Algorithm to get the distance of a point in the world to a plane in the world. Gist created for http://wp.me/p1tYzm-38

distanceToPlane.glsl

//http://mathworld.wolfram.com/Point-PlaneDistance.html
float distanceToPlane(float3 planePosition, float3 planeNormal, float3 pointInWorld)
{
  //w = vector from plane to point
  float3 w = - ( planePosition - pointInWorld );
  return ( 
    planeNormal.x * w.x + 
    planeNormal.y * w.y + 
    planeNormal.z * w.z 
  ) / sqrt ( 
    planeNormal.x * planeNormal.x +
    planeNormal.y * planeNormal.y +
    planeNormal.z * planeNormal.z 
  );
}