Optimizing Collision Complexity for Large Environments

Learners will implement simplified collision geometry and complex-as-simple collision settings to reduce the computational overhead of high-poly static meshes.

In this lesson, you will learn how to drastically reduce physics-related CPU overhead by replacing high-polygon static mesh collisions with simplified geometry.

The Physics Performance Bottleneck

When you enable "Use Complex Collision as Simple" for a high-poly static mesh, the physics engine creates a triangle-mesh collider for every polygon in your model. In a large environment filled with detailed assets, this forces the CPU to perform raycasts and overlap checks against thousands of unnecessary triangles, leading to significant physics thread stutters.

Implementing Simplified Collision

To optimize, you should switch your collision strategy from per-poly calculation to primitive or convex hull approximations.

Decompose to Convex Hulls: Open your Static Mesh Editor and navigate to the Collision menu. Use the Auto Convex Collision tool. By adjusting the "Hull Count" and "Max Hull Verts," you can create a simplified, convex representation that wraps your mesh tightly without the overhead of thousands of triangles.
Use Simplified Proxy Meshes: For extremely complex objects, create a separate, low-poly mesh in your 3D software that mimics the silhouette of your asset. Import this as your custom collision mesh and set the Static Mesh's Collision Complexity setting to Use Simple Collision as Complex. This instructs the engine to ignore the high-poly geometry during physics calculations entirely.
The "Complex-as-Simple" Warning: Only use Use Complex Collision as Simple for specialized, static gameplay elements (like a terrain mesh that requires precise, non-convex interaction). For everything else, ensure your collision complexity is set to Project Default or Use Simple Collision As Complex.

Visualizing Your Work

Always toggle Show > Collision in your viewport to see exactly how your physics bodies look. If you see dense, overlapping wireframes, you are likely wasting CPU cycles. You want to see clean, sparse shapes that represent the object's general volume, not its surface detail.

Key Takeaway: Never use high-poly mesh geometry for physics; replace it with auto-generated convex hulls or low-poly proxy meshes to keep your physics simulation within the frame budget.