Hello, I'm trying to reproduce your method for billboarding trails, but I've some difficulties... You mentionned "Direction constants" :
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 :
Vector3 dir = Vector3.Normalize(cameraPosition - Position);
Vector3 dir2 = Vector3.Normalize(Vector3.Cross(dir, Direction)); //Direction = UnitZ
Vector3 final = Position + dir2 * OutSideDir; //UnitX
and then multiply by ViewProj matrix
Thank you for your help