k3d/share/shaders/k3d_windowlight.sl:42:  uniform vector inv, right, upv;
k3d/share/shaders/k3d_windowlight.sl:51:  upv = normalize(inv ^ right);
k3d/share/shaders/k3d_windowlight.sl:52:  right = upv ^ inv;
k3d/share/shaders/k3d_windowlight.sl:60:    offset = (PL - center).upv + paneheight * (vpanes / 2);
