Supported DOS graphic drivers.
The DOS library supports the following card parameters for the
Return to text mode.
Let Allegro pick an appropriate graphics driver.
Autodetects a graphics driver, but will only use fullscreen drivers,
failing if these are not available on current platform.
Same as above, but uses only windowed drivers. This will always fail
Special driver for when you want to reliably set a graphics mode and
don't really care what resolution or color depth you get. See the
set_gfx_mode() documentation for details.
The standard 256-color VGA mode 13h, using the GFX_VGA driver. This is
normally sized 320x200, which will work on any VGA but doesn't support
large virtual screens and hardware scrolling. Allegro also provides
some tweaked variants of the mode which are able to scroll, sized
320x100 (with a 200 pixel high virtual screen), 160x120 (with a 409
pixel high virtual screen), 256x256 (no scrolling), and 80x80 (with a
819 pixel high virtual screen).
Mode-X will work on any VGA card, and provides a range of different
256-color tweaked resolutions.
Most of the mode-X drawing functions are slower than in mode 13h, due
to the complexity of the planar bitmap organisation, but solid area
fills and plane-aligned blits from one part of video memory to another
can be significantly faster, particularly on older hardware. Mode-X
can address the full 256k of VGA RAM, so hardware scrolling and page
flipping are possible, and it is possible to split the screen in order
to scroll the top part of the display but have a static status
indicator at the bottom.
Stable mode-X resolutions:
These have worked on every card/monitor that I've tested.
Square aspect ratio: 320x240
Skewed aspect ratio: 256x224, 256x240, 320x200, 320x400,
320x480, 320x600, 360x200, 360x240,
360x360, 360x400, 360x480
Unstable mode-X resolutions:
These only work on some monitors. They were fine on my old machine,
but don't get on very well with my new monitor. If you are worried
about the possibility of damaging your monitor by using these
modes, don't be. Of course I'm not providing any warranty with any
of this, and if your hardware does blow up that is tough, but I
don't think this sort of tweaking can do any damage. From the
documentation of Robert Schmidt's TWEAK program:
Square aspect ratio: 360x270, 376x282, 400x300
Skewed aspect ratio: 256x200, 256x256, 320x350, 360x600,
376x308, 376x564, 400x150, 400x600
"Some time ago, putting illegal or unsupported values or
combinations of such into the video card registers might prove
hazardous to both your monitor and your health. I have *never*
claimed that bad things can't happen if you use TWEAK, although
I'm pretty sure it never will. I've never heard of any damage
arising from trying out TWEAK, or from general VGA tweaking in
Use the VESA 1.x driver.
Use the VBE 2.0 banked mode driver.
Use the VBE 2.0 linear framebuffer driver.
Use the VBE 3.0 driver. This is the only VESA driver that supports the
The standard VESA modes are 640x480, 800x600, and 1024x768. These
ought to work with any SVGA card: if they don't, get a copy of the
SciTech Display Doctor and see if that fixes it. What color depths are
available will depend on your hardware. Most cards support both 15 and
16-bit resolutions, but if at all possible I would advise you to
support both (it's not hard...) in case one is not available. Some
cards provide both 24 and 32-bit truecolor, in which case it is a
choice between 24 (saves memory) or 32 (faster), but many older cards
have no 32-bit mode and some newer ones don't support 24-bit
resolutions. Use the vesainfo test program to see what modes your VESA
Many cards also support 640x400, 1280x1024, and 1600x1200, but these
aren't available on everything, for example the S3 chipset has no
640x400 mode. Other weird resolution may be possible, eg. some Tseng
boards can do 640x350, and the Avance Logic has a 512x512 mode.
The SciTech Display Doctor provides several scrollable low resolution
modes in a range of different color depths (320x200, 320x240, 320x400,
320x480, 360x200, 360x240, 360x400, and 360x480 all work on my ET4000
with 8, 15, or 16 bits per pixel). These are lovely, allowing
scrolling and page flipping without the complexity of the mode-X
planar setup, but unfortunately they aren't standard so you will need
Display Doctor in order to use them.
VBE/AF is a superset of the VBE 2.0 standard, which provides an API
for accessing hardware accelerator features. VBE/AF drivers are
currently only available from the FreeBE/AF project or as part of the
SciTech Display Doctor package, but they can give dramatic speed
improvements when used with suitable hardware. For a detailed
discussion of hardware acceleration issues, refer to the documentation
for the gfx_capabilities flag.
You can use the afinfo test program to check whether you have a VBE/AF
driver, and to see what resolutions it supports.
The SciTech VBE/AF drivers require nearptr access to be enabled, so
any stray pointers are likely to crash your machine while their
drivers are in use. This means it may be a good idea to use VESA while
debugging your program, and only switch to VBE/AF once the code is
working correctly. The FreeBE/AF drivers do not have this problem.
An unchained 640x400 mode, as described by Mark Feldman in the PCGPE.
This uses VESA to select an SVGA mode (so it will only work on cards
supporting the VESA 640x400 resolution), and then unchains the VGA
hardware as for mode-X. This allows the entire screen to be addressed
without the need for bank switching, but hardware scrolling and page
flipping are not possible. This driver will never be autodetected (the
normal VESA 640x400 mode will be chosen instead), so if you want to
use it you will have to explicitly pass GFX_XTENDED to set_gfx_mode().
There are a few things you need to be aware of for scrolling:
most VESA implementations can only handle horizontal scrolling in four
pixel increments, so smooth horizontal panning is impossible in SVGA modes.
A significant number of VESA implementations seem to be very buggy when it
comes to scrolling in truecolor video modes, so you shouldn't depend on
this routine working correctly in the truecolor resolutions unless you can
be sure that SciTech Display Doctor is installed. Hardware scrolling may
also not work at all under Windows.
Triple buffering is only possible with certain drivers: it will work in any
DOS mode-X resolution if the timer retrace simulator is active (but this
doesn't work correctly under Windows 95), plus it is supported by the
VBE 3.0 and VBE/AF drivers for a limited number graphics cards.