README.Porting
author Sam Lantinga <slouken@libsdl.org>
Thu, 02 Apr 2009 04:43:36 +0000
branchSDL-1.2
changeset 4167 a6f635e5eaa6
parent 1484 b2b476a4a73c
child 1946 103760c3a5dc
permissions -rw-r--r--
Fixed bug #611

From Tim Angus 2008-08-12 11:18:06

I'm one of the maintainers of ioquake3.org, an updated version of the
Quake 3 engine. Relatively recently, we moved ioq3 to use SDL as a
replacement for 95% of the platform specific code that was there. On the
whole it's doing a great job but unfortunately since the move we've been
getting complaints about the quality of the mouse input on the Windows
platform to the point where for many the game is unplayable. Put in
other terms, the current stable SDL 1.2 is basically not fit for purpose
if you need high quality mouse input as you do in a first person shooter.

Over the weekend I decided to pull my finger out and actually figure out
what's going on. There are basically two major problems. Firstly, when
using the "windib" driver, mouse input is gathered via the WM_MOUSEMOVE
message. Googling for this indicates that often this is known to result
in "spurious" and/or "missing" mouse movement events; this is the
primary cause of the poor mouse input. The second problem is that the
"directx" driver does not work at all in combination with OpenGL meaning
that you can't use DirectInput if your application also uses OpenGL. In
other words you're locked into using the "windib" driver and its poor
mouse input.

In order to address these problems I've done the following:

* Remove WM_MOUSEMOVE based motion event generation and replace with
calls to GetCursorPos which seems much more reliable. In order to
achieve this I've moved mouse motion out into a separate function that
is called once per DIB_PumpEvents.

* Remove the restriction on the "directx" driver being inoperable in
combination with OpenGL. There is a bug for this issues that I've
hijacked to a certain extent
(http://bugzilla.libsdl.org/show_bug.cgi?id=265). I'm the first to admit
I don't really understand why this restriction is there in the first
place. The commit message for the bug fix that introduced this
restriction (r581) isn't very elaborate and I couldn't see any other bug
tracking the issue. If anyone has more information on the bug that was
avoided by r581 it would be helpful as I/someone could then look into
addressing the problem without disabling the "directx" driver.

* I've also removed the restriction on not being allowed to use
DirectInput in windowed mode. I couldn't see any reason for this, at
least not from our perspective. I have my suspicions that it'll be
something like matching up the cursor with the mouse coordinates...

* I bumped up the DirectInput API used to version 7 in order to get
access to mouse buttons 4-7. I've had to inject a little bit of the DX7
headers into SDL there as the MinGW ones aren't up to date in this respect.
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* Porting To A New Platform
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  The first thing you have to do when porting to a new platform, is look at
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include/SDL_platform.h and create an entry there for your operating system.
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The standard format is __PLATFORM__, where PLATFORM is the name of the OS.
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Ideally SDL_platform.h will be able to auto-detect the system it's building
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on based on C preprocessor symbols.
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There are two basic ways of building SDL at the moment:
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1. The "UNIX" way:  ./configure; make; make install
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   If you have a GNUish system, then you might try this.  Edit configure.in,
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   take a look at the large section labelled:
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	"Set up the configuration based on the target platform!"
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   Add a section for your platform, and then re-run autogen.sh and build!
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2. Using an IDE:
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   If you're using an IDE or other non-configure build system, you'll probably
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   want to create a custom SDL_config.h for your platform.  Edit SDL_config.h,
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   add a section for your platform, and create a custom SDL_config_{platform}.h,
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   based on SDL_config.h.minimal and SDL_config.h.in
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   Add the top level include directory to the header search path, and then add
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   the following sources to the project:
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	src/*.c
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	src/audio/*.c
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	src/cdrom/*.c
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	src/cpuinfo/*.c
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	src/events/*.c
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	src/file/*.c
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	src/joystick/*.c
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	src/stdlib/*.c
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	src/thread/*.c
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	src/timer/*.c
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	src/video/*.c
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	src/audio/disk/*.c
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	src/video/dummy/*.c
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	src/joystick/dummy/*.c
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	src/cdrom/dummy/*.c
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	src/thread/generic/*.c
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	src/timer/dummy/*.c
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	src/loadso/dummy/*.c
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Once you have a working library without any drivers, you can go back to each
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of the major subsystems and start implementing drivers for your platform.
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If you have any questions, don't hesitate to ask on the SDL mailing list:
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	http://www.libsdl.org/mailing-list.php
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Enjoy!
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	Sam Lantinga				(slouken@libsdl.org)
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