https://bugzilla.libsdl.org/show_bug.cgi?id=5308
The udev code labels devices that are found by this code with
ID_INPUT_KEY which in turn gets used by SDL to label the devices as
SDL_UDEV_DEVICE_KEYBOARD.
This was missing for the code path when udev is not running and as such
devices such as the power button of a phone was not detected as keyboard
input and no devices were emitted.
Anything with X, Y and Z axes but no buttons is probably an
accelerometer (this is the assumption made in udev).
Signed-off-by: Simon McVittie <smcv@collabora.com>
Previously we only checked for at least one button or key and at least
the X and Y absolute axes, but this has both false positives and false
negatives.
Graphics tablets, trackpads and touchscreens all have buttons and
absolute X and Y axes, but we don't want to detect those as joysticks.
On normal Linux systems ordinary users do not have access to these
device nodes, but members of the 'input' group do.
Conversely, some game controllers only have digital buttons and no
analogue axes (the Nintendo Wiimote is an example), and some have axes
and no buttons (steering wheels or flight simulator rudders might not
have buttons).
Use the more elaborate heuristic factored out from SDL's udev code path
to handle these cases.
In an ideal world we could use exactly the same heuristic as udev's
input_id builtin, but that isn't under a suitable license for inclusion
in SDL, so we have to use a parallel implementation of something
vaguely similar.
Signed-off-by: Simon McVittie <smcv@collabora.com>
This works on capability bitfields that can either come from udev or
from ioctls, so it is equally applicable to both udev and non-udev
input device detection.
Signed-off-by: Simon McVittie <smcv@collabora.com>
