Gamasutra - Features


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by Jeff Lander
Gamasutra
February 08, 2000

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Features

Listing 3. A damped spring force.

p1 = &system[spring->p1];
p2 = &system[spring->p2];
VectorDifference(&p1->pos,&p2->pos,&deltaP); // Vector distance
dist = VectorLength(&deltaP); // Magnitude of deltaP

Hterm = (dist - spring->restLen) * spring->Ks; // Ks * (dist - rest)

VectorDifference(&p1->v,&p2->v,&deltaV); // Delta Velocity Vector
Dterm = (DotProduct(&deltaV,&deltaP) * spring->Kd) / dist; // Damping Term

ScaleVector(&deltaP,1.0f / dist, &springForce); // Normalize Distance Vector
ScaleVector(&springForce,-(Hterm + Dterm),&springForce); // Calc Force
VectorSum(&p1->f,&springForce,&p1->f); // Apply to Particle 1
VectorDifference(&p2->f,&springForce,&p2->f); // - Force on Particle 2

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