ListView中加了背景图后，怎样让这个图片拉伸显示？或者居中显示？

Question

我已经实现了往Listview中加背景图，并让上面的图标透明。
但是不知道怎样让这个图片居中或拉伸显示。
其实我是想模拟桌面，代码如下：unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ComCtrls, ImgList, CommCtrl, ShellCtrls, ShellAPI, ShellConsts, ShlObj,
  ComObj, ExtCtrls;type
  TForm1 = class(TForm)
    ListView1: TListView;
    ShellListView1: TShellListView;
    procedure FormCreate(Sender: TObject);
    procedure ListView1CustomDraw(Sender: TCustomListView;
      const ARect: TRect; var DefaultDraw: Boolean);
    procedure ListView1CustomDrawItem(Sender: TCustomListView;
      Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
  private
    FBkBmp: TBitmap;
    FLargeImages: TImageList;
    bWallPaper: Boolean;
    WallStyle: DWORD;
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.FormCreate(Sender: TObject);
var
  i: Integer;
  Item: TListItem;
  FileInfo: TSHFileInfo;
  ADeskTop: IActiveDesktop;
  wallpaper:PwideChar;
  StrWallPaper: string;
  WPO: TWallpaperOpt;
begin
  ListView1.Color:=GetSysColor(COLOR_DESKTOP);
  ListView1.Font.Color:=clWhite;
  ListView1.Font.Size:=8;
  ListView1.Font.Name:='Tahoma';
  ListView1.ViewStyle:=vsIcon;  { 返回桌面墙纸和墙纸的显示模式：居中、平铺、拉伸 }
  ADeskTop:=CreateComObject(CLSID_ActiveDesktop) as IActiveDesktop;
  GetMem(wallpaper,500);
  ADeskTop.GetWallpaper(wallpaper,500,0);
  WPO.dwSize:=SizeOf(WPO);
  ADeskTop.GetWallpaperOptions(WPO, 0);
  WallStyle:=WPO.dwStyle;
  StrWallPaper:=string(Wallpaper);
  FreeMem(wallpaper);  if Trim(StrWallPaper) <> '' then
  begin
    FBkBmp:=TBitmap.Create;
    FBkBmp.LoadFromFile(StrWallPaper);
    FBKBmp.Transparent:=True;
    bWallPaper:=True;
  end else bWallPaper:=False;  { 得到桌面上项目的图标列表 }
  ListView1.Clear;
  FLargeImages:=TImageList.Create(Self);
  FLargeImages.ShareImages:=True;
  FLargeImages.Handle:=SHGetFileInfo(PChar(SRFDesktop),
    0, FileInfo, SizeOf(FileInfo),
    SHGFI_LARGEICON or SHGFI_SYSICONINDEX or SHGFI_TYPENAME or SHGFI_USEFILEATTRIBUTES);
  ListView1.LargeImages:=FLargeImages;  { 利用放在窗体上的 ShellListView 来得到当前桌面的项目 }  
  for i:=0 to ShellListView1.Items.Count-1 do
  begin
    Item:=ListView1.Items.Add;
    Item.Caption:=ShellListView1.Folders[i].DisplayName;
    Item.SubItems.Add(ShellListView1.Folders[i].PathName);
    Item.ImageIndex:=ShellListView1.Folders[i].ImageIndex(True);
  end;
end;procedure TForm1.ListView1CustomDraw(Sender: TCustomListView;
  const ARect: TRect; var DefaultDraw: Boolean);
begin
  if bWallPaper then
  begin
{ 关键是这个地方 }
    if WallStyle = WPSTYLE_TILE then
    begin  { 平铺模式 }
      Sender.Brush.Bitmap:=FBKBmp;
      Sender.Canvas.Brush.Bitmap:=FBKBmp;
      Sender.Canvas.FillRect(ARect);
    end else
    if WallStyle = WPSTYLE_STRETCH then
    begin  { 拉伸模式 }
      Sender.Canvas.StretchDraw(ARect,FBkBmp);
      { 用这个方法，显示出来很不正常，用什么办法替代呢？ }
    end else
    if WallStyle = WPSTYLE_CENTER then
    begin  { 居中模式 }
      { 不知道怎么写？ }
    end;
  end;
end;procedure TForm1.ListView1CustomDrawItem(Sender: TCustomListView;
  Item: TListItem; State: TCustomDrawState; var DefaultDraw: Boolean);
var
  Images:TCustomImageList;
  R: TRect;
  iStyle: Integer;
begin
  with Sender as TListView do
  begin
    Images:=LargeImages; { ListView.ViewStyle必须设为 vsIcon } 
    if Images <> nil then
    begin
      R:=Item.DisplayRect(drIcon);
      if cdsSelected in State then iStyle:=ILD_SELECTED or ILD_TRANSPARENT
      else iStyle:=ILD_TRANSPARENT;
      ImageList_DrawEx(Images.Handle, Item.ImageIndex, Canvas.Handle,
        R.Left+(R.Right-R.Left-Images.Width) div 2,
        R.Top+(R.Bottom-R.Top-Images.Height) div 2,0, 0,
        clNone, clNone, iStyle);
    end;
    R:=Item.DisplayRect(drLabel);
    if cdsSelected in State then
    begin
      Canvas.Brush.Style := bsSolid;
      SetTextColor(Canvas.Handle,clWhite);
      SetBkColor(Canvas.Handle,clNavy);
      SetBkMode(Canvas.Handle,Windows.OPAQUE);
      DrawText(Canvas.Handle, PAnsiChar(Item.Caption),
        Length(Item.Caption), R, DT_CENTER or DT_WORDBREAK);
    end else
    begin
      Canvas.Brush.Style:=bsClear;
      SetBkMode(Canvas.Handle,Windows.TRANSPARENT);
      Canvas.Font.Style:=[fsBold];
      DrawText(Canvas.Handle, PAnsiChar(Item.Caption),
        Length(Item.Caption), R, DT_CENTER or DT_WORDBREAK);
    end;
    DefaultDraw:=False;
  end;
end;end.

Answer 1

拉伸用如下的方法：
  SetStretchBltMode(Bmp.Canvas.Handle, STRETCH_HALFTONE);
  StretchBlt(Bmp.Canvas.Handle, 0, 0, Bmp.Width, Bmp.Height, SrcBmp.Canvas.Handle, 0, 0,
    SrcBmp.Width, SrcBmp.Height, SRCCOPY);居中当然是算出开始的位置来了，以Bmp为例：
x:=(ARect.Right-ARect.left-bmp.width)div 2;
y:=(ARect.Bottom-ARect.top-bmp.height)div 2;
canvas.draw(x,y,bmp); 

Answer 2

to xzhifei:
SrcBmp 是什么呀？具体我这个程序，应该怎么写？

Answer 3

SetStretchBltMode(Sender.Canvas.Handle, STRETCH_HALFTONE);
  StretchBlt(Sender.Canvas.Handle, 0, 0, Sender.Width, Sender.Height, FBKBmp.Canvas.Handle, 0, 0,
    FBKBmp.Width, FBKBmp.Height, SRCCOPY);

Answer 4

To wgqcsdn:
你的程序不能通过。执行到  
  FBkBmp:=TBitmap.Create;
  FBkBmp.LoadFromFile(StrWallPaper);
提示：
Bitmap image is not valid.
也难怪，因为这时StrWallPaper等于'C:\WINNT\Web\Wallpaper\城堡.jpg'，图像是jpg格式的，而FBkBmp是位图，能LoadFromFile吗？要进行图像格式的转换吧。

Answer 5

我知道了，现在只支持 Bmp 格式的！

Answer 6

呵呵，有一个iconoption 设置里面的值

Answer 7

ShellListView1  得到桌面