LineBasicMaterial

• Set vertexColors to true and add a color attribute to give each vertex its own tint.
• Transparent lines need transparent and opacity set together to blend correctly.
• fog controls whether the line fades into scene fog with distance.

const geometry = new THREE.BufferGeometry().setFromPoints([
  new THREE.Vector3(-5, 0, 0),
  new THREE.Vector3(0, 3, 0),
  new THREE.Vector3(5, 0, 0)
]);

const material = new THREE.LineBasicMaterial({
  color: 0x4aa3df,
  transparent: true,
  opacity: 0.9
});

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

import { Line2 } from 'three/addons/lines/Line2.js';
import { LineGeometry } from 'three/addons/lines/LineGeometry.js';
import { LineMaterial } from 'three/addons/lines/LineMaterial.js';

const lineGeometry = new LineGeometry();
lineGeometry.setPositions([-5, 0, 0, 0, 3, 0, 5, 0, 0]);

const lineMaterial = new LineMaterial({
  color: 0x4aa3df,
  linewidth: 3,          // 单位是像素
  worldUnits: false
});
lineMaterial.resolution.set(window.innerWidth, window.innerHeight);

const thick = new Line2(lineGeometry, lineMaterial);
thick.computeLineDistances();
scene.add(thick);

• Expecting thick lines fails; use LineMaterial with resolution or fat-line geometry instead.
• Judging a line's color is affected by colorSpace and tone mapping, so compare it in scene.