Example code - rotate() via mouse control and map()

float mouseXMap;
float mouseYMap;

void setup() {
  size(500, 500);
  rectMode(CENTER);
}

void draw() {
  background(0);
  mouseXMap = map(mouseX,0,width,0,TWO_PI);
  mouseYMap = map(mouseY,0,height,0,3);
  translate(width/2, height/2);
  rotate(mouseXMap);
  scale(mouseYMap);
  rect(0, 0, 200, 50);
}