; by Picnic

     format PE GUI 4.0
     entry start

     include "win32ax.inc"

     COLUMNS = 6
     ROWS = 6

     TILEW = 40
     TILEH = 40
     BORDER = 4

     WHITE = 0xFFFFFF
     YELLOW = 0xFFFF
     BLUE = 0xFF0000

     SCRAMBLE = 500
     XWDTH = COLUMNS * 4

macro get x,y
{
     mov eax,y
     mov ebx,x
     imul eax,eax,XWDTH
     mov eax,dword[map+eax+ebx*4]
}

macro set x,y,value
{
     mov ebx,value
     mov eax,y
     mov ecx,x
     imul eax,eax,XWDTH
     mov dword[map+eax+ecx*4],ebx
}

macro flip x,y
{
     local .a, .b
     get x,y
     cmp eax,BLUE
     jne .b
     mov eax,YELLOW
     jmp .a
     .b:
     mov eax,BLUE
     .a:
     set x,y,eax
}


section ".data" data readable writeable

     _class TCHAR "FASMWIN32",0
     _title TCHAR "Flip Flop",0
     _error TCHAR "Startup failed.",0

     align 4
     _btnx dd BORDER
     _btny dd BORDER + (TILEH+BORDER) * ROWS
     _wndw dd 2 * BORDER + (TILEW+BORDER) * COLUMNS
     _wndh dd 50 + BORDER + (TILEH+BORDER) * ROWS
     _wndx dd ?
     _wndy dd ?
     hwnd dd ?
     map rd COLUMNS*ROWS

     align 4
     wc WNDCLASS 0,WindowProc,0,0,0,0,0,COLOR_BTNFACE+1,0,_class
     msg MSG


section ".code" code readable executable

   start:
     invoke GetModuleHandle,0
     mov dword[wc.hInstance],eax
     invoke LoadIcon,0,IDI_APPLICATION
     mov dword[wc.hIcon],eax
     invoke LoadCursor,0,IDC_ARROW
     mov dword[wc.hCursor],eax
     invoke CreateSolidBrush,WHITE
     mov dword[wc.hbrBackground],eax
     invoke RegisterClass,addr wc
     test eax,eax
     jz error

     invoke GetSystemMetrics,SM_CXSCREEN
     shr eax,1
     mov ecx,dword[_wndw]
     sar ecx,1
     sub eax,ecx
     mov dword[_wndx],eax

     invoke GetSystemMetrics,SM_CYSCREEN
     shr eax,1
     mov ecx,dword[_wndh]
     sar ecx,1
     sub eax,ecx
     mov dword[_wndy],eax

     invoke CreateWindowEx,0,addr _class,addr _title,WS_VISIBLE+WS_DLGFRAME+WS_SYSMENU,\
                dword[_wndx],dword[_wndy],dword[_wndw],dword[_wndh],0,0,dword[wc.hInstance],0
     mov dword[hwnd],eax
     test eax,eax
     jz error

  msgloop:
     invoke GetMessage,msg,0,0,0
     cmp eax,1
     jb endloop
     jne msgloop
     invoke TranslateMessage,msg
     invoke DispatchMessage,msg
     jmp msgloop
  error:
     invoke MessageBox,0,addr _error,0,MB_ICONERROR+MB_OK
  endloop:
     invoke ExitProcess,dword[msg.wParam]


proc WindowProc hwnd:dword,wmsg:dword,wparam:dword,lparam:dword

     local ps:PAINTSTRUCT

     push ebx esi edi
     cmp dword[wmsg],WM_CREATE
     je .wmcreate
     cmp dword[wmsg],WM_COMMAND
     je .wmcommand
     cmp dword[wmsg],WM_LBUTTONDOWN
     je .wmlbuttondown
     cmp dword[wmsg],WM_PAINT
     je .wmpaint
     cmp dword[wmsg],WM_CLOSE
     je .wmclose
  .defwndproc:
     invoke DefWindowProc,dword[hwnd],dword[wmsg],dword[wparam],dword[lparam]
     jmp .finish
  .wmcreate:
     stdcall CreateMap
     invoke CreateWindowEx,0,"BUTTON","Scramble",WS_CHILD or WS_VISIBLE,\
              dword[_btnx],dword[_btny],140,22,dword[hwnd],SCRAMBLE,dword[wc.hInstance],0
     jmp .finish
  .wmcommand:
     .if ( dword[wparam] = SCRAMBLE )
        stdcall CreateMap
        stdcall DrawMap
     .endif
     jmp .finish
  .wmlbuttondown:
     stdcall LButtonClick,dword[lparam],dword[lparam]
     jmp .finish
  .wmpaint:
     invoke BeginPaint,dword[hwnd],addr ps
     stdcall DrawMap
     invoke EndPaint,dword[hwnd],addr ps
     jmp .finish
  .wmclose:
     invoke PostQuitMessage,0
     xor eax,eax
  .finish:
     pop edi esi ebx

     ret
endp


; If x,y coords are valid then flip neighbour tiles, redraw map and check if user wins.
proc FlipTiles x:dword,y:dword

     pushad
     .if ( dword[x] >= 0 ) & ( dword[x] <= COLUMNS-1 ) & ( dword[y] >= 0 ) & ( dword[y] <= ROWS-1 )
        flip dword[x],dword[y]
        .if ( dword[x] > 0 )
           push dword[x]
           dec dword[x]
           flip dword[x],dword[y]
           pop dword[x]
        .endif
        .if ( dword[x] < COLUMNS-1 )
           push dword[x]
           inc dword[x]
           flip dword[x],dword[y]
           pop dword[x]
        .endif
        .if ( dword[y] > 0 )
           push dword[y]
           dec dword[y]
           flip dword[x],dword[y]
           pop dword[y]
        .endif
        .if ( dword[y] < ROWS-1 )
           inc dword[y]
           flip dword[x],dword[y]
        .endif
        stdcall DrawMap
        stdcall CheckWin
     .endif
     popad

     ret
endp


; Convert mouse coords into 2D map coords and call FlipTiles.
proc LButtonClick\
    x:dword,y:dword

     local hdc dd ?

     pushad
     invoke GetDC,dword[hwnd]
     mov dword[hdc],eax
     and dword[x],0xFFFF
     shr dword[y],16
     invoke GetPixel,dword[hdc],dword[x],dword[y]
     .if ( eax <> WHITE )
        xor edx,edx
        mov eax,dword[y]
        mov ebx,TILEH+BORDER
        div ebx
        mov dword[y],eax
        xor edx,edx
        mov eax,dword[x]
        mov ebx,TILEW+BORDER
        div ebx
        mov dword[x],eax
        stdcall FlipTiles,dword[x],dword[y]
     .endif
     invoke ReleaseDC,dword[hwnd],dword[hdc]
     popad

     ret
endp


; Fill map array with random colors values yellow or blue.
proc CreateMap

     pushad
     xor ecx,ecx
     .while ( ecx < COLUMNS*ROWS )
        mov dword[map+ecx*4],BLUE
        rdtsc
        and eax,eax
        .if ( PARITY? )
           mov dword[map+ecx*4],YELLOW
        .endif
        inc ecx
     .endw
     popad

     ret
endp


; Count yellow color values in map array.
proc CheckWin

     pushad
     xor ecx,ecx
     xor eax,eax
     .while ( ecx < COLUMNS*ROWS )
        cmp dword[map+ecx*4],YELLOW
        jne @f
        inc eax
       @@:
        inc ecx
     .endw
     .if ( eax = COLUMNS*ROWS )
        invoke MessageBox,dword[hwnd],<"Puzzle Completed.">,addr _title,MB_OK or MB_ICONINFORMATION
     .endif
     popad

     ret
endp


; Draw a 2D grid of tiles.
proc DrawMap

     local x dd ?
     local y dd ?

     pushad
     mov dword[y],0
     .while ( dword[y] < ROWS )
         mov dword[x],0
        .while ( dword[x] < COLUMNS )
           imul esi,dword[x],TILEW+BORDER
           add esi,BORDER
           imul edi,dword[y],TILEH+BORDER
           add edi,BORDER
           get dword[x],dword[y]
           stdcall DrawTile,esi,edi,eax
           inc dword[x]
        .endw
        inc dword[y]
     .endw
     popad

     ret
endp


; Draw a tile at x,y with black pen and b brush.
proc DrawTile\
    x:dword, y:dword, b:dword

     local hdc dd ?
     local brush dd ?

     pushad
     invoke GetDC,dword[hwnd]
     mov dword[hdc],eax
     invoke GetStockObject,BLACK_PEN
     invoke SelectObject,dword[hdc],eax
     invoke CreateSolidBrush,dword[b]
     mov dword[brush],eax
     invoke SelectObject,dword[hdc],dword[brush]
     mov eax,dword[x]
     add eax,TILEW
     mov ecx,dword[y]
     add ecx,TILEH
     invoke RoundRect,dword[hdc],dword[x],dword[y],eax,ecx,8,8
     invoke DeleteObject,dword[brush]
     invoke ReleaseDC,dword[hwnd],dword[hdc]
     popad

     ret
endp


section ".idata" import data readable writeable

     library\
     kernel32,"KERNEL32.DLL",\
     user32,"USER32.DLL",\
     gdi32,"GDI32.DLL"

     include "\api\kernel32.inc"
     include "\api\user32.inc"
     include "\api\gdi32.inc"
    

. X X X | X X . X | X . X X | X X X .
X . X . | . . . X | X . . . | . X . X
X X . . | X X X . | . X X X | . . X X
X . . . | . X . . | . . X . | . . . X    

Only 1 out of every 16 games are actually winnable. The buttons are not "independent" - try pushing any of these combinations: ... And you end up back where you started. This shows that you could do without, for example, all the bottom buttons, by pushing instead all the other buttons in the combination containing it; thus you have only 12 bits of influence (4096 accessible states) rather than the 16 bits one might expect (all 65536 states accessible). And if you are not lucky enough to start in one of the 4096 states that are accessible from the all-tiles-yellow state, then nothing you do can win that game.

     _wndw dd 10 + BORDER + (TILEW+BORDER) * COLUMNS
     _wndh dd 56 + BORDER + (TILEH+BORDER) * ROWS