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javascript - Three.js 保持相机在物体后面

转载 作者:行者123 更新时间:2023-11-29 15:17:04 29 4
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简短版本:如何让相机跟随 Three.js 场景中由物理控制的对象?

长版:我正在处理 Three.js 场景,其中 W、A、S、D 键沿平面移动球体。然而,到目前为止,我还没有想出如何让相机跟随球体的后面。

在下面的示例中,如果只按 W 键,相机就会完美地跟随球体。但是,如果按下 A 或 D,球体开始转动,并且摄像机不再位于球后方。如果球体开始转动,我希望摄像机随之转动,因此摄像机始终紧跟在球体后面,并且始终与球体保持恒定距离。随着用户继续按 W,球将继续相对于相机向前滚动。

在之前的场景中[ demo ]],我能够通过创建球体,将该球体添加到一个组中,然后在每一帧中使用以下代码来实现此行为:

var relativeCameraOffset = new THREE.Vector3(0,50,200);
var cameraOffset = relativeCameraOffset.applyMatrix4(sphereGroup.matrixWorld);
camera.position.x = cameraOffset.x;
camera.position.y = cameraOffset.y;
camera.position.z = cameraOffset.z;
camera.lookAt(sphereGroup.position);

上面演示中的关键是旋转 sphere,同时保持 sphereGroup 不旋转,这样我就可以计算 un 上的 cameraOffset -旋转的sphereGroup

在下面的演示中,球体的位置由 Cannon.js 物理库控制,当力施加到 body 时,它会平移和旋转球体。有谁知道如何让相机跟随下面场景中的球体后面?

/**
* Generate a scene object with a background color
**/

function getScene() {
var scene = new THREE.Scene();
scene.background = new THREE.Color(0x111111);
return scene;
}

/**
* Generate the camera to be used in the scene. Camera args:
* [0] field of view: identifies the portion of the scene
* visible at any time (in degrees)
* [1] aspect ratio: identifies the aspect ratio of the
* scene in width/height
* [2] near clipping plane: objects closer than the near
* clipping plane are culled from the scene
* [3] far clipping plane: objects farther than the far
* clipping plane are culled from the scene
**/

function getCamera() {
var aspectRatio = window.innerWidth / window.innerHeight;
var camera = new THREE.PerspectiveCamera(75, aspectRatio, 0.1, 10000);
camera.position.set(0, 2000, -5000);
camera.lookAt(scene.position);
return camera;
}

/**
* Generate the light to be used in the scene. Light args:
* [0]: Hexadecimal color of the light
* [1]: Numeric value of the light's strength/intensity
* [2]: The distance from the light where the intensity is 0
* @param {obj} scene: the current scene object
**/

function getLight(scene) {
var light = new THREE.PointLight( 0xffffff, 0.6, 0, 0 )
light.position.set( -2000, 1000, -2100 );
scene.add( light );

var light = new THREE.PointLight( 0xffffff, 0.15, 0, 0 )
light.position.set( -190, 275, -1801 );
light.castShadow = true;
scene.add( light );

// create some ambient light for the scene
var ambientLight = new THREE.AmbientLight(0xffffff, 0.8);
scene.add(ambientLight);
return light;
}

/**
* Generate the renderer to be used in the scene
**/

function getRenderer() {
// Create the canvas with a renderer
var renderer = new THREE.WebGLRenderer({antialias: true});
// Add support for retina displays
renderer.setPixelRatio(window.devicePixelRatio);
// Specify the size of the canvas
renderer.setSize(window.innerWidth, window.innerHeight);
// Enable shadows
renderer.shadowMap.enabled = true;
// Specify the shadow type; default = THREE.PCFShadowMap
renderer.shadowMap.type = THREE.PCFSoftShadowMap;
// Add the canvas to the DOM
document.body.appendChild(renderer.domElement);
return renderer;
}

/**
* Generate the controls to be used in the scene
* @param {obj} camera: the three.js camera for the scene
* @param {obj} renderer: the three.js renderer for the scene
**/

function getControls(camera, renderer) {
var controls = new THREE.TrackballControls(camera, renderer.domElement);
controls.zoomSpeed = 0.4;
controls.panSpeed = 0.4;
return controls;
}

/**
* Get stats
**/

function getStats() {
stats = new Stats();
stats.domElement.style.position = 'absolute';
stats.domElement.style.top = '0px';
stats.domElement.style.right = '0px';
document.body.appendChild( stats.domElement );
return stats;
}

/**
* Get grass
**/

function getGrass() {
var texture = loader.load('http://4.bp.blogspot.com/-JiJEc7lH1Is/UHJs3kn261I/AAAAAAAADYA/gQRAxHK2q_w/s1600/tileable_old_school_video_game_grass.jpg');
texture.wrapS = texture.wrapT = THREE.RepeatWrapping;
texture.repeat.set(10, 10);
var material = new THREE.MeshLambertMaterial({
map: texture,
side: THREE.DoubleSide,
});
return material;
}

function getPlanes(scene, loader) {
var planes = [];
var material = getGrass();
[ [4000, 2000, 0, 0, -1000, 0] ].map(function(p) {
var geometry = new THREE.PlaneGeometry(p[0], p[1]);
var plane = new THREE.Mesh(geometry, material);
plane.position.x = p[2];
plane.position.y = p[3];
plane.position.z = p[4];
plane.rotation.y = p[5];
plane.rotation.x = Math.PI / 2;
plane.receiveShadow = true;
planes.push(plane);
scene.add(plane);
})
return planes;
}

/**
* Add background
**/

function getBackground(scene, loader) {
var imagePrefix = 'sky-parts/';
var directions = ['right', 'left', 'top', 'bottom', 'front', 'back'];
var imageSuffix = '.bmp';
var geometry = new THREE.BoxGeometry( 4000, 4000, 4000 );
// Add each of the images for the background cube
var materialArray = [];
for (var i = 0; i < 6; i++)
materialArray.push( new THREE.MeshBasicMaterial({
//map: loader.load(imagePrefix + directions[i] + imageSuffix),
color: 0xff0000,
side: THREE.BackSide
}));
var sky = new THREE.Mesh( geometry, materialArray );
scene.add(sky);
return sky;
}

/**
* Add a character
**/

function getSphere(scene) {
var geometry = new THREE.SphereGeometry( 30, 12, 9 );
var material = new THREE.MeshPhongMaterial({
color: 0xd0901d,
emissive: 0xaa0000,
side: THREE.DoubleSide,
flatShading: true
});
var sphere = new THREE.Mesh( geometry, material );
// allow the sphere to cast a shadow
sphere.castShadow = true;
sphere.receiveShadow = false;
// create a group for translations and rotations
var sphereGroup = new THREE.Group();
sphereGroup.add(sphere)
sphereGroup.castShadow = true;
sphereGroup.receiveShadow = false;
scene.add(sphereGroup);
return [sphere, sphereGroup];
}

/**
* Initialize physics engine
**/

function getPhysics() {
world = new CANNON.World();
world.gravity.set(0, -400, 0); // earth = -9.82 m/s
world.broadphase = new CANNON.NaiveBroadphase();
world.broadphase.useBoundingBoxes = true;
var solver = new CANNON.GSSolver();
solver.iterations = 7;
solver.tolerance = 0.1;
world.solver = solver;
world.quatNormalizeSkip = 0;
world.quatNormalizeFast = false;
world.defaultContactMaterial.contactEquationStiffness = 1e9;
world.defaultContactMaterial.contactEquationRelaxation = 4;
return world;
}

/**
* Generate the materials to be used for contacts
**/

function getPhysicsMaterial() {
var physicsMaterial = new CANNON.Material('slipperyMaterial');
var physicsContactMaterial = new CANNON.ContactMaterial(
physicsMaterial, physicsMaterial, 0.0, 0.3)
world.addContactMaterial(physicsContactMaterial);
return physicsMaterial;
}

/**
* Add objects to the world
**/

function addObjectPhysics() {
addFloorPhysics()
addSpherePhysics()
}

function addFloorPhysics() {
floors.map(function(floor) {
var q = floor.quaternion;
floorBody = new CANNON.Body({
mass: 0, // mass = 0 makes the body static
material: physicsMaterial,
shape: new CANNON.Plane(),
quaternion: new CANNON.Quaternion(-q._x, q._y, q._z, q._w)
});
world.addBody(floorBody);
})
}

function addSpherePhysics() {
sphereBody = new CANNON.Body({
mass: 1,
material: physicsMaterial,
shape: new CANNON.Sphere(30),
linearDamping: 0.5,
position: new CANNON.Vec3(1000, 500, -2000)
});
world.addBody(sphereBody);
}

/**
* Store all currently pressed keys & handle window resize
**/

function addListeners() {
window.addEventListener('keydown', function(e) {
pressed[e.key.toUpperCase()] = true;
})
window.addEventListener('keyup', function(e) {
pressed[e.key.toUpperCase()] = false;
})
window.addEventListener('resize', function(e) {
windowHalfX = window.innerWidth / 2;
windowHalfY = window.innerHeight / 2;
camera.aspect = window.innerWidth / window.innerHeight;
camera.updateProjectionMatrix();
renderer.setSize(window.innerWidth, window.innerHeight);
if (typeof(controls) != 'undefined') controls.handleResize();
})
}

/**
* Update the sphere's position
**/

function moveSphere() {
var delta = clock.getDelta(); // seconds
var moveDistance = 500 * delta; // n pixels per second
var rotateAngle = Math.PI / 2 * delta; // 90 deg per second

// move forwards, backwards, left, or right
if (pressed['W'] || pressed['ARROWUP']) {
sphereBody.velocity.z += moveDistance;
}
if (pressed['S'] || pressed['ARROWDOWN']) {
sphereBody.velocity.z -= moveDistance;
}
if (pressed['A'] || pressed['ARROWLEFT']) {
sphereBody.velocity.x += moveDistance;
}
if (pressed['D'] || pressed['ARROWRIGHT']) {
sphereBody.velocity.x -= moveDistance;
}
}

/**
* Follow the sphere
**/

function moveCamera() {
camera.position.x = sphereBody.position.x + 0;
camera.position.y = sphereBody.position.y + 50;
camera.position.z = sphereBody.position.z + -200;
camera.lookAt(sphereGroup.position);
}

function updatePhysics() {
world.step(1/60);
sphereGroup.position.copy(sphereBody.position);
sphereGroup.quaternion.copy(sphereBody.quaternion);
}

// Render loop
function render() {
requestAnimationFrame(render);
renderer.render(scene, camera);
moveSphere();
updatePhysics();
if (typeof(controls) === 'undefined') moveCamera();
if (typeof(controls) !== 'undefined') controls.update();
if (typeof(stats) !== 'undefined') stats.update();
};

// state
var pressed = {};
var clock = new THREE.Clock();

// globals
var scene = getScene();
var camera = getCamera();
var light = getLight(scene);
var renderer = getRenderer();
var world = getPhysics();
var physicsMaterial = getPhysicsMaterial();
//var stats = getStats();
//var controls = getControls(camera, renderer);

// global body references
var sphereBody, floorBody;

// add meshes
var loader = new THREE.TextureLoader();
var floors = getPlanes(scene, loader);
var background = getBackground(scene, loader);
var sphereData = getSphere(scene);
var sphere = sphereData[0];
var sphereGroup = sphereData[1];

addObjectPhysics();
addListeners();
render();
body { margin: 0; overflow: hidden; }
canvas { width: 100%; height: 100%; }
<script src='https://cdnjs.cloudflare.com/ajax/libs/three.js/88/three.min.js'></script>
<script src='https://cdnjs.cloudflare.com/ajax/libs/cannon.js/0.6.2/cannon.js'></script>

评论问题的回答

@jparimaa 我认为最直观的实现方式是让 W 增加向前的动量,S 增加向后的动量,A 和 D 围绕球旋转摄像机。这可能吗?

@HariV 您链接到的控件是我在没有上述物理的演示中使用的控件。是否有可能使该逻辑适用于物理学?

最佳答案

我认为如果 W 键始终相对于相机“向前”移动球,这对用户来说是最直观的

一种选择是计算球和相机之间的方向并向该方向添加速度。在这种情况下,如果你向前插入球,那么你可以旋转相机而不影响球的速度。只有在旋转后按 W/S 才会改变方向。我不确定这是否是您想要的,但也许这会给您一些想法。

我试过下面的代码(rotation是初始化为0的全局变量)

function moveSphere() {
var delta = clock.getDelta(); // seconds
var moveDistance = 500 * delta; // n pixels per second
var dir = new THREE.Vector3(sphereBody.position.x, sphereBody.position.y, sphereBody.position.z);
dir.sub(camera.position).normalize(); // direction vector between the camera and the ball
if (pressed['W'] || pressed['ARROWUP']) {
sphereBody.velocity.x += moveDistance * dir.x;
sphereBody.velocity.z += moveDistance * dir.z;
}
if (pressed['S'] || pressed['ARROWDOWN']) {
sphereBody.velocity.x -= moveDistance * dir.x;
sphereBody.velocity.z -= moveDistance * dir.z;
}
}

function moveCamera() {
var delta = clock.getDelta();
var sensitivity = 150;
var rotateAngle = Math.PI / 2 * delta * sensitivity;
if (pressed['A'] || pressed['ARROWLEFT']) {
rotation -= rotateAngle;
}
if (pressed['D'] || pressed['ARROWRIGHT']) {
rotation += rotateAngle;
}
var rotZ = Math.cos(rotation)
var rotX = Math.sin(rotation)
var distance = 200;
camera.position.x = sphereBody.position.x - (distance * rotX);
camera.position.y = sphereBody.position.y + 50;
camera.position.z = sphereBody.position.z - (distance * rotZ);
camera.lookAt(sphereGroup.position);
}

关于javascript - Three.js 保持相机在物体后面,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/48107006/

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