递增显示 three.js TubeGeometry

Question

我可以显示一个 THREE.TubeGeometry 数字如下

下面的代码，link 到 jsbin

<html>
<body>
<script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r75/three.js"></script>

<script>
    // global variables
    var renderer;
    var scene;
    var camera;
    var geometry;

    var control;

    var count = 0;
    var animationTracker;

    init();
    drawSpline();

    function init()
    {
        // create a scene, that will hold all our elements such as objects, cameras and lights.
        scene = new THREE.Scene();

        // create a camera, which defines where we're looking at.
        camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);

        // create a render, sets the background color and the size
        renderer = new THREE.WebGLRenderer();
        renderer.setClearColor('lightgray', 1.0);
        renderer.setSize(window.innerWidth, window.innerHeight);

        // position and point the camera to the center of the scene
        camera.position.x = 0;
        camera.position.y = 40;
        camera.position.z = 40;
        camera.lookAt(scene.position);

        // add the output of the renderer to the html element
        document.body.appendChild(renderer.domElement);
    }

    function drawSpline(numPoints)
    {
        var numPoints = 100;
//        var start = new THREE.Vector3(-5, 0, 20);
        var start = new THREE.Vector3(-5, 0, 20);
        var middle = new THREE.Vector3(0, 35, 0);
        var end = new THREE.Vector3(5, 0, -20);

        var curveQuad = new THREE.QuadraticBezierCurve3(start, middle, end);

        var tube = new THREE.TubeGeometry(curveQuad, numPoints, 0.5, 20, false);
        var mesh = new THREE.Mesh(tube, new THREE.MeshNormalMaterial({
            opacity: 0.9,
            transparent: true
        }));

        scene.add(mesh);
        renderer.render(scene, camera);
    }
</script>
</body>
</html>

但是，我想逐步显示，就像正在加载的弧线一样，它作为起点开始，逐步绘制，最后看起来如下所示完成后弧形。

我一直在努力，并且能够通过存储弧覆盖的所有 points/coordinates 并在连续坐标之间画线来做到这一点，这样我就得到了 'arc loading incrementally' 感觉。但是，有没有更好的方法来实现这一目标？这是 link 到 jsbin

也在这里添加代码

<!DOCTYPE html>
<html>
<head>
    <title>Incremental Spline Curve</title>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/three.js/r75/three.js"></script>
    <style>
        body {
            margin: 0;
            overflow: hidden;
        }
    </style>
</head>
<script>

    // global variables
    var renderer;
    var scene;
    var camera;
    var splineGeometry;

    var control;

    var count = 0;
    var animationTracker;

//    var sphereCamera;
    var sphere;
    var light;

    function init() {

        // create a scene, that will hold all our elements such as objects, cameras and lights.
        scene = new THREE.Scene();

        // create a camera, which defines where we're looking at.
        camera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 0.1, 1000);

        // create a render, sets the background color and the size
        renderer = new THREE.WebGLRenderer();
//        renderer.setClearColor(0x000000, 1.0);
        renderer.setClearColor( 0xffffff, 1 );
        renderer.setSize(window.innerWidth, window.innerHeight);

        // position and point the camera to the center of the scene
        camera.position.x = 0;
        camera.position.y = 40;
        camera.position.z = 40;
        camera.lookAt(scene.position);

        // add the output of the renderer to the html element
        document.body.appendChild(renderer.domElement);

//        //init for sphere
//        sphereCamera = new THREE.PerspectiveCamera(45, window.innerWidth / window.innerHeight, 1, 1000);
//        sphereCamera.position.y = -400;
//        sphereCamera.position.z = 400;
//        sphereCamera.rotation.x = .70;

        sphere = new THREE.Mesh(new THREE.SphereGeometry(0.8,31,31), new THREE.MeshLambertMaterial({
            color: 'yellow',
        }));

        light = new THREE.DirectionalLight('white', 1);
//        light.position.set(0,-400,400).normalize();
        light.position.set(0,10,10).normalize();

        //get points covered by Spline
        getSplineData();
    }

    //save points in geometry.vertices
    function getSplineData() {
        var curve = new THREE.CubicBezierCurve3(
                new THREE.Vector3( -5, 0, 10 ),
                new THREE.Vector3(0, 20, 0 ),
                new THREE.Vector3(0, 20, 0 ),
                new THREE.Vector3( 2, 0, -25 )
        );

        splineGeometry = new THREE.Geometry();
        splineGeometry.vertices = curve.getPoints( 50 );

        animate();
    }

    //scheduler loop
    function animate() {
        if(count == 50)
        {
            cancelAnimationFrame(animationTracker);
            return;
        }

        //add line to the scene
        drawLine();

        renderer.render(scene, camera);
  //      renderer.render(scene, sphereCamera);

        count += 1;
//        camera.position.z -= 0.25;
//        camera.position.y -= 0.25;
        animationTracker = requestAnimationFrame(animate);
    }

    function drawLine() {
        var lineGeometry = new THREE.Geometry();
        var lineMaterial = new THREE.LineBasicMaterial({
            color: 0x0000ff
        });
        console.log(splineGeometry.vertices[count]);
        console.log(splineGeometry.vertices[count+1]);
        lineGeometry.vertices.push(
                splineGeometry.vertices[count],
                splineGeometry.vertices[count+1]
        );

        var line = new THREE.Line( lineGeometry, lineMaterial );
        scene.add( line );
    }

    // calls the init function when the window is done loading.
    window.onload = init;

</script>
<body>
</body>
</html>

缺点：用上面的方法做的缺点是，一天结束时，我在连续的点之间画一条线，所以我失去了 TubeGeometry 中很多可能的效果，例如，厚度、透明度等

请建议我另一种方法来获得 TubeGeometry 的平滑增量加载。

Answer 1

我对 three.js 不是很熟悉。但我想我可以提供帮助。我有两个解决方案给你。两者都基于相同的原则：围绕新曲线构建新的 TubeGeometry 或重建当前的 TubeGeometry。

解决方案 1（简单）：

var CurveSection = THREE.Curve.create(function(base, from, to) {
  this.base = base;
  this.from = from;
  this.to = to;
}, function(t) {
  return this.base.getPoint((1 - t) * this.from + t * this.to);
});

您定义了一种新型曲线，它只是从给定曲线中选择一段。用法：

var curve = new CurveSection(yourCurve, 0, .76); // Where .76 is your percentage

现在你可以建造一个新的管子了。

解法 2（数学！）：

你正在为你的圆弧使用二次贝塞尔曲线，太棒了！这条曲线是一条抛物线。您只需要该抛物线的一部分，而这又是一条抛物线，只是具有其他界限。

我们需要的是一段贝塞尔曲线。假设曲线由 A（起点）、B（方向）、C（终点）定义。如果我们想将起点更改为点 D，将终点更改为点 F，我们需要点 E，即 D 和 F 中曲线的方向。因此 D 和 F 中抛物线的切线必须与 E 相交.所以下面的代码会给我们想要的结果：

// Calculates the instersection point of Line3 l1 and Line3 l2.
function intersection(l1, l2) {
  var A = l1.start;
  var P = l2.closestPointToPoint(A);
  var Q = l1.closestPointToPoint(P);
  var l = P.distanceToSquared(A) / Q.distanceTo(A);
  var d = (new THREE.Vector3()).subVectors(Q, A);
  return d.multiplyScalar(l / d.length()).add(A);
}

// Calculate the tangentVector of the bezier-curve
function tangentQuadraticBezier(bezier, t) {
  var s = bezier.v0,
      m = bezier.v1,
      e = bezier.v2;
  return new THREE.Vector3(
    THREE.CurveUtils.tangentQuadraticBezier(t, s.x, m.x, e.x),
    THREE.CurveUtils.tangentQuadraticBezier(t, s.y, m.y, e.y),
    THREE.CurveUtils.tangentQuadraticBezier(t, s.z, m.z, e.z)
  );
}

// Returns a new QuadraticBezierCurve3 with the new bounds.
function sectionInQuadraticBezier(bezier, from, to) {
  var s = bezier.v0,
      m = bezier.v1,
      e = bezier.v2;

  var ns = bezier.getPoint(from),
      ne = bezier.getPoint(to);
  var nm = intersection(
    new THREE.Line3(ns, tangentQuadraticBezier(bezier, from).add(ns)),
    new THREE.Line3(ne, tangentQuadraticBezier(bezier, to).add(ne))
  );
  return new THREE.QuadraticBezierCurve3(ns, nm, ne);
}

这是一种非常数学化的方法，但如果您需要贝塞尔曲线的特殊属性，这就是方法。

注意：第一种方案最简单。我不熟悉 Three.js 所以我不知道实现动画的最有效方法是什么。 Three.js 似乎没有使用贝塞尔曲线的特殊属性，所以解决方案 2 可能没那么有用。

我希望你从中得到了一些有用的东西。

Answer 2

THREE.TubeGeometryreturns一个THREE.Geometry。通过将几何转换为

THREE.BufferGeometry，您可以访问属性 drawRange，您可以将其设置为动画网格绘制：

var nEnd = 0, nMax, nStep = 90; // 30 faces * 3 vertices/face

...

// geometry
var geometry = new THREE.TubeGeometry( path, pathSegments, tubeRadius, radiusSegments, closed );

// to buffer goemetry
geometry = new THREE.BufferGeometry().fromGeometry( geometry );
nMax = geometry.attributes.position.count;

...

function animate() {

    requestAnimationFrame( animate );

    nEnd = ( nEnd + nStep ) % nMax;

    mesh.geometry.setDrawRange( 0, nEnd );

    renderer.render( scene, camera );

}

fiddle: http://jsfiddle.net/k73pxyL2/

编辑：另一种方法，参见。

three.js r.75

Answer 3

通常你可以使用.getPointAt()到"get a vector for point at relative position in curve according to arc length"的方法在曲线长度的一定百分比处得到一个点。

所以通常情况下如果你想绘制70%的曲线并且一条完整的曲线被绘制成100段。那么你可以这样做：

var percentage = 70;
var curvePath = new THREE.CurvePath();

var end, start = curveQuad.getPointAt( 0 );

for(var i = 1; i < percentage; i++){
    end = curveQuad.getPointAt( percentage / 100 );
    lineCurve = new THREE.LineCurve( start, end );
    curvePath.add( lineCurve );
    start = end;
}

但我认为这对您的 curveQuad 不起作用，因为 getPointAt 方法未针对此类型实现。解决方法是在这样的数组中为您的曲线获取 100 点：

points = curve.getPoints(100);

然后你可以做几乎相同的事情：

var percentage = 70;
var curvePath = new THREE.CurvePath();

var end, start = points[ 0 ];

for(var i = 1; i < percentage; i++){
    end = points[ percentage ]
    lineCurve = new THREE.LineCurve( start, end );
    curvePath.add( lineCurve );
    start = end;
}

现在您的 curvePath 包含您要用于绘制管道的线段：

// draw the geometry
var radius = 5, radiusSegments = 8, closed = false;
var geometry = new THREE.TubeGeometry(curvePath, percentage, radius, radiusSegments, closed);

Here a fiddle 并演示如何动态使用它

递增显示 three.js TubeGeometry

Incrementally display three.js TubeGeometry

javascript

three.js

spline