学步园

    在QQ中，我可以调节面板的透明度。如果我们自己编程，应该如何实现呢？

    （一）半透明窗体

     在windows2000以及后续产品中下增加了一些API,可以轻易的实现半透明的窗体，源程序如下：

interface

uses

  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs;

const//定义常量

  WS_EX_LAYERED = $80000;

  AC_SRC_OVER = $0;

  AC_SRC_ALPHA = $1;

  AC_SRC_NO_PREMULT_ALPHA = $1;

  AC_SRC_NO_ALPHA = $2;

  AC_DST_NO_PREMULT_ALPHA = $10;

  AC_DST_NO_ALPHA = $20;

  LWA_COLORKEY = $1;

  LWA_ALPHA = $2;

  ULW_COLORKEY = $1

  ULW_ALPHA = $2

  ULW_OPAQUE = $4

type

  TForm1 = class(TForm)

  procedure FormCreate(Sender: TObject);

  private

  { Private declarations }

  public

  { Public declarations }

  end;

function SetLayeredWindowAttributes(hwnd:HWND; crKey:Longint; bAlpha:byte; dwFlags:longint ):longint; stdcall; external user32;//函数声明

var

Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.FormCreate(Sender: TObject);

var l:longint;

begin

  l:=getWindowLong(Handle, GWL_EXSTYLE);

  l := l Or WS_EX_LAYERED;

  SetWindowLong (handle, GWL_EXSTYLE, l);

  SetLayeredWindowAttributes (handle, 0, 180, LWA_ALPHA);

//第二个参数是指定透明颜色

//第二个参数为0则使用第四个参数设置alpha值，从0到255

end;

end.

     （二） 透明窗体的实现

      将一个FORM变成透明的实质性手段就是拦截CMEraseBkgnd消息。

unit Utransform; interface uses Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs, StdCtrls, ExtCtrls;

type TForm1 = class(TForm)

    private { Private declarations }

    public { Public declarations }

       PROCEDURE CMEraseBkgnd(var Message:TWMEraseBkgnd);Message WM_ERASEBKGND;

end;

var Form1: TForm1;

implementation

{$R *.DFM}

procedure TForm1.CMEraseBkgnd(var Message: TWMEraseBkgnd);
begin
brush.style:=bsClear;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Form1.Brush.Style := bsClear;//如果只拦截消息，没有这里的设置，窗内的标题栏一样会显示    Form1.BorderStyle := bsNone
end;

procedure TForm1.BitBtn1Click(Sender: TObject);
begin
  close;
end;