Inheritance

Inheritance lets you define reusable base objects and derive new ones with small overrides.

Compdown uses two keys:

• _id: defines a reusable template
• _extends: references an existing _id in the same array

Where inheritance works

• compositions
• compositions[].layers
• _timeline.layers

How merging works

• Object values are merged deeply.
• Array values are replaced (not concatenated).
• Scalar values are overridden by the child.

Composition example

compositions:
  - _id: sceneBase
    name: Scene-01
    duration: 30
    framerate: 24
    color: ff8000

  - _extends: sceneBase
    name: Scene-02

Layer example (inside _timeline)

_timeline:
  layers:
    - _id: textBase
      name: Base
      type: text
      text: Hello
      fontSize: 96
      transform:
        position: [960, 540]
        opacity: 100

    - _extends: textBase
      name: Title
      text: Welcome
      transform:
        opacity: 85

Result:

• Title inherits type, fontSize, and transform.position
• transform.opacity is overridden to 85

Layer example (inside a composition)

compositions:
  - name: Main
    layers:
      - _id: nullBase
        name: Base Null
        type: null
        enabled: false

      - _extends: nullBase
        name: Controller

Validation rules

Compdown fails validation when:

• _extends points to an unknown _id
• _id is duplicated in the same array
• inheritance is circular (a -> b -> a)
• _id or _extends is not a non-empty string