Farsight - Rain on the Player's Glasses

The same shot with the lens pass off on the left and on on the right — Lens pass off on the left, on on the right.

The goal

In Farsight you're wearing glasses, and it rains a lot. We wanted the rain to actually collect on your glasses when you're outside, as a small touch that makes you feel like you're there.

Since the drops are right in front of your eyes, they should be blurry and warp what's behind them. And they should react to you: building up when you're out in the open, drying once you head inside, and staying off while your umbrella's up.

How it works

It's a single full-screen pass on the player camera. No textures, no particles. It runs before post-processing, so bloom and grading hit the drops the same way they hit everything else. There are three parts to it: where the drops go, what each drop looks like, and how wet your glasses are.

1. Placing the drops

The screen gets split into a grid, and each cell turns its position into a random number. That number picks whether there's a drop in the cell, how big it is and where it sits. Drops always stay inside their cell, so none of them get cut off at the edges.

Screen divided into cells, each shaded by its random value

A random value per cell, then one drop per cell. These show the layout only.

Three grids are stacked on top of each other for big, medium and small drops. The edge blur is the same width no matter how big the drop is, so the small ones are basically all blur. They end up as faint smudges, which is pretty much what tiny droplets look like on real glasses.

Large, medium and small drop layers on a game frame, then combined — Large, medium and small layers on a frame from the game, then all three together.

2. Drawing a drop

Each drop works like a tiny lens. Inside it, we sample the image from a point pushed away from the drop's centre, which flips and bends whatever's behind it.

Checker pattern before and after one drop's refraction

Blurring every drop separately would be expensive, so instead we make two blurry copies of the whole frame first, at a quarter and a sixteenth of the resolution. The drops sample from those, so they're always soft and it's basically free.

The two blurred copies, then a game frame before and after the pass.

3. How wet the glasses are

Everything runs off one wetness value between 0 and 1. Each drop has its own threshold, so as it goes up, drops pop in and grow one at a time, and as it goes down they shrink away again.

Drops appearing on a game frame as wetness rises, then drying away

float size = lerp(0.14, 0.4, r2.x * r2.y)
           * saturate((cover - h * 0.95) * 5.0);

A small C# script sets that value based on what you're doing. Outside, your glasses get fully wet in about 25 seconds, and they dry in about 8 once you're indoors. Looking up at the sky gets them wet twice as fast, and looking down slows it right down. The umbrella keeps them dry, until you look up past 35 degrees. Past 60 it doesn't help at all.

Rain beads on the lenses, the umbrella opens and the lenses dry — Drops build up, the umbrella opens, and the glasses clear.

The images on this page were rendered with a Python port of the shader, run on frames from the game.