1，功能介绍

Threejs获取鼠标点击位置、实现鼠标点击人物行走、人物头顶显示名称标签、镜头跟随人物移动并且镜头围绕人物旋转，类似游戏中第三人称、鼠标点击位置有动画效果，如下效果图

2，功能实现

获取鼠标点击位置，使用Threejs射线Raycaster和数学库中Plane平面，官方文档地址：three.js docs，平面（Plane）是在三维空间中无限延伸的二维平面，原理就是创建一个射线与平面相交，取相交位置的点就是鼠标点击的位置

// 拾取对象
function pickupObjects(event) {
  // 点击屏幕创建光线投射用于进行鼠标拾取
  var raycaster = new THREE.Raycaster();

  // 将鼠标位置归一化为设备坐标。x 和 y 方向的取值范围是 (-1 to +1)
  var vector = new THREE.Vector2((event.clientX / window.innerWidth) * 2 - 1, -(event.clientY / window
						.innerHeight) * 2 + 1);

  var fxl = new THREE.Vector3(0, 1, 0);
  // 创建平面 设置平面法向量Vector3 和 原点到平面距离
  var groundplane = new THREE.Plane(fxl, 1);
  raycaster.setFromCamera(vector, camera);
  var ray = raycaster.ray;
  let intersects = ray.intersectPlane(groundplane);
  console.log(intersects)
}

document.addEventListener('click', pickupObjects);

这里注意平面法向量Vector3(0, 1, 0) 代表平面的正方向是沿Y轴向上的，距离1代表平面到原点的距离，符号代表和法向量的方向相反，所以这个平面在Y轴正方向。

引入人物模型，使用模型加载器THREE.GLTFLoader加载人物模型，人物头顶显示名称标签并播放人物站立动画，注意播放动画需要requestAnimationFrame实时更新动画

// 加载人物模型，模型glb格式
let gloader = new THREE.GLTFLoader()
gloader.load("model/people.glb", result => {
	peopleObj = result.scene;
	peopleAnimations = result.animations;

	// 主人物名字，并设置相对位置
	let spriteText = getTextCanvas("左本博客");
	spriteText.position.set(0, 2, 0);
	peopleObj.add(spriteText);

	// 组合对象添加到场景中
	scene.add(peopleObj);

	// 默认播放人物站立动画
	mixer = new THREE.AnimationMixer(peopleObj);
	mixerArr.push(mixer)
	activeAction = mixer.clipAction(peopleAnimations[0]);
	activeAction.play();
})

人物名称标签，创建Canvas写入文本，使用THREE.CanvasTexture从Canvas元素中创建纹理贴图作为材质THREE.SpriteMaterial，创建一个物体精灵（Sprite）

// 创建文字精灵
var getTextCanvas = function(text) {
	let option = {
			fontFamily: 'Arial',
			fontSize: 30,
			fontWeight: 'bold',
			color: '#ffffff',
			actualFontSize: 0.08,
		},
		canvas, context, textWidth, texture, materialObj, spriteObj;
	canvas = document.createElement('canvas');
	context = canvas.getContext('2d');
	// 先设置字体大小后获取文本宽度
	context.font = option.fontWeight + ' ' + option.fontSize + 'px ' + option.fontFamily;
	textWidth = context.measureText(text).width;

	canvas.width = textWidth;
	canvas.height = option.fontSize;

	context.textAlign = "center";
	context.textBaseline = "middle";
	context.fillStyle = option.color;
	context.font = option.fontWeight + ' ' + option.fontSize + 'px ' + option.fontFamily;
	context.fillText(text, textWidth / 2, option.fontSize / 1.8);

	texture = new THREE.CanvasTexture(canvas);
	materialObj = new THREE.SpriteMaterial({
		map: texture
	});
	spriteObj = new THREE.Sprite(materialObj);
	spriteObj.scale.set(textWidth / option.fontSize * option.actualFontSize, option.actualFontSize, option
		.actualFontSize);

	return spriteObj;
}

鼠标点击位置动画，使用图片加载器THREE.ImageLoader加载如下透明图片，创建canvas作为THREE.MeshBasicMaterial材质贴图并设置透明和两面渲染，设置定时顺序更新材质

// 鼠标点击位置出现动画效果
function clickEffect() {
	var textures = [];
	var index = 0;
	var clickEffectMesh;
	
	// 加载图片
	var loader = new THREE.ImageLoader();
	loader.load("img/spotd.png", function(image) {
		let canvas, context, geometry, material, plane;
		let w = image.width;
		let num = image.height / image.width;

		for (let i = 0; i < num; i++) {
			textures[i] = new THREE.Texture();
		}

		for (let i = 0; i < num; i++) {
			canvas = document.createElement('canvas');
			context = canvas.getContext('2d');
			canvas.height = w;
			canvas.width = w;
			context.drawImage(image, 0, w * i, w, w, 0, 0, w, w);
			textures[i].image = canvas;
			textures[i].needsUpdate = true;
		}
		
		// 创建平面几何体，添加图片材质并设置透明和两面渲染
		geometry = new THREE.PlaneGeometry(1, 1);
		material = new THREE.MeshBasicMaterial({
			map: textures[0],
			transparent: true,
			side: THREE.DoubleSide,
		});

		clickEffectMesh = new THREE.Mesh(geometry, material);
		clickEffectMesh.rotateX(Math.PI / 2);
		clickEffectMesh.visible = false;

		scene.add(clickEffectMesh);
	});
	
	// 播放动画，设置定时顺序更新材质
	this.effect = function(x, y, z) {
		clickEffectMesh.visible = true;
		clickEffectMesh.position.set(x, y, z);
		let id = setInterval(function() {
			if (index == 10) {
				index = 0;
				clickEffectMesh.visible = false;
				clearInterval(id);
			}
			clickEffectMesh.material.map = textures[index];
			index++;
		}, 20)
	}
}

 鼠标点击人物行走，使用TWEEN.Tween实现人物行走并播放人物行走动画，设置人物朝向行走方向，更新控制器目标中心位置及相机与人物保持相对距离

// 人物当前位置
let originPositon = new THREE.Vector3(peopleObj.position.x, 0, peopleObj.position.z);
// 任务目标位置
let targetPositon = new THREE.Vector3(intersects.x, 0, intersects.z);
clickEffectObj.effect(intersects.x, 0, intersects.z);
// 移动距离
let distance = originPositon.distanceTo(targetPositon);

peopleObj.lookAt(intersects.x, 0, intersects.z);

// 在传入的时间间隔内，逐渐将此动作的权重（weight）由1降至0
// 判断当前人物是否空闲状态，如果空前则改成步行状态
if (activeAction.getClip() != peopleAnimations[1]) {
	activeAction.fadeOut(0.2);
	activeAction = mixer.clipAction(peopleAnimations[1]);
	activeAction
		.reset()
		.setEffectiveTimeScale(1)
		.setEffectiveWeight(2)
		.fadeIn(0.2)
		.play();
}

if (tween) {
	TWEEN.remove(tween);
}
tween = new TWEEN.Tween(originPositon)
	.to(targetPositon, distance * 800)
	.easing(TWEEN.Easing.Linear.None)
	.onComplete(function() {
		activeAction.fadeOut(0.2);
		activeAction = mixer.clipAction(peopleAnimations[0]);
		activeAction
			.reset()
			.setEffectiveTimeScale(1)
			.setEffectiveWeight(2)
			.fadeIn(0.2)
			.play();
	})
	.onUpdate(function() {
		peopleObj.position.set(this.x, 0.04, this.z);

		let pos = peopleObj.position.clone();
		pos.y = 1;
		controls.target = pos;
		controls.update();
	})
	.start();

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