Hidden or invisible layers are not rendered. This function unhides invisible layer so that they are rendered again.
widget path or layer object of class
layer id. If the widget argument is of class
0 if success otherwise the function throws an error
Visibile layers are rendered, invisible ones are not. If any
ancestor of a layer is set to be invisible then the layer is not rendered
either. The layer visibility flag can be checked with
l_layer_isVisible and the actual visibility (i.e. are all the
ancesters visibile too) can be checked with
Note that layer visibility is not a state of the layer itself, instead is information that is part of the layer collection (i.e. its parent widget).