public CollisionResult SolveCollision(CollisionBody colA, CollisionBody colB)
{
// normalize parameters such that colA is the circle and colB is the box.
// there are only two possibilities, therefore we only need to swap if colB is the circle.
if (colB.Shape is Circle)
{
CollisionBody tmp = colA;
colA = colB;
colB = tmp;
tmp = null;
}
Circle circleA = (Circle)colA.Shape;
Box boxB = (Box)colB.Shape;
Matrix3 transformB = colB.WorldTransform;
float projectedDistance = 0;
float minPenetration = float.MaxValue;
Vector2 distance = colA.Position - colB.Position;
Vector2 mtv = default(Vector2); // the minimum translation vector
Vector2[] axisToCheck = new Vector2[3];
boxB.CalculateOrientation(ref transformB, out axisToCheck[0]);
axisToCheck[1] = Vector2Extensions.PerpendicularLeft(axisToCheck[0]);
float minDistance = float.MaxValue;
Vector2 closestVertex = default(Vector2);
for (int i = 0; i < boxB.Vertices.Length; i++)
{
float vertexDistance = Vector2.DistanceSquared(colA.Position, boxB.Vertices[i]);
if (vertexDistance < minDistance)
{
minDistance = vertexDistance;
closestVertex = colB.Position - boxB.Vertices[i];
}
}
axisToCheck[2] = closestVertex;
Vector2Extensions.SafeNormalize(ref axisToCheck[2]);
for (int i = 0; i < axisToCheck.Length; i++)
{
Vector2 projectionA, projectionB;
projectedDistance = Math.Abs(Vector2.Dot(distance, axisToCheck[i]));
circleA.ProjectOnto(ref axisToCheck[i], out projectionA);
boxB.ProjectOnto(ref transformB, ref axisToCheck[i], out projectionB);
float aSize = projectionA.Length(); //Math.Abs(projectionA.X) + Math.Abs(projectionA.Y);
float bSize = Math.Abs(projectionB.X) + Math.Abs(projectionB.Y);
float abSize = aSize + bSize;
float penetration = abSize - projectedDistance;
// a seperating axis found; there is no collision.
if (penetration <= 0)
{
return(CollisionResult.NoCollision);
}
// project the object along the axis with the smalled penetration depth.
else if (Math.Abs(penetration) < Math.Abs(minPenetration))
{
minPenetration = penetration;
mtv = axisToCheck[i];
}
}
// the distance vector determines the direction of movement. the distance and mtv
// should always oppose each other to repel collisions.
if (Vector2.Dot(distance, mtv) < 0f)
{
mtv = -mtv;
}
// seperating axis could not be found; a collision occurs.
return(new CollisionResult()
{
Us = colA,
Them = colB,
CollisionResponse = minPenetration * mtv,
IsColliding = true
});
}
public void CalculateExtents(ref Matrix3 transform, out Vector2 extents)
{
extents = new Vector2(Radius, 0);
transform.TransformVector(ref extents);
}