Hello everybody.

I'm trying to achieve a bullet trail effect similar to the one seen in Uncharted 4.
Specifically, the bullet smoke trail (not the tracer round).

You can see the effect on the attached files and here:

I don't know how they achieved it, but when people want thicker textured lines, sometimes they use long narrow quads.

Since the line gets distorted, imagine you had a collection of line-segments attached to vertices, with each segment actually being a thin quad.

As the wind blows on the bullet trail (or rather, as you randomly pertube the trail), you distort the line vertices in-equally, distorting the appearance trail. Further, you also fade out the quads to make the trail fade into non-existence, and don't forget the quads themselves can be animated (with subtle smoke animation).

It appears that they are just using a quad strip particle effect and allowing the vertices to drift - this could be achieved by simply generating a single strip to submit to the GPU and then sending a time variable to the vertex shader which then randomly drifts the vertices while fading out the alpha. The goal here is to have the strip facing the camera, which is pretty simple to do, it's virtually the same as having a billboard face the camera. The texture coordinates of the smoke trail could also be allowed to drift lengthwise down the strip at a decelerating speed whilst also spreading out across the width of the strip to create a more vivid dispersal effect.

I got an answer from the fx artist who created these trails in reddit. Here's the link https://www.reddit.com/r/Unity3D/comments/4w0p4t/how_would_you_achieve_these_bullet_trails_smoke/d64b1ma

He uses "ribbons", which looks like a simpler but more limited approach to what you said, @deftware.

Anyway, I like your idea. Do you happen to know about any example on how to do that on Unity?

I don't have any experience with Unity, I've always been a hardcore DIY type. I'm sure it can be pieced together pretty easily. The trick is treating the 'ribbon' (as it were) as just a line of points, ie: connect the dots, and generating the actual quad-strip vertices from those in screen-space. From there it's all about just how you animate the texture across that geometry, making it look like it's drifting down the strip and also drifting in the breeze by randomly pushing the points along the ribbon randomly and in accordance with an overall breeze velocity, I would imagine.