# Control Surface Singleton

> Original: [Purpose of the Control_Surface singleton](https://tttapa.github.io/Control-Surface/Doxygen/d8/df5/control-surface-purpose.html)

The `Control_Surface` object is the central manager for all MIDI elements, interfaces, and lifecycle events.

## Program structure

```cpp pico
#include "pico/stdlib.h"
#include <cs_midi.h>

using namespace cs;

BluetoothMIDI_Interface midi;
NoteButton button {5, {MIDI_Notes::C[4], Channel_1}};

int main() {
    stdio_init_all();
    Control_Surface.begin();
    while (true) {
        Control_Surface.loop();
        sleep_ms(1);
    }
}
```

## Responsibilities

1. **Initialization** — `begin()` activates all registered MIDI interfaces, output elements, input elements, and selectors.
2. **Periodic updates** — `loop()` polls physical inputs (buttons, pots, encoders), sends MIDI when values change, and dispatches incoming MIDI to input elements.
3. **Message routing** — connects output elements to the default MIDI interface and delivers incoming messages to matching input elements.

## Element registration

Elements register themselves on construction and deregister on destruction. No explicit `add()` calls needed.

## Enable/disable

Elements can be removed from the update loop at runtime:

```cpp pico
button.disable();  // stops polling and sending
button.enable();   // re-adds to update loop
```

## Without the singleton

For direct MIDI sending/receiving without the element system, use the interface object directly:

```cpp pico
midi.begin();
midi.sendNoteOn({MIDI_Notes::C[4], Channel_1}, 127);
midi.update();
```