addArcSlice (startAngle, percent, color, permanent) {
    const size = Math.PI * percent;
    const slice = new THREE.RingGeometry(this.innerRadius - arcMeterWidth, this.innerRadius - 1, 30, 8, startAngle, size);
    const mat = new THREE.MeshBasicMaterial({
      color: new THREE.Color(color.r, color.g, color.b), side: THREE.DoubleSide, transparent: true, opacity: color.a
    });
    const mesh = new THREE.Mesh(slice, mat);
    mesh.position.set(0, 0, this.surfaceDepth + 5);
    mesh.rotation.y = Math.PI;
    mesh.userData.context = 'arc';
    mesh.userData.defaultOpacity = color.a;

    if (!permanent) { this.arcMeterSegments.push(mesh); }
    this.container.add(mesh);

    return { mesh: mesh, angle: startAngle + size };
  }
Add a new slice to the arc meter

@param {number} startAngle The angle (in radians) to start drawing the arc slice
@param {number} percent The percent of the arc to fill with this new arc slice
@param {string} color A string representation of the color to make this slice
@param {boolean=} permanent Whether to include this slice permanently (Added for the use of the background color slice)