Support object grabbing

[EdwardLu2018]

Would be great to have a way to grab and drag objects like super hands has. Needs to be done in a distributed manner, however.

Maybe whenever a user grabs an object, it will constantly publish its world position every 10 Hz?

[hi-liang]

We need a new clientEvent grab-start or somesuch.

Just childs the object to grabber, based on the initial offset between them (will keep it pose-locked to hand)

More important part is other clients validating that the object being grabbed is a grabbable and some other stuff, as this would otherwise result in some violation of our objectId-vs-topic checks

[hi-liang]

Actually that's still a problem when you release, because non-editor users still can't write the new (stationary) position of the grabbable object.

Maybe persist needs to special case the grab-end message and allow it to update pos/rot only in persist

[mwfarb]

Joey has done some work on this, this week.

• Preliminary tests publishing any controller button/stick events.
• Preliminary tests with a Python program consuming those events and deciding how to simulate a grab.

[mwfarb]

It would be good to decide if this is an:

• A-frame side natural parenting.
• A Python app.

[mwfarb]

Would be great to have a way to grab and drag objects like super hands has. Needs to be done in a distributed manner, however.

Maybe whenever a user grabs an object, it will constantly publish its world position every 10 Hz?

If the object is a child of the hand, the existing 10Hz parent publish should take care of this.

[EdwardLu2018]

Huh, parents handle publishing pose of children? I didn't know that...

[EdwardLu2018]

Related to #532

[hi-liang]

This is partially supported "natively" in AFRAME from v1.5.0.

Does not of course, address network publishing, persist updating, or state conflicts of grabbed or graber