POINT returns the 'colour' of the specified pixel.
A = POINT (X,Y)
10 REM Invert the graphics screen 20 FOR X = 0 TO 239 30 FOR Y = 0 TO 63 40 IF POINT(X,Y) = 1 THEN PRESET (X,Y) ELSE PSET (X,Y) 50 NEXT Y:NEXT X
An odd number returned by the function indicates a black pixel, while an even number indicates a white pixel. If the co-ordinates are out of range then -1 is returned.