/*public CollisionResult CollideCircleWithEdgeAtTime(Circle circle, Vector2 I, Vector2 J, out double t)
* {
* t = -1;
*
* // Circle moves along path MN
* Vector2 M = circle.Position;
* Vector2 N = circle.Position + circle.Velocity;
* Vector2 MN = circle.Velocity;
*
* double timeOfIntersection = -1;
*
* if (!PhysicsObject.TimeOfIntersection(M, N, I, J, out timeOfIntersection, out double uCA)) return CollisionResult.None;
*
* // The first colliding edge, in vector form
* Vector2 IJ = J - I;
*
* // Angle between MN and IJ
* double a = Math.Atan2((MN.X * IJ.Y - MN.Y * IJ.X), Vector2.Dot(MN, IJ));
*
* // Distance between center of circle and point of intersection at time t
* double distCenterToIntersection = Math.Abs(circle.Radius / Math.Sin(a));
*
* // Report the actual time of collision given the circle's radius
* t = timeOfIntersection - (distCenterToIntersection / MN.Length());
*
* if (t >= 0 && t <= 1)
* {
* // First two parameters are zero since we don't need to report collision info for the triangle itself
* //TODO: new velocity for circle is more complex than just Vector2.Negate(MN)
* return new CollisionResult(Vector2.Zero, Vector2.Zero, M + (float)(t - 0.01) * MN, Vector2.Negate(MN));
* }
*
*
* return CollisionResult.None;
* }*/
public CollisionResult CollideCircleWithEdgeAtTime(float s, Circle circle, Vector2 I, Vector2 J, out double t)
{
t = -1; //arbitrary error case
// Circle moves along path MN
Vector2 M = circle.Position;
Vector2 N = circle.Position + circle.Velocity * s;
Vector2 MN = N - M;
// Collide with IJ translated by the normal of the circle's radius in length
Vector2 IJ = J - I;
Vector2 normIJ = new Vector2(IJ.Y, -IJ.X); //negate the Y value because the edge runs clockwise
normIJ.Normalize();
double timeOfEdgeIntersection = -1;
if (Vector2.Dot(normIJ, MN) <= 0) // Only collide edge if we are moving toward it
{
Vector2 scaledNormIJ = normIJ * circle.Radius;
Vector2 P = I + scaledNormIJ;
Vector2 Q = J + scaledNormIJ;
timeOfEdgeIntersection = -1;
bool intersectsEdge = PhysicsObject.TimeOfIntersection(M, N, P, Q, out timeOfEdgeIntersection, out double u);
if (!intersectsEdge || u < 0 || u > 1)
{
timeOfEdgeIntersection = -1; // Invalid intersections
}
}
// Collide circle as point with a new circle with center I and the same radius as circle (corner circle)
//TODO: we shouldn't create an object every time - create a struct circle representation or equivalent method
Circle point = new Circle()
{
Position = circle.Position, Velocity = circle.Velocity
};
Circle corner = new Circle()
{
Position = I, Radius = circle.Radius
};
double timeOfCornerIntersection = -1;
CollisionResult cornerCollisionResult = point.CollideCircleAtTime(s, corner, out timeOfCornerIntersection);
// Earliest wins
CircleEdgeCollision first = FirstCircleEdgeCollision(timeOfEdgeIntersection, timeOfCornerIntersection);
if (first == CircleEdgeCollision.None)
{
return(CollisionResult.None); // No valid times
}
Vector2 normMN = Vector2.Normalize(MN);
Vector2 negNormMN = Vector2.Negate(normMN);
if (first == CircleEdgeCollision.Edge)
{
t = timeOfEdgeIntersection;
Vector2 newCirclePos = M + (float)t * MN + normIJ * SEPARATION;
Vector2 newCircleVel = (2 * Vector2.Dot(normIJ, negNormMN) * normIJ - negNormMN) * circle.Velocity.Length();
return(new CollisionResult(Vector2.Zero, Vector2.Zero, newCirclePos, newCircleVel));
}
else
{
t = timeOfCornerIntersection;
//Vector2 newCirclePos = M + (float)t * MN - 0 * normMN; //Separation of .5 unit
//Vector2 newCircleVel = Vector2.Normalize(newCirclePos - I) * circle.Velocity.Length();
Vector2 newCirclePos = cornerCollisionResult.PositionA;
Vector2 newCircleVel = cornerCollisionResult.VelocityA;
newCirclePos += Vector2.Normalize(newCirclePos - I) * SEPARATION;
return(new CollisionResult(Vector2.Zero, Vector2.Zero, newCirclePos, newCircleVel));
}
}
