Low Poly Snow Shader
/With the environmental simulation getting near to finished it was time to start looking at how to visualize the weather. I'm using Tenkuko Dynamic Sky for my overall lighting and day/night cycle. It's not perfect, but makes my scenes look so much better than I could do on my own. It's worth every dollar.
Tenkuko does a great job for general lighting it also has functionality to support rain, snow, fog and clouds. The clouds aren't perfect and probably won't work for a low poly game. What Tenkuko doesn't have is snow accumulation. So I started doing a bit of research to find a solution.
Global Snow
I headed over to the Unity Asset store and picked up Global Snow. It's beautiful. Truly. It supports flat shaded snow as well as two other modes that produce more realistic snow. The asset doesn't require you to change shaders or materials, but simply adds a script to your camera.
I was seriously impressed. It took maybe 5-10 minutes of messing around with settings and I was pretty happy with how my scene looked. The bummer came when looking at the performance hit. Now a little performance hit is no big deal. The the snow scripts are not going to be used all the time. Plus the game is not an action game so a small frame rate drop is not a big deal. All the same I'm still aiming for 60+ fps on reasonable hardware.
Full disclosure, the scene I'm running this in is huge. The terrain is roughly 2 km square and its totally NOT optimized. Meshes are not joined and no occlusion culling is being used. Many of my trees have no LOD on top of all that. Unity says it's rendering 10+ million verts, so not a tiny scene. Still a 5-10 ms hit is a lot. Not a deal breaker, but enough to make me look for another solution. The last line in the profiler is a script I'm using to control my custom shader.
If I had a smaller scene or a simpler game I'd definitely look at Global Snow as a potential snow solution. I may give it another try once my scene is more optimized too.
Custom Shader
This is probably what I should have done first, but like a lot of us out there in game developer shaders scare me and seem like black magic. I watched a video or two and dusted off an old shader book I had. The result was the creation of a custom low poly (flat shaded) snow shader using Shader Forge to create the shader.
If you haven't seen Shader Forge it's worth a look. The interface is all visual/nodes but it compiles as a proper shader script. This means that shaders can be shared and run on computers that don't have Shader Forge. In theory this should also make the shader run more efficiently - not sure how it would compare to a carefully coded shader.
The snow shader has height dependent snow and frost (upper left nodes). The frost essentially eases or fades in/out the snow. The shader also has a snow coverage slider that allows a selection based on normals so that snow can be just on top all over or somewhere in between (middle nodes).
Producing the shader took me a handful of hours. Mostly because I'm totally new to shaders. But the result is pretty decent. Granted it's not a complex shader, but I'm still pretty happy with it. Below is a screenshot using my shader (same angle), compare it to the earlier screenshot using Global Snow.
Is mine better? No. No way. But it is a whole lot faster. I didn't get exact numbers but at most I saw 0.5 ms difference between my shader and the standard shader (I'm rendering 10+ million verts in a very un-optimized scene). I suspect that was just random fluctuations more than anything.
Some work on the "snow texture" to give a bit more depth and variety will make the two very comparable. Probably moving the snow color just a bit away from pure white will also help.
Tutorials
I'll probably make another post, but if you're interested to see what I've done or better yet try it out and tell me how to do it better. You can check out my YouTube series on the snow shader.
