I've never used OpenXCom before, but something was obvious to me :
- The geoscape view can be upscaled using filters, but it's obviously to benefit of
additional details, thanks to the higher resolution
- The battlefield can be upscaled, but for the same reason : to benefit of
a larger view of the battlefield, thanks to the higher resolution
However, the Base view is stuck at low res.
My issue, though, is not hi-res versus lo-res.My issue is that OpenXCom is hard to play on modern screens with giant resolutions (1920x1280...) because the base view appears tiny. Even the scaled up geoscape and battlefield views are also starting to reach their limit and could be much larger in the game window.
I think it's time you start thinking about some sort of zooming system in the video options. Just a simple
nearest neighbour scaling up in 2x
or 3x or 4x (or 5x or more, for the future), to keep the game playable.
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On a side note: I've been part of such projects and I know that this kind of stuff can require quite a lot of refactoring. The simpler way goes through just upscaling the rendering. The harder way goes through rethinking the size and font of buttons and popup windows. With the irritating issue of mixed resolutions (e.g. a higher font resolution in a 320x200 game). We trust you with that