Parent / Attach system

[ElusiveMori]

@LinearBoundAutomaton proposed adding a parenting/attachment system to YARP2.

Standing questions:

• Should we use units or special effects for attachments?
• How will the user experience look? Commands, spells, etc.?
• What are the performance implications for updating/moving these attachments? It is likely they will need to be moved every frame for a smooth experience.
• What changes need to made in the Save/Load system to support this? (This is mostly my job)

@LinearBoundAutomaton, please provide a short summary of how you envision this.

[ElusiveMori]

Here are my personal thoughts.

I think we should use the existing EffectProxy package and extend it to suit our needs.

Regarding UX, there's 2 approaches I can think of:

1. Purely command-based syntax:

• attach <id> to attach a model with the specified id to the root of the unit.
• atch list list all attachments on the unit, with their IDs, from 0 to ...
• atch 0 x/y/z move an attachment
• atch 0 p/y/r rotate an attachment (pitch/yaw/roll)
• atch 0 scale scale an attachment

2. Unit-based system
   You spawn a regular unit/building like you would normally, and give it a special ability, e.g. aa parent. You position the unit however you'd like next to the parent unit, and then cast that ability on the parent, turning the unit into a special effect and calculating all the relative offsets, at which point the unit is removed.

[ElusiveMori]

Setting this as low priority while LBA has gone silent. Will work on this later.