'Rope   Version 2
SCREEN 12

' Setup & initialise variables
' ============================
CONST w = 640, h = 480               ' screen dimensions
CONST pi = 3.141592
CONST ropex = w / 2, ropey = h / 2
CONST ropemid = 90                   ' middle point of swing (try 270!)
CONST ropebend = 370                 ' increase to reduce amount of bend
angle = ropemid + 5: ropedir = 1
ropespd = 2.3                        ' ropes speed
ropeacc = .1                         ' ropes acceleration
                           
DIM s(359), c(359)                   ' lookup tables for sin/cos values
FOR d = 0 TO 359
  s(d) = SIN(d * (pi / 180))
  c(d) = COS(d * (pi / 180))
NEXT d

' Main loop
' =========
DO
  ropecolor = 14: GOSUB drawrope     ' draw rope as yellow
  WAIT &H3DA, 8                      ' wait for screen refresh
  ropecolor = 0: GOSUB drawrope      ' draw rope as black (erase)
LOOP UNTIL INKEY$ = CHR$(27)         ' exit if ESC pressed
END

' Update and draw the rope
' ========================
drawrope:
IF ropecolor = 0 THEN GOTO skipupdate
IF ropedir = 1 THEN
  IF angle < ropemid THEN ropespd = ropespd + ropeacc ELSE ropespd = ropespd - ropeacc
ELSE
  IF angle < ropemid THEN ropespd = ropespd - ropeacc ELSE ropespd = ropespd + ropeacc
END IF
angle = angle + ropespd * ropedir
IF ropespd < .1 THEN ropedir = -ropedir: ropespd = 0
skipupdate:
FOR rad = 10 TO 232 STEP 7
  bend = (angle - ropemid) / ropebend
    ang = angle + bend * rad
    CIRCLE (ropex + c(ang) * rad, ropey + s(ang) * rad), 4, ropecolor
  NEXT rad
RETURN

'==================================================================
'     270           These indicate the directions the rope will be
'      Ý                pointing depending on the value of 'angle'
' 180--+--0/360
'    / Ý \               EG: If angle=45 then rope points down & right
' 135 90  45