boolean shiftPressed;
String drawText = "";

void setup()
{
  textFont(createFont("SansSerif", 16), 16);
  fill(0);
  frameRate(2);
}

void draw()
{
  background(192);
  text(frameCount, 16, 16);
  text(drawText, 16, 32);
}

void keyPressed()
{
  if (key == CODED && keyCode == SHIFT)
    shiftPressed = true;
}

void keyReleased()
{
  shiftPressed = false;
}

void mousePressed()
{
  drawText = shiftPressed ? "shift-click" : "click";
}

void mouseReleased()
{
  drawText = "";
}