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Input: document event types and codes and their intended use
This commit adds the file Documentation/input/event-codes.txt. Acked-by: Henrik Rydberg <rydberg@euromail.se> Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net> Signed-off-by: Chase Douglas <chase.douglas@canonical.com> Signed-off-by: Chris Bagwell <chris@cnpbagwell.com> Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
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Chase Douglas
Dmitry Torokhov
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The input protocol uses a map of types and codes to express input device values
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to userspace. This document describes the types and codes and how and when they
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may be used.
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A single hardware event generates multiple input events. Each input event
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contains the new value of a single data item. A special event type, EV_SYN, is
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used to separate input events into packets of input data changes occurring at
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the same moment in time. In the following, the term "event" refers to a single
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input event encompassing a type, code, and value.
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The input protocol is a stateful protocol. Events are emitted only when values
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of event codes have changed. However, the state is maintained within the Linux
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input subsystem; drivers do not need to maintain the state and may attempt to
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emit unchanged values without harm. Userspace may obtain the current state of
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event code values using the EVIOCG* ioctls defined in linux/input.h. The event
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reports supported by a device are also provided by sysfs in
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class/input/event*/device/capabilities/, and the properties of a device are
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provided in class/input/event*/device/properties.
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Types:
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==========
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Types are groupings of codes under a logical input construct. Each type has a
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set of applicable codes to be used in generating events. See the Codes section
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for details on valid codes for each type.
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* EV_SYN:
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- Used as markers to separate events. Events may be separated in time or in
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space, such as with the multitouch protocol.
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* EV_KEY:
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- Used to describe state changes of keyboards, buttons, or other key-like
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devices.
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* EV_REL:
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- Used to describe relative axis value changes, e.g. moving the mouse 5 units
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to the left.
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* EV_ABS:
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- Used to describe absolute axis value changes, e.g. describing the
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coordinates of a touch on a touchscreen.
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* EV_MSC:
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- Used to describe miscellaneous input data that do not fit into other types.
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* EV_SW:
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- Used to describe binary state input switches.
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* EV_LED:
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- Used to turn LEDs on devices on and off.
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* EV_SND:
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- Used to output sound to devices.
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* EV_REP:
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- Used for autorepeating devices.
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* EV_FF:
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- Used to send force feedback commands to an input device.
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* EV_PWR:
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- A special type for power button and switch input.
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* EV_FF_STATUS:
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- Used to receive force feedback device status.
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Codes:
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==========
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Codes define the precise type of event.
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EV_SYN:
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----------
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EV_SYN event values are undefined. Their usage is defined only by when they are
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sent in the evdev event stream.
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* SYN_REPORT:
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- Used to synchronize and separate events into packets of input data changes
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occurring at the same moment in time. For example, motion of a mouse may set
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the REL_X and REL_Y values for one motion, then emit a SYN_REPORT. The next
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motion will emit more REL_X and REL_Y values and send another SYN_REPORT.
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* SYN_CONFIG:
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- TBD
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* SYN_MT_REPORT:
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- Used to synchronize and separate touch events. See the
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multi-touch-protocol.txt document for more information.
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EV_KEY:
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----------
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EV_KEY events take the form KEY_<name> or BTN_<name>. For example, KEY_A is used
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to represent the 'A' key on a keyboard. When a key is depressed, an event with
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the key's code is emitted with value 1. When the key is released, an event is
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emitted with value 0. Some hardware send events when a key is repeated. These
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events have a value of 2. In general, KEY_<name> is used for keyboard keys, and
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BTN_<name> is used for other types of momentary switch events.
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A few EV_KEY codes have special meanings:
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* BTN_TOOL_<name>:
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- These codes are used in conjunction with input trackpads, tablets, and
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touchscreens. These devices may be used with fingers, pens, or other tools.
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When an event occurs and a tool is used, the corresponding BTN_TOOL_<name>
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code should be set to a value of 1. When the tool is no longer interacting
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with the input device, the BTN_TOOL_<name> code should be reset to 0. All
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trackpads, tablets, and touchscreens should use at least one BTN_TOOL_<name>
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code when events are generated.
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* BTN_TOUCH:
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BTN_TOUCH is used for touch contact. While an input tool is determined to be
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within meaningful physical contact, the value of this property must be set
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to 1. Meaningful physical contact may mean any contact, or it may mean
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contact conditioned by an implementation defined property. For example, a
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touchpad may set the value to 1 only when the touch pressure rises above a
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certain value. BTN_TOUCH may be combined with BTN_TOOL_<name> codes. For
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example, a pen tablet may set BTN_TOOL_PEN to 1 and BTN_TOUCH to 0 while the
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pen is hovering over but not touching the tablet surface.
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Note: For appropriate function of the legacy mousedev emulation driver,
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BTN_TOUCH must be the first evdev code emitted in a synchronization frame.
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Note: Historically a touch device with BTN_TOOL_FINGER and BTN_TOUCH was
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interpreted as a touchpad by userspace, while a similar device without
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BTN_TOOL_FINGER was interpreted as a touchscreen. For backwards compatibility
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with current userspace it is recommended to follow this distinction. In the
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future, this distinction will be deprecated and the device properties ioctl
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EVIOCGPROP, defined in linux/input.h, will be used to convey the device type.
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* BTN_TOOL_FINGER, BTN_TOOL_DOUBLETAP, BTN_TOOL_TRIPLETAP, BTN_TOOL_QUADTAP:
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- These codes denote one, two, three, and four finger interaction on a
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trackpad or touchscreen. For example, if the user uses two fingers and moves
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them on the touchpad in an effort to scroll content on screen,
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BTN_TOOL_DOUBLETAP should be set to value 1 for the duration of the motion.
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Note that all BTN_TOOL_<name> codes and the BTN_TOUCH code are orthogonal in
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purpose. A trackpad event generated by finger touches should generate events
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for one code from each group. At most only one of these BTN_TOOL_<name>
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codes should have a value of 1 during any synchronization frame.
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Note: Historically some drivers emitted multiple of the finger count codes with
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a value of 1 in the same synchronization frame. This usage is deprecated.
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Note: In multitouch drivers, the input_mt_report_finger_count() function should
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be used to emit these codes. Please see multi-touch-protocol.txt for details.
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EV_REL:
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----------
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EV_REL events describe relative changes in a property. For example, a mouse may
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move to the left by a certain number of units, but its absolute position in
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space is unknown. If the absolute position is known, EV_ABS codes should be used
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instead of EV_REL codes.
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A few EV_REL codes have special meanings:
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* REL_WHEEL, REL_HWHEEL:
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- These codes are used for vertical and horizontal scroll wheels,
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respectively.
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EV_ABS:
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----------
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EV_ABS events describe absolute changes in a property. For example, a touchpad
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may emit coordinates for a touch location.
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A few EV_ABS codes have special meanings:
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* ABS_DISTANCE:
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- Used to describe the distance of a tool from an interaction surface. This
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event should only be emitted while the tool is hovering, meaning in close
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proximity of the device and while the value of the BTN_TOUCH code is 0. If
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the input device may be used freely in three dimensions, consider ABS_Z
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instead.
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* ABS_MT_<name>:
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- Used to describe multitouch input events. Please see
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multi-touch-protocol.txt for details.
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EV_SW:
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----------
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EV_SW events describe stateful binary switches. For example, the SW_LID code is
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used to denote when a laptop lid is closed.
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Upon binding to a device or resuming from suspend, a driver must report
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the current switch state. This ensures that the device, kernel, and userspace
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state is in sync.
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Upon resume, if the switch state is the same as before suspend, then the input
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subsystem will filter out the duplicate switch state reports. The driver does
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not need to keep the state of the switch at any time.
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EV_MSC:
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----------
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EV_MSC events are used for input and output events that do not fall under other
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categories.
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EV_LED:
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----------
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EV_LED events are used for input and output to set and query the state of
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various LEDs on devices.
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EV_REP:
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----------
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EV_REP events are used for specifying autorepeating events.
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EV_SND:
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----------
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EV_SND events are used for sending sound commands to simple sound output
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devices.
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EV_FF:
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----------
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EV_FF events are used to initialize a force feedback capable device and to cause
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such device to feedback.
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EV_PWR:
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----------
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EV_PWR events are a special type of event used specifically for power
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mangement. Its usage is not well defined. To be addressed later.
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Guidelines:
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==========
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The guidelines below ensure proper single-touch and multi-finger functionality.
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For multi-touch functionality, see the multi-touch-protocol.txt document for
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more information.
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Mice:
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----------
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REL_{X,Y} must be reported when the mouse moves. BTN_LEFT must be used to report
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the primary button press. BTN_{MIDDLE,RIGHT,4,5,etc.} should be used to report
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further buttons of the device. REL_WHEEL and REL_HWHEEL should be used to report
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scroll wheel events where available.
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Touchscreens:
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----------
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ABS_{X,Y} must be reported with the location of the touch. BTN_TOUCH must be
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used to report when a touch is active on the screen.
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BTN_{MOUSE,LEFT,MIDDLE,RIGHT} must not be reported as the result of touch
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contact. BTN_TOOL_<name> events should be reported where possible.
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Trackpads:
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----------
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Legacy trackpads that only provide relative position information must report
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events like mice described above.
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Trackpads that provide absolute touch position must report ABS_{X,Y} for the
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location of the touch. BTN_TOUCH should be used to report when a touch is active
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on the trackpad. Where multi-finger support is available, BTN_TOOL_<name> should
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be used to report the number of touches active on the trackpad.
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Tablets:
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----------
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BTN_TOOL_<name> events must be reported when a stylus or other tool is active on
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the tablet. ABS_{X,Y} must be reported with the location of the tool. BTN_TOUCH
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should be used to report when the tool is in contact with the tablet.
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BTN_{STYLUS,STYLUS2} should be used to report buttons on the tool itself. Any
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button may be used for buttons on the tablet except BTN_{MOUSE,LEFT}.
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BTN_{0,1,2,etc} are good generic codes for unlabeled buttons. Do not use
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meaningful buttons, like BTN_FORWARD, unless the button is labeled for that
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purpose on the device.
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