Oldest existing source code of mine (good old C64!) :-)

basic

10 REMGOSUB2000
20 V=53248:AD=8192:A1=PEEK(V+17):A2=PEEK(V+24)
30 POKEV+17,59:POKEV+24,24
60 FORI=1024TO2023
70 POKEI,16
80 NEXTI
90 FORI=8192TO16383:POKEI,0:NEXTI
120 REMFORX=0TO319
121 REMY=100
122 REMGOSUB1000
130 REMNEXTX
140 REMFORY=0TO199
141 REMX=160
142 REMGOSUB1000
150 REMNEXTY
160 X=160:Y=100:U=1
210 GETT$:IFT$=""THEN210
220 IFT$="A"THEN X=X-1
230 IFT$="D"THEN X=X+1
240 IFT$="W"THEN Y=Y-1
250 IFT$="S"THEN Y=Y+1
260 IFT$="X"THEN U=U*(-1)
265 IFT$="Q"THEN 300
270 IF U>0 THEN GOSUB1000
280 GOTO210
290 REMTP
300 POKEV+17,A1:POKEV+24,A2
310 PRINT""
999 END
1000 OY=320*INT(Y/8)+(Y AND 7)
1010 OX=8*INT(X/8)
1020 MA=2^((7-X) AND 7)
1030 AV=AD+OY+OX
1040 POKEAV,PEEK(AV)OR MA
1050 RETURN
2000 PRINT"LINEARIS FUGGVENY: F(X)=A * X + B"
2010 INPUT"A ERTEKE";A%
2020 INPUT"B ERTEKE";B%
2030 RETURN