/** * Linear Motion.  *  * Changing a variable to create a moving line.   * When the line moves off the edge of the window,  * the variable is set to 0, which places the line * back at the bottom of the screen.  */ float a = 100;void setup() {  size(640, 200);  stroke(255);}void draw() {  background(51);  a = a - 0.5;  if (a < 0) {     a = height;   }  line(0, a, width, a);  }