Uses of layers in Unity

You can use layers to optimize your project and workflow. Common uses of layers include: * Layer-based rendering. * Layer-based collision.

Use the Camera culling mask with layers.

You can render only the objects in a particular layer, or selection of layers, if you use the Camera’s culling mask. To change the culling mask, select the camera you want to use, and select the Culling Mask dropdown in the Inspector window. If you clear the checkbox of a layer, it doesn’t render in the scene.

Note: UI elements and screen space canvas children are exceptions to this and render regardless.

Ray cast with layers

You can use layers to specify which GameObjects that a ray cast can intersect with. To make a ray cast ignore a GameObject, you can assign it to the Ignore Raycast layer, or pass a LayerMask to the ray cast API call.

If you don’t pass a LayerMask to the ray cast API call, Unity uses Physics.DefaultRaycastLayers which matches every layer except Ignore Raycast.

The Physics.Raycast function uses a bitmask, and each bit determines if a layer is ignored by rays or not. If all bits in the layerMask are on, the ray collides against all colliders. If the layerMask = 0, there are no collisions.

For example, if you want to cast a ray on layer 8, see the code sample below:

int layerMask = 1 << 8;

// Does the ray intersect any objects which are in layer 8?
if (Physics.Raycast(transform.position, Vector3.forward, Mathf.Infinity, layerMask))
{
    Debug.Log("The ray hit the player");

You can then do the inverse, so that the ray collides with all layers except layer 8.

void Update ()
{
    // Bit shift the index of the layer (8) to get a bit mask
    int layerMask = 1 << 8;

    // This casts rays only against colliders in layer 8.
    // But to collide against everything except layer 8, use the ~ operator because it inverts a bitmask.
    layerMask = ~layerMask;

    RaycastHit hit;
    // Does the ray intersect any objects excluding layer 8.
    if (Physics.Raycast(transform.position, transform.TransformDirection (Vector3.forward), out hit, Mathf.Infinity, layerMask))
    {
        Debug.DrawRay(transform.position, transform.TransformDirection (Vector3.forward) * hit.distance, Color.yellow);
        Debug.Log("Did Hit");
    }
    else
    {
        Debug.DrawRay(transform.position, transform.TransformDirection (Vector3.forward) *1000, Color.white);
        Debug.Log("Did not Hit");
    }
}

Note: If you don’t pass a layerMask to the Raycast function, it still ignores colliders that use the IgnoreRaycast layer.