MidiFilter

class MidiFilter {
protected:
  const char* identity;
  void (*ptr)(MidiMsg*, MidiFilter*);
public:
  void filter(MidiMsg*) const;
  virtual void apply(State*) const;
  virtual void unapply(State*) const;
};

const char* identity

The subclass should initialize this member to point to a string which is the name of the subclass. (e. g. "Transposer")

void (*ptr)(MidiMsg* m, MidiFilter* f)

The subclass should initialize this member to point to a function which filters message m based on MidiFilter f. The reason this is a pointer to a static function, rather than a virtual member function, is that virtual functions don't seem to work right at interrupt time.

void filter(MidiMsg* m)

This member function filters m.

void apply(State* s)

This member function modifies s to the state it would be if the filter was applied, assuming it was not applied before.

void unapply(State* s)

This member function modifies s to the state it would be if the filter was not applied, assuming it was applied before.