Howto: if layermask contains layer?

Hi

I have searched a bit on the forum for how to see if a layermasks layer is enabled, although I can only find how you create a layermask.
The reason is that when building a custom inspector you can't create a LayerMask field, so I'm trying to create one myself.

Is it something like

Code (csharp):

1. if (layermask == 1<<layer)

?

 

It's not quite as simple as that, unfortunately. The layer mask is an integer, and you need to test just a single bit. You need to do something like:-

Code (csharp):

1. if (((layermask >> layer)  1) == 1) {
2.    ...
3. }

What this does is shift the bit that you want to test into the rightmost bit (ie, the digit that represents the value of 1). The bitwise-and operator then sets all bits except this one to zero. The value in the integer is then the value of the specific bit you want to test - it will be zero if false and one if true.

 

Hi

Thanks for the answer.
Although, like 10 seconds before you answered I found another solution:

Code (csharp):

1. if (layermask == (layermask | (1 << layer))) {

i.e if layermask equals layermask + my layer
And now I got a full LayerMask field for custom inspectors

Code (csharp):

1. public static int LayerMaskField (LayerMask selected) {
2.         ArrayList layers = new ArrayList ();
3.         ArrayList layerNumbers = new ArrayList ();
4.         string name = "";
5.         for (int i=0;i<32;i++) {
6.             string layerName = LayerMask.LayerToName (i);
7.             if (layerName != "") {
8.                 if (selected == (selected | (1 << i))) {
9.                     layers.Add ("> "+layerName);
10.                     name += layerName+", ";
11.                 } else {
12.                     layers.Add (layerName);
13.                 }
14.                 layerNumbers.Add (i);
15.             }
16.         }
17.         bool preChange = GUI.changed;
18.         GUI.changed = false;
19.         int[] LayerNumbers = layerNumbers.ToArray (typeof(int)) as int[];
20.         int newSelected = EditorGUILayout.Popup ("Mask",-1,layers.ToArray(typeof(string)) as string[],EditorStyles.layerMaskField);
21.         if (GUI.changed) {
22.             if (selected == (selected | (1 << LayerNumbers[newSelected]))) {
23.                 selected = ~(1 << LayerNumbers[newSelected]);
24.                 Debug.Log ("Set Layer "+LayerMask.LayerToName (LayerNumbers[newSelected]) + " To False "+selected.value);
25.             } else {
26.                 Debug.Log ("Set Layer "+LayerMask.LayerToName (LayerNumbers[newSelected]) + " To True "+selected.value);
27.                 selected = selected | (1 << LayerNumbers[newSelected]);
28.             }
29.         } else {
30.             GUI.changed = preChange;
31.         }
32.         return selected;
33.     }

 

By the way, custom editor scripts CAN use the default inspector:
public override void OnInspectorGUI ()
{
base.OnInspectorGUI();
// ...More code here
}

And for any custom fields, use [HideInInspector] right next to the decleration.

 

Those are both "harder" than this more common method (and IMO also less intuitive):

Code (CSharp):

1. if (layerMask & (1 << layer) != 0)
2. {
3.     Debug.Log("I belong in this mask.");
4. }

It works because the 1 << layer creates an int with a single bit shifted over layer number times (layer 1 gives you 0001, layer 2 gives you 0010, layer 3 gives you 0100, etc). Then by using the bitwise and operator (&) it will return any bits that exist in both integers. So, it gives you a 0 if no bits match.

 

at least in Unity 2020, this throws an error: error CS0019: Operator '&' cannot be applied to operands of type 'LayerMask' and 'bool'

 

Not just in Unity 2020 ^^. Have a look at the Operators Precedence in C#. So the shift operator has the highest priority of the 3 operators we used. Therefore the brackets he used are pointless since the shift is done first anyways. However the issue is that the comparison operator

!=

has a higher priority than the bitwise AND operator

&

. So when we break down his code it actually tries to do this

Code (CSharp):

1. int mask = 1 << layer;
2. bool tmp = mask != 0;
3. bool result = layerMask & tmp;
4. if(result)
5.  

hopefully you see the result line makes no sense since we try to use the bitwise AND between a layermask and a boolean value. What you have to do is using brackets like this

if ((layerMask & 1 << layer) != 0)

This will result in this code

Code (CSharp):

1. int mask = 1 << layer;
2. int tmp = layermask & mask ;
3. bool result = tmp != 0;
4. if(result)
5.