Hi there,
I just tried this game.
I was confused because it showed the xbox buttons instead of keyboard keys even though I had no gamepad plugged in. I then plugged in the gamepad and restarted the game, yet the game does not recognize any button presses.

I think I figured out what is going on, but it is really odd. Here is part of the console output:

Controller 0, SynPS/2 Synaptics TouchPad, will use generic MonoGameJoystick support.
Controller 1, Xbox Gamepad (userspace driver), will use generic MonoGameJoystick support.

Yep, it looks like the game recognizes my touchpad as controller, which is really stupid. And indeed, the game reacts to the touchpad, but it's obviously unplayable this way.

Does someone know a fix or workaround?

Thanks for your help, but this is not my problem.
Without any gamepad plugged in there is no /dev/js*.

On startup the game writes:
$ GOG\ Games/Rogue\ Legacy/start.sh
Running Rogue Legacy
AL lib: (WW) alc_initconfig: Failed to initialize backend "pulse"
EXT_swap_control_tear unsupported. Fall back to standard VSync.
Adding language dictionary for language: English
Controller 0, SynPS/2 Synaptics TouchPad, will use generic MonoGameJoystick support.
Loading Config file
...

Why it thinks that the touchpad is a joystick I do not know. Here is what evtest says about the touchpad:
Input driver version is 1.0.1
Input device ID: bus 0x11 vendor 0x2 product 0x7 version 0x1b1
Input device name: "SynPS/2 Synaptics TouchPad"
Supported events:
Event type 0 (EV_SYN)
Event type 1 (EV_KEY)
Event code 272 (BTN_LEFT)
Event code 273 (BTN_RIGHT)
Event code 325 (BTN_TOOL_FINGER)
Event code 330 (BTN_TOUCH)
Event code 333 (BTN_TOOL_DOUBLETAP)
Event code 334 (BTN_TOOL_TRIPLETAP)
Event type 3 (EV_ABS)
Event code 0 (ABS_X)
Value 2155
Min 1472
Max 5888
Resolution 75
Event code 1 (ABS_Y)
Value 4420
Min 1408
Max 4820
Resolution 105
Event code 24 (ABS_PRESSURE)
Value 0
Min 0
Max 255
Event code 28 (ABS_TOOL_WIDTH)
Value 0
Min 0
Max 15
Event code 47 (ABS_MT_SLOT)
Value 1
Min 0
Max 1
Event code 53 (ABS_MT_POSITION_X)
Value 0
Min 1472
Max 5888
Resolution 75
Event code 54 (ABS_MT_POSITION_Y)
Value 0
Min 1408
Max 4820
Resolution 105
Event code 57 (ABS_MT_TRACKING_ID)
Value 0
Min 0
Max 65535
Properties:
Property type 0 (INPUT_PROP_POINTER)
Property type 3 (INPUT_PROP_SEMI_MT)

Comparing that to my mice I guess the game or mono or FNA may look for events like ABS_X and assume that devices that support those events are joypads. A failing heuristic. It is just a guess though.

Other things I have tried that correctly do not find a joystick:
jstest-gtk
sdl2-jstest --list
wine control.exe joy.cpl

No cigar, and I remember why I hate writing udev rules.

I could not get the vendor or product id the usual way:
$ udevadm info -a -n /dev/input/event18

Udevadm info starts with the device specified by the devpath and then
walks up the chain of parent devices. It prints for every device
found, all possible attributes in the udev rules key format.
A rule to match, can be composed by the attributes of the device
and the attributes from one single parent device.

looking at device '/devices/platform/i8042/serio4/input/input25/event18':
KERNEL=="event18"
SUBSYSTEM=="input"
DRIVER==""

looking at parent device '/devices/platform/i8042/serio4/input/input25':
KERNELS=="input25"
SUBSYSTEMS=="input"
DRIVERS==""
ATTRS{name}=="SynPS/2 Synaptics TouchPad"
ATTRS{phys}=="isa0060/serio4/input0"
ATTRS{properties}=="9"
ATTRS{uniq}==""

looking at parent device '/devices/platform/i8042/serio4':
KERNELS=="serio4"
SUBSYSTEMS=="serio"
DRIVERS=="psmouse"
ATTRS{bind_mode}=="auto"
ATTRS{description}=="i8042 AUX3 port"
ATTRS{firmware_id}=="PNP: LEN0017 PNP0f13"
ATTRS{protocol}=="SynPS/2"
ATTRS{rate}=="80"
ATTRS{resetafter}=="5"
ATTRS{resolution}=="200"
ATTRS{resync_time}=="0"

looking at parent device '/devices/platform/i8042':
KERNELS=="i8042"
SUBSYSTEMS=="platform"
DRIVERS=="i8042"
ATTRS{driver_override}=="(null)"

looking at parent device '/devices/platform':
KERNELS=="platform"
SUBSYSTEMS==""
DRIVERS==""


Evtest however says: Input device ID: bus 0x11 vendor 0x2 product 0x7 version 0x1b1

I installed the variant of udev-joystick-blacklist that should remove the device and added this line to /usr/lib/udev/rules.d/51-these-are-not-joysticks-rm.rules

SUBSYSTEM=="input", ATTRS{idVendor}=="0002", ATTRS{idProduct}=="0007", ENV{ID_INPUT_JOYSTICK}=="?*", ENV{ID_INPUT_JOYSTICK}=""
SUBSYSTEM=="input", ATTRS{idVendor}=="0002", ATTRS{idProduct}=="0007", KERNEL=="js[0-9]*", RUN+="/bin/rm %E{DEVNAME}", ENV{ID_INPUT_JOYSTICK}=""

Yet the touchpad still works and is recognized by Rogue Legacy.

However, because there are no additional or wrong js or event devices present and no other program recognizes the touchpad as joypad I am of the opinion that the game is at fault.


I found one way to work around this issue: remove the kernel module responsible for the touchpad. In my case: rmmod i8042

However, I do not think that should be necessary.

I actually am running linux 4.9.6.

Thanks, I will contact the developers.