Ray marching Volume

[Lutojar]

I trying make ray-marching volume shader in VEX. I want use it to create Volume Light Effect as i use in RenderMan in Maya.

I take simple example of RSL code without any patterns

volume smoke (

float density = 60;

float integstart = 0, integend = 1000;

float stepsize = 0.1;

float debug = 0;

color scatter = 1;   /* for sky, try (1, 2.25, 21) */

float lightscale = 15;

)

{
point Worigin = P - I;
vector incident = vtransform ("shader", I);
point origin = transform ("shader", Worigin);
vector IN, WIN;
float tau;
color Cv = 0, Ov = 0;		   /* net color & opacity of volume */
color dC, dO;				   /* differential color & opacity */
float ss, dtau, last_dtau;
color li, last_li, lighttau;
color scat;
point PP, PW;
float f, i;

  float end = min (length (incident), integend) - 0.0001;

  /* Integrate forwards from the start point */
float d = integstart + random()*stepsize;
 if (d < end) {
	IN = normalize (incident);
	WIN = vtransform ("shader", "current", IN);
	dtau = 0;
	li = 0;
	ss = min (stepsize, end-d);
	d += ss;

	  while (d <= end) {
		 PP = origin + d*IN; 
		 PW = Worigin + d*WIN;
		 last_dtau = dtau;
		 last_li = li;

		 li = 0;
		 illuminance (PW, vector(0,0,1), PI) { li += Cl; }

		 dtau = density;

		  /* Our goal now is to find dC and dO, the color and opacity
		  * of the portion of the volume covered by this step.
		 */

		 tau = .5 * ss * (dtau + last_dtau);
		 lighttau = .5 * ss * (li*dtau + last_li*last_dtau);

		 scat = -tau * scatter;
		 dO = 1 - color (exp(comp(scat,0)), exp(comp(scat,1)), exp(comp(scat,2)));
		 dC = lighttau * dO;

		  /* Now we adjust Cv/Ov to account for dC and dO */
		  Cv += (1-Ov)*dC;
		  Ov += (1-Ov)*dO;

		  ss = max (min (ss, end-d), 0.005);
		  d += ss;
	 }
 }

  Ci = lightscale*Cv + (1-Ov)*Ci;
  Oi = Ov + (1-Ov)*Oi;

}

I make It in VEX builder and assign to Fog Object (as usual for volume shaders)

but it is no effect there

Does anybody can show me example of Ray Marchin Volume shader for Mantra?

my scene:

Volume_RayMarching.zip

[poltergeist]

http://forums.odforce.net/index.php?showtopic=3865