10 CLEAR ALL
20 SCREEN 4
30 PRINT "Press the mouse button to draw. Press any key to quit."
40 FIBER Chalk()
50     mx=-1:my=-1
60     YIELD
70     IF MOUSE.BUTTONS>0 THEN
80         nmx=MOUSE.X/4:nmy=MOUSE.Y/4
90         INK PLASMA.COLOR
100         IF mx=-1 AND my=-1 THEN PLOT nmx,nmy ELSE LINE mx,my,nmx,nmy
110         mx=nmx:my=nmy
120     ELSE
130         mx=-1:my=-1
140     END IF
150     GOTO 60
160 END FIBER
170 START Chalk()
180 DO
190     RESUME Chalk()
200     PAUSE
210 LOOP WHILE INKEY$=""
