https://threejs.org/docs/index.html#api/en/materials/LineBas...
const material = new THREE.LineBasicMaterial( { color: 0xffffff, linewidth: 1, linecap: 'round', //ignored by WebGLRenderer linejoin: 'round' //ignored by WebGLRenderer } );
yeah it says on that page "Due to limitations of the OpenGL Core Profile with the WebGL renderer on most platforms linewidth will always be 1 regardless of the set value." anyway yeah I was trying to be snide
Ah, I see. Seems like there's a bunch of 2D cruft in the graphics hardware that hasn't been touched since 3D became possible.