Hello, I'm trying to reproduce your method for billboarding trails, but I've some difficulties... You mentionned "Direction constants" :
plus a direction constant indicating left or right side of the strip
Assuming direction of the segment is UnitZ, and the normal of the segment UnitY : direction constants are UnitX for thie left side and -UnitX for the right part ? I mean, these two vectors point outside the segment. But the result is not correct.
Here is how I implemented your description :
but I am now crossing the segment axis with the direction from the segment to the camera