isOverstretched method
True when the spring is longer than ratio x its resting length.
Implementation
bool isOverstretched(double ratio) {
final double dx = p2.x - p1.x;
final double dy = p2.y - p1.y;
final double dz = p2.z - p1.z;
return dx * dx + dy * dy + dz * dz > restSquared * ratio * ratio;
}