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README  - 0.97.10
Technical README
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10. Using X

Please read all of this for a more complete X information ;-)

10.1 Latest Info

From Uwe Bonnes <bon@elektron.ikp.physik.th-darmstadt.de>:

xdos from dosemu version pre- with the patch from my last messages should now be more capable. In particular it should now understand the keys from the keypad-area (the keys the most right on a MF-Keyboard) and numlock and keyevents in the range of the latin characters, even when you run xdos from a remote X-terminal.

If it dosen't work for you as expected, please check out the following:

  • Don't specify "keycode" for X-support. The keycode-option is something specific for a special X-server, here XFree86, and so isn't portable and I disencourage its use.
  • Check out whether your key sends a sensible ksym, with e.g."xev". If it sends something sensible which you think should be mapped by xdos, please let me know details.
  • If you are running xdos on XFree86, version 3.1.1 and newer and the keys of the keypad-area don't work, you have two options:
    • Comment out the line " ServerNumLock " in /usr/X11R6/lib/X11/XFConfig
    • Feed the following file to xmodmap. From what I understand from the docs, XFree-3.1.1 should do that intrinsicly, but for me it didn't. This is a part of the file /usr/X11R6/lib/X11/etc/xmodmap.std
      ! When using ServerNumLock in your XF86Config, the following codes/symbols
      ! are available in place of 79-81, 83-85, 87-91
      keycode  136 = KP_7
      keycode  137 = KP_8
      keycode  138 = KP_9
      keycode  139 = KP_4
      keycode  140 = KP_5
      keycode  141 = KP_6
      keycode  142 = KP_1
      keycode  143 = KP_2
      keycode  144 = KP_3
      keycode  145 = KP_0
      keycode  146 = KP_Decimal
      keycode  147 = Home
      keycode  148 = Up
      keycode  149 = Prior
      keycode  150 = Left
      keycode  151 = Begin
      keycode  152 = Right
      keycode  153 = End
      keycode  154 = Down
      keycode  155 = Next
      keycode  156 = Insert
      keycode  157 = Delete

10.2 Slightly older information

From Rainer Zimmermann <zimmerm@mathematik.uni-marburg.de>

Some basic information about dosemu's X support. Sometimes it's even sort of useable now.

What you should take care of:

  • Do a 'xmodmap -e "keycode 22 = 0xff08"' to get use of your backspace key.
  • Do a 'xmodmap -e "keycode 107 = 0xffff"' to get use of your delete key.
  • Make sure dosemu has X support compiled in. (X_SUPPORT = 1 in the Makefile)
  • you should have the vga font installed. See README.ncurses.
  • start dosemu with 'dos -X' from an X terminal window. Or make a link to 'dos' named 'xdos' - when called by that name, dosemu will automatically assume -X. There is also a new debug flag 'X' for X-related messages. To exit xdos, use 'exitemu' or select 'Close' aka 'Delete' (better not 'Destroy') from the 'Window' menu.
  • there are some X-related configuration options for dosemu.conf. See examples/config.dist for details.
  • starting xdos in the background (like from a window manager menu) appears not to work for some reason.
  • Keyboard support in the dosemu window isn't perfect yet. It probably could be faster, some key combos still don't work (e.g. Ctrl-Fn), etc. However, input through the terminal window (i.e. the window you started dosemu from) is still supported. If you have problems, you *might* be better off putting your focus in there.
  • Keyboard support of course depends on your X keyboard mappings (xmodmap). If certain keys don't work (like Pause, Backspace,...), it *might* be because you haven't defined them in your xmodmap, or defined to something other than dosemu expects.
  • using the provided icon (dosemu.xpm):
    • you need the xpm (pixmaps) package. If you're not sure, look for a file like /lib/libXpm.so.*
    • you also need a window manager which supports pixmaps. Fvwm is fine, but I can't tell you about others. Twm probaby won't do.
    • copy dosemu.xpm to where you usually keep your pixmap (not bitmap!) files (perhaps /usr/include/X11/pixmaps)
    • tell your window manager to use it. For fvwm, add the following line to your fvwmrc file:
           Icon "xdos"   dosemu.xpm
      This assumes you have defined a PixmapPath. Otherwise, specify the entire pathname.
    • note that if you set a different icon name than "xdos" in your dosemu.conf, you will also have to change the fvwmrc entry.
    • restart the window manager. There's usually an option in the root menu to do so.
    Now you should see the icon whenever you iconify xdos.

    Note that the xdos program itself does not include the icon - that's why you have to tell the window manager. I chose to do it this way to avoid xdos requiring the Xpm library.

  • If anything else does not work as expected, don't panic :-) Remember the thing is still under construction. However, if you think it's a real bug, please tell me.

important changes to previous version (pre53_17):

  • fixed focus handling at startup
  • support for 21/28/43/50 line modes! (43+50 look a bit funny, though... I use the 8x16 font for all modes)
  • .xpm icon
  • fixed startup error handling (won't hang now if display not found)
  • limited window size

10.3 Status of X support (Sept 5, 1994)


  • X_update_screen (video output)
  • implement cursor
  • fix cursor/scrolling bugs
  • fix Scroll (video/terminal.c) (?)
  • fix banner message (initialization) (works after video cleanup, dunno why :)
  • check video memory dirty bit
  • X event handling (close, expose, focus etc.)
  • fixed cursor initialization
  • cleaned up cursor handling
  • added 'xdos' calling method
  • disable 'mouse' serial ports in X mode
  • write direct scroll routine (not used yet, though)
  • care about int10 calls -ok?
  • Handle close ("delete") window event - (copied from xloadimage)
  • X keyboard support (pcemu code, heavily modified)
  • Mouse support
  • X configuration (display, updatefreq, updatelines,... what else?)
  • int10 video mode switches (resize window)
  • Window SizeHints (fixed size or max size?)
  • create icon :-)

ToDo (in no special order)

  • xor cursor? blinking cursor?
  • use mark's scroll detector
  • jump scroll?
  • fine-tune X_update_screen
  • graphics support?
  • allow non-standard font heights via bios
  • cut & paste

10.4 The appearance of Graphics modes (November 13, 1995)

Erik Mouw <J.A.K.Mouw@et.tudelft.nl> & Arjan Filius <I.A.Filius@et.tudelft.nl>

We've made some major changes in X.c that enables X to run graphics modes. Unfortunately, this disables the cut-and-paste support, but we think the graphics stuff is much more fun (after things have established, we'll put the cut-and-paste stuff back). The graphics is done through vgaemu, the VGA emulator. Status of the work:


  • Video memory. 1 Mb is allocated. It is mapped with mmap() in the VGA memory region of dosemu (0xa00000-0xbfffff) to support bank switching. This is very i386-Linux specific, don't be surprised if it doesn't work under NetBSD or another Linux flavour (Alpha/Sparc/MIPS/etc).
  • The DAC (Digital to Analog Converter). The DAC is completely emulated, except for the pelmask. This is not difficult to implement, but it is terribly slow because a change in the pelmask requires a complete redraw of the screen. Fortunately, the pelmask changes aren't used often so nobody will notice ;-)
  • The attribute controller is partially emulated. (Actually, only reads and writes to the ports are emulated)
  • The working modes are 0x13 (320x200x256) and some other 256 color modes.
  • To do (in no particular order): font support in graphics modes (8x8, 8x16, 9x16, etc), text mode support, 16, 4 and 2 color support, better bank switching, write the X code out of vgaemu to get it more generic.


  • VESA set/get mode, get information and bankswitch functions work.
  • All VESA 256 color (640x480, 800x600, 1024x768) modes work, but due to bad bank switch code in vgaemu they won't display right.
  • A VESA compatible video BIOS is mapped at 0xc00000. It's very small, but in future it's a good place to store the BIOS fonts (8x8, 8x16) in.
  • To do: implement the other VESA functions.


  • Added own colormap support for the 256 color modes.
  • Support for vgaemu.
  • Some cleanups.
  • To do: remove text support and let vgaemu do the text modes, put back the cut-and-paste stuff, more cleanups.
  • NOTE: we've developed on X servers with 8 bit pixel depths (XF86_SVGA) so we don't know how our code behaves on other pixel depths. We don't even know if it works.

As stated before, this code was written for Linux (tested with 1.2.13 and 1.3.39) and we don't know if it works under NetBSD. The mmap() of /proc/self/mem and mprotect() magic in vgaemu are very (i386) Linux specific.


10.5 The new VGAEmu/X code (July 11, 1997)

Steffen Winterfeldt <Steffen.Winterfeldt@itp.uni-leipzig.de>

I've been working on the X code and the VGA emulation over the last few months. This is the outcome so far:

  • graphics support in X now works on all X servers with color depth >= 8
  • the graphics window is resizeable
  • support for hi- and true-color modes (using Trident SVGA mode numbers and bank switching)
  • some basic support for mode-X type graphics modes (non-chain4 modes as used by e.g. DOOM)
  • some even more basic support for 16 color modes
  • nearly full VESA 2.0 support
  • gamma correction for graphics modes
  • video memory size is configurable via dosemu.conf
  • initial graphics window size is configurable

The current implementation supports 4 and 8 bit SVGA modes on all types of X display. Hi-color modes are supported only on displays matching the exact color depth (15 or 16); true color modes are supported only on true color X displays, but always both 24 bit and 32 bit SVGA modes.

In addition, the current hi- and true color support does not allow resizing of the graphics window and gamma correction is ignored.

As the typical graphics mode with 320x200x8 will be used often with large scalings and modern graphics boards are pretty fast, I added something to eat up your CPU time: you can turn on the bilinear interpolation. It greatly improves the display quality (but is rather slow as I haven't had time yet to implement an optimized version - it's plain C for now). If the bilinear filter is too slow, you might instead try the linear filter which interpolates only horizontally.

Note that (bi)linear filtering is not available on all VGA/X display combinations. The standard drawing routines are used instead in such cases.

If a VGA mode is not supported on your current X display, the graphics screen will just remain black. Note that this does not mean that xdos has crashed.

The VESA support is (or should be) nearly VBE 2.0 compatible. As a reference I used several documents including the unofficial VBE 2.0 specs made available by SciTech Software. I checked this against some actual implementations of the VBE 2.0 standard, including SciTech's Display Doctor (formerly known as UniVBE). Unfortunately implementations and specs disagree at some points. In such cases I assumed the actual implementation to be correct.

The only unsupported VBE function is VGA state save/restore. But this functionality is rarely used and its lack should not cause too much problems.

VBE allows you to use the horizontal and vertical scrolling function even in text modes. This feature is not implemented.

If you think it causes problems, the linear frame buffer (LFB) can be turned of via dosemu.conf as well as the protected mode interface. Note, however, that LFB modes are faster than banked modes, even in DOSEmu.

The default VBE mode list defines a lot of medium resolution modes suitable for games (like Duke3D). You can still create your own modes via dosemu.conf. Note that you cannot define the same mode twice; the second (and all subsequent) definitions will be ignored.

Modes that are defined but cannot be supported due to lack of video memory or because they cannot be displayed on your X display, are marked as unsupported in the VBE mode list (but are still in it). Note that there is currently no support of 4 bit VESA modes.

The current interface between VGAEmu and X will try to update all invalid video pages at a time. This may, particularly in hi-res VBE/SVGA modes, considerably disturb DOSEmu's signal handling. That cannot be helped for the moment, but will be addressed soon (by running an extra update thread).

If you really think that this is the cause of your problem, you might try to play with veut.max_max_len in env/video/n_X.c, near line 2005. This variable limits the amount of video memory that is updated during one timer interrupt. This way you can dramatically reduce the load of screen updates, but at the same rate reduce your display quality.

Gamma correction works in both 4 and 8 bit modes. As the dosemu.conf parser doesn't support float values, it must be specified as a percentage value: gamma 100 = gamma 1.0. Higher values give brighter graphics, lower make them darker. Reasonable values are within a range of 50 ... 200.

You can specify the video memory size that the VGA emulator should use in dosemu.conf. The value will be rounded up to the nearest 256 kbyte boundary. You should stick to typical values like 1024, 2048 or 4096 as not to confuse DOS applications. Note that whatever value you give, 4 bit modes are only supported up to a size of 800x600.

You can influence the initial size of the graphics window in various ways. Normally it will have the same size (in pixel) as the VGA graphics mode, except for mode 0x13 (320x200, 256 colors), which will be scaled by the value of mode13fact (defaults to 2). Alternatively, you can directly specify a window size in dosemu.conf via winsize. You can still resize the window later.

The config option fixed_aspect allows you to fix the aspect ratio of the graphics window while resizing it. Alternatively, aspect_43 ties the aspect ratio to a value of 4:3. The idea behind this is that, whatever the actual resolution of a graphics mode is in DOS, it is displayed on a 4:3 monitor. This way you won't run into problems with modes such as 640x200 (or even 320x200) which would look somewhat distorted otherwise.

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