//
// uses mouseX - stores the current x location of the mouse
// uses pmouseX - stores the previous x location of mouse
// calc difference and rotate a rectangle according to this value
//
// NOTE using transformations
//   to update a transformation
// 1. reset the matrix each time  
//       resetMatrix(); loads unity matrix
// 2. position the origin screen center 
//      translate(width/2, height/2);
// 3. apply rotation in radians  
//      rotate(radians(tot_ang));
//
// april 2013
//

int tot_ang = 0;     // set up global variables
int r = 255;         // 3 RGB colours
int g = 0;
int b = 0;
int r_inc = -5;      // colour increments
int g_inc = 5;
int b_inc = 5;

void setup()
{
  size(500, 500);
  colorMode(RGB, 1.0); 
  stroke(256 , 0 , 0);  // red outline
  rectMode(CENTER);     // draw rect about its center
  background(255, 255, 0);   // yellow - clears screen each time
  fill(r,g,b);          // rect fill col 255,0,0 (red)
  rect(0,0,50,50);     // draw rect
  smooth();
}

void draw()
{
  int val;
 
  val = mouseX - pmouseX;    // current mouse - previous mouse x movement
  if (val!=0)
  {
    rotate_rect(val);
  }

}

void rotate_rect(int v)
{
   background(255, 255, 0);   // yellow - clears screen each time
   tot_ang += v;

  resetMatrix();
  translate(width/2, height/2);  // position origin in screen center
  rotate(radians(tot_ang));      // set rotation
  r -= 2;
  if (r<0) r = 0;
  fill(r,g,b);         // fill rect
  rect(0,0,50,50);     // draw rect
}