/*
  We have generalized the control knobs to a class. In this class, the 
 constructor requires 4 inputs: an image, and initial x, y coordinates, and an
 initial angle. The update() function computes a new angle based upon movement
 of the mouse in the y-direction. The draw() function rotates the image by the 
 specified angle. This allows us to "turn" an image that looks like a knob.
 Of course this requires the image to be perfectly centered for things to look
 good. An alternative approach is to graphically draw an image of a knob.
 */
class Control {
  PImage img;
  float x;
  float y;
  float a;

  Control(PImage img0, float x0, float y0, float a0) {
    img = img0;
    x = x0;
    y = y0;
    a = a0;
  }

  void update() {
    a -= mouseY - pmouseY;
    a = constrain(a, -135, 135);
  }

  void draw() {
    pushMatrix();
    translate(x, y);
    rotate(radians(a));
    image(img, 0, 0);
    popMatrix();
  }
}