Opacity slider for minimap

[mrofa]

Like in the title

[FluffierThanThou]

tricky to do in the current implementation, for two reasons;

First - we're using a Window to draw with, using the standard WindowStack system. I can't set opacity in there. We'd have to use ImmediateWindows I think (that's what floatmenus use).

Second - the minimap is really a series of textures for each overlay. Messing with 'overall' opacity levels would give some odd stacking results.

[Miner239]

Maybe no need for 'overall' opacity levels, just the base terrain coloring. That way we can set all textures' opacity without regard for the stacking.

[ForsakenShell]

It should be possible to do a final composite texture without opacity and then render that individually with the opacity setting. There are options to disable drawing the shadow and background for windows, this should be entirely doable with a couple minor changes.