/// <summary>
/// This tells if a sphere is BEHIND, in FRONT, or INTERSECTS a plane, also it's distance
/// </summary>
public static MySpherePlaneIntersectionEnum GetSpherePlaneIntersection(ref BoundingSphereD sphere, ref MyPlane plane, out float distanceFromPlaneToSphere)
{
// First we need to find the distance our polygon plane is from the origin.
float planeDistance = plane.GetPlaneDistance();
// Here we use the famous distance formula to find the distance the center point
// of the sphere is from the polygon's plane.
distanceFromPlaneToSphere = (float)(plane.Normal.X * sphere.Center.X + plane.Normal.Y * sphere.Center.Y + plane.Normal.Z * sphere.Center.Z + planeDistance);
// If the absolute value of the distance we just found is less than the radius,
// the sphere intersected the plane.
if (Math.Abs(distanceFromPlaneToSphere) < sphere.Radius)
{
return(MySpherePlaneIntersectionEnum.INTERSECTS);
}
else if (distanceFromPlaneToSphere >= sphere.Radius)
{
// Else, if the distance is greater than or equal to the radius, the sphere is
// completely in FRONT of the plane.
return(MySpherePlaneIntersectionEnum.FRONT);
}
// If the sphere isn't intersecting or in FRONT of the plane, it must be BEHIND
return(MySpherePlaneIntersectionEnum.BEHIND);
}
/// <summary>
/// Method returns intersection point between sphere and triangle (which is defined by vertexes and plane).
/// If no intersection found, method returns null.
/// See below how intersection point can be calculated, because it's not so easy - for example sphere vs. triangle will
/// hardly generate just intersection point... more like intersection area or something.
/// </summary>
public static Vector3? GetSphereTriangleIntersection(ref BoundingSphereD sphere, ref MyPlane trianglePlane, ref MyTriangle_Vertices triangle)
{
// Vzdialenost gule od roviny trojuholnika
float distance;
// Zistim, ci sa gula nachadza pred alebo za rovinou trojuholnika, alebo ju presekava
MySpherePlaneIntersectionEnum spherePlaneIntersection = GetSpherePlaneIntersection(ref sphere, ref trianglePlane, out distance);
// Ak gula presekava rovinu, tak hladam pseudo-priesecnik
if (spherePlaneIntersection == MySpherePlaneIntersectionEnum.INTERSECTS)
{
// Offset ktory pomoze vypocitat suradnicu stredu gule premietaneho na rovinu trojuholnika
Vector3 offset = trianglePlane.Normal * distance;
// Priesecnik na rovine trojuholnika, je to premietnuty stred gule na rovine trojuholnika
Vector3 intersectionPoint;
intersectionPoint.X = (float)(sphere.Center.X - offset.X);
intersectionPoint.Y = (float)(sphere.Center.Y - offset.Y);
intersectionPoint.Z = (float)(sphere.Center.Z - offset.Z);
if (GetInsidePolygonForSphereCollision(ref intersectionPoint, ref triangle)) // Ak priesecnik nachadza v trojuholniku
{
// Toto je pripad, ked sa podarilo premietnut stred gule na rovinu trojuholnika a tento priesecnik sa
// nachadza vnutri trojuholnika (tzn. sedia uhly)
return intersectionPoint;
}
else // Ak sa priesecnik nenachadza v trojuholniku, este stale sa moze nachadzat na hrane trojuholnika
{
Vector3? edgeIntersection = GetEdgeSphereCollision(ref sphere.Center, (float)sphere.Radius / 1.0f, ref triangle);
if (edgeIntersection != null)
{
// Toto je pripad, ked sa priemietnuty stred gule nachadza mimo trojuholnika, ale intersection gule a trojuholnika tam
// je, pretoze gula presekava jednu z hran trojuholnika. Takze vratim suradnice priesecnika na jednej z hran.
return edgeIntersection.Value;
}
}
}
// Sphere doesn't collide with any triangle
return null;
}
