/** Infinite plane, abstract because unbounded plane does
 *  not work well with spatial grid
 * @author: Phil Gage
 */
abstract class AbstractPlane extends AbstractObject {
    Vector3 normal;  // surface normal
    Point point;     // any point on plane
    double d;        // distance from origin to plane

    // for Polygon
    AbstractPlane (Color color) {
        super(color);
    }

    AbstractPlane (Point point, Vector3 normal, Color color) {
        super(color);
        this.point = point;
        this.normal = normal;
        this.normal.normalize();
        d = -point.dot(this.normal);
    }

    double intersect (Ray r, Intersection intersection) {
        double t;
        ++Statistics.intersectionCount; // stats
        // Equation of plane: ax + by + cz + d = 0
        // where normal = (a,b,c) and point on plane = (x,y,z)
        // distance t = -(d+dot(normal,origin))/(dot(normal,direction)
        t = -(d + r.origin.dot(normal)) / r.direction.dot(normal);
        t += Constants.EPSILON; //?

        // Set intersection object fields
        intersection.obj = null;
        intersection.incident.set(r.direction);
        r.extrapolate(t,intersection.point);
        intersection.normal.set(intersection.point);
        intersection.normal.set(normal);
        // If normal wrong way, flip to avoid shadow on backside?
        // Note ">" here because r is incident and opposite normal
        if (intersection.normal.dot(r.direction) > 0.0)
            intersection.normal.negate();
        return t;
    }

}