The goal of all this is to get an x/y motion reflecting the motion
on the device, i.e. a circle on the device is a circle on the screen.
This is currently done by scaling the y coordinate depending on the screen
ratio vs device ratio. Depending on that ratio the movement on the y axis may
be accelerated (ratio < 1) or slowed (ratio > 1). This leads to the weird
effect that changing the screen ratio by plugging a new monitor changes the
speed of the touchpad.
Use a different algorithm: calculate the physical movement on the device, map
that to the same-ish distance on the screen, then convert that back into a
device-specific vector. This way we get the same mapping regardless of the
current screen dimensions.
Since the pointer accel code doesn't take device resolution into account, make
sure we apply our crazy mapping before we accelerate. This way we accelerate
resolution-independent.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
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