How do I construct a hollow cylinder in Three.js

Question

I'm having difficulties constructing a hollow cylinder in Three.js.

Should I go and construct it using CSG or by stitching the vertices together?

Answer 1

var extrudeSettings = {
    amount : 2,
    steps : 1,
    bevelEnabled: false,
    curveSegments: 8
};

var arcShape = new THREE.Shape();
arcShape.absarc(0, 0, 1, 0, Math.PI * 2, 0, false);

var holePath = new THREE.Path();
holePath.absarc(0, 0, 0.8, 0, Math.PI * 2, true);
arcShape.holes.push(holePath);

var geometry = new THREE.ExtrudeGeometry(arcShape, extrudeSettings);

Answer 2

This solution uses ChandlerPrall's ThreeCSG.js project: http://github.com/chandlerprall/ThreeCSG

(For now, I recommend using the experimental version that supports materials - the uv branch - http://github.com/chandlerprall/ThreeCSG/tree/uvs)

Here's the code you will need:

// Cylinder constructor parameters:  
// radiusAtTop, radiusAtBottom, height, segmentsAroundRadius, segmentsAlongHeight

var smallCylinderGeom = new THREE.CylinderGeometry( 30, 30, 80, 20, 4 );
var largeCylinderGeom = new THREE.CylinderGeometry( 40, 40, 80, 20, 4 );

var smallCylinderBSP = new ThreeBSP(smallCylinderGeom);
var largeCylinderBSP = new ThreeBSP(largeCylinderGeom);
var intersectionBSP = largeCylinderBSP.subtract(smallCylinderBSP);      

var redMaterial = new THREE.MeshLambertMaterial( { color: 0xff0000 } );
var hollowCylinder = intersectionBSP.toMesh( redMaterial );
scene.add( hollowCylinder );

Answer 3

It is unlikely that you would have to stitch vertices together. If your cylinder has no thickness, you can use THREE.CylinderGeometry(). If it does have thickness, you can use CSG.

Answer 4

Use SVGloader to load a circle of desired radius (as an SVG). Set the geometry to ExtrudeBufferGeometry and give it your desired height as depth in the extrude settings object.