Transparent Forms in Delphi
How to make a transparent form under Windows 2000 or XP

   
       
         
   
Many commercial applications (mostly games) uses (semi) transparent forms to attract the users. Under Windows 2000 or XP you can make your Delphi forms transparent by calling SetLayeredWindowAttributes with the desired constant alpha value and/or the color-key.
Note that the third parameter of SetLayeredWindowAttributes is a value that ranges from 0 to 255, with 0 making the window completely transparent and 255 making it completely opaque.

For using this function you have to add following code to your Delphi application:

const
 WS_EX_LAYERED = $80000;
 LWA_COLORKEY = 1;
 LWA_ALPHA    = 2;

type
 TSetLayeredWindowAttributes = function (
     hwnd : HWND;         // handle to the layered window
     crKey : TColor;      // specifies the color key
     bAlpha : byte;       // value for the blend function
     dwFlags : DWORD      // action
     ): BOOL; stdcall;

procedure SetTransparentForm(AHandle : THandle; AValue : byte = 0);
var
 Info: TOSVersionInfo;
 SetLayeredWindowAttributes: TSetLayeredWindowAttributes;
begin
 //Check Windows version
 Info.dwOSVersionInfoSize := SizeOf(Info);
 GetVersionEx(Info);
 if (Info.dwPlatformId = VER_PLATFORM_WIN32_NT) and
 (Info.dwMajorVersion >= 5) then
   begin
     SetLayeredWindowAttributes := GetProcAddress(GetModulehandle(user32), 'SetLayeredWindowAttributes');
      if Assigned(SetLayeredWindowAttributes) then
       begin
        SetWindowLong(AHandle, GWL_EXSTYLE, GetWindowLong(AHandle, GWL_EXSTYLE) or WS_EX_LAYERED);
        //Make form transparent
        SetLayeredWindowAttributes(AHandle, 0, AValue, LWA_ALPHA);
      end;
   end;
end;

Now you can create OnCreate event handler and put next code:

procedure TForm1.FormCreate(Sender: TObject);
begin
 SetTransparentForm(Handle, 100);
end;

Run the application. Just remember, that SetLayeredWindowAttributes
function not available for Windows 98 or Windows NT 4.0
If you want to setup transparency in percents you can use following formula: (255 * Percents) / 100.

You don't need to write a lot of code to fade a window in or out.
The following example shows how to create fade out effect.
First you form become slowly transparent and after disappear from screen completely.

procedure TForm1.Button1Click(Sender: TObject);
var I : integer;
begin
 for i := 100 downto 0 do
  begin
   SetTransparentForm(Handle,i);
   Application.ProcessMessages;
  end;
Close;
end;

It is also possible to make a transparent standard Windows dialog like TFontDialog. To have a dialog box come up as a translucent window,
first create the dialog as usual. Then, create OnShow event handler and make your dialog transparent in the same way as a form.

procedure TForm1.FontDialogShow(Sender: TObject);
begin
 SetTransparentForm(FontDialog.Handle, 100);
end;

 

   
   

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