按需查找立方体的上表面

Question

我要解决的一般问题是找出立方体的哪个面朝上。立方体可以在任何方向一次滚动 90°。如果某个面朝上，立方体就会消失。我正在使用补间来旋转立方体并改变它的位置。

我目前正试图通过创建一条新射线来解决这个问题，它的原点设置在立方体的正上方，它的方向向下短距离，所以它只与立方体的上表面相交。 violet thingy on top of die is ray cast downward into the cube

到目前为止一切顺利。当我检查console.log() 时，我将我的立方体作为相交对象，但是当我尝试通过faceIntersect.face 访问相交面时，它似乎是未定义的。

有问题的功能：

function checkUpperFace(posX, posZ) {

  // get position from passed x- and z-values (y is always above cube)
  // and set direction and length of ray
  var position = new THREE.Vector3( posX, 3, posZ );
  var direction = new THREE.Vector3(0, -1, 0);
  var far = 2;
  // create ray, that goes downwards from above the cube
  var cubeRaycaster = new THREE.Raycaster( position, direction, 0, far );
  // get intersection with upper face of rolled cube
  var faceIntersect = cubeRaycaster.intersectObject( currentCube );

  // add a helper to see the ray
  var arrowHelper = new THREE.ArrowHelper( direction, position, far, 0x770077 );
  scene.add( arrowHelper );

  console.log(faceIntersect); // object is shown with everything I want to know
  console.log(faceIntersect.face); // is shown to be undefined

}

Answer 1

可能不是您的光线投射问题的解决方案，而是另一种方法：您为什么不简单地通过比较旋转欧拉角来检测上表面？例如。 （伪代码）：

if(cube.rotation.x % 360 == 0)
{
    // upper face upwards
}
else if(cube.rotation.x % 360 == 90)
{
    // left face upwards
}

您将不得不处理值公差 (85° - 95°) 负旋转值和超出 PI*2 范围的值，但除此之外，不是更容易吗？

Answer 2

最后我以@unx 推荐的方式做到了，但我真的想避免使用巨大的 if-else 语句，所以我使用了一个数组 rotationLibrary，它具有所有可能的旋转，对应的顶面死。但是由于我用来旋转和移动骰子的补间，它的旋转值并不是真的在点上，因此很难与我在数组中使用它们时的固定旋转值进行比较。

所以我将骰子的旋转值“标准化”为可用于将它们与rotationLibrary 中的值进行比较的值。最后一步是存储/更新立方体对象本身顶部面的结果，以便我可以随时获取它。

// spawn condition:
// 1 on top, 2 facing camera, 3 facing right (seen from camera),
// 4 facing left (see 3), 5 facing away from camera, 6 facing down
var rotationLibrary = [
    {x: 0,      y: 0,   z: 0,   face: 1},
    {x: 0,      y: 90,  z: 0,   face: 1},
    {x: 180,    y: 0,   z: 180, face: 1},
    {x: 0,      y: -90, z: 0,   face: 1},
    {x: -90,    y: 0,   z: 0,   face: 2},
    {x: -90,    y: 0,   z: 90,  face: 2},
    {x: -90,    y: 0,   z: 180, face: 2},
    {x: -90,    y: 0,   z: -90, face: 2},
    {x: 0,      y: 0,   z: 90,  face: 3},
    {x: 90,     y: 90,  z: 0,   face: 3},
    {x: -90,    y: -90, z: 0,   face: 3},
    {x: -90,    y: 90,  z: 180, face: 3},
    {x: 180,    y: 0,   z: -90, face: 3},
    {x: 0,      y: 0,   z: -90, face: 4},
    {x: 90,     y: -90, z: 0,   face: 4},
    {x: -90,    y: 90,  z: 0,   face: 4},
    {x: 180,    y: 0,   z: 90,  face: 4},
    {x: 90,     y: 0,   z: 0,   face: 5},
    {x: 90,     y: 0,   z: -90, face: 5},
    {x: 90,     y: 0,   z: 180, face: 5},
    {x: 90,     y: 0,   z: 90,  face: 5},
    {x: 90,     y: 90,  z: 90,  face: 5},
    {x: 0,      y: 0,   z: 180, face: 6},
    {x: 180,    y: -90, z: 0,   face: 6},
    {x: 180,    y: 90,  z: 0,   face: 6},
    {x: 180,    y: 0,   z: 0,   face: 6}
];

function checkRotationsToGetUpperFace(cube) {
  // create object with "normalized" (brought to quarter-circle-degree-values) degrees
  var normalizedRotation = {
    x: 0,
    y: 0,
    z: 0
  };
  normalizedRotation.x = getNormalizedDegree(cube.rotation._x);
  normalizedRotation.y = getNormalizedDegree(cube.rotation._y);
  normalizedRotation.z = getNormalizedDegree(cube.rotation._z);

  // go through the library that has all the degrees with the corresponding upper face
  for (var i = 0; i < rotationLibrary.length; i++) {
    // check if the objects match, then get the face
    if (rotationLibrary[i].x == normalizedRotation.x &&
      rotationLibrary[i].y == normalizedRotation.y &&
      rotationLibrary[i].z == normalizedRotation.z) {
      cube.face = rotationLibrary[i].face;
    }
  }

  // reattach cube for correct movement later
  THREE.SceneUtils.attach(cube, scene, pivot);
}

function getNormalizedDegree(rotationValue) {
    // transform rotation value into degree value
  var rotValue = rotationValue / (Math.PI / 180);

  // default value is 0, so only check if it should be 90°, 180° or -90°
  var normalizedDegree = 0;
  // x between 45° and 135° ( ~ 90)
  if (rotValue > 45 && rotValue < 135) {
    normalizedDegree = 90;
  }
  // x between -45° and -135° ( ~ -90)
  else if (rotValue < -45 && rotValue > -135) {
    normalizedDegree = -90;
  }
  // x between 135° and 215° or x between -135° and -215° ( ~ 180)
  else if ((rotValue > 135 && rotValue < 215) || (rotValue < -135 && rotValue > -215)) {
    normalizedDegree = 180;
  }

  return normalizedDegree;
}

(http://jsfiddle.net/b2an3pq7/3/)