Delphiran - Delphi Tips Question : How can I
create a transparent form ?
Answer : You do this by defining a window region. Regions are a Windows concept, a
type of GDI object that defines an area. A region can be build using a group of
API function (see CreateRectRgn in win32.hlp and click on the Group link), form
simple geometric shapes like rectangles, ellipses or polygons, or from other
regions. A region can have "holes". Note that there is no easy way to build a
region tracing the outlines of some graphics on a bitmap, it would boil down to
defining a suitable polygon by hand or by examining the pixels on the bitmap one
by one in code to find the boundaries of the graphics.
Once you have
build a suitable region you hand it to SetWindowRgn and your form assumes the
shape of the region. The following example builds a region from all controls on
a form and the forms caption. This makes the best approximation to a transparent
form Windows is capable of since mouse clicks on areas not included in the
window region will be delivered to the windows beneath even if they are
technically covered by the forms windowrect.
procedure TForm1.Button2Click(Sender: TObject);
Var frmRegion, tempRegion: HRGN; i: Integer;
Arect: TRect; Begin frmRegion := 0;
For I:= 0 To ControlCount - 1 DoBegin // create a region for the control aRect := Controls[i].BoundsRect;
// coordinates have to be
window-relative, not client area relative OffsetRect( aRect, clientorigin.x - left, clientorigin.y - top );
tempRegion := CreateRectRgnIndirect( aRect
);
// merge the region with
the "summary" region we are building If frmRegion
= 0 Then frmRegion := tempRegion
ElseBegin CombineRgn( frmRegion, frmRegion, tempRegion, RGN_OR );
DeleteObject( tempRegion ); End;
End; // create a region
for the caption and menu bar and add it to the // summary tempregion := CreateRectRgn( 0, 0, Width,
GetSystemMetrics( SM_CYCAPTION )+
GetSystemMetrics( SM_CYSIZEFRAME )+
GetSystemMetrics( SM_CYMENU ) * Ord(Menu ‹› Nil));
