ExtrudeGeometry: extrudePath.closed is ignored when generating Frenet frames

[VISHNU7KASIREDDY]

Description

ExtrudeGeometry currently calls computeFrenetFrames(segments, false) with a hardcoded closed = false, even when the provided extrudePath has .closed === true.

When a closed spline is used as the extrudePath, the generated Frenet frames are computed as if the path were open. This produces a visible twist or discontinuity at the seam of the extruded geometry.

There is a TODO in the source about this behavior. The fix is to pass the curve's closed flag through to computeFrenetFrames so closed curves get closed Frenet frames.

Suggested minimal change:

Replace:
const frames = extrudePath.computeFrenetFrames( segments, false );

With:
const frames = extrudePath.computeFrenetFrames( segments, !!extrudePath.closed );

Reproduction steps

1. Create a closed CatmullRomCurve3 (or other closed curve) and set curve.closed = true.
2. Create a simple 2D Shape to extrude (e.g. a rectangle or small path).
3. Create an ExtrudeGeometry with the closed curve as extrudePath and a reasonably high steps (e.g. 100).
4. Render the geometry and inspect the seam where the path closes — you will see a twist or discontinuity in the surface normals/UVs that disappears when the Frenet frames are computed in closed mode.

Code

// Minimal reproducible example
const shape = new THREE.Shape();
shape.moveTo(0, 0);
shape.lineTo(1, 0);
shape.lineTo(1, 1);
shape.lineTo(0, 1);
shape.closePath();

const points = [
new THREE.Vector3(1, 0, 0),
new THREE.Vector3(0, 1, 0),
new THREE.Vector3(-1, 0, 0),
new THREE.Vector3(0, -1, 0)
];

const curve = new THREE.CatmullRomCurve3(points);
curve.closed = true; // important: mark curve closed

const extrudeSettings = {
steps: 100,
bevelEnabled: false,
extrudePath: curve
};

const geom = new THREE.ExtrudeGeometry(shape, extrudeSettings);
const mat = new THREE.MeshStandardMaterial({ color: 0x88ccff, side: THREE.DoubleSide });
const mesh = new THREE.Mesh(geom, mat);
scene.add(mesh);

Live example

(If possible, please add a live fiddle or codepen demonstrating the issue. Example template links from the project are below — you can fork one and paste your reproduction)

• [jsfiddle-latest-release WebGLRenderer] (use the project's template)
• [jsfiddle-dev WebGLRenderer] (use the project's template)
• [jsfiddle-latest-release WebGPURenderer] (optional)
• [jsfiddle-dev WebGPURenderer] (optional)

If you want, I can prepare a ready-to-paste jsfiddle snippet from the code above.

Screenshots

No response

Version

Observed on: r152 and main branch (tested locally as of 2025-11-25). (Please update this if you can reproduce on a different release. The bug is present in current main in my tests.)

Device

No response

Browser

No response

OS

No response

[Mugen87]

When a closed spline is used as the extrudePath, the generated Frenet frames are computed as if the path were open. This produces a visible twist or discontinuity at the seam of the extruded geometry.

Please demonstrate this with a live example so we can investigate this issue first.

[Mugen87]

Live example: https://jsfiddle.net/mtpqnz26/1/

The mentioned twist or discontinuity isn't visible to me. Do I overlook something?

[Mugen87]

When inspecting the wireframe of the object, it turns out you create a malformed geometry with many self-intersections. This is not the intended usage ExtrudeGeometry.

I suggest you use a closed path like in https://threejs.org/examples/webgl_geometry_extrude_shapes. This example uses a closed spline which produces longer, tube-like shape. Even in this example the mentioned twist or discontinuity isn't visible as well. The wireframe looks also as expected.