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January 2000: Windows Screen Savers
This tutor focuses on creating Windows Screen Savers. This is to demonstrate that the power of Borland Delphi is not only limited to Database Applications. Check the download section for more Window Screen Saver that was created by Borland Delphi.
Writing a Windows Screen Saver in Borland Delphi.
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Writing a Windows Screen Saver in Borland Delphi can be both Fun and Challenging. It is a simple exercise, but uses a variety of Programming Techniques and Skills. In this Tutor, the basics of writing a Windows Screen Saver will be explained to you, and for those of you that do not like typing, the source code can be downloaded here. Let us look at a list of things we need to understand to create the Windows Screen Saver.
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A Windows Screen Saver is nothing more than just a simple executable application with a "SCR" extension. We can proof that by renaming any Screen Saver Application (SCR) file to have a "EXE" extension. Now, try to execute it by double clicking on the file. So, Delphi can easily create a Windows Screen Saver, just by creating an application with an "EXE" extension and renaming it to a "SCR" extension.
Let us have a look at what Windows expect from a Windows Screen Saver.
There are two basic requirements for any application to be a Windows Screen Saver. One thing that is very important to note, is the way in which Windows activate a screen saver. When you select a screen saver that must activate, you also specify a timeout, indicating how long the screen must display its contents before starting the Windows Screen Saver application. Windows wait the specified time, and if there was no system activity (no keyboard or mouse input), is starts the Windows Screen Saver application. Important to note that it does it every time the timer times out, even if the Windows Screen Saver is already running.
The other important thing to keep in mind, is the way Windows activates the Windows Screen Saver Application. To activate the Windows Screen Saver, a /s is passed to the application, while on the other hand, a /c is passed to the application, to configure it.
What are Window Messages?
The Windows Operating System uses a very simple, but effective way of sending information from one application to another. It uses Windows Messages. It is possible for an application to generate and trap these messages.
OK. Are you ready? Let?s start then. First we create a new application. Set the following properties of the form to the following values:
- Property BorderStyle - Value bsNone
- Property FormStyle - Value fsStayOnTop
- Property WindowState - Value wsMaximized
Event OnShow:
procedure TfrmScreen.FormShow(Sender: TObject);
begin
GetCursorPos(crs);
Application.OnMessage := DeactivateScrnSaver;
ShowCursor(false);
end;
OnHide:
procedure TfrmScreen.FormHide(Sender: TObject);
begin
Application.OnMessage := nil;
ShowCursor(true);
end;
TfrmScreen = class(TForm)
procedure FormActivate(Sender: TObject);
procedure FormHide(Sender: TObject);
public
procedure DeactivateScrnSaver(var Msg : TMsg;
var Handled : boolean);
end;
procedure TfrmScreen.DeactivateScrnSaver(var Msg: TMsg;
varHandled: boolean);
var
done : boolean;
begin
if Msg.message = WM_MOUSEMOVE then
done := (Abs(LOWORD(Msg.lParam)-crs.x)>5)or
(Abs(HIWORD(Msg.lParam)-crs.y)>5)
else
done := (Msg.message = WM_KEYDOWN) or
(Msg.message = WM_ACTIVATE) or
(Msg.message = WM_ACTIVATEAPP) or
(Msg.message = WM_NCACTIVATE);
if done then
frmScreen.Close;
end;
And that?s all there is to creating a simple Windows Screen Saver. Now you can add a second form to your application that handles the configuration of the Windows Screen Saver. Talking about Windows Screen Saver Configuration. We still need to modify our Windows Screen Saver application to recognize different Windows Commands from Command Line Parameters. Let?s have a look at our Project Source. It can be found from Project | View Source.
Var
sParam : String;
iPos : integer;
begin
{/s = Avrivate Screen Saver}
{/c:xxxxxx = Cofiguration}
sParam := UpperCase(ParamStr(1));
{This is to strip only the /c from the command line string}
iPos := Pos(':',sParam);
If iPos > 0 then
sParam := Copy(sParam,1,iPos-1);
if (ParamCount > 0) and (sParam = '/S') then
begin
Application.CreateForm(TfrmScreen, frmScreen);
Application.Run;
end
else
If (ParamCount > 0) and (sParam = '/C') then
begin
Application.CreateForm(TfrmConfig, frmConfig);
Application.Run;
end;
The only thing that is needed in your application is the check for multiple instances of the Windows Screen Saver. This can be done with the hPrevInst variable. Simply encapsulate the program source above in this if statement:
if hPrevInst = 0 then
begin
.
.
.
end;
