/**
 * @(#) $RCSfile: SimpleCameraLoop.as,v $ $Revision: 1.3 $ $Date: 2003/01/29 16:40:19 $
 *
 * Copyright 2003 Orgdot AS. All Rights Reserved.
 * http://dev.swfit.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

/**
 * A simple interactive camera model - based on projection (rotation and scale)
 * of flash movie clips. Rules: The camera back wall is circular and always 
 * perpendicular to the focal point. The centers of the movie clips are projected 
 * through the focal point. For ease of computation / orientation we let the clips
 * exist on the same side of the focal point as the camera back wall.
 *
 * The unrotated xy-coordinates are determined from where they hit the camera wall,
 * and then rotated. If they do not hit the camera back wall, they are set invisible. 
 * The distance from the focal point determines the scale (and / or alpha) of the 
 * movie clips. The rotation of the movie clips is the opposite of the camera. See 
 * MouseEngineLoop for details on camera x, y, z, rotation etc.
 *
 * @author      Olaf Havnes
 * @version     $Revision: 1.3 $ $Date: 2003/01/29 16:40:19 $
 * @since       SWFIT1.0
 */

/**
 * To start with we have a vector in space Pn = (xp, yp, zp) and a vector C (stored in
 * _level0) representing the normal of the camera back wall.
 */

// Get the squared length.
p_len_sq = xp * xp + yp * yp + zp * zp;

// The change should not be so dramatic as to make this very wrong
// NB! Remember to supply an initial p_len!

p_len = (p_len + p_len_sq / p_len) / 2;

// Compute the dot product :
p_dot_c = xp * /:camera_x + yp * /:camera_y + zp * /:camera_z;


// Is the particle on the correct side of the focal point?
if (p_dot_c > 0)
{
    // intersection test: cos (A) > cos (Amax), and p_dot_c = |C| * |P| * cos (A)
    // we have stored some precomputed values at _level0:
    if (p_dot_c * p_dot_c > p_len_sq * /:cisect)
    {
        // show this clip
        _visible = true;
        
        // to find the intersection point we scale the vector P: 
        // Pt = t * P, so that Pt touches the back wall. Then (Pt - C).C = 0,
        // or t = C.C / P.C = |C|^2 / P.C
        t = /:cam_len_sq / p_dot_c;
        
        x_tp = t * xp - /:camera_x;
        y_tp = t * yp - /:camera_y;
        z_tp = t * zp - /:camera_z;

        // project this vector onto the "rotated horizon unit vector" of the camera back wall
        xd = x_tp * /:huv_x + y_tp * /:huv_y + z_tp * /:huv_z;

        // project this vector onto the "rotated verizon unit vector" of the camera back wall
        yd = x_tp * /:vuv_x + y_tp * /:vuv_y + z_tp * /:vuv_z;
    }
    else
    {
        _visible = false;
    }
}
else
{
    // kill the particle ?
    reset = true;
}