Tag:Untiy3D, LayerMask, Bitshift, Ignored layer, Bitmask

BitmaskOpration.cs

 // Turn on the bit using an OR operation:
 private void Show() {
     camera.cullingMask |= 1 << LayerMask.NameToLayer("SomeLayer");
 }
 
 // Turn off the bit using an AND operation with the complement of the shifted int:
 private void Hide() {
     camera.cullingMask &=  ~(1 << LayerMask.NameToLayer("SomeLayer"));
 }
 
 // Toggle the bit using a XOR operation:
 private void Toggle() {
     camera.cullingMask ^= 1 << LayerMask.NameToLayer("SomeLayer");
 }

LayerCache.cs

    static int _player = -1;

    static public int player
    {
        get
        {
            if (_player == -1)
                _player = LayerMask.NameToLayer("Player");
            return _player;
        }
    }

    static int _npc = -1;

    static public int npc
    {
        get
        {
            if (_npc == -1)
                _npc = LayerMask.NameToLayer("NPC");
            return _npc;
        }
    }
    
    static int _platform = -1;

    static public int platform
    {
        get
        {
            if (_platform == -1)
                _platform = LayerMask.NameToLayer("Platform");
            return _platform;
        }
    }

    static int _onewayPlatform = -1;

    static public int onewayPlatform
    {
        get
        {
            if (_onewayPlatform == -1)
                _onewayPlatform = LayerMask.NameToLayer("OnewayPlatform");
            return _onewayPlatform;
        }
    }

LayerCombineAndCompare.cs

// Combine layers
public LayerMask ignoreLayer = LayerCacher.player | LayerCacher.npc;

public LayerMask platformMask = LayerCacher.platform;
public LyaerMask onewayPlatformMask = LayerCacher.oncewayPlatform;

void OnTriggerStay2D(Collider2D other)
{
    // Check whether this object's layer should be ignored.
    LayerMask mask = 1 << other.gameObject.layer;   // Bitshift
    bool isIgnored = (mask & ignoreLayer) == mask;  // Do AND. If combined layermask contains this layer, the result should be the same to it self.
    if (!colliders.Contains(other) && !isIgnored)
    {
        colliders.Add(other);
    }
    
    LayerMask twoWayPlatform = platformMask & ~onewayPlatform;  // Get all objects which on platform layer but not on one way platform layer.
}

// Ref: http://answers.unity3d.com/questions/8715/how-do-i-use-layermasks.html