Static Mesh Combiner

Group scattered environment props by material and merge them into optimized 32-bit meshes in one click

Scattering thousands of trees, rocks, and grass tufts across a landscape can quickly tank game frame rates. Each individual object requires its own draw call (CPU-to-GPU render commands), leading to major CPU bottlenecks, even with GPU instancing.

The Static Mesh Combiner resolves this bottleneck. It groups scattered GameObjects by their shared materials, merges their geometries into single meshes, and configures them with optimized 32-bit index buffers. This can reduce hundreds of draw calls down to a single digit, significantly improving rendering performance.

Technical Mechanism

The mesh merging process uses Unity’s Mesh.CombineMeshes API with custom sub-mesh groupings:

Hierarchy Scan: The engine locates all MeshFilter and MeshRenderer components parented under the active scatter container.
Material Grouping: It builds a dictionary grouping all meshes by their assigned material: $\text{Material Group} = \{ \text{Mesh } A, \text{Mesh } B, \dots \} \quad \text{where } \text{Mat}_A = \text{Mat}_B$
Matrix Transformation: The vertex positions of each individual mesh are transformed from local space to the parent’s world space using their local-to-world transformation matrices.
32-Bit Index Buffer Allocation: By default, Unity meshes use 16-bit index buffers (limiting meshes to 65,535 vertices). The Static Mesh Combiner sets mesh.indexFormat = IndexFormat.UInt32 (32-bit buffers) when combining, allowing it to merge hundreds of thousands of vertices into a single combined mesh.
Collider Generation: The tool automatically combines collider geometries into a single compound mesh collider or retains box/sphere colliders in place for physics performance.

Editor Window Controls

Open the utility from the main window or via Tools → Decnet → Static Mesh Combiner. The GUI features a premium dark header with a sharp steel-grey/green accent.

Target Object: Assign the parent GameObject containing the scattered props you wish to merge (e.g. [Scatter] Forest_Floor).
Combine Settings:
- Generate Colliders: Automatically generates a single optimized mesh collider for the combined geometry.
- Deactivate Originals: Toggles whether to deactivate or completely destroy the original individual GameObjects after combining.
- Save Combined Meshes: If enabled, saves the newly baked .mesh assets to a Baked_Meshes folder in your project directory (necessary for creating prefabs or build staging).
Bake Meshes: Runs the combine operation. The original GameObjects are organized into a backup folder (or deleted), and the combined mesh is rendered in their place.
Undo Combine: Reverts the bake, restoring the individual GameObjects back to their active state with full transform data.

[Before: Individual GameObjects]      [After: Static Combined Mesh]
   Parent [Scatter]                      Parent [Scatter]
     ├── Tree_01 (Mesh + Material)          └── CombinedMesh_Grass (1 Draw Call)
     ├── Tree_02 (Mesh + Material)          └── CombinedMesh_Tree (1 Draw Call)
     └── Grass_01 (Mesh + Material)
     [Total Draw Calls: 300+]               [Total Draw Calls: 2]

Draw Call Reduction Metrics

In a typical scene containing 1,500 low-poly trees and rocks:

Metric	Before Combination	After Combination	Improvement
Draw Calls	$1,524$	$2$	$99.8\%$ Reduction
CPU Frame Time	$8.4\text{ms}$	$1.1\text{ms}$	$7.6\times$ Performance Boost
GPU Overdraw	High (overlapping draw order)	Low (optimized depth sort)	Smooth Frame Pacing

[!WARNING] Combined meshes cannot be individually moved or edited after baking. If you need to paint, erase, or rearrange objects, click Undo Combine (or restore from the backup folder), perform your edits, and then re-bake.

[!TIP] Combined meshes are fully compatible with Unity Occlusion Culling. For extremely large environments, partition your scatters into $50\text{m} \times 50\text{m}$ grid chunks and combine each chunk separately. This allows Unity to cull entire chunks when they are out of the camera’s viewport.