To enable the cheat mode, press "~" and the console will appear. Now, you can enter one of the cheat codes to unlock the corresponding secret option. Use "1" to enable it and "0" to disable the effect. When finished, press "~" again and you will return to the game.
god 1: toggle gode mode
disable_ai 1: enemies won't attack you
noclip 1: unlock walking through walls option
gravity 0: toggle no gravity
speed 300: makes you run faster (default = 125)
debug 1: unlock debug menu
shadows 1: enable shadows
smooth_shadows 1: enable smoth shadows
wire 1: show wireframe
hudenable 0: disable HUD
fps: show FPS