If you have any trouble with Doom Legacy, you might find a solution here.
If you find a solution to a problem that was not listed here, please tell us so that we can update the FAQ and help other people!
First, check that the mouse/joystick is activated : go at the console and type either 'use_mouse' (or use the respective menuitem) or 'use_joystick'. If it is '0' or off then that mouse/joystick is disabled. Set the variable to 1. eg: 'use_mouse 1'.
Once the mouse or joystick is activated, you have to bind the buttons to controls in the setup controls menu.
The original Doom graphics were designed for a 320x200 VGA display with a 4:3 physical aspect ratio. Consequently the pixels on these displays had a 5:6 physical aspect ratio, unlike most modern displays which have square pixels. This makes rendering the graphics on modern displays somewhat complicated.
The menus and intermission screens are scaled at integer ratios to fit the screen. This will often leave bars at the edges. Because these are drawn using color palette graphics from the wad, attempts at finer interpolation required looking up blended colors in a palette which lead to a muddy look. Because of this the menus will be larger or smaller for some video display modes.
The game rendering is fully scaled to display the same view at all video display modes.
In software render mode, Doom Legacy will proportion the display to keep the original display appearance. It will display with filler bars if necessary to do this. The pixels will not be identical to those from the original Doom.
In OpenGL mode using fullscreen, the introduction and intermission pictures are stretched to fill the screen. This does not keep the original aspect ratio. The game rendering is adjusted to approximate the 320x200 screen size, and the field of view of the original software renderer, assuming the display is 4:3. There is a FOV control, but it zooms and does not change the aspect ratio.
When you have a 16:9 display, Doom Legacy displays expecting a 4:3 aspect, and the monitor will stretch it to the 16:9 shape. This will alter the appearance of rooms and sprites. Some monitors can be set to display a 4:3 aspect with black borders. The best alternative is to turn off fullscreen, and choose a window size that fills most of the screen.