Option Base 0
Option Default None
Option Explicit On

Const HEIGHT% = 240
Const WIDTH% = 240
Const MAX_RADIUS! = 110.0

Const INCREASE% = 1, DECREASE% = 2, ANTICLOCKWISE% = 3, CLOCKWISE% = 4

Const SNAKE_SIZE% = 500

Dim radius! = 10
Dim theta! = 0
Dim theta_delta! = 1
Dim snake!(SNAKE_SIZE%, 1)
Dim head% = 200
Dim tail% = 0
Dim display%(240*240/64)

Cls
Circle MAX_RADIUS! + 10.0, MAX_RADIUS! + 10.0, MAX_RADIUS! + 10.0, 2, 1, Rgb(GREY)

Dim cmd%, x!, y!

Dim result%
Dim die% = 0
Dim oldx%, oldy%

On Key on_key()

Do

 oldx% = CInt(x!)
 oldy% = CInt(y!)

 y! = (Sin(Rad(90.0 - theta!)) * radius!)
 If theta! <= 180.0 Then
   x! = Sqr(Abs(radius!^2 - y!^2))
 Else
   x! = -Sqr(Abs(radius!^2 - y!^2))
 EndIf

 snake!(head%, 0) = x!
 snake!(head%, 1) = y!

 Box snake!(tail%, 0) + width% / 2, snake!(tail%, 1) + height% / 2, 4, 4, 1, Rgb(0,0,0), Rgb(0,0,0)
 Box snake!(head%, 0) + width% / 2, snake!(head%, 1) + height% / 2, 4, 4, 1, Rgb(255,0,0), Rgb(255,0,0)

 If oldx% <> CInt(x!) And oldy% <> CInt(y!) Then
   result% = set%(snake!(tail%, 0) + width% / 2, snake!(tail%, 1) + height% / 2)
 Else
   result% = 0
 EndIf
 unset(snake!(tail%, 0) + width% / 2, snake!(tail%, 1) + height% / 2)
 Inc die%, result%
'  If die% = 2 Then End
 If result% = 0 Then die% = 0

 Inc head%
 head% = head% Mod SNAKE_SIZE%
 Inc tail%
 tail% = tail% Mod SNAKE_SIZE%

 Pause 10
 If theta_delta! > 0.0 Then
   Inc theta!, theta_delta!
   If theta! >= 360.0 Then theta! = 0.0
 ElseIf theta_delta! < 0.0 Then
   Inc theta!, theta_delta!
   If theta! <= 0.0 Then theta! = 360.0
 EndIf

 If cmd% = INCREASE% Then
   Inc radius!, 3
 ElseIf cmd% = DECREASE% Then
   Inc radius!, -3
 ElseIf cmd%= CLOCKWISE% Then
   If theta_delta! = 1 Then
     theta_delta! = -1
     Inc radius!, 3
   Endif
 ElseIf cmd%= ANTICLOCKWISE% Then
   If theta_delta! = -1 Then
     theta_delta! = 1
     Inc radius!, 3
   Endif
 EndIf
 If cmd% <> 0 Then cmd% = 0

 radius! = Min(Max(radius!, 3.0), MAX_RADIUS!)

Loop

Function set%(x%, y%)
 Local bit% = y% * 240 + x%
 Local byte% = bit% \ 8
 bit% = bit% Mod 8
 Local value% = Peek(Var display%(), byte%)
 If value% And (1 << bit%) Then set% = 1
 value% = value% Or (1 << bit%)
 Poke Var display%(), byte%, value%
End Function

Sub unset(x%, y%)
 Local bit% y% * 240 + x%
 Local byte% = bit% \ 8
 bit% = bit% Mod 8
 Local value% = Peek(Var display%(), byte%)
 value% = value% Xor (1 << bit%)
 Poke Var display%(), byte%, value%
End Sub

Sub on_key()
 Local k$
 k$ = Inkey$
 Select Case k$
   Case "a" : cmd% = INCREASE%
   Case "z" : cmd% = DECREASE%
   Case "," : cmd% = ANTICLOCKWISE%
   Case "." : cmd% = CLOCKWISE%
 End Select
End Sub

' Copyright (c) 2021 Thomas Hugo Williams
' License MIT <https://opensource.org/licenses/MIT>
' For MMBasic 5.07

Option Base 0
Option Default None
Option Explicit On

Const VERSION$ = "0.2"
Const IS_CMM2% = Left$(Mm.Device$, 17) = "Colour Maximite 2"

If IS_CMM2% Then
 Option Console Serial
 Mode 7
EndIf

' Save "polar-snake.bas"

Const X_OFFSET% = MM.HRes \ 2
Const Y_OFFSET% = MM.VRes \ 2
Const HEIGHT% = 240
Const WIDTH% = 240
Const MAX_RADIUS% = Y_OFFSET% - 5

Const OUTWARD% = 0, CLOCKWISE% = 1, INWARD% = 2, ANTICLOCKWISE% = 3
Const UP% = 5, DOWN% = 6, LEFT% = 7, RIGHT% = 8, FIRE% = 9

Const MAX_SNAKE_SIZE% = 1000

Dim score%
Dim lives% = 3
Dim radius% = MAX_RADIUS% \ 2
Dim theta% = 0
Dim snake%(MAX_SNAKE_SIZE%, 1)
Dim head% = 20
Dim tail% = 0
Dim collision%(360 * MAX_RADIUS% / 64)
Dim direction%
Dim cmd%
Dim result%
Dim apple_x%, apple_y%
Dim snake_x%, snake_y%

On Key on_key()

Const FRAME_DURATION% = 10
Dim next_frame% = Timer + FRAME_DURATION%

Cls
Circle X_OFFSET%, Y_OFFSET%, MAX_RADIUS% + 5, 2, 1, RGB(GREY)

wipe()
show_text("POLAR SNAKE")
Pause 2000
wipe()

Do While lives% > 0
 start_round()

 Do
   snake%(head%, 0) = radius%
   snake%(head%, 1) = theta%
   to_cartesian(radius%, theta%, snake_x%, snake_y%)

   eat_apple()
   draw_snake()

   If set%(radius%, theta%, 1) = 1 Then
     die()
     Exit Do
   EndIf

   result% = set%(snake%(tail%, 0), snake%(tail%, 1))

   move_snake()
   check_direction()
   If apple_x% = -999 Then new_apple() Else eat_apple()

   ' Wait for next "frame".
   Do While Timer < next_frame% : Loop
   Inc next_frame%, FRAME_DURATION%
 Loop

Loop

game_over()

End

Sub start_round()
 Local i%
 radius% = MAX_RADIUS% \ 2
 theta% = 0
 For i% = 0 To Bound(snake%(), 1)
   snake%(i%, 0) = 0
   snake%(i%, 1) = 0
 Next i%
 For i% = 0 To Bound(collision%(), 1)
   collision%(i%) = 0
 Next
 direction% = CLOCKWISE%
 cmd% = 0
 apple_x% = -999
 apple_y% = -999

 Circle X_OFFSET%, Y_OFFSET%, MAX_RADIUS% + 5, 2, 1, RGB(GREY)
 show_text("LIVES: " + Str$(lives%))
 Pause 2000
 wipe()

 next_frame% = Timer + FRAME_DURATION%
End Sub

Sub die()
 Circle snake_x% + X_OFFSET%, snake_y% + Y_OFFSET%, 2, 1, 1, RGB(255,255,0), RGB(255,255,0)
 Pause 500
 Circle snake_x% + X_OFFSET%, snake_y% + Y_OFFSET%, 2, 1, 1, RGB(Black), RGB(Black)
 Inc lives%, -1
 wipe()
End Sub

Sub game_over()
 show_text("GAME OVER")
 Pause 2000
 wipe()
 show_text("SCORE: " + Str$(score%))
 Pause 2000
 wipe()
End Sub

Sub wipe()
 Local r%
 For r% = 10 To MAX_RADIUS% Step 5
   Circle X_OFFSET%, Y_OFFSET%, r% - 5, 5, 1, RGB(0,0,0)
   Circle X_OFFSET%, Y_OFFSET%, r%, 5, 1, RGB(255,0,0)
   Pause 50
 Next
 Circle X_OFFSET%, Y_OFFSET%, r% - 5, 5, 1, RGB(0,0,0)
End Sub

Sub show_text(s$)
 Text X_OFFSET%, Y_OFFSET%, s$, "CM", 1, 2, RGB(Red)
End Sub

Sub to_cartesian(r%, t%, x%, y%)
 Local yy! = Sin(Rad(90 - t%)) * r%
 y% = CInt(yy!)
 x% = Choice(t% <= 180, 1, -1) * CInt(Sqr(Abs(r%^2 - yy!^2)))
End Sub

Function set%(r%, t%, z%)
 Local t_% = Choice(r% = 0, 0, t%)

 Local bit% = r% * 360 + t_%
 Local byte% = bit% \ 8
 bit% = bit% Mod 8
 Local v% = Peek(Var collision%(), byte%)
 If v% And (1 << bit%) Then set% = 1
 If z% Then
   v% = v% Or (1 << bit%)
 Else
   v% = v% And Inv (1 << bit%)
 EndIf
 Poke Var collision%(), byte%, v%
End Function

Sub new_apple()
 If Rnd() < 0.8 Then Exit Sub
 Local r% = Rnd() * MAX_RADIUS%
 If r% < 40 Or Abs(radius% - r%) < 10 Then Exit Sub
 Local t% = Rnd() * 360
 If Abs(theta% - t%) < 10 Then Exit Sub
 to_cartesian(r%, t%, apple_x%, apple_y%)
 draw_apple()
End Sub

Sub eat_apple()
 If Abs(snake_x% - apple_x%) < 6 And Abs(snake_y% - apple_y%) < 6 Then
   erase_apple()
   apple_x% = -999
   Inc score%
   Local i%
   For i% = 1 To 10
     head% = (head% + 1) Mod MAX_SNAKE_SIZE%
     snake%(head%, 0) = radius%
     snake%(head%, 1) = theta%
   Next
 EndIf
End Sub

Sub draw_snake()
 Local x%, y%

 ' Erase tail.
 to_cartesian(snake%(tail%, 0), snake%(tail%, 1), x%, y%)
 Circle x% + X_OFFSET%, y% + Y_OFFSET%, 2, 1, 1, RGB(0,0,0), RGB(0,0,0)

 ' Draw head.
 to_cartesian(snake%(head%, 0), snake%(head%, 1), x%, y%)
 Circle x% + X_OFFSET%, y% + Y_OFFSET%, 2, 1, 1, RGB(255,0,0), RGB(255,0,0)

 Print radius%, theta%, x%, y%
End Sub

Sub move_snake()
 head% = (head% + 1) Mod MAX_SNAKE_SIZE%
 tail% = (tail% + 1) Mod MAX_SNAKE_SIZE%

 Select Case direction%
   Case OUTWARD%
     radius% = Min(radius% + 1, MAX_RADIUS% + 2)

   Case INWARD%
     Inc radius%, - 1
     If radius% < 0 Then
       radius% = -radius%
       theta% = (theta% + 180) Mod 360
       direction% = OUTWARD%
     EndIf

   Case CLOCKWISE%
     Inc theta%, -1 ' Correct this
     If theta% = -1 Then theta% = 359

   Case ANTICLOCKWISE%
     Inc theta%
     If theta% = 360 Then theta% = 0
 End Select
End Sub

Sub check_direction()
 If radius% <= 20 Then Exit Sub
 Select Case cmd%
   Case LEFT%
     Inc direction%, -1
     If direction% < 0 Then direction% = 3
   Case RIGHT%
     Inc direction%, 1
     If direction% > 3 Then direction% = 0
 End Select
 cmd% = 0
End Sub

Sub draw_apple()
 Local x% = apple_x% + X_OFFSET%
 Local y% = apple_y% + Y_OFFSET%
 Line x% - 4, y% - 5, x%, y%, 1, RGB(149,69,53)
 Line x% - 3, y% - 5, x% + 1, y%, 1, RGB(149,69,53)
 Circle x%, y%, 4, 1, 1, RGB(0,255,0), RGB(0,255,0)
End Sub

Sub erase_apple()
 Local x% = apple_x% + X_OFFSET%
 Local y% = apple_y% + Y_OFFSET%
 Line x% - 4, y% - 5, x%, y%, 1, RGB(0,0,0)
 Line x% - 3, y% - 5, x% + 1, y%, 1, RGB(0,0,0)
 Circle x%, y%, 4, 1, 1, RGB(0,0,0), RGB(0,0,0)
End Sub

Sub on_key()
 Select Case LCase$(Inkey$)
   Case "a" : cmd% = UP%
   Case "z" : cmd% = DOWN%
   Case "," : cmd% = LEFT%
   Case "." : cmd% = RIGHT%
   Case " " : cmd% = FIRE%
 End Select
End Sub

' Copyright (c) 2021 Thomas Hugo Williams
' License MIT <https://opensource.org/licenses/MIT>
' For MMBasic 5.07
' Music by Trevor Bailey

Option Base 0
Option Default None
Option Explicit On

Const VERSION$ = "1.0"
Const IS_CMM2% = Left$(MM.Device$, 17) = "Colour Maximite 2"

If IS_CMM2% Then
 Option Console Serial
 Mode 7
 Page Write 1
EndIf

' Save "polar-snake.bas"

Const X_OFFSET% = MM.HRes \ 2
Const Y_OFFSET% = MM.VRes \ 2
Const MAX_RADIUS% = Y_OFFSET% - 5
Const MAX_SNAKE_SIZE% = 1000
Const OUTWARD% = 0, CLOCKWISE% = 1, INWARD% = 2, ANTICLOCKWISE% = 3
Const UP% = 5, DOWN% = 6, LEFT% = 7, RIGHT% = 8, FIRE% = 9

' These would be constants but MMBasic does not support constant arrays
Dim SOUNDFX_NOTHING%(1) = (&hFFFFFFFFFFFFFFFF, &hFFFFFFFFFFFFFFFF)
Dim SOUNDFX_EAT%(1)     = (&hFFFFFFFFFF100C04, &hFFFFFFFFFFFFFFFF)
Dim SOUNDFX_DIE%(2)     = (&h0F10111213141516, &h0708090A0B0C0D0E, &hFF00010203040506)
Dim SOUNDFX_WIPE%(2)    = (&h0706050403020100, &h0F0E0D0C0B0A0908, &hFF16151413121110)

Dim score%
Dim lives% = 3
Dim difficulty% = 1
Dim game_type% = 1
Dim radius% = MAX_RADIUS% \ 2
Dim theta%
Dim snake%(MAX_SNAKE_SIZE%, 1)
Dim head%
Dim tail%
Dim collision%(360 * MAX_RADIUS% / 64)
Dim direction%
Dim cmd%
Dim apple_x%, apple_y%
Dim snake_x%, snake_y%
Dim frame_duration%
Dim next_frame%

Dim music_flag% = 1
Dim music_ptr% = Peek(CFunAddr music_data) + 4
Dim soundfx_flag% = 1
Dim soundfx_ptr% = Peek(VarAddr SOUNDFX_NOTHING%())

' Music and sound effects are played on SetTick interrupts.
SetTick 250, play_music, 1
SetTick 40, play_soundfx, 2

On Key on_key()

CLS
draw_border()

Do
 show_title()
 show_menu()
 init_game()
 Do While lives% > 0
   game_loop()
 Loop
 show_game_over()
 show_score()
Loop

End

Sub show_title()
 clear_display()
 Text X_OFFSET%, Y_OFFSET% - 15, "POLAR SNAKE", "CM", 1, 2, RGB(White)
 Text X_OFFSET%, Y_OFFSET% + 8, "(c) 2021 Thomas Hugo Williams", "CM", 7, 1, RGB(Red)
 Text X_OFFSET%, Y_OFFSET% + 20, "www.sockpuppetstudios.com", "CM", 7, 1, RGB(Red)
 Text X_OFFSET%, Y_OFFSET% + 40, "PRESS " + Choice(IS_CMM2%, "SPACE", "SELECT"), "CM", 1, 1, RGB(White)
 If IS_CMM2% Then Page Copy 1 To 0, B
 wait()
End Sub

Sub clear_display()
 Circle X_OFFSET%, Y_OFFSET%, MAX_RADIUS% + 3, 1, 1, RGB(BLACK), RGB(BLACK)
 draw_border()
End Sub

Sub draw_border()
 Circle X_OFFSET%, Y_OFFSET%, MAX_RADIUS% + 5, 2, 1, RGB(GREY)
End Sub

Sub wait(duration%)
 cmd% = 0
 If duration% = 0 Then
   Do While cmd% <> FIRE% : Loop
 Else
   Local expires% = Timer + duration%
   Do While Timer < expires% And cmd% <> FIRE% : Loop
 EndIf
End Sub

Sub show_menu()
 Const x% = X_OFFSET% - 45
 Local item% = 0, update% = 1

 clear_display()

 Text X_OFFSET%, Y_OFFSET% + 70, "Music by Trevor Bailey", "CM", 7, 1, RGB(Red)
 Text X_OFFSET%, Y_OFFSET% + 85, "Game Version " + VERSION$, "CM", 7, 1, RGB(Red)

 Do

   If update% Then
     Text x%, Y_OFFSET% - 65, "START GAME", , 1, 1, RGB(White)
     Text x%, Y_OFFSET% - 45, "DIFFICULTY: " + Str$(difficulty%), , 1, 1, RGB(White)
     Text x%, Y_OFFSET% - 25, "GAME TYPE:  " + Str$(game_type%), , 1, 1, RGB(White)
     Text x%, Y_OFFSET%  - 5, "MUSIC:    " + Choice(music_flag%, " ON", "OFF"), , 1, 1, RGB(White)
     Text x%, Y_OFFSET% + 15, "SOUND FX: " + Choice(soundfx_flag%, " ON", "OFF"), , 1, 1, RGB(White)
     Text x%, Y_OFFSET% + 35, "QUIT", , 1, 1, RGB(White)
     Text x% - 10, Y_OFFSET% - 65 + item% * 20, Chr$(137), , 1, 1, RGB(Red)
     If IS_CMM2% Then Page Copy 1 To 0, B
     Pause 100
     cmd% = 0
     update% = 0
   EndIf

   Select Case cmd%
     Case UP%
       If item% > 0 Then
         Text x% - 10, Y_OFFSET% - 65 + item% * 20, Chr$(137), , 1, 1, RGB(Black)
         Inc item%, -1
         update% = 1
       EndIf

     Case DOWN%
       If item% < 5 Then
         Text x% - 10, Y_OFFSET% - 65 + item% * 20, Chr$(137), , 1, 1, RGB(Black)
         Inc item%
         update% = 1
       EndIf

     Case LEFT%, RIGHT%, FIRE%
       Select Case item%
         Case 0
           If cmd% = FIRE% Then Exit

         Case 1 ' Difficulty
           Inc difficulty%, Choice(cmd% = LEFT%, -1, 1)
           difficulty% = Min(5, Max(difficulty%, 1))
           update% = 1

         Case 2 ' Game type
           Inc game_type%, Choice(cmd% = LEFT%, -1, 1)
           game_type% = Min(2, Max(game_type%, 1))
           update% = 1

         Case 3 ' Music
           music_flag% = Not music_flag%
           update% = 1

         Case 4 ' Sound FX
           soundfx_flag% = Not soundfx_flag%
           update% = 1

         Case 5 ' Quit
           If cmd% = FIRE% Then End

       End Select

     Case Else
       cmd% = 0

   End Select

   If update% = 1 Then start_soundfx(Peek(VarAddr SOUNDFX_EAT%()))

 Loop
End Sub

Sub init_game()
 lives% = 3
 score% = 0
 head% = 20
 tail% = 0
 frame_duration% = 5 + (6 - difficulty%)
End Sub

Sub game_loop()
 clear_display()
 Text X_OFFSET%, Y_OFFSET%, "LIVES: " + Str$(lives%), "CM", 1, 2, RGB(White)
 If IS_CMM2% Then Page Copy 1 To 0, B
 wait(2000)
 wipe()

 init_round()

 Do
   eat_apple()
   If apple_x% = -999 Then new_apple()
   draw_snake()
   If IS_CMM2% Then Page Copy 1 To 0, I
   If Not move_snake%() Then Exit
   check_direction()

   ' Wait for next "frame".
   Do While Timer < next_frame% : Loop
   Inc next_frame%, frame_duration%
 Loop

 die()
End Sub

Sub wipe()
 Local r%
 start_soundfx(Peek(VarAddr soundfx_wipe%()))
 For r% = 10 To MAX_RADIUS% Step 5
   Circle X_OFFSET%, Y_OFFSET%, r% - 5, 5, 1, RGB(0,0,0)
   Circle X_OFFSET%, Y_OFFSET%, r%, 5, 1, RGB(255,0,0)
   If IS_CMM2% Then Page Copy 1 To 0, B
   Pause 30
 Next
 clear_display()
 If IS_CMM2% Then Page Copy 1 To 0, B
End Sub

Sub init_round()
 Local i%
 radius% = MAX_RADIUS% \ 2
 theta% = 0
 For i% = 0 To Bound(snake%(), 1)
   snake%(i%, 0) = 0
   snake%(i%, 1) = 0
 Next i%
 snake%(head%, 0) = radius%
 snake%(head%, 1) = theta%
 to_cartesian(radius%, theta%, snake_x%, snake_y%)
 For i% = 0 To Bound(collision%(), 1)
   collision%(i%) = 0
 Next
 direction% = CLOCKWISE%
 cmd% = 0
 apple_x% = -999
 apple_y% = -999
 next_frame% = Timer + frame_duration%
End Sub

Sub to_cartesian(r%, t%, x%, y%)
 Local yy! = Sin(Rad(90 - t%)) * r%
 y% = Cint(yy!)
 x% = Choice(t% <= 180, 1, -1) * Cint(Sqr(Abs(r%^2 - yy!^2)))
End Sub

Sub eat_apple()
 If Abs(snake_x% - apple_x%) < 6 And Abs(snake_y% - apple_y%) < 6 Then
   start_soundfx(Peek(VarAddr SOUNDFX_EAT%()))
   draw_apple(0)
   apple_x% = -999
   Inc score%
   Local i%
   For i% = 1 To 10
     head% = (head% + 1) Mod MAX_SNAKE_SIZE%
     snake%(head%, 0) = radius%
     snake%(head%, 1) = theta%
   Next
 EndIf
End Sub

Sub draw_snake()
 Local x%, y%

 ' Erase tail.
 to_cartesian(snake%(tail%, 0), snake%(tail%, 1), x%, y%)
 Circle x% + X_OFFSET%, y% + Y_OFFSET%, 2, 1, 1, RGB(Black), RGB(Black)

 ' Redraw apple incase we have erased part of it.
 draw_apple(1)

 ' Draw head.
 Circle snake_x% + X_OFFSET%, snake_y% + Y_OFFSET%, 2, 1, 1, RGB(Red), RGB(Red)

'  Print radius%, theta%, snake_x%, snake_y%
End Sub

Sub die()
 start_soundfx(Peek(VarAddr soundfx_die%()))
 Local i% = head%, x%, y%
 Local sz% = Choice(head% > tail%, head% - tail%, head% + MAX_SNAKE_SIZE% - tail%)
 Local count%
 Do While i% <> tail%
   to_cartesian(snake%(i%, 0), snake%(i%, 1), x%, y%)
   Circle x% + X_OFFSET%, y% + Y_OFFSET%, 2, 1, 1, RGB(0,0,0), RGB(0,0,0)
   Inc i%, -1
   If i% < 0 Then i% = Bound(snake%(), 1)
   Inc count%
   If count% >= sz% \ 100 Then
     draw_border()
     If IS_CMM2% Then Page Copy 1 To 0, B
     count% = 0
   EndIf
 Loop

 ' Ensure last element of tail is deleted.
 to_cartesian(snake%(tail%, 0), snake%(tail%, 1), x%, y%)
 Circle x% + X_OFFSET%, y% + Y_OFFSET%, 2, 1, 1, RGB(0,0,0), RGB(0,0,0)
 If IS_CMM2% Then Page Copy 1 To 0, B

 ' Wait for the dying sound effect to complete.
 Do While Peek(Byte soundfx_ptr%) <> &hFF : Loop

 Inc lives%, -1
End Sub

Sub show_game_over()
 clear_display()
 Text X_OFFSET%, Y_OFFSET%, "GAME OVER", "CM", 1, 2, RGB(White)
 If IS_CMM2% Then Page Copy 1 To 0, B
 wait(5000)
End Sub

Sub show_score()
 clear_display()
 Text X_OFFSET%, Y_OFFSET%, "SCORE: " + Str$(score%), "CM", 1, 2, RGB(White)
 If IS_CMM2% Then Page Copy 1 To 0, B
 wait(5000)
End Sub

Function move_snake%()
 ' Clear the tail from the collision map.
 Local ignored% = set%(snake%(tail%, 0), snake%(tail%, 1), 0)

 head% = (head% + 1) Mod MAX_SNAKE_SIZE%
 tail% = (tail% + 1) Mod MAX_SNAKE_SIZE%

 Select Case direction%
   Case OUTWARD%
     radius% = radius% + 1
     If radius% > MAX_RADIUS% Then Exit Function

   Case INWARD%
     Inc radius%, - 1
     If radius% < 0 Then
       radius% = -radius%
       theta% = (theta% + 180) Mod 360
       direction% = OUTWARD%
     EndIf

   Case CLOCKWISE%
     Inc theta%, -1 ' Correct this
     If theta% = -1 Then theta% = 359

   Case ANTICLOCKWISE%
     Inc theta%
     If theta% = 360 Then theta% = 0
 End Select

 snake%(head%, 0) = radius%
 snake%(head%, 1) = theta%
 to_cartesian(radius%, theta%, snake_x%, snake_y%)

 ' Set the head, if it is already set then return 0.
 move_snake% = Not set%(radius%, theta%, 1)
End Function

Function set%(r%, t%, z%)
 Local t_% = Choice(r% = 0, 0, t%)

 Local bit% = r% * 360 + t_%
 Local byte% = bit% \ 8
 bit% = bit% Mod 8
 Local v% = Peek(Var collision%(), byte%)
 If v% And (1 << bit%) Then set% = 1
 If z% Then
   v% = v% Or (1 << bit%)
 Else
   v% = v% And INV (1 << bit%)
 EndIf
 Poke Var collision%(), byte%, v%
End Function

Sub check_direction()
 If radius% <= 20 Then Exit Sub
 If game_type% = 1 Then
   Select Case cmd%
     Case LEFT%
       Inc direction%, -1
       If direction% < 0 Then direction% = 3
     Case RIGHT%
       Inc direction%, 1
       If direction% > 3 Then direction% = 0
   End Select
 Else
   Select Case cmd%
     Case UP%
       direction% = OUTWARD%
     Case DOWN%
       direction% = INWARD%
     Case LEFT%
       direction% = ANTICLOCKWISE%
     Case RIGHT%
       direction% = CLOCKWISE%
   End Select
 EndIf
 cmd% = 0
End Sub

Sub new_apple()
 If Rnd() < 0.8 Then Exit Sub
 Local r% = Rnd() * MAX_RADIUS%
 If r% < 40 Or Abs(radius% - r%) < 10 Then Exit Sub
 Local t% = Rnd() * 360
 If Abs(theta% - t%) < 10 Then Exit Sub
 to_cartesian(r%, t%, apple_x%, apple_y%)
 draw_apple(1)
End Sub

Sub draw_apple(show%)
 If apple_x% = -999 Then Exit Sub
 Local x% = apple_x% + X_OFFSET%
 Local y% = apple_y% + Y_OFFSET%
 Local stalk% = Choice(show%, RGB(Brown), RGB(Black))
 Local apple% = Choice(show%, RGB(Green), RGB(Black))
 Line x% - 4, y% - 5, x%, y%, 1, stalk%
 Line x% - 3, y% - 5, x% + 1, y%, 1, stalk%
 Circle x%, y%, 4, 1, 1, apple%, apple%
End Sub

Sub on_key()
 Select Case LCase$(Inkey$)
   Case "a" : cmd% = UP%
   Case "z" : cmd% = DOWN%
   Case "," : cmd% = LEFT%
   Case "." : cmd% = RIGHT%
   Case " " : cmd% = FIRE%
 End Select
End Sub

' Called from interrupt to play next note of music.
Sub play_music()
 If music_flag% Then
   Local note% = Peek(Byte music_ptr%)
   If note% = &hFF Then
     music_ptr% = Peek(CFunAddr music_data) + 4
     note% = Peek(Byte music_ptr%)
   EndIf
   Play Sound 1, B, s, 440 * 2 ^ ((note% - 2) / 12.0), 15
   Inc music_ptr%
 Else
   Play Sound 1, B, O
 EndIf
End Sub

' Start a new sound effect.
Sub start_soundfx(ptr%)
 If Not soundfx_flag% Then Exit Sub

 ' Wait for current sound effect to end.
 Do While Peek(Byte soundfx_ptr%) <> &hFF : Loop

 soundfx_ptr% = ptr%

 ' Wait for first note of new sound effect to play.
 Do While soundfx_ptr% = ptr% : Loop
End Sub

' Called from interrupt to play next note of current sound effect.
Sub play_soundfx()
 If soundfx_flag% Then
   Local note% = Peek(Byte soundfx_ptr%)
   If note% < &hFF Then
     Play Sound 2, B, s, 440 * 2 ^ ((note% - 2) / 12.0)
     Inc soundfx_ptr%
   Else
     Play Sound 2, B, O
   EndIf
 Else
   Play Sound 2, B, O
 EndIf
End Sub

CSub music_data()
 00000000
 00000220 09000905 09000905 09000905 09000905 09000905 09000905 09000905
 09000905 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 0C0E0C13
 0704000C 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 091D0511
 0509051D 1515150E 15151516 1515150E 15151516 10131513 10131513 10131513
 00040013 1515150E 15151516 1515150E 15151516 13111013 15131115 16151316
 00000C18 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 0C0E0C13
 0704000C 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 091D0511
 0509051D 1515150E 15151516 1515150E 15151516 10131513 10131513 10131513
 00040013 1515150E 15151516 1515150E 15151516 13111013 15131115 16151316
 00000C18 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 0C0E0C13
 0704000C 18181815 1818181A 18181815 1818181A 15161816 13111516 15161816
 13111516 18181815 1518151A 18181815 1818181A 15161813 15131516 091D0511
 0509051D FFFFFFFF
End CSub