In this lesson, you will learn how to define the physical boundaries of your character using primitive collision shapes within a Physics Asset to ensure accurate interactions with the world.
The Physics Asset: Your Character’s "Physical Shell"
While your Skeletal Mesh handles visual movement, the Physics Asset (PhAT) acts as the "hollow" physical shell that the game engine uses for ragdolls, hit detection, and physical collisions. Without these shapes, your character would simply pass through walls or ignore projectiles.
Choosing the Right Primitive
When you open your Physics Asset, you define your character's boundaries using three basic shapes: Spheres, Capsules, and Boxes.
- Capsules: These are the gold standard for limbs (arms and legs) because they provide smooth, organic collision that handles sliding and limb movement well.
- Spheres: Best for joints like shoulders, elbows, or knees where you need a flexible pivot point that doesn’t clip through the mesh during heavy rotation.
- Boxes: Ideal for flat, static surfaces like a torso or a character's backpack, where you need a predictable, rigid edge.
Managing Bodies in the PhAT Editor
To manage these, you select a bone in the hierarchy, right-click, and choose Add or Replace Bodies. Once a shape is created, you use the standard transformation tools (W, E, R) to fit the primitive to the mesh.
Pro-Tip for Beginners: Do not try to make the collision shapes perfectly match the visual mesh. If you make them too complex (like adding too many small boxes to fingers), your character’s physics will jitter or cause performance drops. Instead, focus on a "tight but simple" fit. Think of it as wrapping your character in a simplified mannequin suit.
Once your primitives are placed, always verify the collision by dragging your mesh into a level and checking the "Collision" view mode (Alt+C). If the character falls correctly or blocks an incoming projectile, your physical shell is successfully configured.
Key Takeaway: Use the simplest primitives possible—Capsules and Spheres—to create a "shrink-wrapped" physical shell around your character’s bones, balancing collision accuracy with engine performance.