babylon.js 学习笔记(5)-526互联

前面我们画的小房子，基本上都是用内置的标准形状组合而成，但并非所有对象都这么简单，今天我们来画一个小汽车，汽车由多个零件组成，控制这些零件的缩放、位置、旋转，如果每个都单独用代码来修改position/roration/scaling，未免太复杂，幸好babylon.js中，对象有所谓的child/parent 关系。简单来说，如果A是B的parent，则对A的任何位置/缩放/旋转，其child也会同步受影响，但child可以在parent的基础上，再独立叠加新变化。有没有发现，这很符合遗传学，孩子必然长得象父母，但是又有些自己的特征。

一、理解 parent / child 关系

const createScene = () => {
    const scene = new BABYLON.Scene(engine);

    const camera = new BABYLON.ArcRotateCamera("camera", -Math.PI / 2.2, Math.PI / 2.5, 15, new BABYLON.Vector3(0, 0, 0));
    camera.attachControl(canvas, true);

    const light = new BABYLON.HemisphericLight("light", new BABYLON.Vector3(0, 1, 0));

    //方块6个面的颜色
    const faceColors = [];
    faceColors[0] = BABYLON.Color3.Blue();
    faceColors[1] = BABYLON.Color3.Teal()
    faceColors[2] = BABYLON.Color3.Red();
    faceColors[3] = BABYLON.Color3.Purple();
    faceColors[4] = BABYLON.Color3.Green();
    faceColors[5] = BABYLON.Color3.Yellow();

    const boxParent = BABYLON.MeshBuilder.CreateBox("Box", { faceColors: faceColors });
    const boxChild = BABYLON.MeshBuilder.CreateBox("Box", { size: 0.5, faceColors: faceColors });
    //小方块是大方块的child
    boxChild.setParent(boxParent);

    //child的独立特征
    boxChild.position.x = 0;
    boxChild.position.y = 2;
    boxChild.position.z = 0;

    boxChild.rotation.x = Math.PI / 4;
    boxChild.rotation.y = Math.PI / 4;
    boxChild.rotation.z = Math.PI / 4;

    //parent的位置变化，将影响child
    boxParent.position.x = 2;
    boxParent.position.y = 0;
    boxParent.position.z = 0;

    boxParent.rotation.x = 0;
    boxParent.rotation.y = 0;
    boxParent.rotation.z = -Math.PI / 4;

    //辅助坐标轴，方便理解
    const boxChildAxes = localAxes(1.5, scene);
    boxChildAxes.parent = boxChild;
    showAxis(5, scene);
    return scene;
}




//坐标轴
const showAxis = (size, scene) => {
    const makeTextPlane = (text, color, size) => {
        const dynamicTexture = new BABYLON.DynamicTexture("DynamicTexture", 50, scene, true);
        dynamicTexture.hasAlpha = true;
        dynamicTexture.drawText(text, 5, 40, "bold 36px Arial", color, "transparent", true);
        const plane = new BABYLON.Mesh.CreatePlane("TextPlane", size, scene, true);
        plane.material = new BABYLON.StandardMaterial("TextPlaneMaterial", scene);
        plane.material.backFaceCulling = false;
        plane.material.specularColor = new BABYLON.Color3(0, 0, 0);
        plane.material.diffuseTexture = dynamicTexture;
        return plane;
    };

    const axisX = BABYLON.Mesh.CreateLines("axisX", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(size, 0, 0), new BABYLON.Vector3(size * 0.95, 0.05 * size, 0),
        new BABYLON.Vector3(size, 0, 0), new BABYLON.Vector3(size * 0.95, -0.05 * size, 0)
    ]);
    axisX.color = new BABYLON.Color3(1, 0, 0);
    const xChar = makeTextPlane("X", "white", size / 8);
    xChar.position = new BABYLON.Vector3(0.9 * size, -0.05 * size, 0);

    const axisY = BABYLON.Mesh.CreateLines("axisY", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(0, size, 0), new BABYLON.Vector3(-0.05 * size, size * 0.95, 0),
        new BABYLON.Vector3(0, size, 0), new BABYLON.Vector3(0.05 * size, size * 0.95, 0)
    ]);
    axisY.color = new BABYLON.Color3(0, 1, 0);
    const yChar = makeTextPlane("Y", "white", size / 8);
    yChar.position = new BABYLON.Vector3(0, 0.9 * size, -0.05 * size);

    const axisZ = BABYLON.Mesh.CreateLines("axisZ", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(0, 0, size), new BABYLON.Vector3(0, -0.05 * size, size * 0.95),
        new BABYLON.Vector3(0, 0, size), new BABYLON.Vector3(0, 0.05 * size, size * 0.95)
    ]);
    axisZ.color = new BABYLON.Color3(0, 1, 1);
    const zChar = makeTextPlane("Z", "white", size / 8);
    zChar.position = new BABYLON.Vector3(0, 0.05 * size, 0.9 * size);
};

//小方块的坐标轴
localAxes = (size, scene) => {
    const local_axisX = BABYLON.Mesh.CreateLines("local_axisX", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(size, 0, 0), new BABYLON.Vector3(size * 0.95, 0.05 * size, 0),
        new BABYLON.Vector3(size, 0, 0), new BABYLON.Vector3(size * 0.95, -0.05 * size, 0)
    ], scene);
    local_axisX.color = new BABYLON.Color3(1, 0, 0);

    local_axisY = BABYLON.Mesh.CreateLines("local_axisY", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(0, size, 0), new BABYLON.Vector3(-0.05 * size, size * 0.95, 0),
        new BABYLON.Vector3(0, size, 0), new BABYLON.Vector3(0.05 * size, size * 0.95, 0)
    ], scene);
    local_axisY.color = new BABYLON.Color3(0, 1, 0);

    const local_axisZ = BABYLON.Mesh.CreateLines("local_axisZ", [
        new BABYLON.Vector3.Zero(), new BABYLON.Vector3(0, 0, size), new BABYLON.Vector3(0, -0.05 * size, size * 0.95),
        new BABYLON.Vector3(0, 0, size), new BABYLON.Vector3(0, 0.05 * size, size * 0.95)
    ], scene);
    local_axisZ.color = new BABYLON.Color3(0, 1, 1);


    const local_origin = new BABYLON.TransformNode("local_origin");

    local_axisX.parent = local_origin;
    local_axisY.parent = local_origin;
    local_axisZ.parent = local_origin;

    return local_origin;
}

代码有点长，坐标轴的部分可以先不管，只看createScene即可。

在线地址：https://yjmyzz.github.io/babylon_js_study/day05/01.html

二、理解 ExtrudePolygon

ExtrudePolygon方法可以画出一些不规则形状，比如下面：

const buildCar = () => {
    //base
    const outline = [
        new BABYLON.Vector3(-0.3, 0, -0.1),
        new BABYLON.Vector3(0.2, 0, -0.1),
    ]

    //top
    outline.push(new BABYLON.Vector3(0, 0, 0.1));
    outline.push(new BABYLON.Vector3(-0.3, 0, 0.1));

    //back formed automatically
    const car = BABYLON.MeshBuilder.ExtrudePolygon("car", { shape: outline, depth: 0.2 });

    return car;
}

在线地址：https://yjmyzz.github.io/babylon_js_study/day05/02.html

具体画的过程，可以结合下面的图理解：简单来说，A->B->C->D 先画出1个梯形，然后向下拉长，就得到了这个模型。

再完善一下，把车头及轮子加上

const createScene = () => {
    const scene = new BABYLON.Scene(engine);

    const camera = new BABYLON.ArcRotateCamera("camera", -Math.PI / 2, Math.PI / 2.5, 3, new BABYLON.Vector3(0, 0, 0));
    camera.attachControl(canvas, true);
    const light = new BABYLON.HemisphericLight("light", new BABYLON.Vector3(0, 1, 0));

    //造车身
    const car = buildCar();
    //安装轮子
    buildWheel(car);

    showAxis(0.8, scene);

    return scene;
}

//车身
const buildCar = () => {
    //base
    const outline = [
        new BABYLON.Vector3(-0.3, 0, -0.1),
        new BABYLON.Vector3(0.2, 0, -0.1),
    ]

    //curved front
    for (let i = 0; i < 20; i++) {
        outline.push(new BABYLON.Vector3(0.2 * Math.cos(i * Math.PI / 40), 0, 0.2 * Math.sin(i * Math.PI / 40) - 0.1));
    }

    //top
    outline.push(new BABYLON.Vector3(0, 0, 0.1));
    outline.push(new BABYLON.Vector3(-0.3, 0, 0.1));

    //back formed automatically
    const car = BABYLON.MeshBuilder.ExtrudePolygon("car", { shape: outline, depth: 0.2 });

    return car;
}


//轮子
const buildWheel = (car) => {
    const wheelRB = BABYLON.MeshBuilder.CreateCylinder("wheelRB", { diameter: 0.125, height: 0.05 })
    wheelRB.parent = car;
    wheelRB.position.z = -0.1;
    wheelRB.position.x = -0.2;
    wheelRB.position.y = 0.035;

    const wheelRF = wheelRB.clone("wheelRF");
    wheelRF.position.x = 0.1;

    const wheelLB = wheelRB.clone("wheelLB");
    wheelLB.position.y = -0.2 - 0.035;

    const wheelLF = wheelRF.clone("wheelLF");
    wheelLF.position.y = -0.2 - 0.035;
}

在线地址：https://yjmyzz.github.io/babylon_js_study/day05/03.html

最后再加上贴图：

const createScene = () => {
    const scene = new BABYLON.Scene(engine);

    const camera = new BABYLON.ArcRotateCamera("camera", -Math.PI / 2, Math.PI / 2.5, 3, new BABYLON.Vector3(0.2, -0.20, 1.5));
    camera.attachControl(canvas, true);
    const light = new BABYLON.HemisphericLight("light", new BABYLON.Vector3(0, 1, 0));

    const car = buildCar();
    car.rotation.x = -Math.PI / 2;

    showAxis(0.6, scene);

    return scene;
}

const buildCar = () => {
    //base
    const outline = [
        new BABYLON.Vector3(-0.3, 0, -0.1),
        new BABYLON.Vector3(0.2, 0, -0.1),
    ]

    //curved front
    for (let i = 0; i < 20; i++) {
        outline.push(new BABYLON.Vector3(0.2 * Math.cos(i * Math.PI / 40), 0, 0.2 * Math.sin(i * Math.PI / 40) - 0.1));
    }

    //top
    outline.push(new BABYLON.Vector3(0, 0, 0.1));
    outline.push(new BABYLON.Vector3(-0.3, 0, 0.1));

    //car face UVs
    const faceUV = [];
    faceUV[0] = new BABYLON.Vector4(0, 0.5, 0.38, 1);
    faceUV[1] = new BABYLON.Vector4(0, 0, 1, 0.5);
    faceUV[2] = new BABYLON.Vector4(0.38, 1, 0, 0.5);

    //car material
    const carMat = new BABYLON.StandardMaterial("carMat");
    carMat.diffuseTexture = new BABYLON.Texture("../assets/img/car.png");

    //back formed automatically
    const car = BABYLON.MeshBuilder.ExtrudePolygon("car", { shape: outline, depth: 0.2, faceUV: faceUV, wrap: true });
    car.material = carMat;


    //wheel face UVs
    const wheelUV = [];
    wheelUV[0] = new BABYLON.Vector4(0, 0, 1, 1);
    wheelUV[1] = new BABYLON.Vector4(0, 0.5, 0, 0.5);
    wheelUV[2] = new BABYLON.Vector4(0, 0, 1, 1);

    //car material
    const wheelMat = new BABYLON.StandardMaterial("wheelMat");
    wheelMat.diffuseTexture = new BABYLON.Texture("../assets/img/wheel.png");

    const wheelRB = BABYLON.MeshBuilder.CreateCylinder("wheelRB", { diameter: 0.125, height: 0.05, faceUV: wheelUV })
    wheelRB.material = wheelMat;

    wheelRB.parent = car;
    wheelRB.position.z = -0.1;
    wheelRB.position.x = -0.2;
    wheelRB.position.y = 0.035;

    const wheelRF = wheelRB.clone("wheelRF");
    wheelRF.position.x = 0.1;

    const wheelLB = wheelRB.clone("wheelLB");
    wheelLB.position.y = -0.2 - 0.035;

    const wheelLF = wheelRF.clone("wheelLF");
    wheelLF.position.y = -0.2 - 0.035;

    return car;
}

在线地址：https://yjmyzz.github.io/babylon_js_study/day05/04.html

参考文档：https://doc.babylonjs.com/features/introductionToFeatures/chap3/carmat

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