本篇將要介紹的這個 MeshNormalMaterial 網格法向量材質,是一種比較特殊的材質。它使得物體的每一個面的顏色都從該面向外指的法向量計算得到的。所謂法向量是指與面垂直的向量。法向量在 three.js 庫中有着廣泛的應用。它可以用來決定光的反射方向,在三維物體上映射材質時起到輔助作用。還可以在計算光照、陰影時提供有用信息,從而爲物體表面像素上色。
想要理解 MeshNormalMaterial 材質,最直觀的就是先來看一個具體的示例,完整代碼如下:
<!DOCTYPE html>
<html>
<head>
<title>示例 04.04 - MeshNormalMaterial</title>
<script src="../build/three.js"></script>
<script src="../build/js/controls/OrbitControls.js"></script>
<script src="../build/js/libs/stats.min.js"></script>
<script src="../build/js/libs/dat.gui.min.js"></script>
<script src="../jquery/jquery-3.2.1.min.js"></script>
<style>
body {
/* 設置 margin 爲 0,並且 overflow 爲 hidden,來完成頁面樣式 */
margin: 0;
overflow: hidden;
}
/* 統計對象的樣式 */
#Stats-output {
position: absolute;
left: 0px;
top: 0px;
}
</style>
</head>
<body>
<!-- 用於 WebGL 輸出的 Div -->
<div id="webgl-output"></div>
<!-- 用於統計 FPS 輸出的 Div -->
<div id="stats-output"></div>
<!-- 運行 Three.js 示例的 Javascript 代碼 -->
<script type="text/javascript">
var scene;
var camera;
var render;
var webglRender;
var canvasRender;
var controls;
var stats;
var guiParams;
var ground;
var cube;
var sphere;
var plane;
var activeMesh;
var meshMaterial;
var ambientLight;
$(function() {
stats = initStats();
scene = new THREE.Scene();
webglRender = new THREE.WebGLRenderer( {antialias: true, alpha: true} ); // antialias 抗鋸齒
webglRender.setSize(window.innerWidth, window.innerHeight);
webglRender.setClearColor(0x000000, 1.0);
//webglRender.shadowMap.enabled = true; // 允許陰影投射
render = webglRender;
camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 30, 1000); // 2147483647
camera.position.set(-50, 40, 50);
var target = new THREE.Vector3(0, 0 , 0);
controls = new THREE.OrbitControls(camera, render.domElement);
controls.target = target;
camera.lookAt(target);
$('#webgl-output')[0].appendChild(render.domElement);
window.addEventListener('resize', onWindowResize, false);
ambientLight = new THREE.AmbientLight(0x000000);
scene.add(ambientLight);
// 加入一個平面
var groundGeometry = new THREE.PlaneGeometry(100, 100, 4, 4);
var groundMaterial = new THREE.MeshBasicMaterial({color: 0x777777});
ground = new THREE.Mesh(groundGeometry, groundMaterial);
ground.rotation.set(-0.5 * Math.PI, 0, 0); // 沿着 X軸旋轉-90°
scene.add(ground);
// 定義 cube, sphere, plane
var cubeGeometry = new THREE.BoxGeometry(15, 15, 15);
var sphereGeometry = new THREE.SphereGeometry(14, 20, 20);
var planeGeometry = new THREE.PlaneGeometry(14, 14, 4, 4);
// 網格法向量材質不支持 color 屬性
meshMaterial = new THREE.MeshNormalMaterial({flatShading: true});
cube = new THREE.Mesh(cubeGeometry, meshMaterial);
sphere = new THREE.Mesh(sphereGeometry, meshMaterial);
plane = new THREE.Mesh(planeGeometry, meshMaterial);
cube.position.set(0, 12, 2);
sphere.position.set(0, 14, 2);
plane.position.set(0, 12, 2);
/** 用來保存那些需要修改的變量 */
guiParams = new function() {
this.rotationSpeed = 0.02;
this.opacity = meshMaterial.opacity;
this.transparent = meshMaterial.transparent;
this.wireframe = meshMaterial.wireframe;
this.wireframeLinewidth = meshMaterial.wireframeLinewidth;
this.visible = meshMaterial.visible;
this.side = 'front';
this.flatShading = meshMaterial.flatShading;
this.selectedMesh = 'cube';
this.arrows = false;
this.addMesh = function(e) {
scene.remove(activeMesh);
switch (e) {
case "cube":
activeMesh = cube;
break;
case "sphere":
activeMesh = sphere;
break;
case "plane":
activeMesh = plane;
break;
}
scene.add(activeMesh);
};
this.addArrows = function(needsArrows) {
activeMesh.children = [];
if (!needsArrows) return;
for (var f = 0, fl = activeMesh.geometry.faces.length; f < fl; f++) {
var face = activeMesh.geometry.faces[f];
var centroid = new THREE.Vector3(0, 0, 0);
centroid.add(activeMesh.geometry.vertices[face.a]);
centroid.add(activeMesh.geometry.vertices[face.b]);
centroid.add(activeMesh.geometry.vertices[face.c]);
centroid.divideScalar(3);
var arrow = new THREE.ArrowHelper(
face.normal,
centroid,
2,
0x3333FF,
0.5,
0.5);
activeMesh.add(arrow);
}
};
}
/** 定義 dat.GUI 對象,並綁定 guiParams 的幾個屬性 */
var gui = new dat.GUI();
var folder = gui.addFolder('Mesh');
folder.open();
folder.add(guiParams, 'opacity', 0.1, 1.0).onChange(function(e) {
meshMaterial.opacity = e;
});
folder.add(guiParams, 'transparent').onChange(function(e) {
meshMaterial.transparent = e;
});
folder.add(guiParams, 'wireframe').onChange(function(e) {
meshMaterial.wireframe = e;
});
folder.add(guiParams, 'wireframeLinewidth', 1, 20).onChange(function(e) {
meshMaterial.wireframeLinewidth = e;
});
folder.add(guiParams, 'visible').onChange(function(e) {
meshMaterial.visible = e;
});
folder.add(guiParams, 'side', ['front', 'back', 'double']).onChange(function(e) {
console.log(e);
switch (e) {
case "front":
meshMaterial.side = THREE.FrontSide;
break;
case "back":
meshMaterial.side = THREE.BackSide;
break;
case "double":
meshMaterial.side = THREE.DoubleSide;
break;
}
meshMaterial.needsUpdate = true;
});
folder.add(guiParams, 'flatShading').onChange(function(e) {
meshMaterial.flatShading = e;
meshMaterial.needsUpdate = true;
});
folder.add(guiParams, 'selectedMesh', ['cube', 'sphere', 'plane']).onChange(function(e) {
guiParams.addMesh(e);
guiParams.addArrows(guiParams.arrows);
});
folder.add(guiParams, 'arrows').onChange(function(e){
guiParams.addArrows(e);
});
guiParams.addMesh(guiParams.selectedMesh);
renderScene();
});
/** 渲染場景 */
function renderScene() {
stats.update();
rotateMesh(); // 旋轉物體
requestAnimationFrame(renderScene);
render.render(scene, camera);
}
/** 初始化 stats 統計對象 */
function initStats() {
stats = new Stats();
stats.setMode(0); // 0 爲監測 FPS;1 爲監測渲染時間
$('#stats-output').append(stats.domElement);
return stats;
}
/** 當瀏覽器窗口大小變化時觸發 */
function onWindowResize() {
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
render.setSize(window.innerWidth, window.innerHeight);
}
/** 旋轉物體 */
function rotateMesh() {
scene.traverse(function(mesh) {
if (mesh instanceof THREE.Mesh && mesh != ground) {
//mesh.rotation.x += guiParams.rotationSpeed;
mesh.rotation.y += guiParams.rotationSpeed;
//mesh.rotation.z += guiParams.rotationSpeed;
}
});
}
</script>
</body>
</html>
以上示例運行效果如下所示: