Modified version of https://makerworld.com/en/models/2474475-simple-cad-joystick#profileId-2717096

Joystick-Mouse.c

#include <Mouse.h>
#include <Keyboard.h>

#define X A0
#define Y A1
#define SW 2

#define DEAD 25
#define MOUSE_SPEED 10
#define TICK 10
#define LOCK 150

bool pan = 0;
bool moving = 0;

int prev = HIGH;

unsigned long tToggle = 0;
unsigned long tTick = 0;

inline void apply() {

  if (!pan)
    Keyboard.press(KEY_LEFT_SHIFT);

}

inline void releaseAll() {

  Keyboard.release(KEY_LEFT_SHIFT);

}

void setup() {

  Keyboard.begin();
  Mouse.begin();

  pinMode(SW, INPUT_PULLUP);

}

void loop() {

  unsigned long now = millis();

  int b = digitalRead(SW);

  if (prev == HIGH && b == LOW && now - tToggle > LOCK) {

    tToggle = now;

    pan = !pan;

    if (moving) {
      releaseAll();
      apply();
    }

  }

  prev = b;

  if (now - tTick < TICK)
    return;

  tTick = now;

  int dx = analogRead(X) - 512;
  int dy = analogRead(Y) - 512;

  if (abs(dx) > DEAD || abs(dy) > DEAD) {

    if (!moving) {
      moving = 1;
      apply();
    }

    int mouseX = (dx * MOUSE_SPEED) / 512;
    int mouseY = (dy * MOUSE_SPEED) / 512;

    Mouse.move(mouseX, mouseY, 0);

  }
  else if (moving) {

    moving = 0;

    releaseAll();

  }

}