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doc/user: explain why we are doing motion normalization

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Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
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Peter Hutterer 2021-03-10 16:46:43 +10:00
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doc/user/normalization-of-relative-motion.rst
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@ -27,6 +27,11 @@ libinput applies a dpi-dependent acceleration function. At low speeds, a
movement speed increases, acceleration is applied - at high speeds a low-dpi
device will roughly feel the same as a higher-dpi mouse.
The reason for the normalization is convenience: a caller can assume that a
delta of 1 should result in a movement of 1 pixel on a traditional
(low-dpi) screen. On screens with high resolutions, the caller must scale
according to the UI scale factors.
This normalization only applies to accelerated coordinates, unaccelerated
coordinates are left in device-units. It is up to the caller to interpret
those coordinates correctly.