Differences to X-COM (OpenApoc)

OpenApoc is an open-source C++17 reimplementation of X-COM: Apocalypse (1997). While aiming to faithfully recreate the original game, OpenApoc introduces many improvements, bug fixes, and new features. All new gameplay features are optional and can be toggled through the More Options menu.

This page documents the known differences between OpenApoc and the original game. For general OpenApoc information, see the OpenApoc main page.

Technical Improvements

OpenApoc runs natively on modern hardware and operating systems, removing the need for DOS emulation:

Platform support: Windows (MSVC 2019+), Linux (GCC 8+/Clang 7+), and macOS (including Apple Silicon)
Modern resolutions: Supports any screen resolution and display scaling, with windowed, fullscreen, and borderless modes
Performance: Runs at 60 FPS with OpenGL 2.0+ / GLES 3.0 rendering
Human-readable save games: Game state is stored as XML in ZIP archives, editable with any text editor
Mod support: Full modding via XML data files, Lua scripting, and a configurable mod loading system
Multi-monitor support: Can be placed on any display in multi-monitor setups
Configurable audio: Separate volume controls for music and sound effects

New Gameplay Options

All new gameplay features are accessible through the More Options menu and can be individually enabled or disabled. Default values are listed — ON means the feature is enabled by default in OpenApoc.

Cityscape Options

Option	Description	Default
Improved city control scheme	Completely new control scheme with modifier keys (see Improved Controls section). Can be disabled to restore vanilla controls.	ON
Ferry checks relationship when buying	Transtellar checks its relationship with X-COM before providing transport services	ON
Allow manual use of teleporters in city	Players can manually route vehicles through teleporter buildings for quick transport	ON
Allow manual ferrying of cargo and non-combatants	Manual control over ferry transport of cargo and non-combat personnel	ON
Allow soldiers to call taxi	Soldiers can use taxis for transport (restricted to civilians in the original)	ON
Allow attacking owned vehicles	Allows X-COM to attack its own vehicles (impossible in the original game)	ON
Call existing transport instead of spawning them	Reuses existing transport vehicles instead of spawning new ones	ON
Attempt to recover agent equipment dropped in city	Equipment dropped by agents in the city is automatically recovered	ON
Enforce vehicle cargo limits	Strict enforcement of vehicle cargo capacity	OFF
Allow nearby vehicles to pick up loot	Nearby X-COM vehicles can collect loot from crash sites	ON
Allow loot to be stashed in the building	Recovered loot can be deposited in buildings	ON
Armored roads	Roads have damage reduction, making them harder to destroy	ON
Unsupported ground vehicles crash	Ground vehicles without road support will crash (weapons and modules may be lost)	ON
Vehicles crash when entering dimension gates	Vehicles incapable of dimensional travel crash when entering gates	ON
Vehicles crash when out of fuel	Vehicles crash when their fuel runs out	ON
Successful raid collapses building	Buildings collapse after a successful raid	OFF
Any hit on hostile building provokes retaliation	Stray shots hitting hostile buildings trigger retaliation	OFF
Put market stock on the right side	Market stock displayed on the right side of the transaction screen	ON
Left clicking icon opens equip menu	Left-clicking a unit's icon opens the equipment screen	OFF
Skip turbo movement calculations	Performance optimization that skips turbo movement math	OFF
Allow ATVs to initiate UFO recovery missions	All Terrain Vehicles can start UFO recovery missions	ON
Show vehicles in current dimension only	Vehicle list filters to show only the current dimension	ON
Add prefix to non-X-COM vehicles	Non-X-COM vehicles are prefixed with * in vehicle lists for easy identification	ON
Don't follow vehicles in strategy view	Disables automatic camera following in strategy (isometric) view	OFF
Use currency formatting	Monetary values displayed with currency formatting (e.g., $1,234,567)	ON

Other Cityscape differences:

Aircraft weapons may be unequipped (not possible in the original game)

Battlescape Options

Option	Description	Default
Explosions damage instantly	Explosions cause damage immediately rather than with a delay	ON
X-Com 1 (UFO) Damage model (0-200%)	Uses the UFO: Enemy Unknown damage randomization model (0-200% of base damage) instead of Apocalypse's model	OFF
Gravlift sounds	Sound effects play when units enter or exit gravlifts	ON
Throwing requires proper facing and pose	Units must face the target and be in the correct stance before throwing	ON
Ammunition explodes when blown up	Carried ammunition detonates when a unit or vehicle is destroyed	ON
Display unit paths in battle	Movement paths are visually displayed during tactical combat	ON
Display additional unit icons (fatal, psi)	Extra status icons shown for fatal wounds and psionic effects	ON
Allow force-firing parallel to the ground	Force-fire mode allows shots aimed parallel to the ground plane	ON
Require LOS to maintain psi attack	Psionic attacks require maintained line of sight to the target	OFF
Hitting vehicle shield produces alternate sound	Different sound effect when vehicle shields absorb damage	ON
All units run and kneel by default	Units default to running movement and kneeling stance	ON
Automatically reload weapons when empty	Weapons auto-reload from carried ammunition when a clip is expended	ON
Weapons autoreload only same ammo type	Auto-reload only uses the same ammunition type that was previously loaded	ON
Mousewheel changes vertical level in battlescape	Mouse scroll wheel changes the displayed map level	ON
Select squad with single click	Single-click squad number buttons to select the entire squad	OFF
Disable scrolling sounds	Turns off the sound effect when scrolling the map	OFF

General Options

Option	Description	Default
Show debug commands on screen	Displays debug/cheat command buttons in the interface	ON
Allow unloading clips and quick equip	Advanced inventory controls: Shift+click for auto-equip, Ctrl+click to remove clips	ON
Enable agent equipment templates	Save and load agent equipment loadouts with number keys (Ctrl+1-0 to save, 1-0 to apply)	ON
Seed RNG on game start	Seeds the random number generator at game start for varied gameplay	ON
Enable mouse capture for the window	Captures the mouse cursor within the game window	OFF

Mod Options

Option	Description	Default
Max tile repair per night	Maximum number of scenery tiles construction vehicles repair each night (0-100)	5
Scenery repair cost factor	Percentage of original price organizations pay for scenery repair (0-100%)	10%
Stunning hurts relationships	Stunning units belonging to an organization damages X-COM's relationship with them	OFF
Initiating raid hurts relationships	Starting a raid on a building damages the relationship with its owner	OFF
(MOD) Original Brainsucker Launcher SFX	Uses the original game's Brainsucker Launcher sound effect	ON
(MOD) Invulnerable roads	Roads cannot be damaged or destroyed	OFF
(MOD) Griffon becomes All-Terrain	The Griffon AFV becomes an all-terrain vehicle capable of off-road movement	ON
(MOD) Wolfhound APC becomes All-Terrain	The Wolfhound APC becomes an all-terrain vehicle	ON
Vehicles crash on low HP	Vehicles crash when their health drops critically low (weapons and modules may be lost)	OFF

Cheat Options

OpenApoc provides a dedicated cheat menu not present in the original game:

Option	Description	Default
Infinite ammo	Unlimited ammunition for all X-COM agents and vehicles	OFF
Damage inflicted multiplier	Multiplier for damage dealt by X-COM (0x - 5x)	1.0x
Damage received multiplier	Multiplier for damage taken by X-COM (0x - 5x)	1.0x
Hostiles multiplier	Multiplier for the number of hostile units spawned (0.5x - 3x)	1.0x
Stat growth multiplier	Multiplier for agent stat growth rate (0x - 99.5x)	1.0x

Additional cheat buttons: Give All Research, Make All Orgs Friendly/Hostile, Make All Orgs Utopia/Chaos, Modify Funds, Set Time Before Midnight, Fast Forward to End of Day/Week/Month.

Improved Controls

The original game's city controls were inconsistent and limited. OpenApoc introduces a completely new control scheme using modifier keys. This can be disabled via the "Improved city control scheme" option to restore vanilla behavior.

Cityscape Mouse Controls

Input	Action
Left Click on building	Open building screen (base screen if building contains a base)
Right Click on building	Open building screen
Shift + Left Click	Order attack vehicle
Shift + Right Click	Order follow vehicle / go to location
Alt + Shift + Left Click	Order attack building
Alt + Shift + Right Click	Order go to building
Alt + Left Click	Open UFOpaedia for object (vehicle type, building function, projectile source)
Alt + Right Click	Open UFOpaedia for object's owner
Ctrl + move order (agents)	Force agents to move on foot (never call taxi), allows personal teleporter use
Ctrl + move order (vehicles)	Allows manual use of city teleporters
Ctrl + attack order	Forces vehicles to attack target (instead of UFO recovery or escort)
Ctrl + Left Click (selection)	Add unit/vehicle to selection (additive selection)
Right Click (selection)	Remove unit/vehicle from selection
Middle Click	Move camera to location

Cityscape Mouse on Vehicle/Agent Icons

Input	Action
Shift + Right Click	Open location screen
Ctrl + Shift + Right Click	Open equipment screen
Alt + Shift + Right Click	Open equipment screen

Agent Equipment Controls

Input	Action
Shift + Click	Auto-equip item to first available slot, or auto-remove to stores/ground
Ctrl + Click on weapon	Remove clip from weapon
1-0	Apply saved equipment template to all selected agents
Ctrl + 1-0	Save current agent's equipment set as a template

Battlescape Mouse Controls

Input	Action
Left Click	Order unit to execute action (move/throw/psi/teleport), open probed unit screen, use item
Right Click	Turn towards cursor, focus enemy (real-time), use item auto-function (e.g., prime grenade for impact)
Shift + Left Click	Force-fire at target tile, shot parallel to ground
Shift + Alt + Left Click	Force-fire at target tile, shot aimed at tile's ground
Alt + move order	Unit keeps facing target while moving (strafe/backpedal)
Ctrl + Left Click	Add unit to selection (additive)
Right Click	Remove unit from selection

Battlescape Keyboard

Key	Action
PgUp / PgDown	Change map levels
V	Toggle layering
F2-F4	Movement modes: Prone / Walk / Run
F5-F8	Fire modes: Cease / Aimed / Snap / Auto
F9-F11	Behavior: Evasive / Normal / Aggressive
Backspace	Toggle kneel
1-6	Select squad
Shift + 1-6	Select specific unit in current squad
Shift + Ctrl + 1-6	Add unit to selection
Alt + 1-6	Cycle through spotted enemies of unit
Enter	Open inventory
[ / ]	Throw right / left hand item
' / \	Drop right / left hand item
E	End turn (turn-based mode)
J	Make unit jump (down from a cliff)
S / L	Open save / load menu

General Controls

Key	Action
Mousewheel	Scroll lists
Esc	Go back, close form, cancel
Enter	Confirm, go forward
Space	Pause/Resume time
Tab	Toggle map
C	Toggle follow mode
M	Show message log
Home	Zoom to last event
Arrows	Move camera
0-5 (Cityscape)	Control game speed

Pause Notifications

OpenApoc adds a comprehensive configurable notification system that can pause the game when specific events occur. Each notification can be individually toggled. These are not present in the original game.

City Notifications

UFO spotted
Vehicle damage (light / moderate / heavy / destroyed)
Vehicle escaping (damaged and returning to base)
Vehicle out of ammo
Vehicle low on fuel
Agent died
Agent arrived at base
Cargo / Transfer / Recovery arrived at base
Vehicle repaired / rearmed / refuelled
Not enough ammo / fuel
Unauthorized vehicle detected
X-COM base destroyed

Battle Notifications

Hostile spotted / died
Unknown unit died
Agent died / brainsucked
Agent critically wounded / badly injured / injured
Agent under fire
Agent unconscious / left combat zone
Agent frozen / berserk / panicked / panic over
Psionic attack on unit / unit under psionic control / freed from control

Original Game Bugs Fixed

OpenApoc fixes or avoids several known bugs from the original game:

UFO speed bug: Fixed alien craft having 0 speed in certain conditions
Infiltration screen overflow: Fixed infiltration screen going blank when exceeding 42 days
Security Station turrets (partial): In the original turn-based mode, Security Station turrets did not have their TUs refreshed at the start of turns, rendering them mostly useless after the first shot
Sound issues: Fixed OGG Vorbis music playback issues that could occur in the original
Learning AI: The original game's advertised "learning AI" was effectively non-functional — it stopped working after saving the game and depended on specific CD-ROM file locations. OpenApoc does not attempt to replicate this broken feature
Brainsucker Pod handling: Various fixes for Brainsucker Pod inventory issues, storage space, and alien containment display

Modding Support

Unlike the original game, OpenApoc is designed with modding in mind:

XML data files: Nearly all game data (units, weapons, vehicles, buildings, organizations) is defined in editable XML files
Mod loading system: Mods are loaded from a configurable directory (default: ./data/mods), specified as a colon-separated list
Lua scripting: A Lua scripting system allows custom AI and game logic modifications. Scripts are loaded via the OpenApoc.Mod.ScriptsList configuration option
Editable save games: Since saves are XML in ZIP archives, game state can be manually edited

Features Not Yet Implemented

As of early 2026, OpenApoc is in alpha state. The following features from the original game are not yet fully implemented:

Core Gameplay

Victory and defeat screens
Alien Takeover screen
Full organization diplomacy with dual relationship values (the original tracked two separate relationship scores per organization)
Overspawn mechanic
Full dynamic action music structure
Agent name generator

AI and Movement

Advanced battle AI: cover usage, flanking, grenade throwing, retreat and regrouping behaviors
Intelligent alien movement patterns within the city
True ground vehicle movement with lanes, highways, and overtaking behavior
Evasive/Normal/Aggressive unit AI behavior modes (buttons exist but AI differentiation is incomplete)

Other

Proper portal locations in the Alien Dimension
Full graphs and statistics feedback screens
Organization vehicle AI (buying, selling, managing their own fleets)
Coloured text support in some UI elements

For the full development roadmap, see the Playable Alpha, Beta, and Release 1.0 milestone issues on GitHub.

Debug Mode

OpenApoc includes an extensive debug system not present in the original game. Debug hotkeys are toggled with F1 in both the cityscape and battlescape. When enabled, various diagnostic and cheat functions become available:

Cityscape Debug

Ctrl+Alt+Shift+Click: Destroy scenery / collapse building
Spawn UFOs, repair scenery, warp to alien dimension
Display road pathfinding, walk modes, alien positions, vehicle paths
Dump voxel maps for line of sight/fire analysis
Highlight tubes, roads, and hills with directional filters

Battlescape Debug

Teleport units, stun/remove units, restore stats
Reveal entire map with line-of-sight visualization
Modify morale and psionic stats
Spawn explosions and directional shots
Re-link support lines for map parts

Base Screen Debug

Instantly finish all facility construction
Near-instantly complete research projects