xna - Cube entity collision on plane entity -

how do collision between cube , plane, can sphere on plane cant figure out cube on plane, know must find x,y,z of cube , detection on plane cant figure out.

here collision tester code.

public static bool sphereandsphere(sphere a, sphere b, ref contact contact)     {         // vector centre of particle b centre of particle         vector3 separationvector = b.position - a.position;         float sumofradii = a.radius + b.radius;         float distance = separationvector.length();          if (distance < sumofradii)         {             contact.contactpoint = a.position + separationvector / 2f;             separationvector.normalize();             contact.contactnormal = separationvector;             contact.penetrationdepth = sumofradii - distance;              return true;         }          return false;     }      // assumes origin in centre of world      // , planes boundaries of world , rigid-bodies within boundaries     public static bool sphereandplane(sphere a, planeentity b, ref contact contact)     {         // depth of sphere plane (if negative, no collision)         float depth = vector3.dot(a.position, b.directionfromorigin) + a.radius + b.offsetfromorigin;          if (depth > 0)         {             contact.contactpoint = a.position + (a.radius - depth) * b.directionfromorigin;             contact.contactnormal = -b.directionfromorigin;             contact.penetrationdepth = depth;              return true;         }          return false;     } 

here test on cube on box

public static bool sphereandbox(sphere a, cube b, ref contact contact)     {         vector3 relativepoint = vector3.transform(a.position, matrix.invert(b.worldtransform));          // out check, based on separation axis theorem         if (math.abs(relativepoint.x) - a.radius > b.halfsize.x             || math.abs(relativepoint.y) - a.radius > b.halfsize.y             || math.abs(relativepoint.z) - a.radius > b.halfsize.z)             return false;          vector3 closestpoint = vector3.zero;          closestpoint.x = mathhelper.clamp(relativepoint.x, -b.halfsize.x, b.halfsize.x);         closestpoint.y = mathhelper.clamp(relativepoint.y, -b.halfsize.y, b.halfsize.z);         closestpoint.z = mathhelper.clamp(relativepoint.z, -b.halfsize.z, b.halfsize.z);          float distance = (closestpoint - relativepoint).lengthsquared();          if (distance < a.radius * a.radius)         {             contact.contactpoint = vector3.transform(closestpoint, b.worldtransform);             contact.contactnormal = a.position - contact.contactpoint;             contact.contactnormal.normalize();             contact.penetrationdepth = a.radius - (float)math.sqrt(distance);             return true;         }          return false; } 

if either plane or cube not axis aligned -or- cube (width,length,height) not equivalent, find easiest test each corner position of cube individually against plane instead of cube whole. when first corner crosses plane, register collision.

but if both plane , cube axis aligned and cube symmetrical (wlh), think of cube sphere radius half width of cube.