1 #define NBALLS 3

2

3 uniform float energy[NBALLS];

4 uniform vec3 pos[NBALLS];

5

6 float eval(vec3 p)

7 {

8 float val = 0.0;

9

10 for(int i=0; i<NBALLS; i++) {

11 vec3 dif = p - pos[i];

12 float len_sq = dot(dif, dif);

13 val += 0.1 * energy[i] / len_sq;

14 }

15 return val;

16 }

17

18 #define OFFS 0.01

19

20 void main()

21 {

22 vec3 pos = gl_TexCoord[0].xyz * 2.0 - 1.0;

23

24 float val = eval(pos);

25

26 vec3 grad;

27 grad.x = eval(pos + vec3(OFFS, 0.0, 0.0)) - eval(pos - vec3(OFFS, 0.0, 0.0));

28 grad.y = eval(pos + vec3(0.0, OFFS, 0.0)) - eval(pos - vec3(0.0, OFFS, 0.0));

29 grad.z = eval(pos + vec3(0.0, 0.0, OFFS)) - eval(pos - vec3(0.0, 0.0, OFFS));

30

31 gl_FragColor = vec4(grad, val);

32 }