Halflayer opacity accessed by clicking the hide layer button

[Bug Importer]

Apply a 3 state function to the "toggle visibility layer"
button, to these functions: visible, 50% opacity, hidden.
This feature is a good function for us who want to make
framebased animation, each layer is one frame, a base
object that whould be animated is copied to next layer,
and when modifying that layer i can view previous one
with an 50% (or user configured value) opacity for
guidlines of my object modification/movement(s)..

[Peter Lewerin (vermeil-deactivatedaccount)]

There is now an opacity slider in the Layers dialog, but the combobox in the main window hasn't got one.

Alternatively right-clicking (or shift-clicking, or whatever) could toggle between 50% opacity on one hand and the regular visible/hidden state on the other.