A basic snake toy. The snake is represented by a series of boxes, each move as independent sprites, which can be driven around the screen using the PicoCalc arrow keys. Hitting 'q' quits. When the snake collides with the wall, or itself, it beeps and turns the head of the snake red. Using the arrow keys it can still be driven around, once it is no longer colliding with anything the red square will turn yellow again.

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/*
  A simple snake toy using sprites
  Use arrow keys to change direction
  q to quit
*/
'double buffer animation
FRAMEBUFFER create
FRAMEBUFFER write f
CLS RGB(black)

'window dimensions
Const w = MM.HRES : Const h =  MM.VRES
Dim integer i
Dim integer exit_flag = 0

'snake properties
Const snk = RGB(yellow) 'snake color
Const snklen = 25 'snake length
Const snkw = 5 'width of snake segments
Dim integer px = w\2 'head x position
Dim integer py = h\2 'head y position
Dim integer vx=1 'head x velocity
Dim integer vy=0 'heax y velocity
Dim integer stop_flag=0 'snake stopped?

'create a box for each snake segment
'read it into a sprite
Const hdid = 2
Sprite set transparent 0
Box px,py,snkw,snkw,2,snk,snk
Sprite read hdid,px,py,snkw,snkw
Sprite copy hdid,hdid+1,snklen

'save a red sprite for collisions
Const hit = RGB(red)
Const colid = snklen+3
Box px,py,snkw,snkw,2,hit,hit
Sprite read colid,px,py,snkw,snkw


'initialize snake head and body positions
Dim x(snklen), y(snklen)
For i=0 To snklen
 x(i) = px - i*(snkw+1)
 y(i) = py
Next i

'draw play field
CLS RGB(black)
Box 0,0,w,h,2,RGB(blue)
For i=0 To snklen
 Sprite show i+2,x(i),y(i),1
Next i

'main loop
On key changedir
Sprite interrupt collision
Do
 move
 update
 draw
 Pause 100
Loop Until exit_flag = 1
CLS
End

Sub move
 'update x
 new.px = px + vx*(snkw+1)
 If new.px > w-snkw Then new.px=px:collision
 If new.px < 1 Then new.px=px:collision
 px = new.px

 'update y
 new.py = py + vy*(snkw+1)
 If new.py > h-snkw Then new.py=py:collision
 If new.py < 1 Then new.py=py:collision
 py = new.py
End Sub

Sub changedir
 Local string k$
 k$ = Inkey$

 'reset snake head
 If stop_flag = 1 Then
  stop_flag = 0
  Sprite swap colid,hdid
 End If

 'select direction of travel
 Select Case Asc(k$)
  Case 128 'up arrow
   vx = 0
   vy = -1
  Case 129 'down arrow
   vx = 0
   vy = 1
  Case 130 'left arrow
   vx = -1
   vy = 0
  Case 131 'right arrow
   vx = 1
   vy = 0
  Case 113 'q
   exit_flag = 1
  Case Else
   Print "I don't know that one"
 End Select
End Sub

Sub update
 If stop_flag = 0 Then
  For i=snklen To 1 Step -1
   x(i) = x(i-1)
   y(i) = y(i-1)
  Next i
  x(0) = px
  y(0) = py
 End If
End Sub

Sub draw
 If stop_flag = 0 Then
  For i=0 To snklen
   Sprite next i+hdid,x(i),y(i)
  Next i
  Sprite move 'move all sprites
  FRAMEBUFFER copy f,n
 End If
End Sub

Sub collision
 If stop_flag = 0 Then
  stop_flag=1
  vx=0:vy=0
  Play tone 1000,1000,250
  Sprite swap hdid,colid
  FRAMEBUFFER copy f,n
  Save image "snake.bmp"
 End If
End Sub