k3d/share/shaders/k3d_softboxes.sl:167:    varying float pDist = length(ppC - spw); /* in "world" coords */
k3d/share/shaders/k3d_softboxes.sl:168:    theDist = pDist;
k3d/share/shaders/k3d_softboxes.sl:170:    theColor = contrib * ct * boxColor / pow(pDist,decayExp);	/* premultiplied!!!!! */
