How to get the layermask Value ?

[Crocsx]

Hi,

So i read the documentation but I didn’t understood that much, and couldn’t fix my problem.

Actually I have this

    public LayerMask defaultLayer;
    public LayerMask reversedLayer;

I would like to change the layer in a fuction

    void Reverse()
    {
        Debug.Log(reversedLayer.value >> 1);
        if (reversed) {
            gameObject.layer = defaultLayer.value >> 1;
        }
        else
        {
            gameObject.layer = reversedLayer.value >> 1;
        }
        reversed = !reversed;
    }

I tried many solutions, but i always have this :

“A game object can only be in one layer. The layer needs to be in the range [0…31]”

How can i fix it?

thanks

[maccabbe]

First, let’s go over how layers and layermasks work.

A layermask is a group of layers, it can contain no, one, multiple, or all layers. This is done with layers having 32 possible values, 0 to 31, and layersmasks having 32 bits (0 or 1), i.e. 00001111000011110000111100001111. Every bit that is 1 means a layer is in the layermask.

Next, let’s go over how left/right shift operators (<</>>) work. x << y moves all the bits in x left y times. For instance: 101<<2 = 10100. This is useful to convert layers to a layermask. Layer 0 is the 0th bit in a layermask so you can use 1<<0 to get the right bit while layer 31 is the 31th bit in a layermask so you can use 1<<31. Bitwise operations are very inexpensive so converting from layer to layermask is very cheap and then bitwise operations can be used to get the mask you want. I.e. (1<<0) | (1<<31) is the layermask with bits 0 and 31 set to 1.

In your code you are attempting to convert a layermask to a layer. However a layermask can have zero or multiple layers so this doesn’t make sense. The method you are using, right shifting 1 bit, also doesn’t make sense. Supposing that a layermask only has the 16th layer you start with 00000000000000010000000000000000 and end with 00000000000000001000000000000000 instead of 16. Your Debug.Log(reversedLayer.value >> 1); would print the value in decimal which is 32768.

I would suggest not using layermasks if you want to use layers, Instead use strings/ints. For instance if your layers are called “Default” and “Reversed” you can use the following:

public int defaultLayer;
public int reversedLayer;

void Start()
{
    defaultLayer = LayerMask.NameToLayer("Default");
    reversedLayer = LayerMask.NameToLayer("Reversed");
}

void Reverse()
{
    Debug.Log(reversedLayer);
    if (reversed)
    {
        gameObject.layer = defaultLayer;
    }
    else
    {
        gameObject.layer = reversedLayer;
    }
    reversed = !reversed;
}

[guneyozsan]

A quick and dirty way which works if you have only a single layer in your mask.

layerNumber = Mathf.Log(myLayer.value, 2)