Toolbar button icons

I would like to add new tool buttons (close to Selection Tool, Envelop Tool …) for adding new personal functionalities.
However, I did’nt find a way of adding new icons for these buttons.
Does anybody know the process for generating appropriate images ?

Thank you.

Audacity V2.0.3 - Linux

This will involve some programming.

Thank you Steve.
I followed the instructions in the header of AllThemeResources.h but the new tool button is always black.
It seems ImageCache.png is not well generated.

Theme support is an experimental feature that is currently disabled in Audacity.
I’m not able to offer much help with this as I’m not a C++ programmer, but if you want to use Theme support it needs to be enabled in Experimental.h before you compile.

I made it work.
I had to get back the autogenerated file ThemeAsCeeCode.h in my working directory and recompile , although ImageCache.png does not show my new icon (??)
Thanks again.