Creating a Dynamic Sky in Unity

The sky is an important character in Eastshade. In addition to taking up a large portion of the screen at any given moment, it also gives players the sense that the game world has its own beating heart. While I knew I wanted to make the sky spectacular and dynamic, I also didn’t want to spend tons of performance or development time on it. While something like dynamic volumetric clouds can look absolutely awesome and convincing, they are out of my comfort zone technically and are very expensive to render at high enough detail to look realistic. After all, Eastshade is not an airplane simulator! So I opted for a solution with simple parts that I could hone easily with my artist’s eye, rather than a more procedural approach.

The Day Cycle Manager

Firstly, I knew there were going to be a bunch of values to tweak for each distinct time of day, so I wanted one central place to save/load and tweak them all. Since the sky setup is made of quite a few parts and shaders, I was led to create what I call the “DayCycler” component, which looks like this:

This custom inspector may look formidable with its many fields and values, but it’s really just a bunch of references to material values, light values, and rotations pertinent to the global lighting. Inside this component is a simple update loop which interpolates between the most recent and incoming time of day presets. With this simple system, I can go through and tweak each distinct time of day like a painter, and all the in-between times are taken care of for me. No need to manage 20 different IPO curves. The times are 0-1 rather than 24:00 so don’t be confused by times like 0.175 (that would be something like 4:12 AM). There are a lot of things in the world that look at the time of day which are more local, such as a a hanging lantern, or chirping birds. Little lights and audio sources like these drift in and out of memory as the world streams around the player.

Sky Composition

The “sky” is composed of a few different elements:

Fog – Starting with the closest and moving out, we have the all-important fog. I use the fantastic Fog Volume for this. The reason I love fog volume is because of its gorgeous and fairly cheap light in-scattering.

Clouds – Call me old fashioned, but I like the look of photo clouds. My strategy was simply to take photos on a day that the clouds didn’t have a strong sense of light direction, combined with touching up the parts that look too directional. Once I had my 360 degree cloud panorama, I made an alpha mask cutting out the blue parts because I wanted to encapsulate the clouds separate from the atmosphere.

Atmosphere – I find a simple 2-value gradient shader on a dome mesh is sufficient for the atmosphere. The opacity and colors animate with the day cycle.

Sun – I have a sun flare, and an actual sphere mesh with a highly emissive solid color.

Moon – I designed a custom shader for the moon.

Space– The furthest background is the space dome. This dome has a tiling star texture, supplemented with bits of geometry for the larger stars to break up the tiling.

Finally, its important to note that all these things follow the player around as they move.

Not Done!

I’m not done with the sky systems in Eastshade. There are a few things left to do. Among them is come up with some sort of overhead cloud coverage to pass over the player.