball And All 5 Planes

if (TestIntersionPlane(pl1,OldPos[i],uveloc,rt,norm)) {

// Find Intersection Time

rt4=rt*RestTime/rt2;

// If Smaller Than The One Already Stored Replace In Timestep

if (rt4<=lamda) {

// If Intersection Time In Current Time Step

if (rt4<=RestTime+ZERO) if (! ((rt<=ZERO)&&(uveloc.dot(norm)>ZERO)) ) {

normal=norm;

point=OldPos[i]+uveloc*rt;

lamda=rt4;

BallNr=i;

}

}

}

if (TestIntersionPlane(pl2, OldPos[i], uveloc, rt, norm)) {

// …The Same As Above Omitted For Space Reasons

}

if (TestIntersionPlane(pl3, OldPos[i], uveloc, rt, norm)) {

// …The Same As Above Omitted For Space Reasons

}

if (TestIntersionPlane(pl4, OldPos[i], uveloc, rt, norm)) {

// …The Same As Above Omitted For Space Reasons

}

if (TestIntersionPlane(pl5, OldPos[i], uveloc, rt, norm)) {

// …The Same As Above Omitted For Space Reasons

}

// Now Test Intersection With The 3 Cylinders

if (TestIntersionCylinder(cyl1, OldPos[i], uveloc, rt, norm, Nc)) {

rt4 = rt*RestTime/rt2;

if (rt4<=lamda) {

if (rt4<=RestTime+ZERO) if (! ((rt<=ZERO)&&(uveloc.dot(norm)>ZERO)) ) {

normal=norm;

point=Nc;

lamda=rt4;

BallNr=i;

}

}

}

if (TestIntersionCylinder(cyl2, OldPos[i], uveloc, rt, norm, Nc)) {

// …The Same As Above Omitted For Space Reasons

}

if (TestIntersionCylinder(cyl3, OldPos[i], uveloc, rt, norm, Nc)) {

// …The Same As Above Omitted For Space Reasons

}

}

// After All Balls Were Tested With Planes / Cylinders Test For Collision

// Between Them And Replace If Collision Time Smaller

if (FindBallCol(Pos2, BallTime, RestTime, BallColNr1, BallColNr2)) {

if (sounds) PlaySound("Explode.wav", NULL, SND_FILENAME|SND_ASYNC);

if ((lamda==10000) || (lamda>BallTime)) {

RestTime=RestTime-BallTime;

TVector pb1, pb2, xaxis, U1x, U1y, U2x, U2y, V1x, V1y, V2x, V2y;

double a,b;

…

Code Omitted For Space Reasons

The Code Is Described In The Physically Based Modeling Section Under Sphere To Sphere Collision

…

//Update Explosion Array And Insert Explosion

for(j=0; j<20; j++) {

if (ExplosionArray[j]._Alpha<=0) {

ExplosionArray[j]._Alpha=1;

ExplosionArray[j]._Position=ArrayPos[BallColNr1];

ExplosionArray[j]._Scale=1;

break;

}

}

continue;

}

}

// End Of Tests

// If Collision Occured Move Simulation For The Correct Timestep

// And Compute Response For The Colliding Ball

if (lamda != 10000) {

RestTime-=lamda;

for (j=0; j

rt2=ArrayVel[BallNr].mag();

ArrayVel[BallNr].unit();

ArrayVel[BallNr] = TVector::unit( (normal*(2*normal.dot(-ArrayVel[BallNr]))) + ArrayVel[BallNr] );

ArrayVel[BallNr] = ArrayVel[BallNr]*rt2;

// Update Explosion Array And Insert Explosion

for(j=0; j<20; j++) {

if (ExplosionArray[j]._Alpha<=0) {

ExplosionArray[j]._Alpha=1;

ExplosionArray[j]._Position=point;

ExplosionArray[j]._Scale=1;

break;

}

}

} else RestTime=0;

} // End Of While Loop

The Main Global Variables Of Importance Are:

The Main Functions Of Interest Are:

For more information look at the source code. I tried to comment it as best as I could. Once the collision detection and response logic is understood, the source should become very clear. For any more info don't hesitate to contact me.

As I stated at the beginning of this tutorial, the subject of collision detection is a very difficult subject to cover in one tutorial. You will learn a lot in this tutorial, enough to create some pretty impressive demos of your own, but there is still alot more to learn on this subject. Now that you have the basics, all the other sources on Collision Detection and Physically Based Modeling out there should become easier to understand. With this said, I send you on your way and wish you happy collisions!!!

Some information about Dimitrios Christopoulos: He is currently working as a Virtual Reality software engineer at the Foundation of the Hellenic World in Athens/Greece (www.fhw.gr). Although Born in Germany, he studied in Greece at the University of Patras for a B.Sc. in Computer Engineering and Informatics. He holds also a MSc degree (honours) from the University of Hull (UK) in Computer Graphics and Virtual Environments. He did his first steps in game programming using Basic on an Commodore 64, and switched to C/C++/Assembly on the PC platform after the start of his studium. During the last few years OpenGL has become his graphics API of choice. For more information visit his site at: http://members.xoom.com/D_Christop.