Game Maker

A browser-based tool "one step before a game engine": create assets (scenes, cameras, sprites), place them into scenes, tweak their properties in an inspector and press Play – all in one program, all drawn inside a single WebGL canvas.

Live: https://nockal.com/game-maker/ · Widget playground: https://nockal.com/game-maker/?playground

Concepts

Term	Meaning
Asset	Named thing with a type (scene, camera, sprite, behavior, collider, container) and typed properties. Assets have no position.
Scene object	An asset placed into a scene: a link to the asset + a position (x, y, z) + sparse overrides of the asset's properties + an optional parent (another object of the scene). Scenes cannot be placed.
Container	A reusable group ("prefab"): the asset holds a template of objects (asset link, local position, overrides, parent links) centred on its origin. Placing a container creates a container object plus fresh copies of the template below it – ordinary objects, each remembering its template id. Create container turns the current selection into such an asset and replaces the selected objects by one placed container at their centre (world positions unchanged). The template is edited from its instances (see Instance).
Selection	One or more scene objects. Click selects, Ctrl-click adds/removes, dragging on empty scene space draws a rubber band (objects whose position lies inside are selected). Dragging a selected object moves the whole selection; Delete removes it; the inspector offers Create container and Remove from scene for several objects.
Behavior	Logic as an asset: a node graph plus the variables it declares. Placed like anything else (a diamond symbol in the scene); its parent is the owner the graph acts on.
Collider	A shape (box or circle) for collision detection, placed as a child of the object it belongs to (its body). Drawn as a green outline in edit mode only.
Override	A per-object value that replaces the asset's value for one property. Only changed keys are stored; the inspector marks them bold and offers a reset (↺) and an apply (↑) that writes the value into the asset instead.
Default	Every property has a schema default. Asset values that differ from it are marked bold in the inspector and can be reset (↺) the same way an override can.
Instance	An object that is part of a placed container. Its base is the template, not just the asset: position and overrides that differ from the template are bold, ↺ reverts to the template, ↑ ▾ offers Apply to container (template; copies still at the old value follow, copies changed on their own keep theirs) or Apply to asset. Position rows apply to the container directly.
Edit mode	The Scene tab draws the project model; panels, grid, gizmos and drag-to-move are active.
Play mode	The editor switches to a runtime copy of the project (same ids). A World is instantiated from its active scene (one entity per scene object, resolved properties as mutable state) and shown in the Game tab. Systems tick it and mirror their changes into the copy; every panel stays open and edits the copy, which the world picks up immediately. Stop discards world and copy – the saved model is never touched.

The camera defines what is rendered. A camera asset has a view size (width × height, default 640×360) and a zoom; the frame it covers in world units is size / zoom. The Scene tab draws that frame as an outline. The Game tab renders only that frame – fitted into the view with black letterboxing – and objects outside it are culled. A scene without a camera renders nothing in the Game tab. Play has no built-in behaviour (no input, no movement): everything that happens is defined by behavior graphs.

Editing while playing. Play opens the Game tab but leaves the editor fully usable: the Scene tab shows the live positions (symbols, gizmos and dragging included), the hierarchy and inspector show and edit the running objects, the graph can be changed, undo/redo work on the play session's own history. All of it happens in the runtime copy: values a behavior changes appear as overrides (bold, ↺ resets to the asset value), objects a graph destroys vanish from the lists, objects a graph spawns (Spawn node) appear in them – selectable, editable, still only in the runtime copy –, and Esc/Stop brings back exactly what was saved. Autosave pauses while playing.

Behaviors (node graphs)

A behavior asset holds a Blueprint-style graph edited in the Graph tab of the centre area (the Scene tab shows the editable scene, the Game tab the running game). Ports come in two kinds: exec (white arrows, control flow) and data (coloured circles; number, boolean, string, object, any). Event nodes start a pulse; the interpreter follows exec edges and pulls data inputs lazily from connected outputs. Unconnected data inputs use the inline value shown on the node and editable in the inspector.

• Variables are the behavior's own property schema (BehaviorAsset.variables): they appear in the inspector, can be overridden per placed instance, and each running instance gets its own mutable copy. Get variable / Set variable read and write them.
• Owner = parent: a placed behavior is usually parented to the object it controls (inspector → Parent, or drag it onto that object in the hierarchy; dashed line in the viewport). The Owner node returns it; Self returns the behavior itself; Parent walks up from any object.
• Node set (src/core/graph/nodes.ts): events On start, On update, On key down/up/held, On timer, On collision enter/stay/exit · flow Branch, Sequence · data Self, Owner, Parent, Object by name, Get/Set variable, Get/Set property, Get position (local and world), literals, Add/Subtract/Multiply/Divide, Min/Max/Abs/Sqrt/Clamp, Length, Distance, Normalize, Axis input (four keys → a normalized direction, so diagonals are not faster), Compare, And/Or/Not, Key is down, Is touching · actions Move (dx, dy, scale, dt – connect an event's dt for per-second movement), Set position, Spawn (asset setting + x/y/z, optional parent → outputs the new object), Destroy, Log, Stop game. A node type is one registerNode() call; palette, ports, validation and inspector fields are generated from it. A port may declare a default for its inline value (e.g. Move.scale = 1), shown on the node and in the inspector.
• Idiomatic movement (the demo's "Mover", five nodes): On update → Move(Owner, dx = Axis input.x, dy = Axis input.y, scale = Get variable speed, dt = On update.dt).
• Editing: right-click the canvas for the searchable palette, drag port → port to connect (types are checked; a data input holds one link and is replaced), drag nodes, right-click a node or port to delete/disconnect, Delete removes the selected node, wheel zooms, dragging the empty canvas pans. Everything is undoable.
• Selection-bound: the Graph tab shows the behavior the current selection refers to (asset, placed object or node); with nothing or a non-behavior selected it is empty.
• Live view: Play always switches to the Game tab; switch to Graph while playing and the exec edges and nodes that just ran light up – the same canvas draws editor and game, so this costs nothing extra.
• Runtime: BehaviorSystem creates one GraphInterpreter per behavior entity; graphs only touch world entities. A runaway loop throws after 1000 steps and stops play with a notice.

Editor symbols are always on top. The viewport draws scene content (sprites) in an objects layer and editor symbols (camera icon, labels) in an overlay layer above it, so a sprite can never hide a symbol regardless of z or hierarchy order.

Z-order is part of the position. position.z is the draw order of a scene object: higher z is drawn on top; objects with equal z keep their hierarchy (tree) order. It is edited in the inspector next to X/Y, undoable like any move, and applies in edit and play mode alike.

Hierarchy (parenting). Every scene object may have a parent in the same scene (SceneObject.parentId). Positions – including z – are local to the parent; the world position is the sum along the chain (src/core/model/hierarchy.ts). Children move with their parent and are removed with it (also when the parent's asset is deleted); undo brings the whole subtree back. Re-parenting keeps the world position by recomputing the local one, and cycles are rejected. In the Scene objects panel children are indented below their parent; drag a row onto another row to parent it, onto the empty space below the rows (or right-click → Unparent) to move it to the top level; the inspector offers the same as a Parent menu. In play mode entities carry the same parent link: moving a parent entity moves its subtree, Destroy removes it. Get position exposes both the local and the world coordinates.

Colliders and collisions

A collider is an asset (shape box/circle, width/height or radius) placed like any other object – typically as a child of the sprite it belongs to, so its position is the offset from that body and it moves with it. Right-click an object in Scene objects (or press + Add collider in its inspector) to get one with one click: a box collider sized like the sprite, parented at its centre. Colliders can be reused across objects, overridden per instance and stacked (hitbox + hurtbox on one sprite; colliders of the same body never collide with each other). They are editor symbols: green outlines in edit mode, invisible in play mode.

Play runs a CollisionSystem (src/runtime/systems/CollisionSystem.ts) before the behaviors: every frame it tests all collider pairs (world positions applied; touching edges do not count) and sorts them into enter, stay and exit. Detection never pushes anything apart. A behavior receives On collision enter/stay/exit for the colliders of its owner (its parent; itself when top-level): the outputs are other (the other body), other collider and collider (the own one). Is touching(a, b) answers the same question on demand – an object stands for its collider children, a collider for itself. The geometry lives in src/core/properties/collider.ts so editor and runtime agree on it.

Blocking is opt-in per movement: the Move node has a Collide with solids setting (default off). When enabled it moves an object one axis at a time and, after each axis, pushes its solid colliders back to just touch any solid collider they ran into – so the other axis still moves and the object slides along walls. Its blocked x / blocked y outputs tell which axes hit (always false with the setting off). A collider with Trigger (no blocking) enabled (isTrigger, drawn amber instead of green) still produces collision events but never blocks. An overlap that already exists is never resolved (no jolt when objects start stacked or inside a wall) but also never deepened, so such an object can always leave. A move longer than the thinnest collider involved is split into sub-steps – a fast object cannot jump across a thin wall and end up on the other side. Colliders of the moving object and of anything parented under it travel with it and cannot block it. Move without the setting and Set position ignore colliders entirely.

Stack

• PixiJS v8 – rendering and pointer events. No game engine; runtime systems live in src/runtime/.
• Own canvas widget toolkit (src/ui/) – panels, buttons, lists, text/number/color fields, popups. The only DOM element is a hidden <input> used as a keyboard bridge (IME, mobile keyboard, clipboard) while a canvas text field is focused.
• Vite + TypeScript, Vitest for the pure core.
• PHP 8 JSON API (api/) storing one JSON file per project in data/projects/, with atomic writes and an integer revision that rejects stale saves (HTTP 409).

Layout

web/index.html      Vite source page (dev)            index.html   built page (generated, served)
src/core/           model, property schema, resolve, commands, store – no Pixi imports
src/core/graph/     graph model, node registry + built-in nodes, interpreter (headless, unit-tested)
src/runtime/        World, Entity, System interface, Input tracker, CollisionSystem, BehaviorSystem
src/ui/             widget toolkit (generic, knows nothing about assets)
src/viewport/       scene renderer: Scene tab (model, editable) and Game tab (world through its camera)
src/editor/         App composition, state, panels, inspector field factory
src/editor/graph/   GraphEditor (canvas), NodeView, NodePalette
api/                PHP backend            data/projects/   persisted projects
tests/              Vitest unit tests      tools/           e2e.mjs (CDP smoke test), seed-demo/seed-e2e.mjs

The toolbar's right edge shows the frame rate (frames counted over a 0.5 s window, updated twice a second) in edit and play mode alike; __gm.fps() exposes the same number to tests.

Rules that keep it organised: core/ imports nothing from other layers; ui/ never sees assets; position exists only on scene objects; overrides are merged in exactly one place (core/properties/resolve.ts); the inspector is generated from PropertySchema – a new property is one schema line.

Development

Node 22 is required (on this machine: PATH=/opt/node22/bin:$PATH).

npm install
npm run dev          # http://localhost:5175/game-maker/dist/ – API calls are proxied to production
npm test             # unit tests (core)
npm run typecheck
npm run build        # writes dist/ and regenerates index.html
node tools/seed-e2e.mjs <projectId>    # write the fixture scene the e2e checks assert against
node tools/e2e.mjs <projectId>         # headless end-to-end run with screenshots in /tmp/gm-e2e-*.png
node tools/seed-demo.mjs <projectId>   # put the demo project back (the e2e run mutates it)

The e2e run overwrites the project it is pointed at, so it seeds its own fixture first and the demo is restored afterwards. The demo scene (seed-demo.mjs) is free to evolve independently: a "Player" container – green sprite with a collider and the Mover behavior – two "Enemy" container instances, a camera at zoom 0.5 and a Spawner that drops another enemy on Space.

The workspace folder itself is what nginx serves, so npm run build is the deployment.

API

All routes go through api/index.php?r=… (the site's nginx does not pass PATH_INFO).

Method	Route	Body → Result
GET	projects	[{id,name,revision,updatedAt}]
POST	projects	{name} → project document (201)
GET	projects/{id}	{id,name,revision,updatedAt,project}
PUT	projects/{id}	{revision, project} → {revision,updatedAt} or 409 {revision} when stale
DELETE	projects/{id}	204

There is no authentication yet; data/ is world-readable. Both are phase-2 topics.

Keyboard

Ctrl+Z / Ctrl+Shift+Z / Ctrl+Y undo/redo · Delete remove selection · Ctrl+G create container from the selection · Ctrl+Enter play · Esc stop · Tab cycles fields · number fields: drag to scrub (Shift ×10, Alt ×0.1), ↑/↓ step · viewport: wheel zooms, middle-drag or Shift+drag pans, drag on empty space rubber-bands, Ctrl-click toggles an object in the selection (hierarchy rows too).

Not yet

Textures on sprites, editing a container's template directly (today changes reach it only via Apply to container from an instance), reordering the hierarchy, auth, touch-optimised layout, graph comments/groups.