unit Unit1;

interface

uses
Windows, Classes, SysUtils, Graphics, Forms;

type
TRGBArray = array[0..32767] of TRGBTriple;
PRGBArray = ^TRGBArray;

type
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
{ Private declarations }
FRegion: THandle;
function CreateRegion(Bmp: TBitmap): THandle;
end;

var
Form1: TForm1;

implementation

{$R *.dfm}

function TForm1.CreateRegion(Bmp: TBitmap): THandle;
var
X, Y, StartX: Integer;
Excl: THandle;
Row: PRGBArray;
TransparentColor: TRGBTriple;
begin
Bmp.PixelFormat := pf24Bit;

Result := CreateRectRGN(0, 0, Bmp.Width, Bmp.Height);

for Y := 0 to Bmp.Height - 1 do
begin
Row := Bmp.Scanline[Y];

StartX := -1;

if Y = 0 then
TransparentColor := Row[0];

for X := 0 to Bmp.Width - 1 do
begin
if (Row[X].rgbtRed = TransparentColor.rgbtRed) and
(Row[X].rgbtGreen = TransparentColor.rgbtGreen) and
(Row[X].rgbtBlue = TransparentColor.rgbtBlue) then
begin
if StartX = -1 then StartX := X;
end
else
begin
if StartX > -1 then
begin
Excl := CreateRectRGN(StartX, Y, X + 1, Y + 1);
try
CombineRGN(Result, Result, Excl, RGN_DIFF);
StartX := -1;
finally
DeleteObject(Excl);
end;
end;
end;
end;

if StartX > -1 then
begin
Excl := CreateRectRGN(StartX, Y, Bmp.Width, Y + 1);
try
CombineRGN(Result, Result, Excl, RGN_DIFF);
finally
DeleteObject(Excl);
end;
end;
end;
end;

procedure TForm1.FormCreate(Sender: TObject);
var
Bmp: TBitmap;
begin
Bmp := TBitmap.Create;
try
Bmp.LoadFromFile(’C:\YourBitmap.bmp’);
FRegion := CreateRegion(Bmp);
SetWindowRGN(Handle, FRegion, True);
finally
Bmp.Free;
end;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
DeleteObject(FRegion);
end;

end.