Venetian blind crash


The crash has occured in MAP30: Last Call due to a bug with spawn spots.

The venetian blind crash may occasionally occur in vanilla Doom. The name of the error comes from an effect that causes every alternating line of pixels on the screen to be darkened. This makes the screen seem to fold up like Venetian window blinds. It happens because the game quits without resetting the display; the dark vertical lines show a glitched view of the DOS shell.

In DOS this can usually be fixed by issuing the command 'mode co 80' which resets the display to the regular DOS graphics mode, although in severe cases a restart may be the only way to fix the problem. This command will not work in Windows XP or 2000.

Venetian blind crashes are caused by ordinary program errors such as integer division by zero, segmentation or page faults, and illegal opcode execution. However, Doom does not crash as gracefully as some other programs because it fails to shut down its libraries and unhook all interrupts when this happens. This leaves video, audio, and input unusable. Most DOS source ports immediately fixed this by changing the exit behavior and making sure everything is shut down completely even when a crash occurs.

A video showing this error is available at YouTube. In this case, it is the fatal result from retriggering an open door after loading a saved game, an error that was only present in the 1.1 version of Doom.