Ios 游戏引擎Collison Bitmask。。。为什么是0x01等？

在Sprite Kit（iOS开发）和Cocos2d-x（我知道这是Sprite Kit的灵感来源，因此他们使用了很多相同的工具）中都遇到了这种情况，我最终决定弄清楚为什么会发生这种情况：

使用physic引擎时，我创建了一个精灵，并向其中添加了physicsBody。在大多数情况下，我了解如何设置类别、冲突和联系人位掩码，以及它们是如何工作的。问题在于实际的位掩码编号：

SpriteKit：

static const uint32_t missileCategory     =  0x1 << 0;
sprite.physicsBody.categoryBitMask = missileCategory;

---

我完全搞不懂为什么要写0x01或0x1位掩码的原因是，它使您/程序能够轻松、非常快速地计算两个对象之间是否发生碰撞。因此：是这是某种优化

假设我们有三个类别

• 导弹

  0x1很好，但只需再进一步，在其他方向
  
  为什么用十六进制表示法？（
  0x1来回答您的具体问题
  
  “为什么有32种不同的类别可用？我想是32位的
  整数有0-10亿个数字（当然是无符号的）。那为什么呢
  难道我没有几十亿种可能的分类吗？”
  
  答案是，该类别始终被视为32位掩码，其只应设置一个位。因此，以下是有效值：
  
  00000000000000000000000000000001 = 1 = 1 << 0
  00000000000000000000000000000010 = 2 = 1 << 1
  00000000000000000000000000000100 = 4 = 1 << 2
  00000000000000000000000000001000 = 8 = 1 << 3
  00000000000000000000000000010000 = 16 = 1 << 4
  00000000000000000000000000100000 = 32 = 1 << 5
  00000000000000000000000001000000 = 64 = 1 << 6
  00000000000000000000000010000000 = 128 = 1 << 7
  00000000000000000000000100000000 = 256 = 1 << 8
  00000000000000000000001000000000 = 512 = 1 << 9
  00000000000000000000010000000000 = 1024 = 1 << 10
  00000000000000000000100000000000 = 2048 = 1 << 11
  .
  .
  .
  10000000000000000000000000000000 = 2,147,483,648 = 1 << 31
  
  0000000000000000000000000000000 1=1=1您可能希望签出，这有一个很好的示例。这是他们使用位掩码的部分，向上滚动以了解他们将如何设置位掩码。使用0x1 0B10000000000000000000、2147483648、0x80000000或0x1，我无法浏览此部分：“如果导弹和导弹集合！=0{…}”"，依我的想法，导弹是00010，导弹集合是00101，两者都不是0，所以会发生这样的事情……我怎么会不理解它呢？@这是一个按位and，按位and的结果，在两个输入都有1的地方都有1，所有其他位都是0。在您的示例中，00010和00101在同一位置没有任何1，因此对它们进行AND运算的结果为0。
  let player : UInt8 = 0b1 << 0  // 00000001 = 1
  let missile : UInt8 = 0b1 << 1 // 00000010 = 2
  let wall : UInt8 = 0b1 << 2    // 00000100 = 4
  
  let playerCollision = player | missile | wall // 00000111 = 7
  let missileCollision = player | wall          // 00000101 = 5
  
  if player & missileCollision != 0 {
      print("potential collision between player and missile") // prints
  }
  if missile & missileCollision != 0 {
      print("potential collision between two missiles") // does not print
  }
  
  let playerCategory : UInt8 = 0b1 << 0
  let missileCategory : UInt8 = 0b1 << 1
  let wallCategory : UInt8 = 0b1 << 2
  
  struct EntityStruct {
      var categoryBitmask : UInt8
      var collisionBitmask : UInt8
  }
  
  let player = EntityStruct(categoryBitmask: playerCategory, collisionBitmask: playerCategory | missileCategory | wallCategory)
  let missileOne = EntityStruct(categoryBitmask: missileCategory, collisionBitmask: playerCategory | wallCategory)
  let missileTwo = EntityStruct(categoryBitmask: missileCategory, collisionBitmask: playerCategory | wallCategory)
  let wall = EntityStruct(categoryBitmask: wallCategory, collisionBitmask: playerCategory | missileCategory | wallCategory)
  
  func canTwoObjectsCollide(first:EntityStruct, _ second:EntityStruct) -> Bool {
      if first.categoryBitmask & second.collisionBitmask != 0 {
          return true
      }
      return false
  }
  
  canTwoObjectsCollide(player, missileOne)     // true
  canTwoObjectsCollide(player, wall)           // true
  canTwoObjectsCollide(wall, missileOne)       // true
  canTwoObjectsCollide(missileTwo, missileOne) // false
  
  let catA = 0b0001
  let catB = 0b0010
  let catC = 0b0100
  
  static const uint32_t catA =  1 << 0;
  static const uint32_t catB =  1 << 1;
  static const uint32_t catC =  1 << 2;
  
  static const uint32_t catA =  1;
  static const uint32_t catB =  2;
  static const uint32_t catC =  4;
  
  if (bodyA.categoryBitMask & bodyB.collisionBitMask != 0)
  
  00000000000000000000000000000001 = 1 = 1 << 0
  00000000000000000000000000000010 = 2 = 1 << 1
  00000000000000000000000000000100 = 4 = 1 << 2
  00000000000000000000000000001000 = 8 = 1 << 3
  00000000000000000000000000010000 = 16 = 1 << 4
  00000000000000000000000000100000 = 32 = 1 << 5
  00000000000000000000000001000000 = 64 = 1 << 6
  00000000000000000000000010000000 = 128 = 1 << 7
  00000000000000000000000100000000 = 256 = 1 << 8
  00000000000000000000001000000000 = 512 = 1 << 9
  00000000000000000000010000000000 = 1024 = 1 << 10
  00000000000000000000100000000000 = 2048 = 1 << 11
  .
  .
  .
  10000000000000000000000000000000 = 2,147,483,648 = 1 << 31
  
  00000000000000000000000000000001 = 1 = 1 << 0   //Human
  00000000000000000000000000000010 = 2 = 1 << 1   //Alien
  00000000000000000000000000000100 = 4 = 1 << 2   //Soldier
  00000000000000000000000000001000 = 8 = 1 << 3   //Officer
  00000000000000000000000000010000 = 16 = 1 << 4  //Bullet
  00000000000000000000000000100000 = 32 = 1 << 5 //laser
  00000000000000000000000001000000 = 64 = 1 << 6 //powershot