Optimizing Complex Collision and Physics Calculations

In this lesson, you will learn how to identify and replace high-cost collision geometry to minimize Game Thread overhead during movement and physics simulation.

As your world grows in complexity, the Game Thread often hits bottlenecks because the physics engine must perform intersection tests between moving actors and the environment. If your collision meshes are overly detailed (using high-poly Complex Collision rather than Simple Collision), the engine spends precious milliseconds performing "per-poly" intersection math that could be handled by a primitive volume.

Identifying the Bottleneck

First, use the console command p.VisualizeLevelCollision to see exactly what the physics engine is "seeing." If you see dense wireframes around static objects, you are likely hitting the CPU with complex collision. You can confirm this overhead by checking the STAT PHYSICS command; if the Total Body Instances or Scene Complexity numbers are high, your collision setup is too heavy for real-time simulation.

Simplifying the Geometry

The most efficient optimization is to move away from Use Complex Collision as Simple. Instead, generate collision primitives in the Static Mesh Editor using the "Collision" menu.

1. Use Primitive Shapes: Replace complex shapes with a combination of Box, Sphere, or Capsule primitives. A single Convex Hull is significantly cheaper than a 500-poly collision mesh.
2. Simplified Convex Hulls: If you need a custom shape, use the "Auto Convex Collision" tool. Adjust the Hull Count and Max Hull Verts to balance accuracy against performance.
3. Collision Complexity Settings: Ensure your static meshes are set to Use Simple Collision As Complex whenever possible. This tells the engine to ignore the high-poly render mesh for physics traces, using your lightweight primitive collision instead.

Example Configuration

If you find an actor causing a frame-time spike, check its Collision Complexity setting in the Details panel:

// Ensure this is set to avoid high-poly trace overhead
Collision Complexity: Simple And Complex (or Simple Use As Complex)

By substituting expensive polygon-based collision with simplified volumes, you drastically reduce the number of calculations the physics engine must perform, keeping the Game Thread free for critical gameplay logic.

Key Takeaway: Prioritize simple primitive shapes over complex collision meshes to reduce CPU overhead and maintain stable performance during movement and physics simulation.