Imported from skill-one/skills-sh-mirror (skills/enzed/r3f-skills/r3f-geometry/SKILL.md). Install upstream with npx skills add skill-one/skills-sh-mirror --skill r3f-geometry. Copyright stays with the author.

React Three Fiber geometry

Inspect installed Three.js, Fiber, and Drei versions before copying constructor arguments or helper props. Examples target Fiber 9 / React 19 and Three.js r185.

Choose the representation

• Use native JSX geometry for ordinary shapes. args match the Three.js constructor; changing them reconstructs geometry, so animate transforms rather than constructor inputs.
• Use BufferGeometry for custom topology and buffer-based points for large particle sets. Keep generated arrays stable and use deterministic generation when results must be reproducible.
• Use Drei Instances for convenient declarative instances with events. For large or frequently updated sets, read native instancing to avoid per-instance React overhead.
• Instancing shares geometry/material and reduces draw calls. Merely sharing a geometry among separate meshes does not batch their draws.
• Drei Merged creates instancing abstractions from meshes, not BufferGeometry objects; it does not concatenate arbitrary static geometry. For actual merging, inspect mergeGeometries from three/addons/utils/BufferGeometryUtils.js and ensure compatible attributes/indexing.

Declarative instances

Mount below Canvas with lighting. Each Instance belongs to its nearest Instances provider.

import { Instance, Instances } from '@react-three/drei'

export default function Example() {
  return (
    <Instances limit={3} range={3}>
      <boxGeometry args={[0.7, 0.7, 0.7]} />
      <meshStandardMaterial />
      <Instance position={[-1.2, 0, 0]} color="coral" />
      <Instance position={[0, 0, 0]} color="skyblue" />
      <Instance position={[1.2, 0, 0]} color="gold" />
    </Instances>
  )
}

Custom buffers and updates

• position and normal attributes usually have item size 3; UVs have item size 2. Construct JSX buffer attributes with args={[typedArray, itemSize]} and the correct attach, not just array/count props with no constructor arguments.
• Indices refer to vertices; winding determines the front face. Duplicate vertices at hard normals or UV seams. Indexed vertices share all attributes, not just positions.
• Lit geometry needs normals. Use computeVertexNormals() when appropriate; do not recompute every frame if a shader or analytic normals can express the deformation more cheaply.
• After CPU buffer writes, set attribute.needsUpdate = true. Choose dynamic usage before the first GPU upload when buffers will change often.
• Recompute bounding boxes/spheres after geometry changes that affect them. GPU vertex displacement does not update CPU bounds or raycasting automatically.
• UV selection is explicit on modern Three.js: texture.channel selects uv, uv1, uv2, or uv3. Do not unconditionally copy uv into uv2 for AO.
• Avoid rebuilding buffers for pointer movement. If topology is fixed, change attribute contents or uniforms instead.

Helpers and tradeoffs

• Drei Line supports useful line widths; native WebGL line width is limited by the platform. Check worldUnits when choosing screen-space versus world-space thickness.
• Use Drei Text for flat text and Text3D for extruded geometry. Current TextGeometry uses depth, not the historical height; verify the helper's installed types and font format.
• Use Edges for sharp-edge outlines, not as a replacement for screen-space selection effects.
• Bounds and Center change framing/transforms; decide whether they should update after asset loading, resizing, or interaction.
• Segment count should follow silhouette, deformation, and viewing distance. A “high quality” fixed count is not universally better.
• Declaratively created geometry can be owned by R3F. Shared or cached geometry needs a shared lifetime; do not dispose it from one instance while others remain mounted.

Verify

Check bounds/culling after updates, raycast hit positions, resource cleanup, and draw calls. Test at the intended object count; three instances do not establish performance at ten thousand.

Sources

• BufferGeometry, BufferAttribute, InstancedMesh.
• Drei Instances, Merged, Text3D.