Small Basic super slow ??

[Elzaimer]

Hello everybody,

I found this QBASIC program on Facebook :

DIM SHARED pi, r, t, u, v, x
DIM i AS INTEGER, j AS INTEGER
DIM px AS INTEGER, py AS INTEGER
DIM rr AS INTEGER, gg AS INTEGER, bb AS INTEGER
SCREEN 12
RANDOMIZE TIMER
pi = 4 * ATN(1)
r = 2 * pi / 235
t = 4 * RND
x = 0: u = 0: v = 0
CLS
FOR i = 0 TO 249
FOR j = 0 TO 249
u = SIN(i + v) + SIN(r * i + x)
v = COS(i + v) + COS(r * i + x)
x = u + t
px = INT(320 + 108 * u)
py = INT(240 + 108 * v)
IF px >= 0 AND px < 640 AND py >= 0 AND py < 480 THEN
rr = (i * 3) MOD 256
gg = (j * 3) MOD 256
bb = (255 - (i + j) \ 2) MOD 256
LINE (px, py)-(px + 1, py + 1), _RGB(rr, gg, bb), BF
END IF
NEXT j
NEXT i
SLEEP


I tried it on https://qbjs.org/ and as it was nice I converted it to Small Basic (PSGZ709.000) to compare the performances.
The difference is incredible : 6 seconds on SB and less than a second on QBJS.

Somebone has an explanation ? is my convertion bad ? is there a way to get better performances ? Would Svb be faster ?