Then what does »full display« mean? The game uses the full display, anyways, when played in full screen. So what does it stand for?
It's not very easy to describe, but I will try.
First of all there are 2 basic modes:
1. first mode is "stretch to fit", i.e. stretch the original image (320x200) to fit the openxcom resolution (that's why it works well only with 16:10 aspect ratios... on other aspect ratios it has black bars on the sides)
2. second mode is "zoom to fill", i.e. zoom in and the rest of the display is filled with solid color (e.g. black for dialog windows, blue for geoscape controls, etc.) -- there's more magic going on with the globe itself and in the battlescape, but you have asked only about menus/dialogs
The first mode is represented by options: Original, 1.5x Original and 2x Original
The second mode is represented by options: Full display, 1/2 display and 1/3 display
Your question was only about "full display", so let's forget the first mode completely and talk only about second mode.
For menus and dialogs, the original (320x200) is zoomed:
- "full display" = no zoom
- "1/2 display" = 2x zoom
- "1/3 display" = 3x zoom
and the rest is filled with solid color.
Therefore I would not recommend "full display" to anyone (only use I found so far is to make screenshot of the entire battlescape at once).
"1/2 display" is nice if you play on lower resolutions, especially if the ratio is other than 16:10 (for example 854x480).
"1/3 display" is nice if you play on medium resolutions (for example 1280x720)
On high 16:10 resolutions (e.g. 1680x1050, 1920x1200), I would probably recommend the first mode (stretch to fit, for example 2x Original).
On high non 16:10 resolutions (e.g. 1920x1080), you will either have to live with black bars on sides... or as I said in the previous post, play in a window instead at lower resolution (I found 1280x720 to be the best for me so far).