透视投影照相机（Perspective Camera）的构造函数是：

THREE.PerspectiveCamera(fov, aspect, near, far)

让我们通过一张透视照相机投影的图来了解这些参数。

透视图中，灰色的部分是视景体，是可能被渲染的物体所在的区域。fov是视景体竖直方向上的张角（是角度制而非弧度制），如侧视图所示。

aspect等于width / height，是照相机水平方向和竖直方向长度的比值，通常设为Canvas的横纵比例。

near和far分别是照相机到视景体最近、最远的距离，均为正值，且far应大于near。

实例说明

下面，我们从一个最简单的例子学习设置透视投影照相机。

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
    <head>
        <script type="text/javascript" src="libs/three.js"></script>
        
        <script type="text/javascript">
            function init() {
                var renderer = new THREE.WebGLRenderer({
                    canvas: document.getElementById('mainCanvas')
                });
                renderer.setClearColor(0x000000);
                var scene = new THREE.Scene();
                
                // camera
                // canvas size is 400x300
var camera = new THREE.PerspectiveCamera(45, 400 / 300, 1, 10);
camera.position.set(0, 0, 5);
scene.add(camera);
                // a cube in the scene
       // a cube in the scene
var cube = new THREE.Mesh(new THREE.CubeGeometry(1, 1, 1),
        new THREE.MeshBasicMaterial({
            color: 0xff0000,
            wireframe: true
        })
);
scene.add(cube);
                
                // render
                renderer.render(scene, camera);
            }
        </script>
    </head>
    
    <body onload="init()">
        <canvas id="mainCanvas" width="400px" height="300px" ></canvas>
    </body>
</html>

three.js透视投影照相机

接下来，我们来看下fov的改变对渲染效果的影响。我们将原来的45改为60，得到这样的效果：

three.js透视投影照相机

为什么正方体显得更小了呢？我们从下面的侧视图来看，虽然正方体的实际大小并未改变，但是将照相机的竖直张角设置得更大时，视景体变大了，因而正方体相对于整个视景体的大小就变小了，看起来正方形就显得变小了。

three.js透视投影照相机

注意，改变fov并不会引起画面横竖比例的变化，而改变aspect则会改变横竖比例。

  <!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>Three框架</title>
        <script src="libs/Three.js"></script>
        <style type="text/css">
            div#canvas-frame {
                border: none;
                cursor: pointer;
                width: 100%;
                height: 600px;
                background-color: #EEEEEE;
            }

        </style>
        <script>
            var renderer;
            function initThree() {
                width = document.getElementById('canvas-frame').clientWidth;
                height = document.getElementById('canvas-frame').clientHeight;
                renderer = new THREE.WebGLRenderer({
                    antialias : true
                });
                renderer.setSize(width, height);
                document.getElementById('canvas-frame').appendChild(renderer.domElement);
                renderer.setClearColor(0xFFFFFF, 1.0);
            }

            var camera;
            function initCamera() {
                //camera = new THREE.PerspectiveCamera(45, width / height, 1, 10000);
                camera = new THREE.OrthographicCamera( window.innerWidth / - 2, window.innerWidth / 2, window.innerHeight / 2, window.innerHeight / - 2, 10, 1000 );
                camera.position.x = 0;
                camera.position.y = 0;
                camera.position.z = 600;
                camera.up.x = 0;
                camera.up.y = 1;
                camera.up.z = 0;
                camera.lookAt({
                    x : 0,
                    y : 0,
                    z : 0
                });
            }

            var scene;
            function initScene() {
                scene = new THREE.Scene();
            }

            var light;
            function initLight() {
                light = new THREE.AmbientLight(0xFF0000);
                light.position.set(100, 100, 200);
                scene.add(light);
                
                light = new THREE.PointLight(0x00FF00);
                light.position.set(0, 0,300);
                scene.add(light);
            }

            var cube;
            function initObject() {
                var geometry = new THREE.CylinderGeometry( 70,100,200);
                var material = new THREE.MeshLambertMaterial( { color:0xFFFFFF} );
                var mesh = new THREE.Mesh( geometry,material);
                mesh.position = new THREE.Vector3(0,0,0);
                scene.add(mesh);
            }

            function threeStart() {
                initThree();
                initCamera();
                initScene();
                initLight();
                initObject();
                animation();

            }
            function animation()
            {
                changeFov();
                renderer.render(scene, camera);
                requestAnimationFrame(animation);
            }
            
            function setCameraFov(fov)
            {
                camera.fov = fov;
                camera.updateProjectionMatrix();
            }
            
            function changeFov()
            {
                var txtFov = document.getElementById("txtFov").value;
                var val = parseFloat(txtFov);
                setCameraFov(val);
            }
        </script>
    </head>

    <body onload="threeStart();">
        <div id="canvas-frame"></div>
        <div>
            Fov:<input type="text" value="45" id="txtFov"/>(0到180的值)
        </div>
    </body>
</html>

three.js透视投影照相机

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three.js透视投影照相机

实例说明

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