Processing: mouse click with modifier key.

modifier-key.pde

void mouseClicked() {
  if (modifierKey == 'c') {
    println("C+mouse");
  } else if (modifierKey == 's') {
    println("S+mouse");
  }
}

char modifierKey;
void keyPressed() {
  modifierKey = key;
}

void keyReleased() {
  modifierKey = 0;
}