This article comes thanks to Gerard Oei who provided the Delphi source code.
We have already done a tutorial on how to create non-rectangular windows. This tutorial shows how to create a form that is shaped around a bitmap. Like the previous tutorial it uses the SetWindowRGN function. The clever part here is how the region is created.
I will not explain in detail how the code works because I think it will be easier to read the code and let the comments explain what is happening.
As an overview on the form you should place a TImage and set its picture property to be the image that you would like the form to be shaped around. At design time it should look like the following image:
The main part of the code can be found in the function CreateRegion which uses the API functions CreateRectRGN and CombineRGN to great affect. CreateRegion is then called from the form's constructor to shape the form accordingly.
What follows is the Delphi code for shaping the window. You can also download the code at the bottom of this tutorial.
function TForm1.CreateRegion(Bmp: TBitmap): THandle; var X, Y, StartX:Integer; Excl: THandle; Row: PRGBArray; TransparentColor: TRGBTriple; begin // Change the format so we know how to compare // the colors Bmp.PixelFormat := pf24Bit; // Create a region of the whole bitmap // later we will take the transparent // bits away Result := CreateRectRGN(0, 0, Bmp.Width, Bmp.Height); // Loop down the bitmap for Y := 0 to Bmp.Height - 1 do begin // Get the current row of pixels Row := Bmp.Scanline[Y]; // If its the first get the transparent // color, it must be the top left pixel if Y = 0 then begin TransparentColor := Row; end; // Reset StartX (-1) to indicate we have // not found a transparent area yet StartX := -1; // Loop across the row for X := 0 to Bmp.Width do begin // Check for transparency by comparing the color if(X <> Bmp.Width) and (Row[X].rgbtRed = TransparentColor.rgbtRed) and (Row[X].rgbtGreen = TransparentColor.rgbtGreen) and (Row[X].rgbtBlue = TransparentColor.rgbtBlue) then begin // We have (X <> Bmp.Width) in the clause so that // when we go past the end of the row we we can // exclude the remaining transparent area (if any) // If its transparent and the previous wasn't // remember were the transparency started if StartX = -1 then begin StartX := X; end; end else begin // Its not transparent if StartX > -1 then begin // If previous pixels were transparent we // can now exclude the from the region Excl := CreateRectRGN(StartX, Y, X, Y + 1); try // Remove the exclusion from our original region CombineRGN(Result, Result, Excl, RGN_DIFF); // Reset StartX so we can start searching // for the next transparent area StartX := -1; finally DeleteObject(Excl); end; end; end; end; end; end; procedure TForm1.FormCreate(Sender: TObject); var Bmp: TBitmap; begin Bmp := TBitmap.Create; try // We use a TImage to hold the bitmap so that // we can see how the form will look at design // time Bmp.Assign(Image1.Picture); FRegion := CreateRegion(Bmp); SetWindowRGN(Handle, FRegion, True); finally Bmp.Free; end; end;
When the application is run the form should now take the shape of the bitmap, as shown in the following screen shot
Once again I would like to say a big thank you to Gerard Oei for providing the code to this article. You can download the source code here.