#whitesq (predefined symbol)
|bool||Always, except in global sections||Never||No|
This predefined symbol returns true if the x-coordinate and the y-coordinate of the pixel being calculated give an odd number when added together; otherwise, it returns false. If you think of the screen as a large checkerboard with white and black squares with the size of a single pixel, #whitesq returns true for every white pixel.
bool b = #whitesq