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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 movement speed increases, acceleration is applied - at high speeds a low-dpi
device will roughly feel the same as a higher-dpi mouse. 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 This normalization only applies to accelerated coordinates, unaccelerated
coordinates are left in device-units. It is up to the caller to interpret coordinates are left in device-units. It is up to the caller to interpret
those coordinates correctly. those coordinates correctly.