In this lesson, you will learn how to refine your Physics Asset (PhAT) to ensure that your character physics remain performant even when you have many characters interacting in a single scene.
When you create a Physics Asset for a character, Unreal Engine generates collision primitives (spheres, capsules, or boxes) for every bone in your skeleton. While this provides high-fidelity physical reactions, calculating these collisions for dozens of NPCs simultaneously can quickly overwhelm the physics thread, leading to frame drops.
Simplify Your Collision Geometry
The most effective way to optimize is to reduce the "triangle count" of your physics bodies. Avoid using complex hulls when a simple shape will do.
- Merge Primitive Shapes: Instead of creating three separate spheres for a complex hand, replace them with a single, tighter capsule.
- Avoid Overlap: Ensure your collision primitives are not overlapping unnecessarily. Overlapping primitives force the physics solver to perform extra intersection tests every single frame.
Adjusting Physics Settings
You can also tweak the Physics Asset settings to reduce the calculation burden. Within the Physics Asset Editor, you can adjust the Collision Complexity. For characters, you should almost always use Simple Collision rather than Use Complex as Simple.
Furthermore, you can disable collision between specific bones within the Constraint settings to prevent the physics solver from wasting cycles calculating collisions between limbs that never touch, such as the upper arm and the opposite thigh.
Using Profile Instances
Instead of changing settings globally, use Physics Asset Profiles. This allows you to swap to a "Simplified" profile with fewer collision primitives or disabled physics bodies when the character is at a distance from the camera (LODs).
// Example: Conceptual logic for toggling a simpler physics profile
// based on distance or optimization state
void AMyCharacter::UpdatePhysicsOptimization(bool bIsFarAway)
{
if (bIsFarAway)
{
// Switch to a profile with fewer enabled constraints/bodies
GetMesh()->SetPhysicsAsset(LowDetailPhysicsAsset);
}
}
By balancing visual fidelity with geometric simplicity, you maintain a smooth, performant game.
Key Takeaway: Optimize your character physics by minimizing the number of primitive shapes, preventing unnecessary internal overlaps, and utilizing physics profiles to simplify collision geometry at a distance.