k3d/share/shaders/k3d_smoke.sl:33: * with the "__foglight" parameter.  
k3d/share/shaders/k3d_smoke.sl:45:    lightsource("__foglight", foglight);
k3d/share/shaders/k3d_uberlight.sl:168: *   __foglight - the "noisysmoke" shader distributed with BMRT will add
k3d/share/shaders/k3d_uberlight.sl:405:		     output float __foglight = 1;)
