Lunar Lander

globals [
  platform     ;; the x coordinate of the center of the platform
]

turtles-own [
  xvel yvel    ;; x and y components of the lander's velocity
]

to setup
  clear-all
  setup-terrain
  crt 1 [
    set shape "lander"
    set color red
    set size 10
    setxy (platform + max-pxcor)
          (max-pycor - size / 2)
    set heading 0
  ]
  reset-ticks
end 

to setup-terrain
  let terrain-color gray
  set platform platform-width
               + random (world-width - 2 * platform-width)
               + min-pxcor
  ;; first use a turtle to draw the surface of the moon
  ;; including the landing platform
  crt 1 [
    set color gray
    setxy min-pxcor
          floor (min-pycor / 2)
    set heading 90
    repeat world-width [
      set pcolor color
      fd 1
      ;; draw the platform in blue
      if pxcor = platform - (platform-width / 2) [
        set heading 90
        set color blue
      ]
      ;; everything else is moon surface and should be gray
      if pxcor = platform + (platform-width / 2) [
        set color gray
      ]
      ;; and if it isn't the platform it should also be
      ;; jagged so vary ycor by the terrain-bumpiness
      if color != blue [
        ;; random-poisson usually gives small variations, occasionally
        ;; larger ones
        let y ( ycor + one-of [1 -1] * random-poisson ( terrain-bumpiness ) )
        ;; prevent the drawing turtle from wrapping vertically
        ;; while contouring the terrain
          if patch-at 0 (y - ycor) != nobody
          [ set ycor y ]
      ]
    ]
    die
  ]

  ;; then use more turtles to make solid gray below the gray line
  ask patches with [pcolor != black] [
    sprout 1 [
      set heading 180
      ;; if the drawing turtle is already at the bottom it should not continue
      if not can-move? 1 [ die ]
      fd 1
      set pcolor gray
      fd 1
      while [ can-move? 1 ]
      [
        set pcolor gray
        fd 1
      ]
      set pcolor gray
      die
    ]
  ]
end 

to go
  if (not any? turtles) or ([color] of one-of turtles != red)
    [ stop ]
  ask turtles [
    ;; if the module is about to wrap vertically
    ;; stop its ascent
    ifelse ycor + yvel > max-pycor
    [ set xcor (xcor + xvel)
      set yvel 0 ]
    [ setxy (xcor + xvel) (ycor + yvel) ]
    ;; exert the force of gravity
    set yvel yvel - 0.001
    ;; detect crashes and insufficiently soft landings
    if [pcolor] of patch-at 0 -2 != black [
      ifelse (abs yvel > 0.08) or
             (abs xvel > 0.04) or
             (heading != 0) or
             ((pxcor - platform) >= platform-width / 2)
      [ game-over ]
      [ set color green - 1 ]
    ]
    ;; switch back to the shape without the thrusters on
    if shape = "lander2" and timer > 0.3
      [ set shape "lander" ]
  ]
  tick
end 

to game-over  ;; turtle procedure
  set shape "skull"
  set color white
  set heading 0
end 

to rotate-left  ;; turtle procedure
  if shape = "lander" [
    lt 5
  ]
end 

to rotate-right  ;; turtle procedure
  if shape = "lander" [
    rt 5
  ]
end 

to thrust  ;; turtle procedure
  if shape = "lander" [
    set xvel xvel + thrust-amount * dx
    set yvel yvel + thrust-amount * dy
    ;; lander2 has a visual indication that the thrusters are on
    set shape "lander2"
    reset-timer
  ]
end 


; Copyright 2005 Uri Wilensky.
; See Info tab for full copyright and license.