#include "Frustum.h"
#include "VssRay.h"




void
Frustum::Construct(const  AxisAlignedBox3 &box,
				   const  AxisAlignedBox3 &dBox)
{
  // the frustum is defined by set of negative halfspace described by mPlanes
  
  // construct
  Vector3 center = box.Center();
  Vector3 dCenter = dBox.Center();

  // "back plane"
  mPlanes.push_back(Plane3(-VssRay::GetDirection(dCenter.x, dCenter.y), center));

  Vector3 directions[4];
  directions[0] = VssRay::GetDirection(dBox.Min().x, dBox.Min().y);
  directions[1] = VssRay::GetDirection(dBox.Max().x, dBox.Min().y);
  directions[2] = VssRay::GetDirection(dBox.Max().x, dBox.Max().y);
  directions[3] = VssRay::GetDirection(dBox.Min().x, dBox.Max().y);
  
  // side planes
  mPlanes.push_back(Plane3(CrossProd(directions[0], directions[1]), center));
  mPlanes.push_back(Plane3(CrossProd(directions[1], directions[2]), center));
  mPlanes.push_back(Plane3(CrossProd(directions[2], directions[3]), center));
  mPlanes.push_back(Plane3(CrossProd(directions[3], directions[0]), center));


  // now make sure all planes contain the spatial box
  int i, j;
  for (i=0; i < mPlanes.size(); i++) {
	for (j=0; j < 8; j++) {
	  float dist = mPlanes[i].Distance(box.GetVertex(j));
	  if (dist > 0)
		mPlanes[i].mD -= dist;
	}
  }
}

// conservative frustum box intersection
// returns
// 0 - box intersects the frustum
// -1 - box intersects the frustum and is fully inside
// 1 - box does not intersect the frustum

int
Frustum::ComputeIntersection(const  AxisAlignedBox3 &box)
{
  int i;
  int result = -1;
  for (i=0; i < mPlanes.size(); i++) {
	int side = box.Side(mPlanes[i]);
	if (side == 1)
	  return 1;
	if (side > result)
	  result = side;
  }
  return result;
}