Scene & Node System

1. Mental Model

Understanding Myth comes down to grasping its four cooperating layers. From top to bottom, they form the engine's entire runtime flow:

1. App: Handles window creation, context management, and the event loop.
2. Engine: The core carrier, holding the Renderer, Scene Manager, Asset Server, and Input State.
3. Scene: Holds Nodes, Cameras, Lights, environment configuration, and animation mixers.
4. Render Graph: At the lowest level, it dynamically assembles and compiles the rendering pipeline every frame based on the topology of the currently active scene.

2. Nodes & Hierarchy

Spawn Helpers

For prototyping or writing examples, the helper methods from SceneExt are the most concise way to build content. They automatically register geometry and materials in the resource manager:

let cube = scene.spawn_box(1.0, 1.0, 1.0, material, &engine.assets);
let sphere = scene.spawn_sphere(0.5, material, &engine.assets);
let ground = scene.spawn_plane(20.0, 20.0, material, &engine.assets);

Transforms & Parent-Child Hierarchy

Myth manages the scene graph through entity handles. You can easily bind parent-child relationships and manipulate transforms via a fluent interface:

let parent = scene.spawn_box(1.0, 1.0, 1.0, material, &engine.assets);
let child = scene.spawn_sphere(0.35, material, &engine.assets);

// Establish parent-child relationship
scene.attach(child, parent);

// Chainable transform setup
scene.node(&parent).set_position(0.0, 1.0, 0.0);
scene.node(&child).set_position(1.0, 0.0, 0.0);

Two Ways to Access a Node

• scene.node(&handle): Provides a chainable, convenient API (e.g. set_position, look_at), ideal for quick initialization.
• scene.get_node_mut(handle): Returns a mutable reference to the node, ideal for complex logic and low-level component access inside on_update loops.

3. Camera & Environment Control

Camera

The renderer skips scenes that have no active camera. A typical setup:

let camera = scene.add_camera(Camera::new_perspective(45.0, 16.0 / 9.0, 0.1));
scene.node(&camera).set_position(0.0, 2.0, 5.0).look_at(Vec3::ZERO);

// Be sure to mark it as the active camera
scene.active_camera = Some(camera);

Lights

A Myth scene typically blends one or more analytic lights with Image-Based Lighting (IBL).

Directional lights always take the global-lighting path; point and spot lights are managed by the RDG and routed into the high-performance Clustered Lighting track:

// Global directional light, casting the main shadow
scene.add_light(Light::new_directional(Vec3::ONE, 5.0));

// Local point light, participating in clustered light culling
scene.add_light(Light::new_point(Vec3::new(1.0, 0.8, 0.6), 100.0, 0.0));

4. Manual Resource Lifetime

If you need extremely tight control over asset reuse, you can bypass the spawn helpers and interact directly with the engine's resource pools:

// 1. Manually add geometry and material resources
let geo = engine.assets.geometries.add(Geometry::new_box(1.0, 1.0, 1.0));
let mat = engine.assets.materials.add(PhysicalMaterial::default());

// 2. Instantiate a mesh node from the resource handles
let node = scene.add_mesh(Mesh::new(geo, mat));

Next Steps

• Load models and play animations → Assets, glTF & Animation
• Apply realistic materials → PBR Materials