Sorry, but having a globally writable pointer to every texture is just insane and makes any functional management impossible.
This is merely a preparation for adding a real texture manager. That cannot be done if any code can write over the data at will. For that, it now has to make the texture writable first or create a writable empty texture.
These will have to do some texture management bookkeeping so directly changing the values is problematic.
This required changing the parameter interface in polymost.cpp because a few places hacked around with the global state to pass parameters to subfunctions.
