bbc basic. Very simple plasma effect

plasma.bas

   10 DIM S(32) : LET O=0
   20 FOR I=0 TO 32
   30   LET X = (I*(PI/16)) - PI
   40   S(I)=INT(8 * (1 + SIN(X)))
   50 NEXT I
   55 CLS : O = O+1
   60 FOR Y=1 TO 23 : FOR X=1 TO 79
   70     COLOUR S((X*X+Y*Y+O) MOD 32)
   80     PRINT "#";
   90   NEXT : PRINT
  100 NEXT
  110 *FX 19 : *FX 19
  120 GOTO 55