pawn.pas

用于开发税务票据管理的软件

unit Pawn;

interface

uses
  SysUtils, WinTypes, Classes, Graphics,  Piece;

type
//  TPawnPtr = ^TPawn;
  TPawn = class(TPiece)
  private
    { Private declarations }
  protected
    { Protected declarations }
    procedure ChangeColour(NewVal: TColour); override;
    function GetStartingLocation(NumItems: Byte): TPoint; override;
  public
    { Public declarations }
    constructor Create(AOwner: TComponent); override;
    function ValidMove(Where: TPoint): Boolean; override;
  published
    { Published declarations }
  end;

implementation

constructor TPawn.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  if FileExists(FStartDir + 'Pictures\PawnW.bmp') then
  begin
    Picture.LoadFromFile(FStartDir + 'Pictures\PawnW.bmp');
    Picture.Graphic.Transparent := True;
  end;

  Hint := 'Pawn';
  FPrefix := 'P';
  FValue := 1;
end;

function TPawn.ValidMove(Where: TPoint): Boolean;
var
  DiffY: Integer;
begin
  Result := False;
  DiffY := FY - Where.Y;
  if Colour = cWhite then DiffY := DiffY * -1;

  if (Where.X in [1..8]) and (Where.Y in [1..8]) then
  begin
    { Check for moving vertically, i.e. possibly correct non-capture }
    if (Where.X = FX) then
    begin
      { Obviously, a move to the current square is not valid }
      if (Where.Y = FY) then Exit;

      { Check if moved 1 square.  If so, it is valid.  The board itself
        can be responsible for checking there is nothing in the way. }
      if (DiffY = 1) then
      begin
        Result := True;
        Exit;
      end
      else
      begin
        { Check for moving two squares on starting location }
        if (DiffY = 2) then
        begin
          if FNumberMoves = 0 then Result := True;
          Exit;
        end
        else
        { Moving for other than one or two moves - invalid }
          Exit;
      end;
    end
    else
    begin
      { Moving diagonally? }
      if (abs(FX - Where.X) <> 1) then
        Result := False
      else
        Result := DiffY = 1;

        { NOTE! The board will be responsible for checking that the pawn
          can actually capture in the square specified.  The pawn itself
          would not know.  So, any possible move diagonally should be valid
          until further checked.  Also, be sure to check en passant (spelling?) }
    end;
  end;
end;

function TPawn.GetStartingLocation(NumItems: Byte): TPoint;
begin
  if Colour = cWhite then
  begin
    Result.Y := 2;
    Result.X := NumItems;
  end
  else
  begin
    Result.Y := 7;
    Result.X := NumItems - 8;
  end;
end;

procedure TPawn.ChangeColour(NewVal: TColour);
var
  FileName: String;
begin
  inherited ChangeColour(NewVal);
  FileName := FStartDir + 'Pictures\Pawn';
  if FPlayer = cBlack then
     FileName := FileName + 'B.bmp'
  else
      FileName := FileName + 'W.bmp';
  if FileExists(FileName) then
  begin
    Picture.LoadFromFile(FileName);
    Picture.Graphic.Transparent := True;
  end;
end;

end.