threejs-geometry

Create a THREE.BufferGeometry and set attributes with typed arrays: position (3 floats per vertex), normal, uv, and optionally color. Add an index buffer with setIndex to reuse vertices across triangles, then call computeVertexNormals if lighting is needed.

Use THREE.InstancedMesh with a shared geometry and material, setting per-instance transforms via setMatrixAt and optional per-instance colors with setColorAt. This renders all copies in one draw call instead of one per mesh.

BufferGeometry stores per-vertex attributes for a single mesh, while InstancedBufferGeometry adds per-instance attributes via InstancedBufferAttribute for custom shader data beyond transforms. Use InstancedMesh for standard cases and InstancedBufferGeometry when shaders need custom per-instance values.

Missing or incorrect normals cause lighting failures since materials like MeshStandardMaterial require them. Call geometry.computeVertexNormals() after modifying positions, and verify the normal attribute exists with 3 floats per vertex.

Merge static meshes with BufferGeometryUtils.mergeGeometries to reduce draw calls when objects share materials and never move independently. All merged geometries must have identical attribute sets, and you should dispose of unused source geometries afterward.