Self linking in RuntimeMathGraph Example crashes Unity / App

[ecurtz]

I'll continue to look at this in the debugger, but if I attach a node output to an input on the same node in RuntimeMathGraph (either in Unity editor or a built application) it crashes. It isn't from the Destroy() call in UGUIPort.OnEndDrag, but I haven't been able to find anywhere else to break in the xNode code between that and the crash.

OS X, several versions of Unity.

[ecurtz]

Looks like infinite recursion in MathNode.GetValue

[Siccity]

MathGraph is a simple example project. The way it works is simply ask the previous node for its value, and use it to return the next. If you create recursion it will never be able to determine a result as there is no end to the calculation. This could be fixed in MathGraph, but as it is just an example meant to show beginners around, i didn't see it as anything important. After all, a recursive math graph shouldn't exist in the first place.

[ecurtz]

True enough, but recursion in the graphs is something that will come up in a lot of cases, maybe there should be some sort of built-in callback in the connector logic to reject illegal connections?

[ecurtz]

Actually I guess I shouldn't close this, since it's still a nasty crash in the demos. I'll leave it open for you to do as you see fit.

[Siccity]

Connections can be legal in some cases while being illegal in others. I can't make assumptions without getting in the way of some special use cases. But youre right, i should probably make a safeguard in the example

[xiajjjjjjjjjj]

I think you should add an attribute to the input to indicate whether the node can connect itself

[ikold]

In my project, I found it really easy to create a reference loop in node connections, crashing as result, so I created a dependency parameter in OutputAttribute that stores a list of input names that are used to check if a new connection will result in a loop. Check is done recursively during an attempt to connect two ports, with no overhead during other operations on the node graph.

By dependency, I mean a situation where a call GetValue() to get output port value might result in a call GetInputValue() of an input port.

Usage in the example MathNode would look like so:

...
[Input] public float a;
[Input] public float b;

[Output(dependencies = new []{"a", "b"})] public float result;
[Output(dependencies = new []{"a", "b"})] public float sum;
...

It is backward compatible, as it doesn't change anything if you don't use it. I can create a Pull Request if you are interested in this solution.