This ADR defines a set of 512 reserved entities that will be used to facilitate communication between the renderer and the scenes.
In order to facilitate communication between the renderer and the scenes, a special number of reserved entities are needed. These entities hold no special logic compared to other entities, but they have static IDs that systems can use to share information about the renderer, player, camera, etc.
We will reserve 512 static entities numbers, starting at 0. The "0" entity will be the root entity of the scenes, and all other entities will be parented to it by default.
Three static entities are reserved at the moment:
RootEntity = 0PlayerEntity = 1CameraEntity = 2All the components presented in this document MUST be updated at the physics phase of each tick as per ADR-148.
The Transform component of the RootEntity cannot be modified by any system. All
updates coming from the scene MAY be ignored or have no effect.
The UiCanvasInformation component of the RootEntity MUST be set by the renderer
to inform the scene about the current canvas size and the current UI scale. This component is
described in the ADR-124
The EngineInformation component of the RootEntity contains information about the
current frame number, tick number and total elapsed time counters. The component MUST be
updated by the renderer each frame.
The Transform component can be READ/WRITE from the scene. Under normal
circumstances, the Transform updates will be ignored by the renderer, but it is
possible to override the player position when the scene is in control of the
PlayerEntity, this behavior is yet to be formalized.
The Transform component can be READ/WRITE from the scene. Under normal
circumstances, the Transform updates will be ignored by the renderer, but it is
possible to override the camera position when the scene is in control of the
CameraEntity, this behavior is yet to be formalized.
The Cinematic Camera will be implemented applying components to the CameraEntity.
The Cinematic Camera is still in the design phase.
The PointerLocked component (READ ONLY) presence signals the status of the
pointer-locking of the renderer.
The WindowIdle component (READ ONLY) presence signals if the renderer is in
background-mode or it is actively rendering.
The CameraMode { mode = ThirdPerson/FirstPerson } component is used to get the
current camera mode; it is only set from the Renderer.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 and RFC 8174.