name: r3f-geometry
description: BufferGeometry creation, built-in geometries, custom geometry with buffer attributes, instanced meshes for rendering thousands of objects, and geometry manipulation. Use when creating custom shapes, optimizing with instancing, or working with vertex data directly.

R3F Geometry

Geometry defines the shape of 3D objects via vertices, faces, normals, and UVs stored in buffer attributes.

Quick Start

// Built-in geometry
<mesh>
  <boxGeometry args={[1, 1, 1]} />
  <meshStandardMaterial />
</mesh>

// Custom geometry
<mesh>
  <bufferGeometry>
    <bufferAttribute
      attach="attributes-position"
      count={3}
      array={new Float32Array([0, 0, 0, 1, 0, 0, 0.5, 1, 0])}
      itemSize={3}
    />
  </bufferGeometry>
  <meshBasicMaterial side={THREE.DoubleSide} />
</mesh>

Built-in Geometries

All geometries accept args array matching constructor parameters:

// Box: [width, height, depth, widthSegments?, heightSegments?, depthSegments?]
<boxGeometry args={[1, 2, 1, 1, 2, 1]} />

// Sphere: [radius, widthSegments, heightSegments, phiStart?, phiLength?, thetaStart?, thetaLength?]
<sphereGeometry args={[1, 32, 32]} />

// Plane: [width, height, widthSegments?, heightSegments?]
<planeGeometry args={[10, 10, 10, 10]} />

// Cylinder: [radiusTop, radiusBottom, height, radialSegments?, heightSegments?, openEnded?]
<cylinderGeometry args={[0.5, 0.5, 2, 32]} />

// Cone: [radius, height, radialSegments?, heightSegments?, openEnded?]
<coneGeometry args={[1, 2, 32]} />

// Torus: [radius, tube, radialSegments, tubularSegments, arc?]
<torusGeometry args={[1, 0.3, 16, 100]} />

// TorusKnot: [radius, tube, tubularSegments, radialSegments, p?, q?]
<torusKnotGeometry args={[1, 0.3, 100, 16]} />

// Ring: [innerRadius, outerRadius, thetaSegments?, phiSegments?]
<ringGeometry args={[0.5, 1, 32]} />

// Circle: [radius, segments?, thetaStart?, thetaLength?]
<circleGeometry args={[1, 32]} />

// Dodecahedron/Icosahedron/Octahedron/Tetrahedron: [radius, detail?]
<icosahedronGeometry args={[1, 0]} />

Buffer Attributes

Geometry data lives in typed arrays attached as attributes:

Custom Geometry from Scratch

import { useMemo } from 'react';
import * as THREE from 'three';

function Triangle() {
  const geometry = useMemo(() => {
    const geo = new THREE.BufferGeometry();

    // 3 vertices × 3 components (x, y, z)
    const positions = new Float32Array([
      -1, -1, 0,  // vertex 0
       1, -1, 0,  // vertex 1
       0,  1, 0   // vertex 2
    ]);

    // 3 vertices × 3 components (nx, ny, nz)
    const normals = new Float32Array([
      0, 0, 1,
      0, 0, 1,
      0, 0, 1
    ]);

    // 3 vertices × 2 components (u, v)
    const uvs = new Float32Array([
      0, 0,
      1, 0,
      0.5, 1
    ]);

    geo.setAttribute('position', new THREE.BufferAttribute(positions, 3));
    geo.setAttribute('normal', new THREE.BufferAttribute(normals, 3));
    geo.setAttribute('uv', new THREE.BufferAttribute(uvs, 2));

    return geo;
  }, []);

  return (
    <mesh geometry={geometry}>
      <meshStandardMaterial side={THREE.DoubleSide} />
    </mesh>
  );
}

Declarative Buffer Attributes

function Triangle() {
  const positions = useMemo(() => 
    new Float32Array([-1, -1, 0, 1, -1, 0, 0, 1, 0]), 
  []);

  return (
    <mesh>
      <bufferGeometry>
        <bufferAttribute
          attach="attributes-position"
          count={3}
          array={positions}
          itemSize={3}
        />
      </bufferGeometry>
      <meshBasicMaterial side={THREE.DoubleSide} />
    </mesh>
  );
}

Indexed Geometry

Use indices to share vertices between triangles:

function Quad() {
  const geometry = useMemo(() => {
    const geo = new THREE.BufferGeometry();

    // 4 unique vertices
    const positions = new Float32Array([
      -1, -1, 0,  // 0: bottom-left
       1, -1, 0,  // 1: bottom-right
       1,  1, 0,  // 2: top-right
      -1,  1, 0   // 3: top-left
    ]);

    // 2 triangles, 6 indices
    const indices = new Uint16Array([
      0, 1, 2,  // first triangle
      0, 2, 3   // second triangle
    ]);

    geo.setAttribute('position', new THREE.BufferAttribute(positions, 3));
    geo.setIndex(new THREE.BufferAttribute(indices, 1));
    geo.computeVertexNormals();

    return geo;
  }, []);

  return (
    <mesh geometry={geometry}>
      <meshStandardMaterial side={THREE.DoubleSide} />
    </mesh>
  );
}

Dynamic Geometry Updates

import { useRef } from 'react';
import { useFrame } from '@react-three/fiber';
import * as THREE from 'three';

function WavingPlane() {
  const geometryRef = useRef<THREE.BufferGeometry>(null!);

  useFrame(({ clock }) => {
    const positions = geometryRef.current.attributes.position;
    const time = clock.elapsedTime;

    for (let i = 0; i < positions.count; i++) {
      const x = positions.getX(i);
      const y = positions.getY(i);
      const z = Math.sin(x * 2 + time) * Math.cos(y * 2 + time) * 0.5;
      positions.setZ(i, z);
    }

    positions.needsUpdate = true;  // Critical!
    geometryRef.current.computeVertexNormals();
  });

  return (
    <mesh rotation={[-Math.PI / 2, 0, 0]}>
      <planeGeometry ref={geometryRef} args={[10, 10, 50, 50]} />
      <meshStandardMaterial color="royalblue" side={THREE.DoubleSide} />
    </mesh>
  );
}

Instanced Mesh

Render thousands of identical meshes with different transforms in a single draw call:

import { useRef, useMemo } from 'react';
import { useFrame } from '@react-three/fiber';
import * as THREE from 'three';

function Particles({ count = 1000 }) {
  const meshRef = useRef<THREE.InstancedMesh>(null!);

  // Pre-allocate transformation objects
  const dummy = useMemo(() => new THREE.Object3D(), []);

  // Initialize instance matrices
  useEffect(() => {
    for (let i = 0; i < count; i++) {
      dummy.position.set(
        (Math.random() - 0.5) * 10,
        (Math.random() - 0.5) * 10,
        (Math.random() - 0.5) * 10
      );
      dummy.rotation.set(
        Math.random() * Math.PI,
        Math.random() * Math.PI,
        0
      );
      dummy.scale.setScalar(0.1 + Math.random() * 0.2);
      dummy.updateMatrix();
      meshRef.current.setMatrixAt(i, dummy.matrix);
    }
    meshRef.current.instanceMatrix.needsUpdate = true;
  }, [count, dummy]);

  // Animate instances
  useFrame(({ clock }) => {
    for (let i = 0; i < count; i++) {
      meshRef.current.getMatrixAt(i, dummy.matrix);
      dummy.matrix.decompose(dummy.position, dummy.quaternion, dummy.scale);

      dummy.rotation.x += 0.01;
      dummy.rotation.y += 0.01;

      dummy.updateMatrix();
      meshRef.current.setMatrixAt(i, dummy.matrix);
    }
    meshRef.current.instanceMatrix.needsUpdate = true;
  });

  return (
    <instancedMesh ref={meshRef} args={[undefined, undefined, count]}>
      <boxGeometry args={[1, 1, 1]} />
      <meshStandardMaterial color="hotpink" />
    </instancedMesh>
  );
}

Instance Colors

function ColoredInstances({ count = 1000 }) {
  const meshRef = useRef<THREE.InstancedMesh>(null!);

  useEffect(() => {
    const color = new THREE.Color();

    for (let i = 0; i < count; i++) {
      color.setHSL(i / count, 1, 0.5);
      meshRef.current.setColorAt(i, color);
    }

    meshRef.current.instanceColor!.needsUpdate = true;
  }, [count]);

  return (
    <instancedMesh ref={meshRef} args={[undefined, undefined, count]}>
      <sphereGeometry args={[0.1, 16, 16]} />
      <meshStandardMaterial />
    </instancedMesh>
  );
}

Instance Attributes (Custom Data)

function CustomInstanceData({ count = 1000 }) {
  const meshRef = useRef<THREE.InstancedMesh>(null!);

  // Custom per-instance data
  const speeds = useMemo(() => {
    const arr = new Float32Array(count);
    for (let i = 0; i < count; i++) {
      arr[i] = 0.5 + Math.random();
    }
    return arr;
  }, [count]);

  useEffect(() => {
    // Attach as instanced buffer attribute
    meshRef.current.geometry.setAttribute(
      'aSpeed',
      new THREE.InstancedBufferAttribute(speeds, 1)
    );
  }, [speeds]);

  return (
    <instancedMesh ref={meshRef} args={[undefined, undefined, count]}>
      <boxGeometry />
      <shaderMaterial
        vertexShader={`
          attribute float aSpeed;
          varying float vSpeed;
          void main() {
            vSpeed = aSpeed;
            gl_Position = projectionMatrix * modelViewMatrix * instanceMatrix * vec4(position, 1.0);
          }
        `}
        fragmentShader={`
          varying float vSpeed;
          void main() {
            gl_FragColor = vec4(vSpeed, 0.5, 1.0 - vSpeed, 1.0);
          }
        `}
      />
    </instancedMesh>
  );
}

Geometry Utilities

Compute Normals

const geometry = useMemo(() => {
  const geo = new THREE.BufferGeometry();
  // ... set positions
  geo.computeVertexNormals();  // Auto-calculate smooth normals
  return geo;
}, []);

Compute Bounding Box/Sphere

useEffect(() => {
  geometry.computeBoundingBox();
  geometry.computeBoundingSphere();

  console.log(geometry.boundingBox);    // THREE.Box3
  console.log(geometry.boundingSphere); // THREE.Sphere
}, [geometry]);

Center Geometry

const geometry = useMemo(() => {
  const geo = new THREE.BoxGeometry(2, 3, 1);
  geo.center();  // Move to origin
  return geo;
}, []);

Merge Geometries

import { mergeGeometries } from 'three/examples/jsm/utils/BufferGeometryUtils';

const merged = useMemo(() => {
  const box = new THREE.BoxGeometry(1, 1, 1);
  const sphere = new THREE.SphereGeometry(0.5, 16, 16);
  sphere.translate(0, 1, 0);

  return mergeGeometries([box, sphere]);
}, []);

Performance Tips

Disposal

useEffect(() => {
  return () => {
    geometry.dispose();  // Clean up GPU memory
  };
}, [geometry]);

File Structure

r3f-geometry/
├── SKILL.md
├── references/
│   ├── buffer-attributes.md   # Deep-dive on attribute types
│   ├── instancing-patterns.md # Advanced instancing
│   └── procedural-shapes.md   # Algorithmic geometry
└── scripts/
    ├── procedural/
    │   ├── grid.ts            # Grid mesh generator
    │   ├── terrain.ts         # Heightmap terrain
    │   └── tube.ts            # Custom tube geometry
    └── utils/
        ├── geometry-utils.ts  # Merge, center, clone
        └── instancing.ts      # Instance helpers

Reference

• references/buffer-attributes.md — All attribute types and usage
• references/instancing-patterns.md — Advanced instancing techniques
• references/procedural-shapes.md — Generating geometry algorithmically