Welcome back followers of the fearsome!
This week I’ll talk about a cool little visual effect I put in the game: Light shafts. It’s a pretty standard visual effect, so it’s definitely nothing ground breaking, but it does make the game look that much better for very little effort. It was very quick to implement (read: a nice distraction from the monstrous networking task :) ), and I really like the effect.
A while back on our twitch stream I worked on implementing a compute shader to calculate proper volumetric fog, much like the amazing Assassins Creed volumetric fog. I abandoned this approach because it was actually pretty difficult to make it look good in a side scrolling brawler. It was hard to control the fog, created a ton of weird blend mode issues (especially with additive blending) and it also raised the minimum spec because of the compute shader.
Instead of proper volumetric lighting, I’ve opted for a manually placed animated light shafts. This gives us more control over the look, and it also works well in our existing chunk building system.
Last weekend I was playing through Brothers, a tale of two Sons (which is a gorgeous looking game by the way), and they use light shafts in multiple places to create a really cool atmosphere. I wondered how to implement these, as they fluctuate the light over time, yet are always smooth. This blog is about what I came up with.
The light shaft is rendered using alpha blending, using a user-defined color, and using a calculated alpha.
The geometry is 4 triangles, with coded UV’s. the U coordinate is used as the actual U coordinate in the noise texture, and the V coordinate is just used as an alpha multiplier.
The alpha is the product of the user-defined color’s alpha, the sample from the texture, the V coordinate (used as alpha multiplier), and the edge smoothing alpha. The edge smoothing is simply using the (0-1) U coordinate as a parameter for a sine function in the shader to generate a multiplier between 0 and 1 that nicely blends the edges to zero.
The texture coordinates used to render the light shaft is using a thin horizontal sliver of the texture (stretched over the mesh), and is animated over multiple frames to generate the modulation effect in the light shaft.
Here’s a video of the effect in the game:
That’s pretty much it! Simple, but effective. I love putting things like that in the game.
Oh, and as a reminder, we moved our weekly dev-stream to Friday, because Jesse is still in Japan.
Keep lighting those levels!
-Nick
Twitter: Nick: @nickwaanders Jesse: @jouste Caley: @caleycharchuk SlickEntertainment: @SlickEntInc
