Building SDL3 for getting input with KMSDRM display

SDL Development
1

While working on the port of the game Unvanquished from SDL2 to SDL3 I toyed with the KMSDRM display, and yeah the game renders without any X11 or Wayland running, that’s very cool. But then I don’t get any input.

I verified my user is in the input group. I also tried adding read and write permissions to everyone on /dev/input/event* and also tried to run the game engine as root, just to be sure it’s not a matter of missing permission. I never got any input working.

So I guess I likely missed to enable something when building SDL3. Am I right? If yes, what that could be?

1 Like
2

I’m currently building and running SDL 3.2.20, I just noticed SDL 3.2.22 was released some days ago, so I’ll try that as well.

Edit: Same with 3.2.22.

3

Also, maybe my problem isn’t about building SDL3 correctly, as I’m not finding any option I would have forgotten to turn on.
If by any luck SDL3 is built correctly, is there something I actually need to do in game for keyboard/mouse input to work when rendering on KMSDRM?
Also, maybe there is a library I need?

4

Here is output of libinput list-devices:

$ libinput list-devices
Device:           vc4-hdmi
Kernel:           /dev/input/event0
Group:            1
Seat:             seat0, default
Capabilities:     keyboard pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   *button
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   flat *adaptive
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint
Kernel:           /dev/input/event2
Group:            2
Seat:             seat0, default
Capabilities:     keyboard pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint Mouse
Kernel:           /dev/input/event3
Group:            2
Seat:             seat0, default
Capabilities:     pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: disabled
Calibration:      n/a
Scroll methods:   *button
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   flat *adaptive
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint Consumer Control
Kernel:           /dev/input/event4
Group:            2
Seat:             seat0, default
Capabilities:     keyboard pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint
Kernel:           /dev/input/event5
Group:            2
Seat:             seat0, default
Capabilities:     pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint
Kernel:           /dev/input/event6
Group:            2
Seat:             seat0, default
Capabilities:     pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   n/a
Rotation:         n/a

Device:           Lenovo ThinkPad Compact USB Keyboard with TrackPoint
Kernel:           /dev/input/event7
Group:            2
Seat:             seat0, default
Capabilities:     pointer 
Tap-to-click:     n/a
Tap-and-drag:     n/a
Tap drag lock:    n/a
Left-handed:      disabled
Nat.scrolling:    disabled
Middle emulation: n/a
Calibration:      n/a
Scroll methods:   none
Click methods:    none
Disable-w-typing: n/a
Disable-w-trackpointing: n/a
Accel profiles:   n/a
Rotation:         n/a

Can my problem comes from the fact there is an unused input devices listed first?

5

I noticed that evtest /dev/input/event2 reports events for the keyboard and evtest /dev/input/event3 reports events for the mouse, so the inputs are actually working, but not in the SDL application.

6

Do you have to run the configuration tool to configure it to use SDL_INPUT_LINUXEV?

libsdl2_2.30.0+dfsg.orig/SDL2-2.30.0/src/video/kmsdrm/SDL_kmsdrmevents.c

#ifdef SDL_INPUT_LINUXEV
#include “../../core/linux/SDL_evdev.h”
#elif defined SDL_INPUT_WSCONS
#include “../../core/openbsd/SDL_wscons.h”
#endif

void KMSDRM_PumpEvents(_THIS)
{
#ifdef SDL_INPUT_LINUXEV
SDL_EVDEV_Poll();
#elif defined SDL_INPUT_WSCONS
SDL_WSCONS_PumpEvents();
#endif
}