The 'width' and 'height' variables contain the width and height of the display window as defined in the size() function.
Original Processing.org Example: WidthHeight
// All Examples Written by Casey Reas and Ben Fry // unless otherwise stated. size(200, 200); background(127); noStroke(); for(int i=0; i<height; i+=20) { fill(0); rect(0, i, width, 10); fill(255); rect(i, 0, 10, height); }