Question

我使用Three.js来显示飞机，但我似乎找不到改变它的法线的方法。这是一个具有普通属性的Plane类，那么有没有办法使用它而不是PlaneGeometry呢？

Answer 1

PlaneGeometry无法改变其法线，实际上总是（0,0,1）。要使平面几何体面向不同的方向，您需要转换其顶点。这个通过将Plane对象转换为变换矩阵并应用它来完成矩阵到PlaneGeometry。以下是生成转换矩阵的代码：

// Assumes that "plane" is the source THREE.Plane object.
// Normalize the plane
var normPlane=new THREE.Plane().copy(plane).normalize();
// Rotate from (0,0,1) to the plane's normal
var quaternion=new THREE.Quaternion()
  .setFromUnitVectors(new THREE.Vector3(0,0,1),normPlane.normal);
// Calculate the translation
var position=new THREE.Vector3(
  -normPlane.constant*normPlane.normal.x,
  -normPlane.constant*normPlane.normal.y,
  -normPlane.constant*normPlane.normal.z);
 // Create the matrix
var matrix=new THREE.Matrix4()
 .compose(position,quaternion,new THREE.Vector3(1,1,1));
// Transform the geometry (assumes that "geometry"
// is a THREE.PlaneGeometry or indeed any
// THREE.Geometry)
geometry.applyMatrix(matrix);

Answer 2

还有另一种选择可能适合你。您可以使用Mesh类中的 lookAt 方法。此方法继承自Object3D类。您只需指定平面的外观点即可。这样，您可以将PlaneGeometry重用于其他Mesh实例。

var geometry = new THREE.PlaneGeometry( 12, 12 );
var material = new THREE.MeshBasicMaterial( { color: 0x005E99 } );
var plane = new THREE.Mesh( geometry, material );
plane.lookAt(new THREE.Vector3(0.7, 0.7, 0.7));

如何在three.js中更改PlaneGeometry的法线？

2 个答案: