Stuff that came to mind during over 8 months spent with X-PirateZ. All suggestions should be compatible with vanilla games mechanic although main purpose is to reduce workload in huge complex mods.
1) Bindable keys for UfoPedia scrolling, with repeat function. Currently erroneously binded to "Scroll Geoscape" direction and key must be pressed repeatedly to scroll. I'd like to see separate binds (for comfort) and keeping the key pressed would list through ~5-10 entries/sec, after half a sec of initial delay (similarly to writing in Notepad). Clicking with mouse is uber tiresome in huge mod pedias. This ain't no Cookie Clicker. Could be tried to mouse wheel by default with down direction as next entry.
2) [Attachment] Sell screen: Shift+LMB to sell an item would mark for sell every item from the top of list (or to nearest above already marked for selling, to current item) by single quantity increase. Shift+RMB would mark sell all items in entire column between marked and clicked item. Useful in normal gameplay when selling tightly grouped unwanted items but shines when bulk selling unwanted recruits. I'm talking hundreds, all which must be otherwise sold individually, bought for sole purpose to trigger otherwise restricted promotion algorithm.
3) Production screen: CTRL+MMB on item in the list would bring up pedia, same as it does in sell screen. Currently CTRL is unused and behaves same as MMB is clicked, a missed opportunity. While at it, lets have MMB bring up pedia instead and CTRL+MMB bring up tech tree viewer for natural and quicker functionality. Hell, CTRL+MMB isn't even documented properly if at all.
4) Uniform MMB behavior of bringing up pedia entry of clicked item, if researched, wherever applicable. Inside Tech Tree Viewer (TTV), Production, Sell, Transfer, Equip screens, "What to Wear?" armors (in mods), etc. Literally wherever technically doable. And then same with CTRL+MMB to bring up TTV.
5) Interception screens: RMB on minimize one screen would minimize all of them, as it does with approach icons. Restoring a save in such condition would remember if screen were minimized instead of bringing them up on reload.
6) Battlescape minimap: always show map borders? I found out about ALT function whole 3 months into XPZ. FU guys... :)
7) Battlescape Hit-Log simplification: H brings regular, CTRL+H advanced one. In case of conflict with player's custom binds reserve a function key or something. Anything to lessen current finger gymnastics. Could even go away with regular and leave only advanced one. Because reaction fire replaces your shoot damage and then you need to press 3 keys to get that info back.
8) Battlescape save remembers exact screen position instead centering on selected unit. Ideally weapon targeting status too (save scumming par-excellence). Let us live the dream.
9) Meridian's avatar is from "The Whole Nine Yards" movie in case you are wondering. Thought it was "The Jackal"... Btw, someone show him this wall-of-text when he returns from his vacation. Best it catches him at his peak mood.
10) Transfer screen: distribute item across existing bases equally, via some keyboard modifier. Ideally a pop up would let us select which bases exactly but beggars can't be choosers. Very useful for universally needed items in equal quantities: fuel, components, weapons, ammo, etc. After that we could fine tune amounts ourselves but the main work would be effortlessly done.
11) Transfer screen: transfer selected item to current base from all other bases. Possibly in combo with 2) so all selected items are transferred to current base with one action. Useful in more common scenario of having a dedicated production base, where you'd want to scrounge all needed but otherwise scattered materials to. Saves lots of time scrolling through every single base storage for components all the time.
12) Vault screen: mark item (*) to be constantly stockpiled up to a set amount, from purchase if available. Not manufacture as that would entail a whole new complex suggestion. If quantity above set mark nothing would happen. Mark should remain visible in all relevant screens (buy/sell/transfer/manufacture/etc). Say with a prefix/affix * or different colored text or something that makes it stand out in several hundreds long item list. Buying script would run instantly at first and then as often as technically possible (once a day or so). Tally would include items in transfer.
13) Popup message if the player places a new base inside radar coverage range, existing or future maximal. Warding him off potentially regrettable, costly, or simply overlooked mistakes. Also giving subtle reminder that spreading them apart for even global detection is the correct way forward. Message may even be triggered if end result would be significant radar overlap (player could even decide how much via options, in percentage).
14) Option to display only farthest outline radar range circle parts, committing drawing circles inside existing radars. To help de-clutter GEO. When placing a new base ranges would temporary revert to display everything as usual. Could be added as an additional toggle in existing "Toggle Radar Ranges" bind.
15) Battlescape: right-click on End Turn icon applies fastest enemy Fire/AI Movement speeds for that turn. Useful for quicker grinding in low risk missions. Maybe squeeze in Shift+RMB to completely skip showing aliens when player is assured of benign outcome.
16) Battlescape: key combo (ALT+LMB) to force targeting ground square. Atm it's impossible to execute unconscious enemies in squares with a wall next to them using common ranged weapons (from ground level), even if said walls are destroyed, even if only a corner is touched by a wall or a door. Projectile behaves as if you are shooting an invisible standing enemy in such case.
For edge cases where you aren't sure if permanent change is appropriate you could put a toggle option for individual player preferences.
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Huge respect to all those who made OXC/E what it is today, with special thanks to AI coders, and those who uphold stability (didn't get a single crash)!