Making Physics Work | VR Design

There Is No Good Physics Solution

Working within most game engines over the last 10 years, designing physics-focused games hasn't always been enjoyable. With VR as the new frontier of game development, it's more important than ever for physics to react in ways that we expect them to.

Introduction

This article outlines one of the approaches we took for our physical object setup in Deep Cuts VR. We'll discuss how we supported performant physical interactions with over 300 unique objects on the Meta Quest 3 headset.

Setting Up GameObjects Effectively

Creating GameObjects that align with an object-oriented programming (OOP) system of components is crucial. While Unity's component system might be familiar territory, it's worth revisiting the optimal setup:

• Parent GameObject: Serves as the root object.

• Child Components: Include colliders, meshes, particles, and other components.

This hierarchical structure ensures modularity and reusability, making your GameObjects more manageable and efficient.

Prioritizing Physical Calculations

The order and method of physical calculations can significantly impact both performance and user experience.

Use Primitive Colliders Over Convex Hulls

Primitive colliders like boxes, spheres, and capsules are computationally less intensive than convex mesh colliders. Even if they don't perfectly match the object's shape, they often provide a good enough approximation.

Humorous Insight: Approximately 98% of players, even in physics-focused games, won't notice the difference—according to my cat's meticulous research.

Prevent Colliders from Interacting Internally

An often overlooked step is ensuring all colliders within a GameObject ignore each other. This prevents unnecessary calculations and erratic behaviors caused by internal collisions.

Implementation Example:

using UnityEngine;

public class IgnoreInternalCollisions : MonoBehaviour
{
    void Start()
    {
        Collider[] colliders = GetComponentsInChildren<Collider>();
        for (int i = 0; i < colliders.Length; i++)
        {
            for (int j = i + 1; j < colliders.Length; j++)
            {
                Physics.IgnoreCollision(colliders[i], colliders[j]);
            }
        }
    }
}

By recursively applying Physics.IgnoreCollision, you ensure that all child colliders within the GameObject don't interfere with each other.

Embracing Real-World Physics Properties

Assign Realistic Mass Values

Setting realistic mass values for rigidbodies is essential. The mass should be relevant to the world scale, often using the player's mass as a baseline. This leads to more natural interactions and predictable physics behavior.

Utilize Unity's Physics Materials

Don't underestimate the power of Physics Materials. They allow you to fine-tune friction and bounciness, contributing to a more immersive and realistic experience.

• Dynamic Friction: Controls friction when objects are moving.

• Static Friction: Controls friction when objects are stationary.

• Bounciness: Determines how much an object will bounce after a collision.

Optimizing Rendering Performance

Performance isn't solely about physics calculations. Rendering efficiency plays a significant role, especially on resource-constrained devices like the Meta Quest 3.

Reduce Draw Calls

• Batching: Combine multiple meshes into a single mesh when possible.

• Texture Atlasing: Use a single texture for multiple objects to minimize material switches.

Leverage GPU Instancing

GPU instancing allows you to render multiple instances of the same mesh efficiently.

• Material Property Blocks: Use these to vary properties like color without breaking instancing.

• Unique Variations: Apply subtle differences to instances for uniqueness without additional performance costs.

Streamlining Team Workflows with Setup Tools

When collaborating with a team, efficiency is key. Creating setup tools can make object setup a one-click solution for teammates, ensuring consistency and saving time.

• Custom Editor Scripts: Automate repetitive tasks.

• Nested Prefabs: Utilize Unity's nested prefab workflow for modular and scalable project structures.

For more details, check out Unity's Official Documentation on Nested Prefabs.

Conclusion

Designing physics-focused VR games presents unique challenges. By structuring GameObjects effectively, optimizing physical calculations, and embracing real-world physics properties, you can create a performant and immersive experience. Additionally, optimizing rendering performance and streamlining workflows are crucial steps in delivering a high-quality game.