1    package graphics.raytracers.tracer.primatives; 
2     
3    import graphics.raytracers.tracer.geometry.Ray3d; 
4    import graphics.raytracers.tracer.geometry.Vector3d; 
5     
6    public class Sphere extends Primitive { 
7        Vector3d c; 
8        double r, r2; 
9     
10       public Sphere(Vector3d center, double radius) { 
11           c = center; 
12           r = radius; 
13           r2 = r * r; 
14       } 
15    
16       public Isect intersect(Ray3d ry) { 
17           double b, disc, t; 
18           Isect ip; 
19           Vector3d v; 
20           v = Vector3d.sub(c, ry.getStartPoint()); 
21           b = Vector3d.dot(v, ry.getDirection()); 
22           disc = b * b - Vector3d.dot(v, v) + r2; 
23           if (disc < 0.0) { 
24               return null; 
25           } 
26           disc = Math.sqrt(disc); 
27           t = (b - disc < 1e-6) ? b + disc : b - disc; 
28           if (t < 1e-6) { 
29               return null; 
30           } 
31           ip = new Isect(); 
32           ip.t = t; 
33           ip.enter = Vector3d.dot(v, v) > r2 + 1e-6 ? 1 : 0; 
34           ip.prim = this; 
35           ip.surf = surf; 
36           return ip; 
37       } 
38    
39       public Vector3d normal(Vector3d p) { 
40           Vector3d r; 
41           r = Vector3d.sub(p, c); 
42           r.normalize(); 
43           return r; 
44       } 
45    
46       public String toString() { 
47           return "Sphere {" + c.toString() + "," + r + "}"; 
48       } 
49   } 
50