Performance optimization is where your game starts to feel real. Occlusion culling is one of Unity’s cleaner, easiest wins when you want to cut down what the engine renders — and boost FPS.
TL;DR
Occlusion culling hides objects that are completely behind other objects, so they don’t get rendered.
It’s most effective when used with static geometry (walls, buildings, terrain).
You bake occlusion data in Unity’s editor, then enable culling on the camera.
It reduces draw calls and overdraw, which makes rendering cheaper.
But it uses memory and CPU, so don’t assume it’s always “free.”
How It Works
1. Mark Static Geometry
Tag objects (like buildings, rocks, walls) as Static so they participate in occlusion.
2. Bake Occlusion
Open the Occlusion Culling window in Unity.
Adjust parameters like cell size and hole size.
Click “Bake” — this creates visibility data.
3. Enable It on the Camera
Select your main camera.
Turn on “Occlusion Culling” so the camera uses the baked data.
You can visualize culling in the editor to see what’s getting hidden.
Less Overdraw: The GPU doesn’t waste time drawing objects behind others.
Better for Constrained Hardware: On mobile or weaker GPUs, culling gives you real breathing room.
Optimized For Structure: Works really well in scenes with well-defined rooms, architecture, or “chunks” of geometry.
When to Be Careful
Memory Use: The baked occlusion data takes up RAM. If your scene is massive, this can bite back.
CPU Load: Checking what’s occluded at runtime costs CPU cycles.
Dynamic Objects: Things that move a lot don’t occlude as well, so gains may be limited.
Baking Time: If you constantly change static geometry, re-baking can slow down your iteration.
Best Practices
Only run a bake after your static geometry is mostly locked.
Use small cell size for more precision but more memory, larger cell size for speed.
Use occlusion only where it’s clearly beneficial — don’t force it everywhere.
Combine it with other optimizations: LOD, batching, culling, etc.
Conclusion
Occlusion culling is a great performance tool in Unity. When you use it on the right types of scenes, it helps your game run smoother by cutting down on what the GPU even thinks about rendering. But like any optimization, it has trade-offs. Use it smartly, test it, and tune it to your game’s needs.
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