Scene Prototype

It's common that there are multiple scenes and their contents are similar. For example, in the game Reweave, there are many levels and all of them are scenes with very similar functionalities. Do we really need to create a separate scene for every level?

Messenger scenes are flexible enough to make a scene virtual, or a prototype. Here, prototype means that users can create a real scene by calling a genScene function in the prototype by giving it some parameters it needs.

Take Reweave as an example, all the game levels are generated from a single SceneProto. The data used to instantiate a scene prototype includes all the components, background items, player data, etc.

SceneProto is so useful that Messenger core provides some type sugar and helper functions, and Messenger CLI provides a handy command to create scene prototypes (sceneproto in short).

All the CLI commands we used before may add an extra --proto or -p argument to indicate that this scene/layer/component is created in SceneProtos directory instead of Scenes directory.

Besides, CLI adds a new command called "level". Users can create levels of sceneprotos:

messenger level <SceneProto Name> <Level Name>

This will create a scene added to Scenes directory and AllScenes.elm file.