public override bool TestCollisionVsCircle(CircleCollisionHull2D other, ref Collision c)
{
c.a = this;
c.b = other;
// c.status
// check if sqr distance between the center is less that the square of the radii
updatePosition();
other.updatePosition();
// could use dot product
float sqrDistance = (position - other.position).SqrMagnitude();
float sqrRadii = radius + other.radius;
sqrRadii *= sqrRadii;
bool isColiding = sqrDistance <= sqrRadii;
if (!isColiding)
{
return(isColiding);
}
//contact point
// http://paulbourke.net/geometry/circlesphere/
Vector2 difference = other.position - position; //from position to other.position
float distance = difference.magnitude;
float radii = radius + other.radius;
// distance = radii
// Vector2 contact = position + difference;
// Get point halfway between two centers.
Vector2 contact = position + difference * (radius / (radius + other.radius)); //
Vector2 normal = (position - contact).normalized; // vector from contact to center
float overlap = radii - distance; // not sure we need this.
// edge cases - circles overlap completely, or one inside the other.
c.contactCount = 1;
c.contacts = new CollisionHull2D.Collision.Contact[c.contactCount];
c.contacts[0].point = contact;
c.contacts[0].normal = normal;
c.contacts[0].restitution = restitution; // TODO: Is this coefficient or actual number?
// closing velocity
// https://gamedev.stackexchange.com/questions/118162/how-to-calculate-the-closing-speed-of-two-objects
//Vector2 diff = other.position - position;
//Vector2 velDiff = other.particle2D.getVelocity() - particle2D.getVelocity();
//float closingSpeed = Vector2.Dot(velDiff, diff) / diff.magnitude;
//Relative velocity from book
Vector2 relativeVelocity = particle2D.getVelocity() - other.getParticle2D().getVelocity();
float separatingVel = Vector2.Dot(relativeVelocity, normal); // relativeVelocity * normal
// https://math.stackexchange.com/questions/13261/how-to-get-a-reflection-vector
// this would simulate hitting a hard object w/ no velocity loss.
// Vector2 velReflectedOverN = particle2D.getVelocity() - 2 * Vector2.Dot(particle2D.getVelocity(), normal) * normal;
// c.closingVelocity = closingSpeed*velReflectedOverN.normalized;
c.closingVelocity = -separatingVel * normal; //was -seperatingVel
c.status = isColiding;
return(isColiding);
}
