Drawing polygon problem

Hello,

What do we have to do to create a bitmap and draw polygons on it. The
bitmap must
be 1 byte per pixel. We achieved to draw polygons on a form, using it's
handle but it
didn't work on a bitmap created using the following code:

var
 BitmapH:HBitmap;
 pnts: array[0..2] of TPoint;

begin
 BitmapH:=CreateBitmap(50,50,1,8,nil);

 Polygon(Form1.Canvas.Handle, pnts,3); {This code works fine}
 Polygon(BitmapH, pnts,3);             {This doesn't work -> returns 0!}    

end;