// Learning Processing
  // Daniel Shiffman
  // http://www.learningprocessing.com
  
  // Example 5-2: More conditionals
  
  // Three variables for the background color.
  float r = 0;
  float b = 0;
  float g = 0;
  
  void setup() {
    size(200,200);
  }
  
  void draw() {
    // Color the background and draw lines to divide the window in quadrants.
    background(r,g,b);  
    stroke(0);
    line(width/2,0,width/2,height);
    line(0,height/2,width,height/2);
    
    // If the mouse is on the right hand side of the window, increase red.  
    // Otherwise, it is on the left hand side and decrease red.
    if (mouseX > width/2) {
      r = r + 1; 
    } else {
      r = r - 1;
    }
    
    // If the mouse is on the bottom of the window, increase blue.  
    // Otherwise, it is on the top and decrease blue.
    if (mouseY > height/2) {
      b = b + 1; 
    } else {
      b = b - 1; 
    }
    
    // If the mouse is pressed (using the system variable mousePressed)
    if (mousePressed) {
      g = g + 1; 
    } else {
      g = g - 1; 
    }  
    
    // Constrain all color values to between 0 and 255.
    r = constrain(r,0,255);
    g = constrain(g,0,255);
    b = constrain(b,0,255);
  }