Capturing viewport input using the .NET API

A short while ago, we had a question about using the .NET
API to capture mouse clicks to gather points from the viewport. There was some
confusion around it because there were some similarly named interfaces that
made it appear that if implemented, they could help.  Additionally, because we clearly state in the documentation
that you should not derive full plug-ins from the base classes in Autodesk.Max.Plugins namespace, and so those
classes are often ignored. While this warning is true for a full plug-in type,
it turns out some of those supporting classes are still viable and useful to implement.

This is the case for capturing viewport input. After discussing
this with our engineering team, I learned the basic steps are:

1. Derive
   a new class from Autodesk.Max.Plugins.MouseCallBack.
2. Override
   the proc method of this class.
   This is where the mouse clicks and all info will be diverted.
3. Derive
   a new class from Autodesk.Max.Plugins.CommandMode
4. Implement
   all of the abstract methods. Implement the MouseProc
   method to return a new instance of your Autodesk.Max.Plugins.MouseCallBack
   derived class (step # 1)
5. Use
   GlobalInterface.Instance.COREInterface.PushCommandMode
   with new instance of your Autodesk.Max.Plugins.CommandMode
   derived class (step #3)

I have implemented a simple example of this approach and
attached the project here. Currently it is setup to use 3ds Max Design 2014
like the previous samples, but can easily be converted to work with 3ds Max.
See this post for how: Some .NET API Samples