LineBasicMaterial.linejoin not work

Description of the problem

when I set LineBasicMaterial.linejoin as ‘bevel’ or ‘miter’,it not work.The appearance of line joints always be ‘round’.

renderer = new THREE.CanvasRenderer();

var material = new THREE.LineBasicMaterial({
        color: 0x0000ff,
        linewidth: 25,
        linecap: 'round',
        linejoin: 'miter',
});
var geometry = new THREE.Geometry();
geometry.vertices.push(
        new THREE.Vector3( -10, 0, 0 ),
        new THREE.Vector3( 0, 0, 20 ),
        new THREE.Vector3( 10, 0, 0 )
);

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

Three.js version

• Dev
• r85
• …

Browser

• All of them
• Chrome
• Firefox
• Internet Explorer

OS

• All of them
• Windows
• macOS
• Linux
• Android
• iOS

Hardware Requirements (graphics card, VR Device, …)

[Mugen87]

CanvasRenderer has been removed, see #15029

[WestLangley]

I think this is because with CanvasRenderer, the line is rendered as a sequence of individual line segments:

ctx.moveTo(10, 10);
ctx.lineTo(200, 150);

ctx.moveTo(200, 150);
ctx.lineTo(300, 100);

instead of:

ctx.moveTo(10, 10);
ctx.lineTo(200, 150);
ctx.lineTo(300, 100);

Hence, linecap is honored, but linejoin is not.