更改高效的滚动条

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.