The aim of Chocolate Doom is to behave as closely to Vanilla Doom as
possible.  As a result, you may experience problems that you would
also experience when using Vanilla Doom.  These are not "bugs" as
Chocolate Doom is behaving as intended.

This is not intended to be a comprehensive list of Vanilla Doom bugs.
For more information, consult the "engine bugs" page of the Doom Wiki.

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== Game exits after title screen with message about game version ==

The game may exit after the title screen is shown, with a message like
the following:

    Demo is from a different game version!
    (read 106, should be 109)

    *** You may need to upgrade your version of Doom to v1.9. ***
        See: http://doomworld.com/files/patches.shtml
        This appears to be v1.6/v1.666.

This usually indicates that your IWAD file that you are using to play
the game (usually named doom.wad or doom2.wad) is out of date.
Chocolate Doom only supports the v1.9 IWAD file.

To fix the problem, you must upgrade to the v1.9 IWAD file.  The URL
in the message has downloadable upgrade patches that you can use to
upgrade.

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== Game exits when accessing the options menu ==

The game may exit with the message "Bad V_DrawPatch" when accessing
the options menu, if you have your mouse sensitivity set high.

The Doom options menu has a slider that allows the mouse sensitivity
to be controlled; however, it has only a very limited range. It is
common for experienced players to set a mouse sensitivity that is much
higher than what can be set via the options menu. The setup program
allows a larger range of values to be set.

However, setting very high sensitivity values causes the game to exit
when accessing the options menu under Vanilla Doom. Because Chocolate
Doom aims to emulate Vanilla Doom as closely as possible, it does the
same thing.

One solution to the problem is to set a lower mouse sensitivity.
Alternatively, all of the settings in the options menu can be
controlled through Doom's key bindings anyway:

    End game: F7
    Messages on/off: F8
    Graphic detail high/low: F5
    Screen size smaller/larger: -/+
    Sound volume menu: F4

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== Game exits with "Savegame buffer overrun" when saving the game ==

If you are playing on a particularly large level, it is possible that
when you save the game, the game will quit with the message "Savegame
buffer overrun".

Vanilla Doom has a limited size memory bufferthat it uses for saving
games.  If you are playing on a large level, the buffer may be too
small for the entire savegame to fit.  Chocolate Doom allows the limit
to be disabled: in the setup tool, go to the "compatibility" menu and
disable the "Vanilla savegame limit" option.

If this error happens to you, your game has not been lost!  A file
named temp.dsg is saved; rename this to doomsav0.dsg to make it appear
in the first slot in the "load game" menu.  (On Unix systems, you will
need to look in the .chocolate-doom/savegames directory in your home
directory)

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== Game ends suddenly when recording a demo ==

If you are recording a very long demo, the game may exit suddenly.
Vanilla Doom has a limited size memory buffer that it uses to save the
demo into.  When the buffer is full, the game exits.  You can tell if
this happens, as the demo file will be around 131,072 bytes in size.

You can work around this by using the -maxdemo command line parameter
to specify a larger buffer size.  Alternatively, the limit can be
disabled: in the setup tool, go to the compatibility menu and disable
the "Vanilla demo limit" option.

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== Game exits with a message about "visplanes" ==

The game may exit with one of these messages:

    R_FindPlane: no more visplanes
    R_DrawPlanes: visplane overflow (129)

This is known as the "visplane overflow" limit and is one of the most
well-known Vanilla Doom engine limits.  You should only ever experience
this when trying to play an add-on level.  The level you are trying to
play is too complex; it was most likely designed to work with a limit
removing source port.

More information can be found here:

    http://rome.ro/lee_killough/editing/visplane.shtml