Over the weekend, I was finally able to get ribbon trails into the game.

A ribbon trail is basically a bunch of axis-constrained billboards, so let’s start out with an axis-constrained billboard.

Nothing interesting here, we basically have a rectangle plane that’s being rotated along the blue vector.

When you put them side by side, there’s no problem. However if you start turning, there’s going to be problems because of gaps.

What we need to do is make intersecting edges match each other. This changes the the shape of the billboards into trapezoids.

How do we create the trapezoid? We’ll need to get the correct angle to generate the top point and the bottom point. We want to get a vector that is 90 degrees to this.

How do we get this green arrow? If you look closely the green vector is the average of the blue and red. So all we have to do is add the normalized vectors of blue and red, then normalize it.

Now to actually put this to use:

It’s a very good idea to draw the vectors to help with debugging. It’ll save you a lot of time if you don’t get it right the first time!

Now increase the update time from every 1 second to 0.1 seconds and add some fade.

Just play around with the texture, update speed, how many segments it should be, etc… and voilà, you got yourself your very own ribbon trail.