http://www.pudn.com/downloads171/sourcecode/windows/detail791686.html

unit Unit1;
 
interface
 
uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, gdipapi, gdipobj, Menus, StdCtrls;
 
type
  TForm1 = class(TForm)
    PopupMenu1: TPopupMenu;
    ChangeSkin1: TMenuItem;
    N1: TMenuItem;
    Close1: TMenuItem;
    Button1: TButton;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    procedure ShowPNGForm1(PNGFile:string; nTran: integer);
    procedure ShowPNGForm2(PNGFile:string; nTran: integer);
    procedure FormMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure Close1Click(Sender: TObject);
    procedure ChangeSkin1Click(Sender: TObject);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
 
const
  WS_EX_LAYERED = $80000;
  LWA_COLORKEY  = 1;
  LWA_ALPHA     = 2;
  ULW_COLORKEY  = 1;
  ULW_ALPHA     = 2;
  ULW_OPAQUE    = 4;
 
 
 
 
var
  Form1: TForm1;
  bmp, old_bmp : HBITMAP;
  DC : HDC;
  bitmap: tgpbitmap;
  j:integer;
 
 
 
 
  Function UpdateLayeredWindow(hWnd : HWND;
                            hdcDst : HDC; pptDst : PPoint; psize : PSize;
                            hdcSrc : HDC; pptSrc : PPoint;
                            crKey  : COLORREF;
                            pblend : PBlendFunction;
                            dwFlags : DWORD): BOOL; stdcall;
 
 
implementation
 
{$R *.dfm}
 
Function UpdateLayeredWindow; external 'user32.dll';
 
procedure Tform1.ShowPNGForm1(PNGFile:string; nTran: integer);
var
  graphics : TGPGraphics;
  Image: TGPImage;
 
begin
   
 
  graphics := TGPGraphics.Create(DC);
  Image:= TGPImage.Create(PNGFile);
 
  graphics.DrawImage(image, 0, 0);
  //UpdateLayeredWindow(Handle, Canvas.Handle, @pt1, @sz, DC, @pt2,0, @bf,ULW_ALPHA);
end;
 
procedure Tform1.ShowPNGForm2(PNGFile:string; nTran: integer);
var
  pt1, pt2 : TPoint;
  sz : TSize;
  bf : TBlendFunction;
begin
 
  bitmap:=tgpbitmap.Create(PNGFile);
  pt1 := Point(left,top); //窗口做上角的坐标
  pt2 := Point(0, 0); //这个就不用说了，一看见（0，0）就应该明白了
  sz.cx := bitmap.GetWidth;  //尺寸不要超过图像大小，不然窗口就什么都没有了，连个影子都没有
  sz.cy := bitmap.GetHeight;  //同上
  bf.BlendOp := AC_SRC_OVER; //这些死记就行了
  bf.BlendFlags := 0;                  //同上
  if (nTran<0) or (nTran>255) then nTran:=255;
  bf.SourceConstantAlpha := nTran;  //同上
  bf.AlphaFormat := AC_SRC_ALPHA; //同上


 
  DeleteObject(bmp); //前面就是在这里犯的错误，不然占用的内存会无限增大
  bitmap.GetHBITMAP(0,bmp); // HBITMAP是windows标准位图格式，支持透明，这里是从tgpbitmap 转化成 HBITMAP
  DeleteDC(DC);
  DC := CreateCompatibleDC(Canvas.Handle); //API的含义我倒是明白，为什么写这句话我就不明白了，反正就是需要
  old_bmp := SelectObject(DC, bmp); //同上
  UpdateLayeredWindow(Handle, Canvas.Handle, @pt1, @sz, DC, @pt2,0, @bf,ULW_ALPHA);
end;
 
procedure TForm1.FormCreate(Sender: TObject);
begin
  if SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE) or WS_EX_LAYERED) = 0 then ShowMessage(SysErrorMessage(GetLastError));

  ShowPNGForm2('test.png',255);
  J:=1;
end;
 
procedure TForm1.FormDestroy(Sender: TObject);
begin
  SelectObject(DC, old_bmp);
  DeleteObject(bmp);
  DeleteDC(DC);
  bitmap.Free;
end;
 
procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
begin
  if(Button = mbLeft) then
    begin
      ReleaseCapture();
      Perform(WM_SYSCOMMAND, SC_MOVE or HTCAPTION, 0);
    end;
end;
 
procedure TForm1.Close1Click(Sender: TObject);
begin
  Close;
end;
 
procedure TForm1.ChangeSkin1Click(Sender: TObject);
var
  dlgOpen: TOpenDialog;
begin
  dlgOpen := TOpenDialog.Create(Self);
  dlgOpen.Filter := 'PNG file(*.png)|*.png';
  if(dlgOpen.Execute()) then
    begin
      ShowPNGForm2(dlgOpen.FileName,255);
    end;
  dlgOpen.Free;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  ShowMessage('aaa');
end;

end.

--------------------------------------------------

object Form1: TForm1
  Left = 387
  Top = 124
  BorderStyle = bsNone
  Caption = 'Form1'
  ClientHeight = 165
  ClientWidth = 260
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Name = 'MS Sans Serif'
  Font.Style = []
  OldCreateOrder = False
  PopupMenu = PopupMenu1
  OnCreate = FormCreate
  OnDestroy = FormDestroy
  OnMouseDown = FormMouseDown
  PixelsPerInch = 96
  TextHeight = 13
  object Button1: TButton
    Left = 104
    Top = 56
    Width = 75
    Height = 25
    Caption = 'Button1'
    TabOrder = 0
    OnClick = Button1Click
  end
  object PopupMenu1: TPopupMenu
    Left = 16
    Top = 16
    object ChangeSkin1: TMenuItem
      Caption = 'ChangeSkin'
      OnClick = ChangeSkin1Click
    end
    object N1: TMenuItem
      Caption = '-'
    end
    object Close1: TMenuItem
      Caption = 'Close'
      OnClick = Close1Click
    end
  end
end