Mobile & WebGL Optimization Guide

Optimize scatter densities, enforce strict spacing rules, and structure LOD groups for mobile environments

Mobile devices and WebGL builds operate under tight hardware restrictions. High vertex counts, excessive draw calls, and uncompressed textures will cause memory crashes or overheat target devices. To achieve smooth $60\text{ FPS}$ on typical mobile hardware, environment assets must be carefully scattered and optimized.

1. Enforcing Spacing Rules & Clutter Clamping

Random clustering looks beautiful on high-end PCs, but on mobile, overlapping objects waste vertices and fill the screen with unnecessary overdraw.

  • Increase Spacing Limits: Open your ScatterProfile and increase the Minimum Spacing slider. For instance, grass should have a minimum spacing of $0.8\text{m} - 1.5\text{m}$ rather than $0.2\text{m}$.
  • Clamp Clutter Counts: Limit total instances inside your scatter area. In a mobile scene, keep the overall density under 1,500 objects per chunk.
  • Collision Avoidance: Keep Collision Avoidance checked on your profile so that shrubs, trees, and rocks never intersect each other or clip through static obstacles.

2. Prefab and LOD Group Setup

The scattering engine fully supports Unity’s LOD Group component:

  1. Ensure your environmental prefabs have an LODGroup component attached to the root.
  2. Configure three levels of detail:
    • LOD 0: High-detail mesh (only visible up close).
    • LOD 1: Mid-detail mesh with reduced vertex counts.
    • LOD 2 (or LOD 3): Low-detail proxy mesh or a cross-billboard card (visible from far away).
  3. The placement service (ScatterPlacementService.cs) automatically instantiates these LOD group prefabs, and Unity’s renderer handles culling and distance transitions.

3. Draw Call Optimization (Mobile Pipeline)

Even with GPU instancing enabled, mobile devices can bottleneck if they process too many separate draw calls.

  1. GPU Instancing: Ensure your environmental materials have the Enable GPU Instancing checkbox ticked in the inspector. This allows Unity to batch identical meshes.
  2. Combine Meshes: For non-instanced assets (or static background clusters), run the Static Mesh Combiner via Tools → Decnet → Static Mesh Combiner.
    • Group grass tufts and rocks into single combined meshes.
    • Disable/deactivate the original individual transforms to free up scene hierarchies.
    • This reduces CPU overhead by merging multiple draw calls into a single batch.

Mobile Workflow Checklist

When compiling environments for mobile, verify the following:

  • Target hardware in the Performance Budget System is set to Mobile.
  • No red budget alerts are active in your scatter windows.
  • Materials use mobile-optimized shaders (e.g. URP/Simple Lit or custom mobile shaders).
  • Overlap spheres are clear, with no clipping geometries.
  • Static Mesh Combiner has been run on all non-moving background objects.

[!WARNING] WebGL builds do not support dynamic multi-threaded physics raycasts natively in some browsers. If you are baking terrain candidates using Mesh Surface Sampler, perform the bake inside the Unity Editor before compiling the WebGL build. Do not run dynamic bakes at runtime.

[!TIP] Use flat unlit or vertex-lit shaders for grass and ground clutter. Lighting calculations on thousands of individual transparent leaf blades will bottleneck mobile fragment shaders, regardless of how optimized your geometry is.

This site uses Just the Docs, a documentation theme for Jekyll.