QB&MOUSE2.BAS

OpeningScreen:
  COLOR 7, 1: CLS : c1 = 5: c2 = 3: s$ = " K  Q  B  N  R  P "
  FOR i = 2 TO 17: COLOR 7, 1: LOCATE i, 10
    IF i MOD 2 = 1 THEN LOCATE , 7: PRINT 9 - i \ 2;  'Print Row Numbers
    FOR j = 1 TO 8: COLOR c1, c2: PRINT "     "; : SWAP c1, c2  'Squares
    NEXT j: IF i MOD 2 = 1 THEN SWAP c1, c2     'For Next Row Of Squares
  NEXT i: COLOR 7, 1: LOCATE 18, 12
  PRINT "a    b    c    d    e    f    g    h": PRINT     'Print Prompts
  COLOR 5, 7: LOCATE , 12: PRINT s$; : COLOR , 0: PRINT s$: COLOR 7, 1
  PRINT " SingleClick, Left=Select Piece, Right=Put Piece(s) On Board"
  PRINT " Drag A Piece To Move It (Either Left Or Right Drag Will Do)"
  PRINT " DoubleClick, Left ON BOARD=Save, BELOW BOARD=Renew,";
  PRINT " Right OR Esc=End Program"
  PRINT " Press Alt+Enter To Switch Between Screens"; : COLOR 5
  DIM b$(3 TO 17, 12 TO 47), c(3 TO 17, 12 TO 47)
  click = 1: GOSUB DoubleClick                        'Save Blank Screen
  FOR j = 11 TO 46 STEP 5: s$ = " " + MID$(" RNBQKBNR", j \ 5, 1) + " "
    COLOR , 0: LOCATE 3, j: PRINT s$; : LOCATE 5, j: PRINT " P ";
    COLOR , 7: LOCATE 15, j: PRINT " P "; : LOCATE 17, j: PRINT s$;
  NEXT j                   'Display Pieces In Position For Start Of Game
RETURN 
SingleClick:                       'Start Here With presses=1 releases=1
  IF click = 1 THEN   'Single Left Click Gets A Character From Row 20,..
  col = ((cx \ 8 + 1) \ 3) * 3 + 1        '&.. Columns 13, 16, 19,-,46
    cha$ = CHR$(SCREEN(20, col))        'cha$ May Be A Letter Or A Space
    c1 = SCREEN(20, col, 1) \ 16       'Save Background Colour Of Letter
  ELSEIF click = 2 THEN    'Single Right Click Puts Piece On Chess Board
    GOSUB RowCol: GOSUB Test: IF t$ = "No" THEN RETURN       'Fails Test
    COLOR , c1: LOCATE row, col - 1: PRINT " "; cha$; " ";  'Paste Piece
  END IF
RETURN 
DoubleClick: row = (dx \ 8 + 1)    'Start Here With presses=2 releases=2
  IF click = 1 THEN                                   'Double Left Click
    FOR i = 3 TO 17 STEP 2: FOR j = 12 TO 47 STEP 5 'Step To All Squares
      IF row < 18 THEN      'Double Left Click On Board=Save All Squares
        b$(i, j) = CHR$(SCREEN(i, j))               'Save All Characters
        c(i, j) = SCREEN(i, j, 1) \ 16      'Save All Background Colours
      ELSE          'Double Left Click Below Board=Restore Saved Squares
        COLOR , c(i, j): LOCATE i, j - 1: PRINT " "; b$(i, j); " ";
    END IF: NEXT j: NEXT i
  END IF
  IF click = 2 THEN press$ = CHR$(27)   'Double Right Click Ends Program
RETURN 
DragMouseCursor:                   'Start Here With presses=1 releases=0
  GOSUB RowCol: cha$ = CHR$(SCREEN(row, col))    'Piece At Start Of Drag
  GOSUB Test: IF t$ = "No" THEN RETURN                       'Fails Test
  c1 = SCREEN(row, col, 1) \ 16    'Save Color Of Piece At Start Of Drag
  i = row: j = col              'Save Position Of Piece At Start Of Drag
  CALL AssemblyCode(1, 0, 0, 0): LOCATE , , 1, 0, 7   'Show Both Cursors
  WHILE releases < 1                      'Wait For Mouse Button Release
QB&MOUSE2.BAS (end)
    CALL AssemblyCode(3, 0, cx, dx)             'Get cx & dx During Drag
    GOSUB RowCol: LOCATE row, col   'Text Cursor Shows Position For Drop
    bx = click - 1: CALL AssemblyCode(6, bx, 0, 0): releases = bx
  WEND                    'Exit Loop When Button Released At End Of Drag
  CALL AssemblyCode(2, 0, 0, 0): LOCATE , , 0         'Hide Both Cursors
  GOSUB Test: IF t$ = "No" THEN RETURN                       'Fails Test
  c2 = SCREEN(row, col, 1) \ 16: IF c1 = c2 THEN RETURN     'Same Colour
  COLOR , c1: LOCATE row, col - 1: PRINT " "; cha$; " ";    'Paste Piece
  COLOR , SCREEN(i, j - 2, 1) \ 16    'Colour Of Square At Start Of Drag
  LOCATE i, j - 1: PRINT "   ";       'Blank Out Square At Start Of Drag
RETURN 
RowCol:
  row = ((dx \ 8 + 1) \ 2) * 2 + 1   'Chess Pieces In Rows 3, 5, 7 etc..
  col = ((cx \ 8 + 1) \ 5) * 5 + 2        '&.. In Columns 12, 17, 22 etc
RETURN 
Test:   't$="No" If cha$ Not K Q B N R P Or row &/Or col Off Chess Board
  t$ = "Yes": IF cha$ < "B" OR cha$ > "R" THEN t$ = "No"
  IF row < 2 OR row > 17 OR col < 10 OR col > 49 THEN t$ = "No"
RETURN