I have a simple open curve with depth - a simple tube.

I'm animating the tube to grow along the curve using the curve's Start & End Mapping parameters.

The default material is a diffuse black.

I'd like the active 'tip' of the curve to be a different emission material. Think of this like a reverse-fuse, where the emission end follows a set, short length of the 'lengthening' tube. In other words, the emission material follows the tip of the animated curve-end.

This video is a FAILED attempt. All I can do is possibly animate the Math node to limit the material-change to some cut-off point. But I'm looking for an automated way to define a set length of green that follows the end-point of the curve.

Lil help? Cheers.

<https://www.youtube.com/watch?v=d3G0ZMVPBHM>