/** Sphere
 * (see Glassner p 281)
 * @author: Phil Gage
 */
class Sphere extends AbstractObject {
    Point center;
    double radius;
    double radius2;   // radius squared

    private Vector3 v = new Vector3();

    Sphere (Point center, double radius, Color color) {
        super(color);
        this.center = center;
        this.radius = radius;
        this.radius2 = radius*radius;
    }

    double intersect (Ray ray, Intersection intersection) {
        double b, discriminant, t, t1, t2;

        ++Statistics.intersectionCount; // stats
        v.set(center);
        v.subtract(ray.origin);
        b = v.dot(ray.direction);
        discriminant = b*b - v.dot(v) + radius2;
        if (discriminant <= 0.0)
            return 0.0;
        discriminant = Math.sqrt(discriminant);
        t2 = b + discriminant;
        if (t2 < Constants.EPSILON)
            return 0.0;
        t1 = b - discriminant;
        if (t1 > Constants.EPSILON)
            t = t1;
        else
            t = t2;
        // Set intersection object fields
        intersection.obj = null;
        intersection.incident.set(ray.direction);
        ray.extrapolate(t,intersection.point);
        intersection.normal.set(intersection.point);
        intersection.normal.subtract(center);
        intersection.normal.normalize();
        return t;
    }

    /** Return bounding box around this object */
    Extent getExtent () {
        return new Extent (
            new Point(center.x-radius,center.y-radius,center.z-radius),
            new Point(center.x+radius,center.y+radius,center.z+radius));
    }

}