yeah you are right about the layer read layer on the manaul

Code:
    *   The layer parameter can only be set in a definition. For changing it during gameplay, use layer_sort.
    * A7.06 Panels, texts, and view entities with a positive layer value are placed above any view; with a negative layer value they are placed below any view. This can be used to define an image visible in the background of a view that has no sky and a transparent sky_color.
    * A7.08 The view layer parameter can be evaluated in a material effect or shader through the fLayer variable.


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