Add an API for creating separate IPhysicsEnvironment's

[marchc1]

Details

According to the VPhysics page on the Valve Developer Wiki, multiple IPhysicsEnvironments are possible.

A VPhysics environment within which objects are simulated. New IPhysicsObjects are created here, and global settings like gravity can be configured.
IPhysicsEnvironment* physenv is created by default. Multiple environments are entirely possible, which is how Portal and Portal 2 work.

I don't see anything that states this is only a part of Portal and Portal 2, so I am inclined to believe this is possible. Could we get some methods to create/destroy physics environments and move physics objects between them? Adding this would result in better lua-based portals/"bigger on the inside" effects (since it seems adding linked_portal_door) isn't happening due to limitations).

More Details

Was thinking something like this;

local physenv = physenv.CreateEnvironment()
physenv:Destroy()

A PhysicsEnvironment could have most of the methods that the physenv library have, except as self-calling functions, ie.

physenv:GetAirDensity()
physenv:GetGravity()
physenv:SetAirDensity(airDensity)
etc...

As to add physics objects to the physics environment, I don't know how that works under the hood (can physics objects be in multiple physics environments, etc...)

Potential problems??

• What to do when a physics environment is destroyed with physics objects in it? Just push them back to the main physics environment if they are no longer a part of any sub-environment?
• The use cases I provided would be ones where the world is not a part of the physics object; is there a good way to have support for both including the world and not including the world? Not needed, but maybe someone would want a separate physics environment but still have world collision for whatever reason
• Players in different physics objects?
• Can this be done both clientside and serverside in a nice way to be seamless?

[Bonyoze]

This or a method to remove player collisions with the world would be really useful.

[marchc1]

It appears that this is 100% possible to add and the work has already been done for it: https://github.com/RaphaelIT7/gmod-holylib/blob/04f96f64cc500aed9e308c7bf36bbb2f919e5a73/source/modules/physenv.cpp