いかがでしょうか。
#define mmousex (ginfo(0)-(ginfo(4)+(ginfo(10)-ginfo(12))/2))
#define mmousey (ginfo(1)-(ginfo(5)+(ginfo(11)-ginfo(13))-(ginfo(10)-ginfo(12))/2))
screen 0,500,350
oo=100
dim x,oo
dim y,oo
repeat oo
x(cnt)=mmousex:y(cnt)=mmousey
loop
color 0,0,0:boxf
repeat
sx=mmousex:sy=mmousey
if (sx!x(0))or(sy!y(0)){
redraw 0
color 0,0,0:boxf
repeat oo-1
color 48,48,128
line x(oo-cnt-1),y(oo-cnt-1),x(oo-cnt-2),y(oo-cnt-2)
color 255
pset x(oo-cnt-1),y(oo-cnt-1)
x(oo-cnt-1)=x(oo-cnt-2)
y(oo-cnt-1)=y(oo-cnt-2)
loop
x.0=sx:y.0=sy
color 48,48,128
line x(0),y(0),x(1),y(1)
redraw 1
}
wait 1
loop