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Fake proximity events are context dependent and libinput doesn't have access to the context. For example, fake proximity on the Wacom mouse is only required in relative mode - but whether to use relative or absolute events is decided in the caller. Document what the recommended approach is since it's a bit quirky and leave it at that. Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net> Reviewed-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>
49 lines
1.7 KiB
Text
49 lines
1.7 KiB
Text
/**
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@page tablet-support Tablet support
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This page provides details about the graphics tablet
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support in libinput. Note that the term "tablet" in libinput refers to
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graphics tablets only (e.g. Wacom Intuos), not to tablet devices like the
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Apple iPad.
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@section fake-proximity Handling of proximity events
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libinput's @ref LIBINPUT_EVENT_TABLET_PROXIMITY events represent the
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physical proximity limits of the device. In some cases the caller should
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emulate proximity based on the distance events. For example, the Wacom mouse
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and lens cursor tools are usually used in relative mode, lying flat on the
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tablet. A user typically expects that lifting the tool off the tablet to a
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different location has the same effect as with a normal mouse. The proximity
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detection on Wacom tablets however extends further than the user may lift
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the mouse, i.e. the tool may not be lifted out of physical proximity.
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To enable normal use as a mouse it is recommended that the caller treats
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proximity separate from libinput's proximity events. There is no simple way
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to detect the proximity motion threshold, it is different on each tablet and
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differs between tools. The recommended algorithm is to remember the minimum
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distance value seen on the tool and assume a proximity out when the distance
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exceeds a threshold above this minimum value. In pseudo-code:
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@code
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const double threshold = ...;
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static double min;
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static bool in_proximity;
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double value;
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value = libinput_event_pointer_get_axis_value(device,
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LIBINPUT_TABLET_AXIS_DISTANCE);
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if (value < min) {
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min = value;
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return;
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} else if (in_proximity &&
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value > min + threshold) {
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in_proximity = false;
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} else if (!in_proximity &&
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value < min + threshold) {
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in_proximity = true;
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}
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@endcode
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*/
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