It should be no problem to add a function to a class. I can do that to RecordingDemo with no errors.
The class redefinition error suggests something else is going on. I guess it could be a number of things. Off the top of my head: Did you by any chance add something like class TracktionThumbnail ... anywhere? Or did you include the tracktion_TracktionThumbnail.h directly in your own code (it’s not header guarded so that would probably give a class redef error)? Or maybe some other typo or mistake in the code you added?
Can you show exactly what you’re adding?
@dave96 I modified the file in Visual Studio 2019.
When I first saw the error I thought of what @chrhaase suggested. However, my steps to reproduce the error are to pull the master branch of tracktion_engine, generate the examples, open RecordingDemo in Visual Studio 2019, and add the following function to tracktion_Thumbnail.h and tracktion_Thumbnail.cpp respectively:
Okay! I solved the problem. I was using Visual Studio’s generate definition command with Quick Actions and Refactorings. This generated a #include “tracktion_Thumbnail.h” at the top of tracktion_Thumbnail.cpp.