Added the code for joystick support. Currently the left joystick scrolls like a mouse wheel, the right one -- controls the mouse pointer. The joystick sensitivity is as shown:

The joystick is checked every dt=50 ms.  The "dead zone" is .4 mm, then 1 pixel/dt till .7 mm, then 2 pix/dt till 1 mm, then a quadratic function to the maximum speed of 80 pix/dt.