Purpose: These are generalized optimization concepts designed to help you improve the performance of your VRChat worlds. By implementing these practices, you can free up system resources and allocate that performance budget to the visually engaging elements that enhance the user experience, or just overall providing a more performant user experience.
In Unity, almost everything you see or interact with in a scene is an object. Every one of these items is an instance of a GameObject.
A GameObject is essentially a fundamental building block. It holds a Transform component (which defines its position, rotation, and scale in the world) and is then given its specific behavior and functionality by attaching other Components to it.
This includes:
3D Models: Cubes, spheres, terrains, custom imported meshes, etc.
Lights: Directional lights, point lights, spot lights.
Cameras: The perspective through which the player sees the world.
Empty Containers: Used to organize other objects.
UI Elements: Buttons, text, images, and canvases.
When prototyping or outlining worlds, it's easy to build structures out of many separate GameObjects. It is crucial to be aware that every single GameObject consumes a portion of system resources, regardless of its state.
This cost applies even if the GameObject is:
Inactive (disabled).
Invisible (e.g., hidden behind walls or outside the view frustum).
Static or Animated.
While the cost of a single GameObject is usually minuscule, having hundreds or thousands can quickly contribute to overhead, impacting the overall CPU performance and memory usage of your world.
You will almost always gain a performance boost by merging multiple small, static GameObjects into one larger mesh. This optimization is primarily due to reducing the number of Draw Calls and simplifying lighting calculations.
When you have many separate GameObjects, the rendering engine must make a separate Draw Call for each object to tell the GPU what to render. Every draw call introduces overhead, straining the CPU.
By combining these objects into a single large mesh, the engine only needs one draw call to render the entire structure, significantly reducing the CPU load.
The performance boost from lighting comes from Batching. When objects are separate, the engine must perform intensive, per-object calculations for features like:
Shadow Mapping: Determining if and how each object casts or receives shadows.
Light Probes/Reflection Probes: Calculating how light interacts with the material of each individual object.
When objects are merged into one large mesh, these complex calculations are processed more consistently and efficiently across a single surface. This enables the engine to use efficient GPU batching methods, leading to smoother and faster rendering.
A common pitfall in Unity development is the performance impact caused by unnecessary data density in your assets. When downloading prefabs or Unity Asset Store models, it's easy to acquire assets with excessively high vertex counts and textures with resolutions well into the 4K range.
It is essential to manage the data density (vertex count and texture resolution) of your assets to be proportional to their significance in your project.
1. Model Resolution (Vertex Count)
Models are built from vertices (points) and planes (triangles). A model with thousands of vertices is known as a high-poly model and demands more resources from the CPU and GPU to process and render.
An object that will only be viewed from a distance does not need a high-poly count.
By reducing the mesh complexity (using a lower-poly version or LODs), you can save a significant portion of your rendering budget.
2. Texture Resolution
Texture resolution (e.g., 4K, 2K, 512x512) directly affects the amount of VRAM (Video RAM) required on the user's graphics card.
High-resolution (4K) textures should be reserved only for objects that are large, central, or viewed up close by the player.
For less important items, or those viewed far away (like background props), you can save a lot of performance budget by compressing or downscaling the texture resolution to a more reasonable level (e.g., 1K or 512x512).
By correctly balancing the detail of an asset with its importance in the scene, you ensure that you are spending your valuable performance budget where it will have the greatest visual impact.
When creating environments with many identical objects (like fence posts, pillars, rocks, or trees), using a single Prefab instance for all of them, instead of unique GameObjects, offers a substantial performance boost, primarily through Static Batching.
What is a Prefab?
A Prefab is a pre-configured template of a GameObject. Any changes made to the original Prefab asset are instantly reflected across all instances of that Prefab in your scene.
1. Enhanced Static Batching π¦
Static batching is Unity's process of combining geometry from multiple GameObjects into larger meshes at runtime. This drastically reduces the number of Draw Calls (which strains the CPU).
When to Batch: If many separate GameObjects use the exact same Mesh and Material and are marked as Static, Unity can efficiently group and render them together.
Prefab Advantage: Prefab instances inherently use the same Mesh and Material data. By creating your repeating objects from the same Prefab and marking them as Static, you maximize Unity's ability to perform static batching, leading to significant CPU savings.
2. Reduced Memory Footprint (RAM)
While each instance of a Prefab has its own position, rotation, and scale data (Transform), all instances share the same fundamental data, including:
Mesh Data: The geometry (vertices, triangles, etc.) is loaded into memory only once.
Material Data: The shaders and texture information are referenced, not duplicated.
This sharing ensures a much smaller overall memory footprint (RAM usage) compared to having numerous unique GameObjects, which might each inadvertently load unique copies of the same assets.
3. Faster Scene Loading and Editing
Since Prefabs are lightweight references to the master asset, scenes that use many Prefab instances generally load faster. Additionally, if you need to optimize the shared mesh or texture for a repeating element, you only have to make the change once in the master Prefab, and the fix immediately applies across the entire scene.
Managing how often your code executes is critical for performance. While Unity's built-in functions like Update() are convenient, relying on them too heavily can quickly and unnecessarily bog down the user's hardware.
Functions like Update() and FixedUpdate() cause your code to run every frame or every physics step, respectively. If you use these functions to check object states (a practice called polling), the hardware is constantly burdened with checks that often return the same result.
For important, central processes (like player movement or complex physics), using Update() may be necessary and acceptable. However, using it for routine state checks, such as:
Is the door open?
Is the player standing here?
Has the object's color changed?
...can severely degrade performance.
The key to a more performant user experience is to avoid polling and transition to event-driven programming.
While it can be more complex to catch every change only when it happens, this approach is vital for performance. Instead of checking a state every frame, the code only executes when a change occurs (an "event").
Example: Instead of checking in Update() if a button is pressed, the button script itself triggers a specific function only when the collision or interaction occurs. In VRChat a good example is the Interact() function available for colliders.
This design pattern ensures that functions are called only when they are needed, significantly reducing the computational load on the end-user's machine.