// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 5-7: "Bouncing" color
  
  // Two variables for color.
  float c1 = 0;      
  float c2 = 255;    
  
  // Start by incrementing c1.
  float c1dir = 0.1;  
  // Start by decrementing c2.
  float c2dir = -0.1; 
  
  void setup() {
    size(200,200);
  }
  
  void draw() {
    noStroke();
    
    // Draw rectangle on left
    fill(c1,0,c2);
    rect(0,0,100,200);
  
    // Draw rectangle of right
    fill(c2,0,c1);
    rect(100,0,100,200);
  
    // Adjust color values
    c1 = c1 + c1dir;
    c2 = c2 + c2dir;
    
    // Instead of reaching the edge of a window, these variables reach the "edge" of color:  
    // 0 for no color and 255 for full color.  
    // When this happens, just like with the bouncing ball, the direction is reversed.
  
    // Reverse direction of color change 
    if (c1 < 0 || c1 > 255) {
      c1dir *= -1;
    }
  
    if (c2 < 0 || c2 > 255) {
      c2dir *= -1;
    }
  }