I have a requirement
It is to write an animation that emits light beams from a light source similar to a flashlight

My idea is that the light source and the starting point of the light column are at the same position, and the light emission is only the scale in the z direction of the light column

Pictured!

But during actual operation, I found out. . The magnification in THREEJS is to magnify in all directions relative to its own center (if the z direction is stretched, it will also be stretched on both sides) instead of fixing one side and only magnifying in one direction as I thought. . . This also resulted in my simple need. . . Troublesome to implement

Please answer your questions. . . How to change it so that the cone can only be enlarged in one direction of Z. . .