Displaying-a-bitmap-on-the-client-area-of-an-mdi-parent-form


            Question:
How do I display a bitmap to the client area of an MDI parent
form?
Answer:
Here are the necessary steps to add wallpaper to a MDI parent
form:
Create a new project
Set the form's FormStyle to fsMDIForm
Drop an image on the form and select a bitmap into it.
Find the { Private Declarations } comment in the form's
 definition and add these lines right after it:
 FClientInstance : TFarProc;
 FPrevClientProc : TFarProc;
 procedure ClientWndProc(var Message: TMessage);
Find the "implementation" line and the {$R *.DFM} line that
 follows it. After that line, enter this code:
procedure TMainForm.ClientWndProc(var Message: TMessage);
var
 Dc : hDC;
 Row : Integer;
 Col : Integer;
begin
 with Message do
 case Msg of
 WM_ERASEBKGND:
 begin
 Dc := TWMEraseBkGnd(Message).Dc;
 for Row := 0 to ClientHeight div Image1.Picture.Height do
 for Col := 0 to ClientWidth div Image1.Picture.Width do
 BitBlt(Dc,
 Col * Image1.Picture.Width,
 Row * Image1.Picture.Height,
 Image1.Picture.Width,
 Image1.Picture.Height,
 Image1.Picture.Bitmap.Canvas.Handle,
 0,
 0,
 SRCCOPY);
 Result := 1;
 end;
 else
 Result := CallWindowProc(FPrevClientProc,
 ClientHandle,
 Msg,
 wParam,
 lParam);
 end;
end;
In the OnCreate method for the form, type the following lines
of code:
 FClientInstance := MakeObjectInstance(ClientWndProc);
 FPrevClientProc := Pointer(GetWindowLong(ClientHandle,
 GWL_WNDPROC));
 SetWindowLong(ClientHandle,
 GWL_WNDPROC, LongInt(FClientInstance));
Add a new form to your project and set its FormStyle property to
fsMDIChild.
Now you have a working MDI project with "wallpaper" where the image
bitmap is tiled to cover the MDI form's client area.
API Delphi
