Fix banding artifacts of 3D space view's skybox

[Wumpf]

What

Add simple algebraic (doesn't need a texture lookup) dithering to 3D generic skybox in order to fix banding artifacts.
Depending on your screen and screen calibration you may or may not have been annoyed by this in the past (on most of the setups I use it's quite glaring)

Before:

After:

Note the ring artifacts which are mostly gone on the second screenshot - if you can't spot the difference, make sure to look at the screenshots without any scaling with your screen at high brightness relative to your surroundings

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[emilk]

Very nice!

EDIT I actually ran it and compared and OMG IT IS SO MUCH NICER

[Wumpf]

EDIT I actually ran it and compared and OMG IT IS SO MUCH NICER

crazy isn't it 😄
There's still some slight less-clear-cut banding visible under movement for me. I wonder if that's just my screen of if the level calculation isn't entirely correct, but it made sense to me.