three.js使用gpu選取物體并計算交點位置

var raycaster = new THREE.Raycaster();
var mouse = new THREE.Vector2();
function onMouseMove(event) { 
 // 計算鼠標所在位置的設備坐標
 // 三個坐標分量都是-1到1
 mouse.x = event.clientX / window.innerWidth * 2 - 1;
 mouse.y = - (event.clientY / window.innerHeight) * 2 + 1;
}
function pick() { 
 // 使用相機和鼠標位置更新選取光線 
 raycaster.setFromCamera(mouse, camera); 
 // 計算與選取光線相交的物體
 var intersects = raycaster.intersectObjects(scene.children);
}

let maxHexColor = 1;// 更換選取材質
scene.traverseVisible(n => { 
if (!(n instanceof THREE.Mesh)) {
 return;
 }
 n.oldMaterial = n.material;
 if (n.pickMaterial) { // 已經創建過選取材質了
 n.material = n.pickMaterial;
 return;
 }
 let material = new THREE.ShaderMaterial({
 vertexShader: PickVertexShader,
 fragmentShader: PickFragmentShader,
 uniforms: {
 pickColor: {
 value: new THREE.Color(maxHexColor)
 }
 }
 });
 n.pickColor = maxHexColor;
 maxHexColor++;
 n.material = n.pickMaterial = material;
});
 
PickVertexShader：
void main() {
 gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
}
 
PickFragmentShader：
uniform vec3 pickColor;void main() {
 gl_FragColor = vec4(pickColor, 1.0);
}

let renderTarget = new THREE.WebGLRenderTarget(width, height);
let pixel = new Uint8Array(4);// 繪制并讀取像素
renderer.setRenderTarget(renderTarget);
renderer.clear();
renderer.render(scene, camera);
renderer.readRenderTargetPixels(renderTarget, offsetX, height - offsetY, 1, 1, pixel); // 讀取鼠標所在位置顏色
// 還原原來材質，并獲取選中物體
const currentColor = pixel[0] * 0xffff + pixel[1] * 0xff + pixel[2];
let selected = null;

scene.traverseVisible(n => {
 if (!(n instanceof THREE.Mesh)) {
 return;
 }
 if (n.pickMaterial && n.pickColor === currentColor) {
 // 顏色相同

 selected = n; // 鼠標所在位置的物體 
 }
 if (n.oldMaterial) {
 n.material = n.oldMaterial; delete n.oldMaterial;
 }
});

const depthMaterial = new THREE.ShaderMaterial({
 vertexShader: DepthVertexShader,
 fragmentShader: DepthFragmentShader,
 uniforms: {
 far: {
 value: camera.far
 }
 }
});
DepthVertexShader：
precision highp float;
uniform float far;
varying float depth;void main() {
 gl_Position = projectionMatrix * modelViewMatrix * vec4(position, 1.0);
 depth = gl_Position.z / far;
}
DepthFragmentShader：
precision highp float;
varying float depth;void main() {
 float hex = abs(depth) * 16777215.0; // 0xffffff
 float r = floor(hex / 65535.0);
 float g = floor((hex - r * 65535.0) / 255.0); 
 float b = floor(hex - r * 65535.0 - g * 255.0); 
 float a = sign(depth) >= 0.0 ? 1.0 : 0.0; // depth大于等于0，為1.0；小于0，為0.0。
 gl_FragColor = vec4(r / 255.0, g / 255.0, b / 255.0, a);
}

let renderTarget = new THREE.WebGLRenderTarget(width, height);
let pixel = new Uint8Array(4);
scene.overrideMaterial = this.depthMaterial;
renderer.setRenderTarget(renderTarget);
renderer.clear();
renderer.render(scene, camera);
renderer.readRenderTargetPixels(renderTarget, offsetX, height - offsetY, 1, 1, pixel);

if (pixel[2] !== 0 || pixel[1] !== 0 || pixel[0] !== 0) {
 let hex = (this.pixel[0] * 65535 + this.pixel[1] * 255 + this.pixel[2]) / 0xffffff; 
 if (this.pixel[3] === 0) {
 hex = -hex;
 }
 cameraDepth = -hex * camera.far; // 相機坐標系中鼠標所在點的深度（注意：相機坐標系中的深度值為負值）}

let nearPosition = new THREE.Vector3(); // 鼠標屏幕位置在near處的相機坐標系中的坐標
let farPosition = new THREE.Vector3(); // 鼠標屏幕位置在far處的相機坐標系中的坐標
let world = new THREE.Vector3(); // 通過插值計算世界坐標
// 設備坐標
const deviceX = this.offsetX / width * 2 - 1;
const deviceY = - this.offsetY / height * 2 + 1;// 近點
nearPosition.set(deviceX, deviceY, 1); // 屏幕坐標系：(0, 0, 1)
nearPosition.applyMatrix4(camera.projectionMatrixInverse); // 相機坐標系：(0, 0, -far)
// 遠點
farPosition.set(deviceX, deviceY, -1); // 屏幕坐標系：(0, 0, -1)
farPosition.applyMatrix4(camera.projectionMatrixInverse); // 相機坐標系：(0, 0, -near)
// 在相機空間，根據深度，按比例計算出相機空間x和y值。
const t = (cameraDepth - nearPosition.z) / (farPosition.z - nearPosition.z);
// 將交點從相機空間中的坐標，轉換到世界坐標系坐標。
world.set(
 nearPosition.x + (farPosition.x - nearPosition.x) * t,
 nearPosition.y + (farPosition.y - nearPosition.y) * t,
 cameraDepth
);
world.applyMatrix4(camera.matrixWorld);