Global sw = 800
Global sh = 800
Global w = sw/8
Global h = sh/8
Global mode = 0
Global si = -1
Global sj = -1
Global turn = 1
Graphics sw, sh

Dim board(8,8)
Dim pieces(8,8)

Dim dests(8,8)
Dim caps(8,8)

reset_dests()
reset_caps()

For j = 0 To 7
    For i = 0 To 7
        board(i,j) = (i+j) Mod 2
    Next
Next

For x = 0 To 3
    ;pieces(2*x+1,0) =  1
    ;pieces(2*x  ,1) =  1
    pieces(2*x+1,2) =  2
    pieces(2*x  ,5) = -2
    ;pieces(2*x+1,6) = -1
    ;pieces(2*x  ,7) = -1
Next

SetBuffer BackBuffer()
While Not KeyHit(1)
Cls

drawboard()

If check_win() Then

    Color 255,255,255

    Text sw/2, sh/2, "PLAYER " + (1+(turn+1)/2) + " WINS!", 300

Else

highlight()              ; square border hover
highlight_selection()    ; men/kings border hover

If mode <> 2 Then
    compute_dests()     ; legal moves (1 distance)
End If
compute_caps()
highlight_destinations() ; show them (differently for men and kings)

click()                  ; game action

End If

Flip
WaitEvent() ; avoid busylooping
Wend

Function drawboard()
Local t = h/12
For i = 0 To 7
    For j = 0 To 7
        ; draw square
        Color board(i,j)*255,0,0
        Rect i*w, j*h, w, h
        ; draw checker
        If pieces(i,j) <> 0 Then
            checker(i,j)
        End If
    Next
Next
End Function

Function highlight()
i = MouseX() / w
j = MouseY() / h
Color 255, 255, 0
If pieces(i,j) <> 0 Then
    Oval i*w, j*h, w, h, 0
Else
    Rect i*w, j*h, w, h, 0
End If
End Function

Function highlight_selection()
If si >= 0 And sj >= 0 Then
    Color 0,255,0
    Oval si*w, sj*h, w, h, 0
End If
End Function

Function highlight_destinations()
For j = 0 To 7
For i = 0 To 7
If dests(i,j) <> 0 Then
    Select Abs(dests(i,j))
    Case 2
        Color 110,110,210
        Oval i*w, j*h, w, h
        Color 140,140,240
        Oval i*w+(0.2*w), j*h+(0.2*h), w*0.6, h*0.6
    Case 1
        Color 110,110,210
        Oval i*w, j*h, w, h
    End Select
End If
If caps(i,j) <> 0 Then
    Select Abs(caps(i,j))
    Case 2
        Color 110,110,210
        Oval i*w, j*h, w, h
        Color 140,140,240
        Oval i*w+(0.2*w), j*h+(0.2*h), w*0.6, h*0.6
    Case 1
        Color 110,110,210
        Oval i*w, j*h, w, h
    End Select
End If
Next
Next
End Function

Function has_dests(i,j)
Local savei = si
Local savej = sj
si = i
sj = j
compute_dests()
Local has = False
For j = 0 To 7
For i = 0 To 7
    has = has Or dests(i,j) <> 0
Next
Next
si = savei
sj = savej
Return has
End Function

Function compute_dests()
If si >= 0 And sj >= 0 Then
    Select Abs(pieces(si,sj))
    Case 2
        For i1 = si-1 To si+1 Step 2
        For j1 = sj-1 To sj+1 Step 2
            If i1 >= 0 And i1 <= 7 And j1 >= 0 And j1 <= 7 Then
            If pieces(i1,j1) = 0 Then
                dests(i1,j1) = pieces(si,sj)
            End If
            End If
        Next
        Next
    Case 1
        For i1 = si-1 To si+1 Step 2
            j1 = sj+pieces(si,sj)
            If i1 >= 0 And i1 <= 7 And j1 >= 0 And j1 <= 7 Then
            If pieces(i1,j1) = 0 Then
                dests(i1,j1) = pieces(si,sj)
            End If
            End If
        Next
    End Select
End If
End Function

Function reset_dests()
For j = 0 To 7
For i = 0 To 7
dests(i,j) = 0
Next
Next
End Function

Function has_caps(i,j)
Local savei = si
Local savej = sj
si = i
sj = j
compute_caps()
Local has = False
For j = 0 To 7
For i = 0 To 7
    has = has Or caps(i,j) <> 0
Next
Next
si = savei
sj = savej
Return has
End Function

Function compute_caps()
If si >= 0 And sj >= 0 Then
    reset_caps()
    Select Abs(pieces(si,sj))
    Case 2
        For i1 = si-1 To si+1 Step 2
        For j1 = sj-1 To sj+1 Step 2
            If i1 >= 0 And i1 <= 7 And j1 >= 0 And j1 <= 7 Then
            If Sgn(pieces(i1,j1)) = -Sgn(pieces(si,sj)) Then
                j2 = j1+(j1-sj)
                i2 = i1+(i1-si)
                Print "i1 j1"
                Print i1 + " " + j1
                If i2 >= 0 And i2 <= 7 And j2 >= 0 And j2 <= 7 Then
                    If pieces(i2,j2) = 0 Then
                        caps(i2,j2) = pieces(si,sj)
                    End If
                End If
            End If
            End If
        Next
        Next
    Case 1
        For i1 = si-1 To si+1 Step 2
            j1 = sj+pieces(si,sj)
            If i1 >= 0 And i1 <= 7 And j1 >= 0 And j1 <= 7 Then
            If Sgn(pieces(i1,j1)) = -Sgn(pieces(si,sj)) Then
                j2 = j1+pieces(si,sj)
                i2 = i1+(i1-si)
                If i2 >= 0 And i2 <= 7 And j2 >= 0 And j2 <= 7 Then
                    If pieces(i2,j2) = 0 Then
                        caps(i2,j2) = pieces(si,sj)
                    End If
                End If
            End If
            End If
        Next
    End Select
End If
End Function

Function reset_caps()
For j = 0 To 7
For i = 0 To 7
caps(i,j) = 0
Next
Next
End Function


Function checker(i,j)
Select Sgn(pieces(i,j))
Case 1
    Color 200,200,200
Case -1
    Color 80,80,80
End Select
Oval i*w,j*h,w,h
If Abs(pieces(i,j)) = 2 Then
    Color 150,150,150
    Oval i*w+(0.2*w), j*h+(0.2*h), w*0.6, h*0.6
End If
End Function

Function click()
If MouseDown(1) Then
    i = MouseX() / w
    j = MouseY() / h
    Select mode
    Case 0 ; normal
    If Sgn(pieces(i,j)) = turn Then ; turn
        If has_dests(i,j) Or has_caps(i,j) Then
            si = i
            sj = j
            mode = 1
            compute_dests()
            compute_caps()
        End If
    End If
    Case 1 ; element picked
    If i = si And j = sj Then
        ; de-selection
        reset_dests()
        reset_caps()
        si = -1
        sj = -1
        mode = 0
    Else If dests(i,j) = pieces(si,sj) Then ; simple move
        ; move piece
        pieces(i,j) = pieces(si,sj)
        pieces(si,sj) = 0
        reset_dests()
        reset_caps()
        si = -1
        sj = -1
        mode = 0
        turn = -turn
        ; make a king
        If Abs(pieces(i,j)) = 1 And j = (1 - turn)/2*7 Then
            pieces(i,j) = pieces(i,j)*2
        End If
    Else If caps(i,j) = pieces(si,sj) Then ; capture
        remove_cap(si,sj,i,j)
        pieces(i,j) = pieces(si,sj)
        pieces(si,sj) = 0
        If has_caps(i,j) Then
            reset_dests()
            si = i
            sj = j
            mode = 2
        Else
            si = -1
            sj = -1
            mode = 0
            turn = -turn
        End If
    End If
    Case 2 ; we did a capture, we must do more captures
    If caps(i,j) = pieces(si,sj) Then
        remove_cap(si,sj,i,j)
        pieces(i,j) = pieces(si,sj)
        pieces(si,sj) = 0
        If has_caps(i,j) Then
            si = i
            si = j
        Else
            reset_dests()
            reset_caps()
            si = -1
            sj = -1
            mode = 0
            turn = -turn
        End If
    End If
    End Select
End If
End Function

Function remove_cap(si,sj,i,j)
Local ci
Local cj
If i > si Then
ci = si+1
Else
ci = si-1
End If
If j > sj Then
cj = sj+1
Else
cj = sj-1
End If
pieces(ci,cj) = 0
End Function

Function check_win()
Local lights = 0
Local darks = 0
For j = 0 To 7
For i = 0 To 7
If pieces(i,j) > 0 Then
    lights = lights + 1
Else If pieces(i,j) < 0 Then
    darks = darks + 1
End If
Next
Next
Return (lights = 0) Or (darks = 0)
End Function