WinAPI: SetLayeredWindowAttributes 设置窗口的透明

这是来宾 Dolby 在 http://www.cnblogs.com/del/archive/2008/03/08/1081295.html#1096814 询问的问题.

---

//声明:
SetLayeredWindowAttributes(
  Hwnd: THandle;   {窗口句柄}
  crKey: COLORREF; {透明色}
  bAlpha: Byte;    {Alpha 值}
  dwFlags: DWORD   {LWA_COLORKEY(=1)表示使用透明色; LWA_ALPHA(=2)表示使用 Alpha 值}
): Boolean;        {是否成功设置}


//举例(控制外部程序的透明度, 用计算器举了个例子):
unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Button2: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

{设定计算器的 Alpha 透明}
procedure TForm1.Button1Click(Sender: TObject);
var
  h: HWND;
  FormStyle: Integer;
begin
  h := FindWindow('SciCalc', nil);
  FormStyle := GetWindowLong(h, GWL_EXSTYLE);
  SetWindowLong(h, GWL_EXSTYLE, FormStyle or WS_EX_LAYERED);
  SetLayeredWindowAttributes(h, 0, 128, LWA_ALPHA);
end;

{设定计算器中的白色透明}
procedure TForm1.Button2Click(Sender: TObject);
var
  h: HWND;
  FormStyle: Integer;
begin
  h := FindWindow('SciCalc', nil);
  FormStyle := GetWindowLong(h, GWL_EXSTYLE);
  SetWindowLong(h, GWL_EXSTYLE, FormStyle or WS_EX_LAYERED);
  SetLayeredWindowAttributes(h, clWhite, 255, LWA_COLORKEY);
end;

end.