I just added a J solution for the Pendulum Animation task on Rosetta Code:
http://rosettacode.org/wiki/Pendulum_Animation#J
I'm reasonably happy with it (there is something satisfying about making
something move! :-) ),
but any improvements are welcome.
NB.=================================================================
require 'gl2 trig'
coinsert 'jgl2'
DT =: %30 NB. seconds
ANGLE=: 0.25p1 NB. radians
L =: 1 NB. metres
G =: 9.80665 NB. ms_2
VEL =: 0 NB. ms_1
PEND=: noun define
pc pend;pn "Pendulum";
xywh 0 0 320 200;cc isi isigraph rightmove bottommove;
pas 0 0;pcenter;
rem form end;
)
pend_run =: verb def ' wd PEND,'';pshow;timer '',":DT * 1000 '
pend_close =: verb def ' wd ''timer 0; pclose'' '
pend_isi_paint=: verb def ' drawPendulum ANGLE '
sys_timer_z_=: verb define
recalcAngle ''
wd 'psel pend; setinvalid isi'
)
recalcAngle=: verb define
accel=. - (G % L) * sin ANGLE
VEL =: VEL + accel * DT
ANGLE=: ANGLE + VEL * DT
)
drawPendulum=: verb define
width=. {. glqwh''
ps=. (-: width) , 40
pe=. ps + 280 <....@* (cos , sin) 0.5p1 + y NB. adjust orientation
glrgb 91 91 91
glbrush''
gllines ps , pe
glellipse (,~ ps - -:) 40 15
glellipse (,~ pe - -:) 20 20
glrect 0 0 ,width, 40
)
pend_run'' NB. run animation
NB.=================================================================
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