The Launch Game button at the right-hand end of the main toolbar (beside Manage Backups, shown below) opens the Launch Game dialog. From here you choose whether to boot straight into a level, toggle launch options and scripting helpers, then hit Start Alien: Isolation. The button is only enabled for Steam, Epic Games Store and GOG installs, because launching works by patching the game executable.

Options patch the game install and (for some UI mods) replace GFX files under DATA/UI.PAK. Some options aren't supported on all platforms — the Scripting Helpers and Cinematic Tools are Steam-only. The dialog itself is shown below: the level picker sits at the top; a single Launch Options group holds the four UI mods at the top of its left-hand column, with the engine patches, debug tools, Cinematic Tools and Possess Characters filling the rest of both columns; the Scripting Helpers group sits underneath; and Start Alien: Isolation is the button along the bottom. Options that don't apply to your install are greyed out; on the Steam install pictured, with the bundled tools present, everything is available.

The Launch Game dialog on a Steam install with a level chosen; Possess Characters, Enable Hot Reload, Unlock Mouse and Cap FPS are ticked, so their dropdowns are live.

The game loads levels from disk, so if the level you have open has unsaved changes when you press Start Alien: Isolation, OpenCAGE asks whether to save it first. Yes saves the level (as File → Save Level does) and starts the game, No starts it without saving, and Cancel does neither. If the save doesn't go through, the game isn't started either. If you've added models or other content that needs building, cancel and use File → Save and Build Level first (see Save and Build).

While the game is running with Enable Live Link ticked (Steam only), a Live Link button joins Launch Game on the toolbar, to its right. A game started without it, or with Cinematic Tools, gets no button.

Tick Load straight into a level and pick one from the list beneath it (the list is greyed out until the box is ticked) to have the game boot directly into that map — useful for testing a specific level without playing through from the start. Leave it unticked and the game starts at its main menu (FRONTEND) as normal.

The level list on a retail install: the campaign maps plus the DLC ones under PRODUCTION/DLC. FRONTEND is never offered.

The list holds every level in the current game install, including any you've made with Create Level. OpenCAGE preselects the level you're editing (PRODUCTION/BSP_TORRENS above), otherwise your last used choice, and the selection is remembered for next time.

Booting into a level works by writing the level's name into the game executable, and that space is fixed: a level path longer than 32 characters (for a shipped level that's Production/ plus the folder name) can't be launched into, and OpenCAGE will refuse with the message shown below rather than corrupting the patch.

These are the four boxes at the top of the left-hand column of Launch Options. They swap in OpenCAGE's modified pause/frontend/loading/game-over menus by patching GFX files inside UI.PAK (see also the UI Editor), and the file is rewritten the moment you tick or untick a box, so the change is in place whether you launch from this dialog or not:

• Enable Debug Checkpoints — adds debug checkpoints to the pause menu under Load Game. Checkpoints are per-map and load a scripted game state so you can jump to specific moments. They're created in level scripts with the DebugCheckpoint entity.
• Enable Level Selection — frontend menu with level selection (where you'd normally load a save)
• Enable Debug Loadscreen — loading screen that shows debug map info, and also loads quicker than normal by removing artificial wait times
• Add Quit To Menu On Death — game-over menu with quit-to-menu

Engine Patches

The rest of Launch Options — Skip Frontend and Patch Current-Gen Optimisations under the UI mods, plus the debug tools, No UI and Render Constant Ambient in the right-hand column — are written into the game executable the moment you toggle them. OpenCAGE warns if it can't write, which usually means the game is still running. Cinematic Tools and Possess Characters are the exceptions: they're only applied when you launch.

• Skip Frontend — skips the title screen when loading directly into a level
• Patch Current-Gen Optimisations — restores script functionality that was left out of the PC build (the game incorrectly still honours a “current gen” script flag). In vanilla this re-enables things like additional lighting, monitors, and effects.
• No UI — disables the in-game HUD. Also disables UI popups, which can make some actions impossible — useful for screenshots.
• Render Constant Ambient — full-bright “constant ambient” rendering mode

Debug Tools

• Enable UI Memory Overlay — shows current UI memory in an in-game overlay (cUI). Separate from Cathode DebugText entities.
• Enable Memory Logging — writes memory replay logs to a Mem_Replay_Logs folder

Steam-Only Tools

• Enable Cinematic Tools — enables HattiWatti's Cinematic Tools. The box is greyed out when they aren't available — on non-Steam installs, or if the bundled files are missing. Antivirus software may block the injector; if so, add an exclusion for OpenCAGE's cinematic tools. The game can still launch without them. Cinematic Tools and the Scripting Helpers are one or the other: while this box is ticked, the helpers are switched off (see Cinematic Tools or Scripting Helpers).
• Possess Characters — take control of one of the level's characters in-game, the alien included: the chosen key opens a menu of the characters around you. See Possess Characters below.

Hot reloading has moved into the Scripting Helpers group, where you can also choose its key.

Possess Characters

With Possess Characters ticked (Steam only), you can take control of a character in the running game — the alien, an android or a human — and walk it around the level yourself. Pick the key that opens its menu from the dropdown beside the box: F6 by default, with the same choices as the hot reload key. Like the scripting helpers, it runs in OpenCAGE's plugin in the game folder, but it isn't one of them: it stays available with Cinematic Tools ticked.

In the game, press the key to open the Possess a Character menu. It lists the characters the game is running, with what each one is and how far away it is. The one you're facing comes first (marked ahead), then the rest from nearest to furthest. Click one, or pick it with the arrow keys and Enter, to take control of it. While the menu is open the mouse cursor is shown and the game doesn't see your keyboard or mouse. Press the key again or Escape to close it.

The menu in a Survivor map, with the alien still moving through the vents: it's listed, but greyed out until it comes out.

Once you have a character, the camera sits behind it. W, A, S and D move it relative to the camera, Shift makes it go faster and Ctrl slower, and the mouse turns the camera around it. Roll the mouse wheel to bring the camera closer or take it further away: it goes from 1.5 m to 10 m behind the character (4 m to begin with), and stays where you leave it for the next character you take. It moves with its own animations and speeds, along the routes the level's navigation mesh allows it, so the alien moves as the alien does and can't walk through walls. Let go of the keys and it comes to a stop. C gives it the game's own order to crouch, or to stand up again, but the character only looks any different if its animations include crouching: the humans tried so far (the Torrens crew, and the spacesuited crew on LV-426) stay upright, and the alien doesn't take the order. Your own character stands still meanwhile: the game doesn't see your keyboard (apart from Escape, for the pause menu) or mouse. To let go, open the menu and choose Let go, or take another character; the character's own behaviour then takes over again.

The alien possessed: the camera follows behind it, and a note at the bottom of the screen gives the keys.

• A character in the vents (the alien moving backstage) can't be taken: it's shown as in the vents and greyed out until it comes out.
• While you have a character, its own decisions are paused (its senses still work), so the alien won't come after you, but other characters still react to what's around them.
• Every zone of the level is streamed in while you're behind the character, as the game normally only streams in the area around you.
• The camera doesn't avoid walls, so it can end up inside one when the character backs into a corner.
• Going to another level lets go of the character.

The Scripting Helpers group adds runtime tools to the game that make script iteration faster. They're provided by a small plugin OpenCAGE copies into the game folder when any helper is enabled, or Cinematic Tools or Possess Characters are (and removes when none are), configured through OpenCAGE.RuntimeUtils.ini beside it. The plugin only supports the Steam build, so the whole group is greyed out on other platforms. The dropdowns beside Enable Hot Reload, Unlock Mouse and Cap FPS only come alive once their box is ticked, as shown below.

The hot reload key dropdown, open: INSERT is the default, with DELETE, HOME, END, PAGEUP, PAGEDOWN and the function keys as alternatives.

• Enable Hot Reload — press the chosen key in-game to reload the current level, handy for iterating on scripts without a full restart. The key defaults to INSERT; the dropdown beside the option offers DELETE, HOME, END, PAGEUP, PAGEDOWN and F1–F12 as alternatives.
• Unlock Mouse — the game leaves your mouse cursor alone when it starts instead of taking it over, so you can keep working in OpenCAGE while it runs. This is handy with Live Link's camera sync, where you fly the Viewport and the game follows. To look around in the game, click its window and press the chosen key: the game takes the mouse as it normally does. Press the key again to get your cursor back. While the cursor is free, moving it over the game doesn't turn the camera and clicks don't reach the game, but the keyboard still works and so do menus. A note at the top of the game's screen says which way the key just switched it. It's most useful with the game in a window or on another screen. The key defaults to F4, with the same choices as the hot reload key.
• Cap FPS — the game runs at most the chosen number of frames a second: 30, 60 (the default), 90 or 120. The game's clock moves on at least 1/360 of a second every frame, so when a level draws faster than 360 frames a second (a near-empty new level with V-Sync off, say) everything in the game runs too fast. Capping the frame rate keeps it at its proper speed. V-Sync, when it's on, caps the frame rate too.
• Enable DebugText — DebugText script entities draw their text on screen in-game.
• Enable DebugTextStacking — DebugTextStacking script entities draw their text on screen in-game, stacked under one another.
• Enable DebugEnvironmentMarker — DebugEnvironmentMarker script entities draw their text at a world position in-game.
• Enable DebugPositionMarker — DebugPositionMarker script entities draw axes at a world position in-game.
• Enable Live Link — the game serves OpenCAGE's Live Link, and OpenCAGE connects to it by itself a few seconds after the game starts: script edits (entities added or deleted, links, parameters) reach the running level without a reload, entity methods can be triggered from the Entity Inspector or the flowgraph, and the Viewport's camera and the game's can follow each other. Starting the game with it ticked also brings up the Live Link button on the toolbar, switched on. It's for script tweaks only: models, textures, materials and new composites still need the level saved and loaded again (see what Live Link sends).

The debug entities exist in the shipped scripts but draw nothing in the retail game; these options bring them back, so a script that places a DebugText shows its message on screen as it would have in Creative Assembly's own tools. See Debug Text & Markers for what each one draws, and how to show a script's values with them.

Enable Live Link, the last box in the left-hand column of the Scripting Helpers group.

Cinematic Tools or Scripting Helpers

A game started from Launch Game runs either Cinematic Tools or the scripting helpers, never both. They're for different jobs, filming and working on a level's scripts, and both take over the game's camera: Cinematic Tools with their free camera, and Live Link with its camera sync.

While Enable Cinematic Tools is ticked, the Scripting Helpers group is greyed out and its title says why. None of the helpers run in the game, Live Link included, so OpenCAGE shows no Live Link button for that game. The boxes you've ticked in the group stay ticked, and work again as soon as you untick Enable Cinematic Tools. Cinematic Tools still get OpenCAGE's plugin in the game folder, which streams in the level around their free camera.

Enable Cinematic Tools ticked: the Scripting Helpers are greyed out, keeping their ticks for the next game started without Cinematic Tools. Possess Characters isn't a scripting helper, so it stays available.

Open Game On Save never starts Cinematic Tools, so a game it starts runs the helpers as they're ticked, whether or not Enable Cinematic Tools is.

Outside the Launch Game dialog, under the toolbar's Options dropdown (shown below):

• Options → Misc → Open Game On Save — after you save, OpenCAGE launches into the level you're editing. This bypasses the Launch Game dialog, so Cinematic Tools isn't started, but the Scripting Helpers (Hot Reload, Live Link and the rest) are still set up as they're ticked in the dialog, even while Enable Cinematic Tools is ticked there (as Cinematic Tools don't run, nothing else has the game's camera). Off by default. See Options for the rest of the menu.