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我們都知道，three.js庫里面內置了很多著色器通道對象供我們渲染場景，本文將對EffectComposer、RenderPass、FilmPass這三個通道進行學習和實現：
1.RenderPass這個通道會在當前場景（scene）和攝像機（camera）的基礎上渲染出一個新場景，新建：
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let renderPass = new THREE.RenderPass(scene, camera);
2.FilmPass這個通道通過掃描線和失真模擬電視屏幕效果，實現的效果超有時代感，新建：
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let effectFilm = new THREE.FilmPass(0.8, 0.325, 256, false);
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effectFilm.renderToScreen = true;
3.EffectComposer可以理解為著色器通道容器，著色器通道按照先后順序添加進來并執行，新建：
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let composer = new THREE.EffectComposer(renderer);
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composer.addPass(renderPass);
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composer.addPass(effectFilm);
本文實現的demo基于three.js_r86(請自行下載)，代碼所用js文件和圖片都在下載的那個包里面，請讀者自行引用。
實現效果：
代碼：
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<title>shader_2_earth</title>
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<style>
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body{
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margin: 0;
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overflow: hidden;
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}
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</style>
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</head>
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<body>
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<script src="build/three.js"></script>
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<script src="js/libs/stats.min.js"></script>
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<script src="js/libs/dat.gui.min.js"></script>
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<script src="js/controls/OrbitControls.js"></script>
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<script src="js/Detector.js"></script>
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<script src="js/postprocessing/EffectComposer.js"></script>
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<script src="js/postprocessing/ShaderPass.js"></script>
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<script src="js/postprocessing/MaskPass.js"></script>
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<script src="js/postprocessing/FilmPass.js"></script>
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<script src="js/postprocessing/BloomPass.js"></script>
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<script src="js/postprocessing/RenderPass.js"></script>
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<script src="js/shaders/CopyShader.js"></script>
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<script src="js/shaders/FilmShader.js"></script>
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<div id="stats"></div>
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<div id="container"></div>
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<script>
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//檢測webgl的兼容性
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if(!Detector.webgl) Detector.addGetWebGLMessage();
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let scene;
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let camera, renderer, sphere, controls, stats;
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let ambientLight, spotLight;
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let composer;
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let clock;
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main();
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render();
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function main() {
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scene = new THREE.Scene();
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camera = new THREE.PerspectiveCamera(45, window.innerWidth/window.innerHeight, 0.1, 1000);
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camera.position.set(-10, 15, 25);
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camera.lookAt(new THREE.Vector3(0, 0, 0));
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renderer = new THREE.WebGLRenderer({antialias:true});
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renderer.setClearColor(new THREE.Color(0,0,0));
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renderer.setSize(window.innerWidth, window.innerHeight);
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renderer.shadowMapEnabled = true;
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controls = new THREE.OrbitControls(camera);
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controls.autoRotate = false;
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clock = new THREE.Clock();
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ambientLight = new THREE.AmbientLight(0x181818);
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scene.add(ambientLight);
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spotLight = new THREE.SpotLight(0xffffff);
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spotLight.position.set(550, 100, 550);
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spotLight.intensity = 0.6;
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scene.add(spotLight);
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//創建地球
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sphere = createMesh(new THREE.SphereGeometry(10, 60, 60));
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scene.add(sphere);
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document.getElementById("container").appendChild(renderer.domElement);
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/**
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* 添加渲染通道
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*/
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//在當前場景和攝像機的基礎上渲染一個新場景
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let renderPass = new THREE.RenderPass(scene, camera);
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//通過掃描線和失真來實現模擬電視屏幕的效果
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let effectFilm = new THREE.FilmPass(0.8, 0.325, 256, false);
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//將渲染結果輸出到屏幕
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effectFilm.renderToScreen = true;
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//渲染效果組合器，每個通道都按照傳入的順序執行
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composer = new THREE.EffectComposer(renderer);
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composer.addPass(renderPass);
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composer.addPass(effectFilm);
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//菜單欄元素
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let guiFields = {
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"掃描線數量": 256,
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"灰度圖像": false,
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"掃描線強度": 0.3,
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"粗糙程度": 0.8,
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"updateEffectFilm": function () {
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effectFilm.uniforms.grayscale.value = guiFields.灰度圖像;
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effectFilm.uniforms.nIntensity.value = guiFields.粗糙程度;
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effectFilm.uniforms.sIntensity.value = guiFields.掃描線強度;
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effectFilm.uniforms.sCount.value = guiFields.掃描線數量;
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}
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};
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//新建一個菜單欄
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let gui = new dat.GUI();
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gui.add(guiFields, "掃描線數量", 0, 2048).onChange(guiFields.updateEffectFilm);
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gui.add(guiFields, "掃描線強度", 0, 1).onChange(guiFields.updateEffectFilm);
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gui.add(guiFields, "粗糙程度", 0, 3).onChange(guiFields.updateEffectFilm);
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gui.add(guiFields, "灰度圖像").onChange(guiFields.updateEffectFilm);
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stats = initStats();
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}
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//創建一個Mesh
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function createMesh(geometry) {
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//初始化紋理加載器
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let textureLoader = new THREE.TextureLoader();
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//加載圖片
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let uniforms = {
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planetTexture:{value:textureLoader.load("textures/planets/earth_atmos_2048.jpg")},
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specularTexture:{value:textureLoader.load("textures/planets/earth_specular_2048.jpg")},
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normalTexture:{value:textureLoader.load("textures/planets/earth_normal_2048.jpg")}
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};
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//創建phong材料，并進行相應圖片的貼圖
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let planetMaterial = new THREE.MeshPhongMaterial();
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planetMaterial.specularMap = uniforms.specularTexture.value;
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planetMaterial.specular = new THREE.Color(0x4444aa);
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planetMaterial.normalMap = uniforms.normalTexture.value;
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planetMaterial.map = uniforms.planetTexture.value;
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//新建一個mesh
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let mesh = new THREE.SceneUtils.createMultiMaterialObject(geometry, [planetMaterial]);
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return mesh;
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}
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//渲染更新場景
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function render() {
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stats.update();
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let delta = clock.getDelta();
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controls.update(delta);
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sphere.rotation.y += 0.002;
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requestAnimationFrame(render);
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//沒有著色器通道系統默認為WebGLRenderer.render
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//使用著色器通道后，應使用使用composer.render
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composer.render(delta);
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}
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//左上角幀顯示
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function initStats() {
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let stats = new Stats();
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stats.setMode(0);
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stats.domElement.style.position = 'absolute';
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stats.domElement.style.left = '0px';
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stats.domElement.style.top = '0px';
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document.getElementById("stats").appendChild(stats.domElement);
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return stats;
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}
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</script>
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</body>
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</html>
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