k3d/share/shaders/k3d_volcube.sl:6:   StepJitter          - 0-1 jitter the sample position.
k3d/share/shaders/k3d_volcube.sl:188:	     float  StepJitter     = 0;
k3d/share/shaders/k3d_volcube.sl:219:    float  jitter       = (random() - .5) * StepJitter;
