So we finally tried updating the Outer Wilds project to Unity 5 this week! After several thrilling hours of tweaking the entire code base to work with the new (admittedly much-improved) Unity API, the last compile error finally vanished and I eagerly pressed the play button.
This is what I saw.
Those who have played Outer Wilds before know that the game begins with the player character looking up at the sky. This is technically a screenshot of that scene, albeit with a few notable discrepancies. Let's ignore all of the weird graphical artifacts for a moment (those are to be expected when upgrading a project) and focus on the fact that the player character has fallen through the ground and is well on her way to the planet's core. If you haven't played Outer Wilds, I should note that this is not how the game typically starts.
A cursory glance at the error output window revealed the source of the issue.
The console contained 999+ identical errors reading "Non-convex MeshCollider with non-kinematic Rigidbody is no longer supported in Unity 5". Non-convex (or concave) refers to geometry featuring negative topology (valleys, caves, tunnels, etc), and non-kinematic rigidbodies are objects that can be moved by physical forces. This error essentially means that dynamic physics objects can no longer have negatively-curved geometry in Unity 5.
In most games this isn't a problem. The most common use for convex colliders is level/terrain geometry, which by definition is usually static. Objects that need to be simulated with physics tend to be simple enough that their shapes can be approximated by one or more convex colliders. In Outer Wilds, literally everything in the game is moving at very high speeds due to real-time physical forces. Each planet is a non-kinematic rigidbody that is actually rotating about its axis as it zooms around the sun. Every planet also features a terrain that relies on a non-convex mesh collider to prevent smaller physical objects (like the player) from falling through it. Likewise, your ship is a dynamic rigidbody that needs a non-convex collider so that the player can walk around inside the cabin while it's in-flight (fun fact: we have to apply a counter-force to the ship at its point of contact with the player, otherwise the player's weight would cause it to spin ever so slightly). A quick google search revealed that the ability to marry non-convex mesh colliders with non-kinematic rigidbodies was discontinued by the physics engine itself. Unity 5 uses the latest version of Nvidia PhysX, which apparently no longer supports that feature (probably for performance reasons). In short, it's not something that's going to be fixed anytime soon. That leaves us with a few options:
Then again, I suppose we wouldn't want it any other way. --Alex
George Zackrison
7/8/2015 06:02:56 am
That sounds like a huge mess, hope you guys figure it out though!
Matt Steinhauer
7/8/2015 01:27:21 pm
Regarding your question I would all most 100% chose 3. It may delay development. However if you go with 3 then you will be able to have more control all the forces side of the game. Option 4 is the lazy way out IMO and Outer Wilds deserves better than that.
Fun1k
7/21/2015 01:26:13 am
What does Unity 5 offers to Outer Wilds that the game actually needs? On Unity 4 the game seems to run swimmingly, so unless Unity 5 brings something really cool that would improve OW, then why not keep U4?
Jeffly
7/23/2015 02:33:57 am
Seems this game has a lot more physics working under the surface than I knew about! Comments are closed.
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