QTabletEvent Class

The QTabletEvent class contains parameters that describe a Tablet event. More...

Header: #include <QTabletEvent>
CMake: find_package(Qt6 COMPONENTS Gui REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Gui)
qmake: QT += gui
Inherits: QSinglePointEvent

Public Functions

QTabletEvent(QEvent::Type type, const QPointingDevice *dev, const QPointF &pos, const QPointF &globalPos, qreal pressure, float xTilt, float yTilt, float tangentialPressure, qreal rotation, float z, Qt::KeyboardModifiers keyState, Qt::MouseButton button, Qt::MouseButtons buttons)
qreal pressure() const
qreal rotation() const
qreal tangentialPressure() const
qreal xTilt() const
qreal yTilt() const
qreal z() const

Detailed Description

Tablet events are generated from tablet peripherals such as Wacom tablets and various other brands, and electromagnetic stylus devices included with some types of tablet computers. (It is not the same as QTouchEvent which a touchscreen generates, even when a passive stylus is used on a touchscreen.)

Tablet events are similar to mouse events; for example, the x(), y(), pos(), globalX(), globalY(), and globalPos() accessors provide the cursor position, and you can see which buttons() are pressed (pressing the stylus tip against the tablet surface is equivalent to a left mouse button). But tablet events also pass through some extra information that the tablet device driver provides; for example, you might want to do subpixel rendering with higher resolution coordinates (globalPosF()), adjust color brightness based on the pressure() of the tool against the tablet surface, use different brushes depending on the type of tool in use (deviceType()), modulate the brush shape in some way according to the X-axis and Y-axis tilt of the tool with respect to the tablet surface (xTilt() and yTilt()), and use a virtual eraser instead of a brush if the user switches to the other end of a double-ended stylus (pointerType()).

Every event contains an accept flag that indicates whether the receiver wants the event. You should call QTabletEvent::accept() if you handle the tablet event; otherwise it will be sent to the parent widget. The exception are TabletEnterProximity and TabletLeaveProximity events: these are only sent to QApplication and do not check whether or not they are accepted.

The QWidget::setEnabled() function can be used to enable or disable mouse, tablet and keyboard events for a widget.

The event handler QWidget::tabletEvent() receives TabletPress, TabletRelease and TabletMove events. Qt will first send a tablet event, then if it is not accepted by any widget, it will send a mouse event. This allows users of applications that are not designed for tablets to use a tablet like a mouse. However high-resolution drawing applications should handle the tablet events, because they can occur at a higher frequency, which is a benefit for smooth and accurate drawing. If the tablet events are rejected, the synthetic mouse events may be compressed for efficiency.

Note that pressing the stylus button while the stylus hovers over the tablet will generate a button press on some types of tablets, while on other types it will be necessary to press the stylus against the tablet surface in order to register the simultaneous stylus button press.

Notes for X11 Users

If the tablet is configured in xorg.conf to use the Wacom driver, there will be separate XInput "devices" for the stylus, eraser, and (optionally) cursor and touchpad. Qt recognizes these by their names. Otherwise, if the tablet is configured to use the evdev driver, there will be only one device and applications may not be able to distinguish the stylus from the eraser.

Notes for Windows Users

Tablet support currently requires the WACOM windows driver providing the DLL wintab32.dll to be installed. It is contained in older packages, for example pentablet_5.3.5-3.exe.

Member Function Documentation

QTabletEvent::QTabletEvent(QEvent::Type type, const QPointingDevice *dev, const QPointF &pos, const QPointF &globalPos, qreal pressure, float xTilt, float yTilt, float tangentialPressure, qreal rotation, float z, Qt::KeyboardModifiers keyState, Qt::MouseButton button, Qt::MouseButtons buttons)

Construct a tablet event of the given type.

The pos parameter indicates where the event occurred in the widget; globalPos is the corresponding position in absolute coordinates.

pressure gives the pressure exerted on the device dev.

xTilt and yTilt give the device's degree of tilt from the x and y axes respectively.

keyState specifies which keyboard modifiers are pressed (e.g., Ctrl).

The z parameter gives the Z coordinate of the device on the tablet; this is usually given by a wheel on a 4D mouse. If the device does not support a Z-axis (i.e. QPointingDevice::capabilities() does not include ZPosition), pass 0 here.

The tangentialPressure parameter gives the tangential pressure thumbwheel value from an airbrush. If the device does not support tangential pressure (i.e. QPointingDevice::capabilities() does not include TangentialPressure), pass 0 here.

rotation gives the device's rotation in degrees. 4D mice, the Wacom Art Pen, and the Apple Pencil support rotation. If the device does not support rotation (i.e. QPointingDevice::capabilities() does not include Rotation), pass 0 here.

The button that caused the event is given as a value from the Qt::MouseButton enum. If the event type is not TabletPress or TabletRelease, the appropriate button for this event is Qt::NoButton.

buttons is the state of all buttons at the time of the event.

See also pos(), globalPos(), device(), pressure(), xTilt(), yTilt(), uniqueId(), rotation(), tangentialPressure(), and z().

qreal QTabletEvent::pressure() const

Returns the pressure for the device. 0.0 indicates that the stylus is not on the tablet, 1.0 indicates the maximum amount of pressure for the stylus.

See also tangentialPressure().

qreal QTabletEvent::rotation() const

Returns the rotation of the current tool in degrees, where zero means the tip of the stylus is pointing towards the top of the tablet, a positive value means it's turned to the right, and a negative value means it's turned to the left. This can be given by a 4D Mouse or a rotation-capable stylus (such as the Wacom Art Pen or the Apple Pencil). If the device does not support rotation, this value is always 0.0.

qreal QTabletEvent::tangentialPressure() const

Returns the tangential pressure for the device. This is typically given by a finger wheel on an airbrush tool. The range is from -1.0 to 1.0. 0.0 indicates a neutral position. Current airbrushes can only move in the positive direction from the neutrual position. If the device does not support tangential pressure, this value is always 0.0.

Note: The value is stored as a single-precision float.

See also pressure().

qreal QTabletEvent::xTilt() const

Returns the angle between the device (a pen, for example) and the perpendicular in the direction of the x axis. Positive values are towards the tablet's physical right. The angle is in the range -60 to +60 degrees.

Note: The value is stored as a single-precision float.

See also yTilt().

qreal QTabletEvent::yTilt() const

Returns the angle between the device (a pen, for example) and the perpendicular in the direction of the y axis. Positive values are towards the bottom of the tablet. The angle is within the range -60 to +60 degrees.

Note: The value is stored as a single-precision float.

See also xTilt().

qreal QTabletEvent::z() const

Returns the z position of the device. Typically this is represented by a wheel on a 4D Mouse. If the device does not support a Z-axis, this value is always zero. This is not the same as pressure.

Note: The value is stored as a single-precision float.

See also pressure().

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