//
// Test primitives against a viewing frustrum.
//
// Copyright (c) J. Belson	2003.05.29
//
// $Author: jon $	:	$Date: 2003/05/30 17:50:44 $
//


#include <cmath>

#include "frustrum.h"
#include "point3d.h"


/**
 * Constructor.
 * Define a viewing frustrum using the field of view angle
 *  and the near and far clipping panes.
 */
frustrum::frustrum(float view_angle, float near_plane, float far_plane)
{
	fov		= view_angle;
	near	= -near_plane;
	far		= -far_plane;

	k = 1.0/std::tan(fov/2.0);
}


/**
 * Test a point against the viewing frustrum
 * @return True if within frustrum
 */
bool frustrum::test_point(const point3d& p)
{
	if (p.z <= k*p.x && k*p.x <= -p.z
			&& p.y >= p.z && -p.z >= p.y) {
		return true;
	}

	return false;
}


/**
 * Test a patch against the viewing frustrum.  Even if all the
 *  points are outside, part of the patch may be visible.
 * @return True if at least part of patch lies within frustrum.
 */
bool frustrum::test_patch(const point3d p[4])
{
	int flags[4] = {0, 0, 0, 0};

	for (int i=0; i<4; i++) {
		if (p[i].z < far)		flags[i] |= BEHIND;
		if (p[i].z > near)		flags[i] |= INFRONT;

		if (k*p[i].x < p[i].z)	flags[i] |= LEFT;
		if (k*p[i].x > -p[i].z)	flags[i] |= RIGHT;

		// @todo Apply 'k' to next two.
		if (p[i].y < p[i].z)	flags[i] |= ABOVE;
		if (p[i].y > -p[i].z)	flags[i] |= BELOW;
	}

	// If bitwise AND has at least one '1', then all points are
	//  in the same out-of-frustrum region.
	if (flags[0] & flags[1] & flags[2] & flags[3]) {
		return false;
	}
	return true;
}