[Discussion] Overlay API Design

[ShadowApex]

With the inclusion of #238, OpenGamepadUI now has an API that can allow developers to write their own overlays. This issue was opened in order to get input on the API design, as I can foresee a multitude of different ways people might want to write overlays. A big advantage to writing an OpenGamepadUI overlay is that we can leverage Godot's user interface nodes to make multiple overlays play nice with each other and not obscure each other's content.

A working overlay implementation is the Discord Overlay Plugin:

Requirements

Here are some proposed requirements for the overlay API:

• Allow overlays to anchor themselves to a part of the screen and not overlap with other overlay content.
• Allow overlays to be "unmanaged", where they can dictate their own layout.
• Allow overlays to be visible on different layers, allowing some overlay content to overlap.

Nice-to-have features

• Allow user to choose the overlay format for each overlay. (e.g. top-left align, center, etc.)

Implementation

The API implementation is defined in the OverlayProvider class. The OverlayContainer is responsible for arranging the OverlayProvider nodes in the appropriate way.

OverlayProvider

Properties

managed: bool - Whether or not the OverlayContainer should manage the overlay's layout. (Default: true)
layer: int - The layer that the overlay should be drawn on (Default: 0)