Draw a circle (not shaded) with Three.js

Question

I am trying to draw a circle very similar to the orbital patterns on this website. I would like to use Three.js instead of pure WebGL.

Answer 1

Three.js r50 added CircleGeometry. It can be seen (albeit with a face) in the WebGL Geometries example.

The first vertex in the geometry is created at the center of the circle (in r84, see CircleGeometry.js line 71, in r65, see CircleGeometry.js line 18), which is nifty if you are going for that "full Pac-Man" or "uninformative pie chart" look. Oh, and it appears to be necessary if you are going to use any material aside from LineBasicMaterial / LineDashedMaterial.

I've verified that the following code works in both r60 & r65:

var radius   = 100,
    segments = 64,
    material = new THREE.LineBasicMaterial( { color: 0x0000ff } ),
    geometry = new THREE.CircleGeometry( radius, segments );

// Remove center vertex
geometry.vertices.shift();

// Non closed circle with one open segment:
scene.add( new THREE.Line( geometry, material ) );

// To get a closed circle use LineLoop instead (see also @jackrugile his comment):
scene.add( new THREE.LineLoop( geometry, material ) );

PS: The "docs" now include a nice CircleGeometry interactive example: https://threejs.org/docs/#api/geometries/CircleGeometry

Answer 2

The API changed slightly in newer versions of threejs.

var segmentCount = 32,
    radius = 100,
    geometry = new THREE.Geometry(),
    material = new THREE.LineBasicMaterial({ color: 0xFFFFFF });

for (var i = 0; i <= segmentCount; i++) {
    var theta = (i / segmentCount) * Math.PI * 2;
    geometry.vertices.push(
        new THREE.Vector3(
            Math.cos(theta) * radius,
            Math.sin(theta) * radius,
            0));            
}

scene.add(new THREE.Line(geometry, material));

Modify segmentCount to make the circle smoother or more jagged as needed by your scene. 32 segments will be quite smooth for small circles. For orbits such as those on the site you link you, you may want to have a few hundred.

Modify the order of the three components within the Vector3 constructor to choose the orientation of the circle. As given here, the circle will be aligned to the x/y plane.