Mercurial > sdl-ios-xcode
view README.RISCOS @ 4139:568c9b3c0167 SDL-1.2
* Added configure option --enable-screensaver, to allow enabling the screensaver by default.
* Use XResetScreenSaver() instead of disabling screensaver entirely.
Full discussion summary from Erik on the SDL mailing list:
Current behaviour
=================
SDL changes the user's display power management settings without
permission from the user and without telling the user.
The interface that it uses to do so is DPMSDisable/DPMSEnable, which
should only ever be used by configuration utilities like KControl, never
by normal application programs, let alone by the libraries that they
use. Using an interface that is not at all intended for what SDL tries
to achieve means that it will not work as it should. Firstly, the power
management is completely disabled during the whole lifetime of the SDL
program, not only when it should be. Secondly, it makes SDL
non-reentrant, meaning that things will break when multiple SDL programs
are clients of the same X server simultaneously. Thirdly, no cleanup
mechanism ensures that the setting is restored if the client does not do
that (for example if it crashes).
In addition to that, this interface is broken on xorg,
[http://bugs.freedesktop.org/show_bug.cgi?id=13962], so what SDL tries
to do does not work at all on that implementation of the X Window
System. (The reason that the DPMSEnable works in KControl is that it
calls DPMSSetTimeout immediately after,
[http://websvn.kde.org/tags/KDE/3.5.9/kdebase/kcontrol/energy/energy.cpp?annotate=774532#l343]).
The problems that the current behaviour causes
==============================================
1. Information leak. When the user is away, someone might see what the
user has on the display when the user counts on the screensaver
preventing this. This does not even require physical access to the
workstation, it is enough to see it from a distance.
2. Draining battery. An SDL program that runs on a laptop will quickly
drain the battery while the user is away. The system will soon shut down
and require recharging before being usable again, while it should in
fact have consumed very little energy if the user's settings would have
been obeyed.
3. Wasting energy. Even if battery issues are not considered, energy as
such is wasted.
4. Display wear. The display may be worn out.
The problems that the current behaviour tries to solve
======================================================
1. Preventing screensaver while playing movies.
Many SDL applications are media players. They have reasons to prevent
screensavers from being activated while a movie is being played. When a
user clicks on the play button it can be interpreted as saying "play
this movie, but do not turn off the display while playing it, because I
will watch it even though I do not interact with the system".
2. Preventing screensaver when some input bypasses X.
Sometimes SDL uses input from another source than the X server, so
that the X server is bypassed. This obviously breaks the screensaver
handling. SDL tries to work around that.
3. Preventing screensaver when all input bypasses X.
There is something called Direct Graphics Access mode, where a
program takes control of both the display and the input devices from the
X server. This obviously means that the X server can not handle the
screensaver alone, since screensaver handling depends on input handling.
SDL does not do what it should to help the X server to handle the
screensaver. Nor does SDL take care of screeensaver handling itself. SDL
simply disables the screensaver completely.
How the problems should be solved
=================================
The correct way for an application program to prevent the screensaver
under X is to call XResetScreenSaver. This was recently discovered and
implemented by the mplayer developers,
[http://svn.mplayerhq.hu/mplayer?view=rev&revision=25637]. SDL needs to
wrap this in an API call (SDL_ResetScreenSaver) and implement it for the
other video targets (if they do not have a corresponding call, SDL
should do what it takes on that particular target, for example sending
fake key events).
1. When a movie is played, the player should reset the screensaver when
the animation is advanced to a new frame. The same applies to anything
similar, like slideshows.
2. When the X server is handling input, it must handle all input
(keyboards, mice, gamepads, ...). This is necessary, not only to be able
to handle the screensaver, but also so that it can send the events to
the correct (the currently active) client. If there is an input device
that the X server can not handle for some reason (such as lack of Plug
and Play capability), the program that handles the device as a
workaround must simulate what would happen if the X server would have
handled the device, by calling XResetScreenSaver when input is received
from the device.
3. When the X server is not handling the input, it depends on the
program that does to call XResetScreenSaver whenever an input event
occurs. Alternatively the program must handle the screensaver countdown
internally and call XActivateScreenSaver.
| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Fri, 29 Feb 2008 13:55:44 +0000 |
| parents | de3d552b59b2 |
| children | 7c73d5b5a0d6 |
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Readme for RISC OS port of SDL ============================== This document last updated on 2nd Februrary 2006 This is a RISC OS port of the Simple Direct Media Layer (SDL) by Alan Buckley with contributions from Peter Naulls. Details of the SDL can be found at http://www.libsdl.org. The source code including the RISC OS version can be obtained from: http://www.libsdl.org. Pre built libraries and many games and applications compiled for RISC OS using this library can be downloaded from The Unix Porting Project at http://www.riscos.info/unix/. This is released under the LGPL see the file COPYING for details. Compiling applications under RISC OS ==================================== Add -ISDL: for the C compiler flags if you include the files in the SDL directory. e.g. #include "SDL/SDL.h" Add -ISDL:SDL for the C compiler flags if you include the files directly. e.g. #include "SDL/SDL.h" Add -LSDL: -lSDL to the link stage of compilation. For example, to compile the testbitmap.c sample you could use: gcc -ISDL:SDL -LSDL: -lSDL testbitmap.c -otestbitmap RISC OS port of SDL runtime information ======================================= Runtime requirements -------------------- This library currently needs a minimum of RISC OS 3.6. The source code for the library (and a lot of the programs built with it) also need long file names. To use the audio you also need 16 bit sound and to have installed the DigitalRender module by Andreas Dehmel version 0.51 available from his web site: http://home.t-online.de/~zarquon This is loaded when needed by UnixLib. Note: As most programs ported from other OSes use high resolution graphics and a memory back buffer a machine with a StrongARM processor and 1 or 2MB of VRAM (or a better machine) is recomended. RISC OS runtime parameters -------------------------- Several environmental variables have been defined to make porting programs easier (i.e. By setting these variable you do not need to have source code differences between OSes). They are all defined on an application basis. The <appname> used below is found as follows: 1. Use the name of the program unless it is !RunImage 2. Check the folder specification for the folder !RunImage is run from. If it is a folder name use that name, otherwise if it is an environmental variable of the form <XXX$Dir> use the value of XXX. The variables are: SDL$<appname>$TaskName The name of the task for RISC OS. If omitted then <appname> is used for the task name, SDL$<appname>$BackBuffer Set to 1 to use a system memory back buffer for the screen in full screen mode. Some programs on other systems assume their is always a back buffer even though the SDL specification specifies this is not the case. The current RISC OS implementation uses direct writes to the screen if a hardware fullscreen is requested. Set to 2 to use an ARM code full word copy. This is faster than the standard back buffer, but uses aligned words only so it is possible (but unlikely) for it to corrupt the screen for 8bpp and 16bpp modes. Set to 3 to use a RISC OS sprite as the back buffer. This is usually the slowest for most SDL applications, however it may be useful in the future as Sprite acceleration is added to various hardware that runs RISC OS. SDL$<appname>$CloseAction - set the action for the close icon. Again as programs don't match the specification you can set this to 0 to remove the close icon from the main window for applications where this does not affect the program. RISC OS SDL port API notes ========================== Current level of implementation ------------------------------- The following list is an overview of how much of the SDL is implemented. The areas match the main areas of the SDL. video - Mostly done. Doesn't cover gamma, YUV-overlay or OpenGL. Window Manager - Mostly done. SetIcon/IconifyWindow not implemented. Events - Mostly done. Resize and some joystick events missing. Joystick - Currently assumes a single joystick with 4 buttons. Audio - Done CDROM - Not implemented. Threads - Done Timers - Done Thread support can be removed by defining DISABLE_THREADS and recompiling the library. SDL API notes ------------- This section contains additional notes on some specific commands. SDL_SetVideoMode On RISC OS a fullscreen mode directly accesses the screen. This can be modified by the environmental variable (SDL$<appname>$BackBuffer) or by using the SDL_SWSURFACE flag to write to an offscreen buffer that is updated using SDL_UpdateRects. Open GL is not supported so SDL_OPENGL and SDL_OPENGLBLIT flags fail. SDL_RESIZEABLE and SDL_NOFRAME flags are not supported. SDL_SetColors In a wimp mode the screen colours are not changed for a hardware palette instead the RISC OS sprite colour mapping is used to get the best matching colours. SDL_CreateCursor Inverted colour is not supported. SDL_WM_ToggleFullScreen Currently this won't work if the application starts up in Fullscreen mode. Toggling to fullscreen will only work if the monitor is set up to support the exact screen size requested. SDL_EnableUNICODE Unicode translation used here is only really accurate for 7 bit characters. SDL_NumJoysticks/JoystickName etc. Hardcoded to expect only 1 joystick with 4 buttons if the Joystick module is loaded. SDL_GetTicks Timer used has only a centisecond accuracy. This applies to other time related functions. SDL_Delay Modified to poll keyboard/mouse during the delay on the event thread. Notes on current implementation ------------------------------- Keyboard and mouse are polled so if too long a time is spent between a call to SDL_PumpEvents, functions that use it, or SDL_Delay events can be missed.