Matching MSAA behavior from D3D

[colincornaby]

This will make the max AA setting functionally unavailable as 8x will be out of range. However - this will be more consistant with Windows where the max AA setting is typically interperated as 4x or 6x.

[Hoikas]

Does this close #1544?

[colincornaby]

Does this close #1544?

It depends. We probably need to decide.

This technically creates new issues. The high MSAA setting will do nothing on Metal hardware because 6x MSAA is a proprietary AMD extension that may only be available under Direct3D. (Maybe OpenGL on some platforms too?)

Also the 2x MSAA setting is unavailable on some hardware because like the Intel 5100, meaning the low MSAA setting does something.

A few changes have been proposed:

• That we allow 8x MSAA. (I think this is really unplayable on some slower hardware.)
• That we remove 6x MSAA and treat it as an 8x MSAA request. (I'm personally not in favor of this. I think we should keep 6x MSAA, and 8x MSAA is simply awful on Intel 5100 GPUs.)
• That we replace the MSAA with a drop down so we don't have these slider notches that don't do anything.

If we're fine with the following MSAA slider configurations in Metal:

• 1st notch is no MSAA
• 2nd notch is 2x MSAA if the hardware supports it, otherwise no MSAA
• Third notch is 4x MSAA
• Fourth notch is 4x MSAA (because 6x is not supported)

...then we're ok and the issue is closed.

[colincornaby]

Another reason to consider keeping #1544 open is that it also affects the D3D renderer. The D3D renderer also surfaces MSAA modes that are unavailable for the hardware.

[Hoikas]

I'm going to go ahead and merge this because it's an objective improvement and doesn't preclude other fixes.