10  HGR :FULLSCREEN =  PEEK (49234)
 20  HCOLOR= 3
 30  FOR N = 3 TO 279 STEP 4
 40      X1 = 276:Y1 = 189:X2 = N:Y2 = 1: GOSUB 100"PLOT LINE"
 50  NEXT N
 60  FOR N = 3 TO 191 STEP 3
 70      X1 = 276:Y1 = 190:X2 = 2:Y2 = N: GOSUB 100"PLOT LINE"
 80  NEXT N
 90  END
 100 DX =  ABS (X2 - X1)
 110 SX =  SGN (X2 - X1)
 120 DY =  -  ABS (Y2 - Y1)
 130 SY =  SGN (Y2 - Y1)
 140 ERR = DX + DY
 150  FOR WHILE = 0 TO 1 STEP 0
 160      HPLOT X1,Y1
 170      IF X1 = X2 AND Y1 = Y2 THEN  RETURN
 180      E2 = 2 * ERR
 190      IF E2 >  = DY AND X1 = X2 THEN  RETURN
 200      IF E2 >  = DY THEN ERR = ERR + DY:X1 = X1 + SX
 210      IF E2 <  = DX AND Y1 = Y2 THEN  RETURN
 220      IF E2 <  = DX THEN ERR = ERR + DX:Y1 = Y1 + SY
 230  NEXT WHILE