Viewport movement stutter in isometric mods

[ghost]

Most noticeable in the radar widget when moving the viewport. I think this is not limited to the box displayed in the radar widget but that the stutter is actually there when you move the viewport, at least I think that I see it with keyboard scrolling. Side-note: It is also noticeable when cherry-picking a027222 on top of #17308.

See the animation below for the comparsion of RA vs TS:

RA

TS

Edit:
Also present on 5d786f4, so it's not a regression from the render-rework.

[GraionDilach]

Yes, because this has nothing to do with rendering.

The radar box is drawn around the center cell visible. The thing here is that at isometric worlds the axis don't align with the implicated scroll axis, and you constantly switch between map rows/coloumns during scrolling, which the radar box just follows.

Example movement during a left-right scrolling.

[tovl]

It seems the solution then would be to base the radar box around the center WPos instead of the CPos.

[GraionDilach]

Another suggestion which came to my mind is to limit the scrolling to jump two rows/coloumns with each step in a fashion like below (where only Xes are the cells which can be viewport centers). Sounds like simple workaround to me and I don't think it would be much noticable anyway.

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