Reducing Draw Calls and Optimizing Assets in Three.js

Optimizing Three.js scenes is crucial for achieving smooth performance and a good user experience, especially with complex 3D models and environments. Key strategies involve reducing draw calls and efficiently managing assets.

Understanding Draw Calls

A draw call is a command sent from the CPU to the GPU to render objects. Each draw call incurs CPU overhead, so minimizing their number is crucial for performance, especially in complex scenes.

Techniques for Reducing Draw Calls

• InstancedMesh: Use THREE.InstancedMesh when you need to render a large number of objects that share the same geometry and material but have different positions, rotations, or scales. This allows the GPU to render all instances in a single draw call.
• Geometry Merging: For static objects that share the same material, you can merge their geometries into a single BufferGeometry. This combines multiple meshes into one, reducing the number of draw calls to just one for the merged object.
• Texture Atlases: Combine multiple smaller textures into a single, larger texture atlas. This reduces the number of texture swaps the GPU needs to perform.
• Points: For rendering a large number of small, simple elements like particles, consider using THREE.Points, which can render many points in a single draw call.

Techniques for Optimizing Assets

1. Geometry Optimization:

• Low-Poly Models: Design or acquire 3D models with the lowest possible polygon count.
• Decimation/Simplification: Use 3D modeling software to reduce the number of polygons.
• Draco Compression: For GLTF/GLB models, use Draco mesh compression to drastically reduce file sizes.

2. Texture Optimization:

• Appropriate Resolution: Use textures with resolutions appropriate for their on-screen size.
• Power of Two Dimensions: Textures with dimensions that are powers of two (e.g., 256x256) are generally more efficient.
• Compressed Textures: Utilize modern compressed texture formats like Basis Universal or KTX2 for smaller file sizes and faster GPU decoding.

3. Material Optimization:

• Simpler Materials: Choose the simplest material type that meets your visual requirements (e.g., MeshBasicMaterial over MeshStandardMaterial if advanced lighting is not needed).

Culling Techniques

Culling techniques prevent objects that are not visible from being rendered, saving GPU resources.

• Frustum Culling: Three.js automatically performs frustum culling, not rendering objects outside the camera's view.
• Level of Detail (LOD): Use THREE.LOD to render different versions of a model based on its distance from the camera. Distant objects can use lower-polygon models.

General Performance Tips

• Dispose of Unused Resources: Call dispose() on objects, geometries, materials, or textures when they are no longer needed to free up GPU memory.
• Avoid Object Creation in Render Loop: Do not create new Three.js objects (like Vector3) inside the render loop.
• Use BufferGeometry: Always prefer BufferGeometry over the older Geometry class for efficiency.