VisualC.html
author Sam Lantinga <slouken@libsdl.org>
Fri, 29 Feb 2008 13:55:44 +0000
branchSDL-1.2
changeset 4139 568c9b3c0167
parent 4052 b004c6c24a98
child 2207 d63e9f5944ae
child 5893 f3adae5e12cd
permissions -rw-r--r--
* 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.
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<HTML>
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	<HEAD>
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		<TITLE>Using SDL with Microsoft Visual C++</TITLE>
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	</HEAD>
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	<BODY>
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		<H1>
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			Using SDL with Microsoft Visual C++ 5,6&nbsp;and 7
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		</H1>
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		<H3>
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			by <A HREF="mailto:snowlion@sprynet.com">Lion Kimbro </A>and additions by <A HREF="mailto:james@conceptofzero.net">
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				James Turk</A>
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		</H3>
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		<p>
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			You can either use the precompiled libraries from <A HREF="http://www.libsdl.org/download.php">
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				the SDL Download web site </A>, or you can build SDL yourself.
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		</p>
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		<H3>
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			Building SDL
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		</H3>
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		<P>
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			Unzip the <CODE>VisualC.zip</CODE> file into the directory that contains this 
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			file (<CODE>VisualC.html</CODE>).
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		</P>
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		<P>
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			Be certain that you unzip the zip file for your compiler into <strong>this</strong>
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			directory and not any other directory. If you are using WinZip, be careful to 
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			make sure that it extracts to <strong>this</strong> folder, because it's 
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			convenient feature of unzipping to a folder with the name of the file currently 
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			being unzipped will get you in trouble if you use it right now. And that's all 
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			I have to say about that.
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		</P>
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		<P>
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			Now that it's unzipped, go into the VisualC 
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			directory that is created, and double-click on the VC++ file "<CODE>SDL.dsw</CODE>"<STRONG><FONT color="#009900">
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					("<CODE>SDL.sln</CODE>").</FONT></STRONG> This should open up the IDE.
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		</P>
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		<P>
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			You may be prompted at this point to upgrade the workspace, should you be using 
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			a more recent version of Visual C++. If so, allow the workspace to be upgraded.
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		</P>
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		<P>
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			Build the <CODE>.dll</CODE> and <CODE>.lib</CODE> files.
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		</P>
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		<P>
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			This is done by right clicking on each project in turn (Projects are listed in 
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			the Workspace panel in the FileView tab), and selecting "Build".
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		</P>
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		<P>
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			If you get an error about SDL_config.h being missing, you should
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			copy include/SDL_config.h.default to include/SDL_config.h and try again.
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		</P>
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		<P>
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			You may get a few warnings, but you should not get any errors. You do have to 
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			have at least the DirectX 5 SDK installed, however. The latest 
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			version of DirectX can be downloaded or purchased on a cheap CD (my 
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			recommendation) from <A HREF="http://www.microsoft.com">Microsoft </A>.
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		</P>
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		<P>
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			Later, we will refer to the following .lib and .dll files that have just been 
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			generated:
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		</P>
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		<ul>
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    <li> SDL.dll</li>
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    <li> SDL.lib</li>
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    <li> SDLmain.lib</li>
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    </ul>
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		<P>
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			Search for these using the Windows Find (Windows-F) utility, if you don't 
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			already know where they should be. For those of you with a clue, look inside 
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			the Debug or Release directories of the subdirectories of the Project folder. 
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			(It might be easier to just use Windows Find if this sounds confusing. And 
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			don't worry about needing a clue; we all need visits from the clue fairy 
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			frequently.)
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		</P>
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		<H3>
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			Creating a Project with SDL
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		</H3>
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		<P>
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			Create a project as a Win32 Application.
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		</P>
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		<P>
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			Create a C++ file for your project.
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		</P>
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		<P>
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			Set the C runtime to "Multi-threaded DLL" in the menu: <CODE>Project|Settings|C/C++ 
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				tab|Code Generation|Runtime Library </CODE>.
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		</P>
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		<P>
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			Add the SDL <CODE>include</CODE> directory to your list of includes in the 
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			menu: <CODE>Project|Settings|C/C++ tab|Preprocessor|Additional include directories </CODE>
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			.
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			<br>
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			<STRONG><FONT color="#009900">VC7 Specific: Instead of doing this I find it easier to 
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					add the include and library directories to the list that VC7 keeps. Do this by 
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					selecting Tools|Options|Projects|VC++ Directories and under the "Show 
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					Directories For:" dropbox select "Include Files", and click the "New Directory 
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					Icon" and add the [SDLROOT]\include directory (ex. If you installed to 
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					c:\SDL-1.2.5\ add c:\SDL-1.2.5\include).&nbsp;Proceed to&nbsp;change the 
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					dropbox selection to "Library Files" and add [SDLROOT]\lib.</FONT></STRONG>
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		</P>
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			<P>
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				The "include directory" I am referring to is the <CODE>include</CODE> folder 
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				within the main SDL directory (the one that this HTML file located within).
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			</P>
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			<P>
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				Now we're going to use the files that we had created earlier in the Build SDL 
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				step.
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			</P>
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			<P>
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				Copy the following files into your Project directory:
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			</P>
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			<ul>
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     <li> SDL.dll</li>
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     </ul>
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			<P>
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				Add the following files to your project (It is not necessary to copy them to 
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				your project directory):
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			</P>
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			<ul>
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     <li> SDL.lib </li>
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     <li> SDLmain.lib</li>
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     </ul>
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			<P>
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				(To add them to your project, right click on your project, and select "Add 
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				files to project")
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			</P>
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		<P><STRONG><FONT color="#009900">Instead of adding the files to your project it is more 
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					desireable to add them to the linker options: Project|Properties|Linker|Command 
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					Line and type the names of the libraries to link with in the "Additional 
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					Options:" box.&nbsp; Note: This must be done&nbsp;for&nbsp;each&nbsp;build 
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					configuration (eg. Release,Debug).</FONT></STRONG></P>
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		<H3>
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			SDL 101, First Day of Class
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		</H3>
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		<P>
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			Now create the basic body of your project. The body of your program should take 
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			the following form: <CODE>
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				<PRE>
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#include "SDL.h"
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int main( int argc, char* argv[] )
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{
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  // Body of the program goes here.
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  return 0;
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}
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</PRE>
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			</CODE>
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		<P></P>
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		<H3>
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			That's it!
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		</H3>
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		<P>
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			I hope that this document has helped you get through the most difficult part of 
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			using the SDL: installing it. Suggestions for improvements to this document 
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			should be sent to the writers of this document.
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		</P>
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		<P>
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			Thanks to Paulus Esterhazy (pesterhazy@gmx.net), for the work on VC++ port.
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		</P>
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		<P>
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			This document was originally called "VisualC.txt", and was written by <A HREF="mailto:slouken@libsdl.org">
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				Sam Lantinga</A>.
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		</P>
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		<P>
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			Later, it was converted to HTML and expanded into the document that you see 
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			today by <A HREF="mailto:snowlion@sprynet.com">Lion Kimbro</A>.
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		</P>
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		<P>Minor Fixes and Visual C++ 7 Information (In Green) was added by <A HREF="mailto:james@conceptofzero.net">James Turk</A>
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		</P>
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	</BODY>
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</HTML>