rem Rotating Triangle Example
rem
rem   Copyright (C) 2001 P.B. IJdens
rem   Released under the GNU Public License (GPL)

main()

sub main()
  init_scene()
  open_grwin()

  while ( 1 = 1 )
    draw_scene()
    show_scene()
    rotate_scene()    
  wend
end sub

sub open_grwin()
  open window 640, 512
  dispduf = 0
  setdispbuf dispbuf
  setdrawbuf 1 - dispbuf
end sub

sub show_scene()
  dispbuf = 1 - dispbuf
  setdispbuf dispbuf
  setdrawbuf 1 - dispbuf
end sub

sub init_scene()
  dim coords(3,2,2)
  dim centre(2)

  for obj = 1 to 3 step 1
    for corner = 1 to 2 step 1
      for coord = 1 to 2 step 1
        read coords(obj, corner, coord)
      next coord
    next corner
  next obj

  centre(1) = 313
  centre(2) = 259
end sub

sub rotate_scene()
  for obj = 1 to 3 step 1
    for corner = 1 to 2 step 1
      rx = coords(obj, corner, 1) - centre(1)
      ry = coords(obj, corner, 2) - centre(2)

      alpha = pi / 100

      coords(obj, corner, 1) = (rx * cos(alpha) - ry * sin(alpha)) + centre(1)
      coords(obj, corner, 2) = (rx * sin(alpha) + ry * cos(alpha)) + centre(2)
    next corner
  next obj
end sub

sub draw_scene()
  setrgb 0, 0, 0, 77
  clear window

  setrgb 1, 255, 0, 0
  setrgb 2, 0, 255, 0
  setrgb 3, 0, 0, 255

  for obj = 1 to 3 step 1
    gtriangle coords(obj, 1, 1), coords(obj, 1, 2) to coords(obj, 2, 1), coords(obj, 2, 2) to centre(1), centre(2)
  next obj

  setrgb 1, 0, 0, 77
  filled circle centre(1), centre(2), 60

  setrgb 1, 0, 0, 255
  filled circle centre(1), centre(2), 40

  setrgb 1, 255, 255, 255
  text centre(1), centre(2), "YaBasic", "cb"
  text centre(1), centre(2), "Rocks", "ct"
end sub

data 150, 60, 371, 30
data 550, 320, 448, 56
data 400, 480, 100, 400