The editor

./build/src/redgem games/platformer          # opens the editor
./build/src/redgem games/platformer --play   # just plays the game

The editor is built with Dear ImGui (dark theme, Inter and JetBrains Mono fonts, Font Awesome icons):

• Toolbar: move / rotate / scale gizmos, local or world axes, the pivot several selected objects turn and scale around (their middle, or the first one selected), grid snapping (or hold Ctrl while dragging), Play / Pause / Stop, and Build.
• Hierarchy: the object tree with search. Click to select, Ctrl+click to add an object to the selection or take it away, Shift+click to select every row from the last one clicked; double click to frame, drag onto another object to parent it (or onto empty space to unparent; a row of the selection takes the whole selection along), right click for actions (on the whole selection) and to create objects. Scripts and models from the Project panel can be dropped on it.
• Scene: hold the right mouse button and use WASD/QE to fly, wheel to dolly, F to frame the selection, click to pick objects (Ctrl or Shift + click adds or takes away), drag a rectangle to select what shows inside it (with Ctrl or Shift held, added to the selection), W / E / R switch the gizmo. Drop a model on the ground to place it there, or a script on an object to attach it.
• Inspector: name, tag, visible, Template (hidden in the game, copied with Scene.spawn), then one card per component: Transform, Mesh with its materials (color, metallic, roughness, emission and their pictures, see Material pictures), Light (type, color, intensity, range), Camera (field of view, clipping), one card per Ruby script, Physics (body, trigger, collider, mass), vehicle wheels and custom properties. Add Component adds scripts (existing or new), a physics body, a trigger or a property. With several objects selected it shows what they have in common: tag, visible, Template and the Transform, a dash where their values differ. An edit applies to all of them.
• GameObject menu: terrain you sculpt with a brush (see Levels), empty objects, cube / sphere / plane / cylinder / capsule (with colliders), directional / point / spot lights, cameras, and the game's models.
• Your own models, sounds and pictures: drop .glb files (exported from Blender), .wav / .ogg / .mp3 / .flac files and .png / .jpg / .jpeg / .webp pictures from your file manager onto the editor window. They are copied into the game's models/, sounds/ and images/ folders and show up in the Project panel.
• Project: the game's scripts, models, sounds, scenes and images. Double click a script to edit it, a model to add it to the scene, a sound to hear it, a scene to open it (see Scenes), a picture to see it in your system's viewer. New script creates a Behaviour from a template, New scene a scene; Open folder shows the files.
• Console: engine and Ruby output (filter by level), including script errors with backtraces.
• Scripts: each open Ruby file gets its own tab next to the Scene. Drag tabs to split the view anywhere (or press Split right), like a code editor's editor groups. The code is colored as you type: keywords, strings, symbols, comments, numbers, constants and @variables each have a color of the editor's theme. Ctrl+S saves and checks the syntax (errors show the line); Open externally uses your default editor. Play saves all open scripts and reloads them.
• Agent: a chat with a coding agent (Claude Code, Codex or one of your own), in a tab beside the Inspector. It works in the game's folder and sees and changes the open scene through the editor's tools; see The Agent panel.
• View menu: hide the Hierarchy (Ctrl+B), the Inspector (Ctrl+Alt+B) or the bottom panels (Ctrl+J) to give the scene or the code more room; the toolbar's outer buttons toggle the sides.
• Play / Pause / Stop (Ctrl+P, Esc): runs the game inside the Scene view with the current edits and fresh scripts; Stop restores the scene exactly as it was.
• Ctrl+Z / Ctrl+Y undo and redo, Ctrl+D duplicate, Del delete, Ctrl+X / Ctrl+C / Ctrl+V cut, copy and paste, Ctrl+S save. Help > Keyboard Shortcuts lists them all. File > New / Open Game goes back to the hub.

Material pictures

Under a material's color, metallic, roughness and emission, the Inspector lists its five texture slots, each with the picture it shows or None:

• Color map: the surface's colors, tinted by the material's color.
• Surface map: roughness in the green channel and metalness in the blue one (glTF's metallic-roughness map), scaled by the sliders.
• Normal map: small bumps and grooves, as a tangent-space normal map.
• Occlusion map: how much ambient light reaches each spot, in the red channel.
• Glow map: where the surface glows, tinted by the emission color.

Click a slot to pick one of the pictures of the game's images/ folder (or None), or drag a picture from the Project panel's Images onto it. The picture goes inside the scene's .glb (the same picture used twice is stored once), so the scene still shows it in Blender and when copied to another scene; a picture no material shows any more is left out when the scene is saved. Each change is one undo step. PNG, JPEG and still WebP pictures can be used.

Several objects at once

Everything selected moves, turns and scales together with the gizmo (around the middle of the selection, or around the first object selected: the toolbar's pivot button; a scale goes along the pivot's axes, and an object turned another way and stretched unevenly takes the nearest placement without shear), and Duplicate, Delete, Cut, Copy and Paste act on all of it. A child goes along with its selected parent. Each of these is one undo step, however many objects it touches.

Copy takes the selected objects with everything under them: their meshes, materials, pictures, skeletons and animations, scripts and properties, lights and cameras. Paste (Ctrl+V) puts them next to the selected object, or at the top level when nothing is selected; Paste as Child (Ctrl+Shift+V, or the Hierarchy's menu) puts them under the selected object. They land where they were in the world, and a name that is already taken gets a number (Crate.001). Paste works in the scene they came from, in another scene of the game (open it and paste), and in another editor window: the copy goes on the system's clipboard as text. A copy bigger than 64 MB stays in the editor's own clipboard and pastes only in the window it was copied in.

A pasted object has its own copy of its meshes and pictures, even in the scene it was copied from (Duplicate shares them instead).

Undo goes back up to 200 steps, and keeps at most 256 MB for them (its copies of the objects and terrains, and what deleted objects and undone imports were made of: vertices, pictures and their bytes in the scene's file; an estimate, counted as each step begins): past either, the oldest steps go, and what no step can bring back any more is let go of, so a long session with many imports does not keep growing. The latest step always stays, however big.

Saving rewrites the open scene's file in place (only the glTF JSON; meshes and textures are untouched), so the file still opens in Blender. When the file changes on disk (e.g. you re-export from Blender) the editor reloads it automatically, unless you have unsaved edits.

Scenes

A game can have several scenes: levels, missions, menus. Each is a .glb file, known by the name a script loads it with:

Scene	File	Loaded with
main	scene.glb	Game.load_scene("main")
level2	scenes/level2.glb	Game.load_scene("level2")

The game always starts on main (scene.glb); scripts move to the others with Game.load_scene. The editor opens on main too, and edits one scene at a time:

• Open another scene with a double click in the Project panel's Scenes folder, or with File > Open Scene. When the open scene has unsaved edits, the editor asks first (Save, Discard or Cancel), like when closing. Each scene has its own undo history: it starts empty when the scene opens.
• New scene (File > New Scene, or New scene in the Scenes folder) makes scenes/<name>.glb with ground, a sun and a camera, and opens it. Names are lowercase letters, digits, _ and -, starting with a letter (level2, boss-fight); main is taken.
• Save (Ctrl+S) writes the open scene back to its own file. File > Save Scene As writes it as a new scene of the game, which is then the one open. A scene that uses files next to it (textures exported outside the .glb) is not saved into another folder that way, where it would not find them: export it from Blender as a .glb with its textures in it first.
• Play starts the game on the open scene as it is edited, under its own name (Game.scene_name, and its scripts/<name>_scene.rb runs). Stop comes back to it.

The window title and the status bar name the open scene, and the editor follows that scene's file for changes made outside. Built games carry every scene: Build copies the whole game folder, scenes/ included.

Building

Build (in the toolbar, or File > Build Game) asks which system to build for, saves the open scene and the scripts, and builds the game into a folder beside it: <game>-build for the system the editor runs on, <game>-build-<system> for another one (see Building and sharing). The build runs in the background, so the editor keeps working while it does: a box in the Scene view's bottom-right corner shows what is being built, for how long it has been, and the step it is at (copying the game's files, packing the app, signing it). When it ends, the box says how it went: the folder it filled, with Open folder, or what went wrong. The Console keeps the same lines.

One build runs at a time: Build is greyed out until the running one ends. The build reads the game's files from disk, never the scene open in the editor, so you can keep editing while it runs; what you save meanwhile is only sure to be in the next build. Closing the editor while a build runs waits for it, saying so, then closes as usual, asking first about anything edited and not saved (Keep the editor open stays instead). A build is not stopped halfway: the tools it runs would leave half-written files behind.