author Sam Lantinga <>
Thu, 17 Apr 2014 22:36:14 -0700
changeset 8716 0aade9c0203f
parent 1187 19d8949b4584
permissions -rw-r--r--
Fixed bug 2325 - SDL_EnableUNICODE sometimes drops keyboard events completely

Rafał Mużyło

The most annoying part of this bug is that though I've found it in two separate apps, I don't have a trivial testcase for it.

The problem seems to be a condition race, as it's triggered quite randomly (therefore it will be hard to tell whether it really gets fixed, if a probable fix is found).

While it's specific to SDL 1.2, it seems quite similar to the problem described and fixed in

Now, I should start describing the problem.

A game uses Escape to open menu (the exact key might not be important). Upon opening, it calls SDL_EnableUNICODE(1). Upon closing it calls SDL_EnableUNICODE(0).

I have an IME running.

Game uses SDL_PollEvent to get the events.

If Escape is pressed repeatedly, menu is opened and closed, till it eventually freezes in open state.
"freezes" in this context means "app itself still runs, but no keyboard events are getting delivered (though - for example - mouse events still are)". "getting delivered" should mean "SDL_PollEvent is not receiving any".
If it matters, the last delivered keyboard event is a keypress, the release never arrives.

It seems (no guarantees, due to random nature of the freeze) that unsetting XMODIFIERS (which - AFAIU - will disable IME as far as SDL is concerned) prevents the freeze, therefore the reference to that SDL2 thread.
     1 ==============================================================================
     2 Using the Simple DirectMedia Layer with OpenBSD/wscons
     3 ==============================================================================
     5 The wscons SDL driver can be used to run SDL programs on OpenBSD
     6 without running X.  So far, the driver only runs on the Sharp Zaurus,
     7 but the driver is written to be easily extended for other machines.
     8 The main missing pieces are blitting routines for anything but 16 bit
     9 displays, and keycode maps for other keyboards.  Also, there is no
    10 support for hardware palettes.
    12 There is currently no mouse support.
    14 To compile SDL with support for wscons, use the
    15 "--enable-video-wscons" option when running configure.  I used the
    16 following command line:
    18 ./configure --disable-oss --disable-ltdl --enable-pthread-sem \
    19 	    --disable-esd --disable-arts --disable-video-aalib  \
    20 	    --enable-openbsdaudio --enable-video-wscons \
    21 	    --prefix=/usr/local --sysconfdir=/etc
    24 Setting the console device to use
    25 =================================
    27 When starting an SDL program on a wscons console, the driver uses the
    28 current virtual terminal (usually /dev/ttyC0).  To force the driver to
    29 use a specific terminal device, set the environment variable
    32 bash$ SDL_WSCONSDEV=/dev/ttyC1 ./some-sdl-program
    34 This is especially useful when starting an SDL program from a remote
    35 login prompt (which is great for development).  If you do this, and
    36 want to use keyboard input, you should avoid having some other program
    37 reading from the used virtual console (i.e., do not have a getty
    38 running).
    41 Rotating the display
    42 ====================
    44 The display can be rotated by the wscons SDL driver.  This is useful
    45 for the Sharp Zaurus, since the display hardware is wired so that it
    46 is correctly rotated only when the display is folded into "PDA mode."
    47 When using the Zaurus in "normal," or "keyboard" mode, the hardware
    48 screen is rotated 90 degrees anti-clockwise.
    50 To let the wscons SDL driver rotate the screen, set the environment
    51 variable SDL_VIDEO_WSCONS_ROTATION to "CW", "CCW", or "UD", for
    52 clockwise, counter clockwise, and upside-down rotation respectively.
    53 "CW" makes the screen appear correct on a Sharp Zaurus SL-C3100.
    55 When using rotation in the driver, a "shadow" frame buffer is used to
    56 hold the intermediary display, before blitting it to the actual
    57 hardware frame buffer.  This slows down performance a bit.
    59 For completeness, the rotation "NONE" can be specified to use a shadow
    60 frame buffer without actually rotating.  Unsetting
    61 SDL_VIDEO_WSCONS_ROTATION, or setting it to '' turns off the shadow
    62 frame buffer for maximum performance.
    65 Running MAME
    66 ============
    68 Since my main motivation for writing the driver was playing MAME on
    69 the Zaurus, I'll give a few hints:
    71 XMame compiles just fine under OpenBSD.
    73 I'm not sure this is strictly necessary, but set
    75 MY_CPU = arm
    77 in makefile.unix, and
    81 in src/unix/unix.max
    83 to be sure.
    85 The latest XMame (0.101 at this writing) is a very large program.
    86 Either tinker with the make files to compile a version without support
    87 for all drivers, or, get an older version of XMame.  My recommendation
    88 would be 0.37b16.
    90 When running MAME, DO NOT SET SDL_VIDEO_WSCONS_ROTATION!  Performace
    91 is MUCH better without this, and it is COMPLETELY UNNECESSARY, since
    92 MAME can rotate the picture itself while drawing, and does so MUCH
    93 FASTER.
    95 Use the Xmame command line option "-ror" to rotate the picture to the
    96 right.
    99 Acknowledgments
   100 ===============
   102 I studied the wsfb driver for XFree86/Xorg quite a bit before writing
   103 this, so there ought to be some similarities.
   106 --
   107 Staffan Ulfberg <>