program Project2;

{$APPTYPE CONSOLE}

{$R *.res}

uses
  System.SysUtils,
  windows,
  Winapi.Messages,
  Vcl.Dialogs;

var
  swndClass: tagWNDCLASS;
  message: MSG;
  mHwnd: hwnd;
  cxChar, cyChar: Integer;
  cxClient, cyClient: Integer;
  ScrollPos: Integer = 0;

function WindowProc(hwnd: hwnd; uMsg: UINT; wParam: wParam; lParam: lParam): LRESULT; stdcall;
var
  i: integer;
  uHdc: HDC;
  ps: tagPAINTSTRUCT;
  tm: tagTEXTMETRIC;
  si: tagSCROLLINFO;
  str: string;
  TempPos: Integer;
  FirstLine: Integer;
  LastLine: Integer;
begin
  case uMsg of
    WM_CREATE:
      begin
        {获取文本尺寸}
        uHdc := GetDC(hwnd);
        GetTextMetrics(uHdc, tm);
        ReleaseDC(hwnd, uHdc);
        cxChar := tm.tmAveCharWidth;
        cyChar := tm.tmHeight + tm.tmExternalLeading;

        {设置滚动条最大位置}
        SetScrollRange(hwnd, SB_VERT, 0, 100, False);
        SetScrollPos(hwnd, SB_VERT, 20, True);
      end;
    WM_SIZE:
      begin
        {获得客户区的尺寸}
        cxClient := loword(lParam);
        cyClient := HiWord(lParam);
        {设置垂直滚动条范围和面页大小}
        si.cbSize := SizeOf(si);
        si.fMask := SIF_RANGE or SIF_PAGE;
        si.nMin := 0;
        si.nMax := 100;
        si.nPage := cyClient div cychar;
        SetScrollInfo(hwnd, SB_VERT, si, true);
        result := 0;
        Exit;
      end;
    WM_PAINT:
      begin
        uHdc := BeginPaint(hwnd, ps);
        {获得垂直滚动条的位置}
        si.cbSize := SizeOf(si);
        si.fMask := SIF_POS;
        GetScrollInfo(hwnd, SB_VERT, si);
        TempPos := si.nPos;
        {计算需要重绘的区域}
        FirstLine := TempPos + ps.rcPaint.Top div cychar;
        LastLine := TempPos + ps.rcpaint.Bottom div cychar;
        Writeln(format(‘%d,%d‘,[FirstLine,lastline]));
        for i := FirstLine to LastLine do
        begin
          str := ‘Hello world num:‘ + i.ToString;
          TextOut(uHdc, 0, (i - TempPos) * cychar , PWideChar(str), Length(str));
        end;
        EndPaint(hwnd, ps);
      end;
    WM_VSCROLL:
      begin
        {获得垂直滚动条的所有信息}
        si.cbSize := SizeOf(si);
        si.fMask := SIF_ALL;
        GetScrollInfo(hwnd, SB_VERT, si);
        {保存当前滑块位置，迟些进行比较}
        TempPos := si.nPos;
        case LOWORD(wParam) of
          sb_top:
            begin
              {滚动条到顶端}
              si.nPos := si.nMin;
            end;
          SB_BOTTOM:
            begin
              {滚动到底端}
              si.nPos := si.nMax;
            end;
          SB_LINEDOWN:
            begin
              {向下滚动一行}
              Inc(si.nPos);
            end;
          SB_LINEUP:
            begin
             {向上滚动一行}
              Dec(si.nPos);
            end;
          SB_PAGEDOWN:
            begin
              {向下滚动一页}
              si.nPos := si.nPos + si.nPage;
            end;
          SB_PAGEUP:
            begin
             {向上滚动一页}
              si.nPos := si.nPos - si.nPage;
            end;
          SB_THUMBTRACK:
            begin
             {用户正在拖动滚动条}
              si.nPos := si.nTrackPos;
            end;

        end;
        {设置滚动滑块的新位置}
        si.fMask := SIF_POS;
        SetScrollInfo(hwnd, SB_VERT, si, True);
        {获得滑动条滑块的位置，由于窗口调整，它可能不是同一个值}
        GetScrollInfo(hwnd, SB_VERT, si);
        if si.npos  TempPos then
        begin
          writeln(IntToStr(TempPos - si.npos));
          ScrollWindow(hwnd, 0, cychar * (TempPos - si.npos), nil, nil);
          UpdateWindow(hwnd);
        end;

      end;

  end;
  result := DefWindowProc(hwnd, uMsg, wParam, lParam);
end;

begin
  swndClass.cbClsExtra := 0; //窗口类扩展，无
  swndClass.cbWndExtra := 0; //窗口实例扩展
  swndClass.hbrBackground := COLOR_BACKGROUND; //窗口背景颜色黑色
  //LoadCursor()
  swndClass.hCursor := LoadCursor(0, IDC_ARROW); //窗口采用箭头光标
  swndClass.hIcon := LoadIcon(0, IDI_APPLICATION); //窗口最小化图标：采用缺省图标
  swndClass.hInstance := hInstance; //窗口实例句柄
  swndClass.lpfnWndProc := @WindowProc; //窗口处理函数
  swndClass.lpszClassName := ‘myWnd‘; //窗口类名
  swndClass.lpszMenuName := nil; //窗口菜单
  swndClass.style := CS_DBLCLKS; //窗口样式
  if RegisterClass(swndClass) = 0 then
  begin
    Writeln(‘windows class register error!‘);
    Exit;
  end;

  mHwnd := CreateWindowEx(0, ‘myWnd‘, ‘Delphi Windows‘, WS_OVERLAPPEDWINDOW or WS_VSCROLL or WS_HSCROLL,  {滚动条添加}
    CW_USEDEFAULT, CW_USEDEFAULT, 544, 375, HWND_DESKTOP, 0, hInstance, 0);

  ShowWindow(mHwnd, SW_SHOW);
  UpdateWindow(mHwnd);
  while GetMessage(message, 0, 0, 0) do
  begin
    TranslateMessage(message);
    DispatchMessage(message);
  end;
end.