When in game type DEBUGUP. Hold shift while pressing the selected buttons for the described code. Example: K = Shift + k

T - display frame rate
F - toggles fog
C - toggles cloud shadows
M - toggles 3D models
L - toggles Fly mode
E - toggles Enviromental mapping
G - toggles Gourad mapping
P - toggles Phong mapping
S - toggles slow motion

While in debug mode, you can hold Ctrl to run fast and jumping while holding Ctrl will make you jump very high! Press these unlisted buttons for the following commands:

tab = radar / map
caps lock = compass / wind direction meter.
Holding the jump button in water will cause you to float.

Also in debug mode:

* press u to decrease plants
* press i to increase plants
* press [ to decrease view range
* press ] to increase view range
* press o to decrease bump mapping
* press p to increase bump mapping

If you decrease the plants all the way down, they will turn 2D.
You cannot toggle o and p unless the view range is higher.
Increasing the plants or bump mapping will cause the ground and trees to stay 3D at further distances since they are 2D until you get close.