1 varying vec3 pt;

2

3 uniform sampler3D tex;

4 uniform float tmin;

5 uniform float tmax;

6 uniform vec3 res;

7

8 float transfer(float x, float tmin, float tmax)

9 {

10 float dt = 0.25 * (tmax - tmin);

11 return smoothstep(tmin - dt, tmin + dt, x) *

12 (1.0 - smoothstep(tmax - dt, tmax + dt, x));

13 }

14

15 vec3 calc_normal(vec3 p, float texel)

16 {

17 vec3 offs = 1.0 / res;

18

19 float dfdx = texture3D(tex, p + vec3(offs.x, 0.0, 0.0)).x - texel;

20 float dfdy = texture3D(tex, p + vec3(0.0, offs.y, 0.0)).x - texel;

21 float dfdz = texture3D(tex, p + vec3(0.0, 0.0, offs.z)).x - texel;

22

23 return -normalize(vec3(dfdx, dfdy, dfdz));

24 }

25

26 void main()

27 {

28 const vec3 ldir = vec3(-1.0, 1.0, 2.0);

29

30 if(max(pt.x, max(pt.y, pt.z)) > 1.0 || min(pt.x, min(pt.y, pt.z)) < 0.0)

31 discard;

32

33 float texel = texture3D(tex, pt).x;

34 float val = transfer(texel, tmin, tmax);

35

36 vec3 normal = gl_NormalMatrix * calc_normal(pt, texel);

37 float ndotl = max(dot(normalize(ldir), normal), 0.0);

38

39 gl_FragColor = vec4(ndotl, ndotl, ndotl, val);

40 }