8. Using X

This chapter provides some hints and tips for using DOSEMU in X.

8.1. Basic information

If you start dosemu in X it brings up its own window, in which you can also execute graphical programs such as games. To force text-only execution of DOSEMU in an xterm or other terminal (konsole, gnome-terminal, and so on), you need to run dosemu -t.

Use dosemu -w to start DOSEMU in fullscreen mode. When running DOSEMU, you can flip between fullscreen and windowed mode by pressing <Ctrl><Alt><F>. The graphics window is resizeable.

Some DOS applications want precise mouse control that is only possible if the mouse cursor is trapped in the DOSEMU window. To enable this you need to grab the mouse by pressing <Ctrl><Alt><Home>. Similarly, you can grab the keyboard by pressing <Ctrl><Alt><K>, or <Ctrl><Alt><Shift><K> if your window manager already grabs <Ctrl><Alt><K>. After you grab the keyboard all key combinations (including <Alt><Tab> and so on) are passed to DOSEMU. In fullscreen mode the mouse and keyboard are both automatically grabbed.

Use <Ctrl><Alt><Pause> to pause and unpause the DOSEMU session, which is useful if you want it to sit silently in the background when it is eating too much CPU time. Press <Ctrl><Alt><PgDn> or click the close button of the window to exit DOSEMU.

DOSEMU uses bitmapped internal fonts by default, so it can accurately simulate a real VGA card text mode. It is also possible to use X fonts. The advantages of these is that they may be easier on the eyes, and are faster, in particular if you use DOSEMU remotely. Any native DOS font setting utilities do not work, however. To set an X font use the provided xmode.com utility, using

    xmode -font vga
at the DOS prompt or
    $_X_font = "vga"
in dosemu.conf. The provided fonts are vga, vga8x19, vga11x19, vga10x24, vga12x30, vga-cp866, and vga10x20-cp866.

If the mouse is not grabbed, then you can copy and paste text if the DOSEMU window is in text mode. This uses the standard X mechanism: select by dragging the left mouse button, and paste by pressing the middle mouse button.

8.2. More detailed information, hints and tips

What you might take care of:

8.3. The VGA Emulator

In X, a VGA card is emulated. The same happens if you use the SDL library using dosemu -S. This emulation (vgaemu) enables X to run graphics modes.

Some features:

As the typical graphics mode with 320x200x8 will be used often with large scalings and modern graphics boards are pretty fast, Steffen Winterfeldt 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 DOSEMU has crashed.

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).

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/render.c. 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. It must be specified as a float value, e.g. $_X_gamma=(1.0). Higher values give brighter graphics, lower make them darker. Reasonable values are within a range of 0.5 ... 2.0.

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 $_X_winsize. You can still resize the window later.

The config option $_X_fixed_aspect allows you to fix the aspect ratio of the graphics window while resizing it. Alternatively, $_X_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.

For planar modes (for instance, most 16 colour modes, but also certain 256-colour modes: mode-X), vgaemu has to switch to partial cpu emulation. This can be slow, but expect it to improve over time.