BabylonJS - Ribbon
Ribbon 以路径数组作为输入，并沿着这些路径绘制线条。它使用复杂的逻辑来获取坐标。在下面给出的示例中，我们使用贝塞尔曲线方程来绘制丝带。贝塞尔曲线主要用于 3D 游戏中，以模拟平滑曲线。曲线需要控制点，曲线沿着控制点绘制。
演示
<!doctype html>
<html>
<head>
<meta charset = "utf-8">
<title>BabylonJs - Basic Element-Creating Scene</title>
<script src = "babylon.js"></script>
<style>
canvas {width: 100%; height: 100%;}
</style>
</head>
<body>
<canvas id = "renderCanvas"></canvas>
<script type = "text/javascript">
var canvas = document.getElementById("renderCanvas");
var engine = new BABYLON.Engine(canvas, true);
var createScene = function() {
var scene = new BABYLON.Scene(engine);
scene.clearColor = new BABYLON.Color3(0.8, 0.8, 0.8);
var camera = new BABYLON.ArcRotateCamera("Camera", 3 *Math.PI / 2, Math.PI / 2, 50, BABYLON.Vector3.Zero(), scene);
camera.attachControl(canvas, false);
// 灯光
var light = new BABYLON.HemisphericLight("hemi", new BABYLON.Vector3(0, 1, 0), scene);
light.groundColor = new BABYLON.Color3(0.2, 0.2, 0.5);
light.intensity = 0.6;
var light2 = new BABYLON.PointLight("light2", new BABYLON.Vector3(-20, 0, -20), scene);
light2.diffuse = BABYLON.Color3.White();
light2.specular = BABYLON.Color3.Green();
light2.intensity = 0.6;
// 材料
var mat = new BABYLON.StandardMaterial("mat1", scene);
mat.alpha = 1.0;
mat.diffuseColor = new BABYLON.Color3(0.5, 0.5, 1.0);
//mat.backFaceCulling = false;
mat.wireframe = true;
// cubic Bézier function
// cubicBezier(vector3Origin, vector3Control1, vector3Control2, vector3Destination, segmentNumber)
var cubicBezier = function(v0, v1, v2, v3, nb) {
var bez = [];
var step = 1 / nb;
var equation = function(t, val0, val1, val2, val3) {
var res = (1 -t)*(1-t)*(1-t) * val0 + 3 * t * (1-t)*(1-t) * val1 + 3 * t*t *(1-t) * val2 + t*t*t * val3;
return res;
};
for(var i = 0; i <= 1; i += step) {
bez.push( new BABYLON.Vector3(equation(i, v0.x, v1.x, v2.x, v3.x), equation(i, v0.y, v1.y, v2.y, v3.y), equation(i, v0.z, v1.z, v2.z, v3.z)) );
}
bez.push(v3);
return bez;
};
var populatePath = function(p) {
var pi2 = Math.PI * 2;
var i = p / 25 ;
var path = cubicBezier( new BABYLON.Vector3(3 * Math.cos(pi2 * i),-10, 3 * Math.sin(pi2 *i)),
new BABYLON.Vector3(12 * Math.cos(pi2 * i), p/5 ,10 * Math.sin(pi2 * i)),
new BABYLON.Vector3(15 * Math.cos(pi2 * i), p/2 ,8 * Math.sin(pi2 * i)),
new BABYLON.Vector3(3 * Math.cos(pi2 * i), 10, 3 * Math.sin(pi2 * i)), 50);
return path;
};
// path visualizer helper
var showPath = function(path, scene) {
var line = BABYLON.Mesh.CreateLines("line", path, scene )
};
var paths = [];
for (var p = 0; p < 20; p++) {
paths[p] = populatePath(p);
showPath(paths[p], scene);
}
var ribbon = new BABYLON.Mesh.CreateRibbon("ribbon", paths, false, false, null, scene);
ribbon.material = mat;
scene.registerBeforeRender(function() {
light2.position = camera.position;
});
return scene;
};
var scene = createScene();
engine.runRenderLoop(function() {
scene.render();
});
</script>
</body>
</html>
输出
上述代码行生成以下输出 −
语法
varribbon = new BABYLON.Mesh.CreateRibbon("ribbon",paths,false,false,null,scene);
ribbon 使用 x、y 和 z 方向的路径数组。上面使用的贝塞尔曲线方程在此处计算 −
var cubicBezier = function(v0, v1, v2, v3, nb) {
var bez = [];
var step = 1 / nb;
var equation = function(t, val0, val1, val2, val3) {
var res = (1 -t)*(1-t)*(1-t) * val0 + 3 * t * (1-t)*(1-t) * val1 + 3 * t*t *(1-t) * val2 + t*t*t * val3;
return res;
};
for(var i = 0; i <= 1; i += step) {
bez.push( new BABYLON.Vector3(equation(i, v0.x, v1.x, v2.x, v3.x), equation(i, v0.y, v1.y, v2.y, v3.y), equation(i, v0.z, v1.z, v2.z, v3.z)) );
}
bez.push(v3);
return bez;
};
贝塞尔曲线方程
var res = (1 -t)*(1-t)*(1-t) * val0 + 3 * t * (1-t)*(1-t) * val1 + 3 * t*t *(1-t) * val2 + t*t*t * val3;
babylonjs_parametric_shapes.html
