Scripting Rustic UI assets with HTML and CSS

Web assets are .html, .htm, or .css files under ui/. The directory rule is enforced: they are not accepted as gameplay assets elsewhere. Rustic structurally validates the document and executes inline <script> content in the same bundled, sandboxed JavaScript behavior runtime used by .js scripts. It does not embed a browser renderer and does not replace the editor shell.

Create the file with the Explorer so the editor registers its Asset ID and scope. Attach it as a global, scene, or object component through the editor; never insert a path or source string into scene metadata.

HTML behavior

<!doctype html>
<html>
  <head>
    <style>
      /* Valid content, but not a rendered browser stylesheet in this release. */
      body { margin: 0; }
    </style>
  </head>
  <body>
    <script>
      globalThis.behavior = {
        Start() {
          rustic.log("info", "web behavior started");
        },
        Update(dt) {},
        OnDestroy() {},
      };
    </script>
  </body>
</html>

Inline script blocks and project-relative <script src="..."> files are combined and evaluated as one sandboxed JavaScript behavior. Linked files must remain inside the play snapshot. A CSS-only asset has no callbacks and is therefore a valid no-op behavior. Module imports, DOM queries, events, fetches, storage, and layout APIs are not available.

Canonical callbacks are Start, FixedUpdate, Update, OnEnable, OnDisable, and OnDestroy; snake-case spellings remain compatible. Collision callbacks are not currently bound by the embedded Web/JavaScript adapter. Only methods actually present on globalThis.behavior run.

Available inline JavaScript API

Inline code receives rustic, Game, and instance exactly as described in the JavaScript guide:

const [x, y, z] = rustic.get_translation();
rustic.set_translation(x, y + 1, z);
rustic.set_property("score", 10);
rustic.EditAttribute("Color", [1.0, 1.0, 1.0]);

const camera = Game.scene.Find("Room.Camera");
Game.setCurrentCamera(camera);
instance.add("Cube");

if (rustic.key("KeyW").held) {
  rustic.log("info", "forward key held in Play");
}

JavaScript mutations are applied in command order after the callback. Properties must be declared and type-compatible. Scene lookup returns stable IDs; JavaScript Game.scene.List() currently returns path strings. Instance operations are queued and do not return the created ID. The Play input limits also apply to inline JavaScript: only held WASD, arrow, and Shift state is forwarded from the embedded Play viewport.

Security and limitations

Inline code cannot call another script object, and API 1.0 does not yet expose script-level Engine Event emit/subscribe; use shared engine state for coordination.

Inline code has no DOM, filesystem, network, Node APIs, processes, environment variables, package loading, or editor/backend access. Source must be UTF-8 and no larger than 1 MiB. Syntax/structure is validated before Play or reload. A validation failure leaves the previous good instance running; a callback failure disables only the failing behavior. Use Web assets for lifecycle-driven UI logic or future-facing content organization, not for browser rendering in the current release.

Target another scene object

See Edit scene objects for named-scene hierarchy calls, supported attributes, copyable examples, and native SDK calls to edit another object. Use your language's native call syntax and its current runtime limitations.