This is a bug in Farseer. (Version 3.3.1)
I opened up the Farseer source code to the method in question (World.SolveTOI
) and found two calls to Debug.Assert
. And, in fact, in my copy of the code, I've actually already come across this bug and commented one of them out, specifically:
Debug.Assert(typeA == BodyType.Dynamic || typeB == BodyType.Dynamic);
Basically it doesn't want to attempt to handle contacts between two bodies that are static.
Fortunately the code immediately below actually checks for essentially the same condition, and continue
s the loop if that is the case:
bool awakeA = bA.Awake && typeA != BodyType.Static;
bool awakeB = bB.Awake && typeB != BodyType.Static;
// Is at least one body awake?
if (awakeA == false && awakeB == false)
{
continue;
}
So it's quite safe to simply comment out or remove the assertion. (You should, of course, be building Farseer from source - it makes life much easier.)
To reproduce the Farseer bug: Have two static bodies and one dynamic body that is in contact with both, then make the dynamic body static. The assert will trigger.
The assert is in the contact handling loop. Normally a pair of static bodies wouldn't create contacts. But if a body starts out as dynamic, contacts can be created - they don't get removed when the body is made static.