Editing Screensaver (section)

== Underlying architecture ==
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Screensavers are usually designed and coded using a variety of programming languages as well as graphics interfaces. Typically the authors of screensavers use the [[C (programming language)|C]] or [[C++]] programming languages, along with [[Graphics Device Interface]] (GDI), such as [[OpenGL]] ("Open Graphics Library", which works on many, if not most, platforms capable of [[3D rendering]]), or alternatives such as [[Microsoft DirectX]] (which is limited to [[Microsoft]] platforms, mainly [[Microsoft Windows]] and the [[Microsoft Xbox]]), to craft their final products. Several [[OS X]] screensavers are created and designed using [[Quartz Composer]]. The screensaver interfaces indirectly with the operating system to cause the physical display screen to be overlaid with one or more graphic "scenes". The screensaver typically terminates after receiving a message from the operating system that a key has been pressed or the mouse has been moved.

=== Microsoft Windows ===
[[File:StarfieldSimulation.gif|alt=Animation of stars becoming bigger and moving away from the center of the image, simulating moving towards the stars.|thumb|A recreation of Starfield Simulation, one of the screensavers added in [[Windows 95]].]]
If the system detects inactivity lasting longer than the time specified in the [[Control Panel (Windows)|control panel]], check if the active program is a simple program (and not another screensaver) by sending the "<code>WM_SYSCOMMAND</code>" message with the "<code>SC_SCREENSAVE</code>" argument. If the program calls in response the standard system function (<code>DefWindowProc</code>), the screensaver defined in the control panel screen runs.

A Windows screensaver is a regular [[Portable Executable]] (PE) with the <code>.scr</code> file extension. This enables [[malware]] authors to add ".scr" to the name of any [[win32]] [[executable]] file, and thereby increase likelihood that users of [[Microsoft Windows]] will run it unintentionally. In addition, this program should support the following [[Command-line interface|command line]] parameters:<ref>{{Cite web |title=INFO: Screen Saver Command Line Arguments |url=http://support.microsoft.com/kb/182383 |url-status=live |archive-url=https://web.archive.org/web/20140202212351/http://support.microsoft.com/kb/182383 |archive-date=2014-02-02 |access-date=2014-02-01 |publisher=[[Microsoft]]}}</ref>

With no parameter – shows the Settings dialog box or do nothing.
 ScreenSaver.scr <code>/s</code>
Runs the screensaver.
 ScreenSaver.scr <code>/p</code> or <code>/l</code> <HWND>
Previews the screensaver as child of window. <code><HWND></code> (presented as unsigned [[decimal number]]) is an identifier ([[Handle (computing)|handle]]) of the window in which the preview should appear.
 ScreenSaver.scr <code>/c</code>
Shows the Settings dialog box, modal to the foreground window.
 ScreenSaver.scr <code>/a </code><HWND>

Changes password, modal to window <code><HWND></code>. Windows 95 screensavers must handle it.

=== macOS ===
Under macOS, screensavers are regular macOS application bundles with the <code>.saver</code> file extension.<ref>{{Cite web |title=ScreenSaverView - ScreenSaver {{!}} Apple Developer Documentation |url=https://developer.apple.com/documentation/screensaver/screensaverview |url-status=live |archive-url=https://web.archive.org/web/20180925180703/https://developer.apple.com/documentation/screensaver/screensaverview |archive-date=2018-09-25 |access-date=2018-09-25 |website=Developer.Apple.com |publisher=[[Apple Inc.]] |language=en}}</ref>

Internally, the screensaver must define a class that is subclass of <code>ScreenSaverView</code>. The new class must be assigned as <code>NSPrincipalClass</code> in the xcode project, so that when the screensaver is launched by the system, this class gets instantiated.

=== Atari ===
As one of the first screensavers appeared in [[8-bit]] Atari computers, forcing systemic color changes when the computer is idle lasting a few minutes (different times depending on the model), stored in the system [[Read-only memory|ROM]] of the computer.