/// <summary>
/// Determine whether a box and a sphere intersect.
/// </summary>
/// <param name="box">Box physics object</param>
/// <param name="sphere">Sphere physics object</param>
public static bool BoxSphereCollision(BoxBody box, SphereBody sphere)
{
// reference frame: box at (0, 0, 0), sides aligned with axes
var sphereCoordsRelative = sphere.Position - box.Position;
// to transform coordinate system to have box be axis-aligned, we apply
// the reverse of the rotation to the sphere coordinates
var inverse = new Quaternion(box.Rotation.X, box.Rotation.Y, box.Rotation.Z, -box.Rotation.W);
var sphereCoordsTransformed = Vector3.Transform(sphereCoordsRelative, inverse);
// to check collision, we need to know if the shortest distance between the box
// and the center of the sphere is smaller than the radius of the sphere
// X coordinate of closest point = sphere.X if sphere.x is between the minimum
// and maximum x coordinate of the box - same for y and z
var boxMinX = -box.Size.X / 2;
var boxMaxX = +box.Size.X / 2;
var boxMinY = -box.Size.Y / 2;
var boxMaxY = +box.Size.Y / 2;
var boxMinZ = -box.Size.Z / 2;
var boxMaxZ = +box.Size.Z / 2;
var closestPointToSphereX = Math.Clamp(sphereCoordsTransformed.X, boxMinX, boxMaxX);
var closestPointToSphereY = Math.Clamp(sphereCoordsTransformed.Y, boxMinY, boxMaxY);
var closestPointToSphereZ = Math.Clamp(sphereCoordsTransformed.Z, boxMinZ, boxMaxZ);
return(Vector3.DistanceSquared(sphereCoordsTransformed, new Vector3(closestPointToSphereX, closestPointToSphereY, closestPointToSphereZ))
< Math.Pow(sphere.Radius, 2));
}
/// <summary>
/// Finds the vertices of a box body.
/// </summary>
/// <returns>A List containing the positions of the vertices.</returns>
public static Vector3[] FindVertices(BoxBody box)
{
var vertices = new Vector3[8];
var boxMinX = -box.Size.X / 2;
var boxMaxX = +box.Size.X / 2;
var boxMinY = -box.Size.Y / 2;
var boxMaxY = +box.Size.Y / 2;
var boxMinZ = -box.Size.Z / 2;
var boxMaxZ = +box.Size.Z / 2;
vertices[0] = new Vector3(boxMinX, boxMinY, boxMinZ);
vertices[1] = new Vector3(boxMinX, boxMinY, boxMaxZ);
vertices[2] = new Vector3(boxMinX, boxMaxY, boxMinZ);
vertices[3] = new Vector3(boxMinX, boxMaxY, boxMaxZ);
vertices[4] = new Vector3(boxMaxX, boxMinY, boxMinZ);
vertices[5] = new Vector3(boxMaxX, boxMinY, boxMaxZ);
vertices[6] = new Vector3(boxMaxX, boxMaxY, boxMinZ);
vertices[7] = new Vector3(boxMaxX, boxMaxY, boxMaxZ);
// The resulting vectors are still relative to the axis-aligned box
for (var i = 0; i < vertices.Length; i++)
{
vertices[i] = Vector3.Transform(vertices[i], box.Rotation) + box.Position;
}
return(vertices);
}
/// <summary>
/// Creates a box body.
/// </summary>
/// <param name="simulation">The simulation to use.</param>
/// <param name="position">The position of the body.</param>
/// <param name="rotation">The rotation of the body.</param>
/// <param name="size">The size of the body (length in x, y and z direction).</param>
/// <returns>The box body that was created.</returns>
public static BoxBody Create(PhysicsSimulation simulation, Vector3 position, Quaternion rotation, Vector3 size)
{
var obj = new BoxBody(simulation);
obj.Size = size;
obj.Position = position;
obj.Rotation = rotation;
obj.Vertices = FindVertices(obj);
simulation.Register(obj);
return(obj);
}
public static BoxBody Create(PhysicsSimulation simulation, Vector3 position, Quaternion rotation, Vector3 size)
{
var shape = new Box(size.X, size.Y, size.Z);
shape.ComputeInertia(1, out var inertia);
var index = simulation.Simulation.Shapes.Add(shape);
var collidable = new CollidableDescription(index, 0.1f);
var activity = new BodyActivityDescription(0);
var pose = new RigidPose(position, rotation);
var descriptor = BodyDescription.CreateDynamic(pose, inertia, collidable, activity);
var handle = simulation.Simulation.Bodies.Add(descriptor);
var obj = new BoxBody(simulation, handle);
simulation.Register(obj);
return(obj);
}
/// <summary>
/// Determine whether a capsule and a box intersect.
/// </summary>
/// <param name="capsule">The capsule</param>
/// <param name="box">The box</param>
public static bool CapsuleBoxCollision(CapsuleBody capsule, BoxBody box)
{
throw new NotImplementedException("Capsule-box collision checks are not implemented.");
}
/// <summary>
/// Determine whether two boxes intersect.
/// </summary>
/// <remarks>
/// Not 100% accurate; it only checks vertex-face collisions, not edge-edge.
/// However, this should be accurate enough for our use case.
/// </remarks>
/// <param name="firstBox">The first box</param>
/// <param name="secondBox">The second box</param>
public static bool BoxBoxCollision(BoxBody firstBox, BoxBody secondBox)
{
return(firstBox.ContainsAnyPoint(secondBox.Vertices) || secondBox.ContainsAnyPoint(firstBox.Vertices));
}
