Mega Code Archive
Shaping a Form around a Bitmap
<![CDATA[
Title: Shaping a Form around a Bitmap
Question: How to Shap a form around a bitmap
Answer:
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.
Shaping the Form
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.
The Sample Code
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[0];
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;
Conclusion
When the application is run the form should now take the shape of the bitmap, as shown in the following screen shot
]]>