// This program draws a quadrilateral to the screen
// in black and white.  When the user presses keys,
// it toggles the program between white on black and 
// black on white.
void setup(){
  size(500,200);
}

void draw(){
  background(255);
  stroke(0);
  fill(0);
  quad(20,20,20,70,60,90,60,40);
}

// REMINDER:  Three ways to have memory
// 1. Implicitly: Do things with permanent effects
// 2. Parameters: Define a parameter that stores the value that
//    changes, and use that parameter in your drawing code.
// 3. Modes: Define a variable that stores the 'mode' your
//    program is in. Test for the parameter and do different
//    things depending on its value.