PinchHandler QML Type

Handler for pinch gestures. More...

Properties

Signals

Detailed Description

\inheritsMultiPointHandler \inqmlmodule QtQuick \ingroup qtquick-input-handlers

PinchHandler is a handler that interprets a multi-finger gesture to interactively rotate, zoom, and drag an Item. Like other Input Handlers, by default it is fully functional, and manipulates its target, which is the Item within which it is declared.


It has properties to restrict the range of dragging, rotation, and zoom.

If it is declared within one Item but is assigned a different target, it handles events within the bounds of the outer Item but manipulates the target Item instead:

 import QtQuick

 Item {
     width: 640
     height: 480

     Rectangle {
         id: map
         color: "aqua"
         width: 400
         height: 300
     }

     PinchHandler {
         target: map
     }
 }

A third way to use it is to set target to null and react to property changes in some other way:

 import QtQuick

 Window {
     width: 320; height: 240
     visible: true
     title: handler.persistentRotation.toFixed(1) + "° " +
            handler.persistentTranslation.x.toFixed(1) + ", " +
            handler.persistentTranslation.y.toFixed(1) + " " +
            (handler.persistentScale * 100).toFixed(1) + "%"

     PinchHandler {
         id: handler
         target: null
         persistentScale: 0.25
         onTranslationChanged: (delta) => {
             image.x -= delta.x
             image.y -= delta.y
         }
     }

     Image {
         id: image
         source: "images/album-cover.jpg"
         scale: handler.persistentScale
         x: -600; y: -450
     }
 }

Note: The pinch begins when the number of fingers pressed is between minimumPointCount and maximumPointCount, inclusive. Until then, PinchHandler tracks the positions of any pressed fingers, but if it's a disallowed number, it does not scale or rotate its target, and the active property remains false.

See also PinchArea, QPointerEvent::pointCount(), QNativeGestureEvent::fingerCount(), and Qt Quick Examples - Pointer Handlers.

Property Documentation

acceptedButtons : flags

\internal

This property is not used in PinchHandler.


[read-only] active : bool

\readonly

This property is true when all the constraints (epecially minimumPointCount and maximumPointCount) are satisfied and the target, if any, is being manipulated.


[read-only] activeRotation : real

\readonly

The rotation of the pinch gesture in degrees, with positive values clockwise. It is 0 when the gesture begins. If target is not null, this will be automatically added to its rotation. Otherwise, bindings can be used to do arbitrary things with this value.

See also QtQuick::PinchHandler::rotationAxis.activeValue.


[read-only] activeScale : real

\readonly

The scale factor while the pinch gesture is being performed. It is 1.0 when the gesture begins, increases as the touchpoints are spread apart, and decreases as the touchpoints are brought together. If target is not null, its scale will be automatically multiplied by this value. Otherwise, bindings can be used to do arbitrary things with this value.

See also QtQuick::PinchHandler::scaleAxis.activeValue.


[read-only] activeTranslation : QPointF

\readonly

The translation of the cluster of points while the pinch gesture is being performed. It is 0, 0 when the gesture begins, and increases as the eventPoint(s) are dragged downward and to the right. After the gesture ends, it stays the same; and when the next pinch gesture begins, it is reset to 0, 0 again.

Note: On some touchpads, such as on a macOS trackpad, native gestures do not generate any translation values, and this property stays at (0, 0).


[read-only] centroid : QtQuick::handlerPoint

\readonly

A point exactly in the middle of the currently-pressed touch points. The target will be rotated around this point.


maximumRotation : real

\deprecated[6.5] Use rotationAxis.maximum

The maximum acceptable rotation to be applied to the target.


maximumScale : real

\deprecated[6.5] Use scaleAxis.maximum

The maximum acceptable scale to be applied to the target.


minimumRotation : real

\deprecated[6.5] Use rotationAxis.minimum

The minimum acceptable rotation to be applied to the target.


minimumScale : real

\deprecated[6.5] Use scaleAxis.minimum

The minimum acceptable scale to be applied to the target.


persistentRotation : real

The rotation to be applied to the target if it is not null. Otherwise, bindings can be used to do arbitrary things with this value. While the pinch gesture is being performed, activeRotation is continuously added; after the gesture ends, it stays the same; and when the next pinch gesture begins, it begins to be modified by activeRotation again.

It's possible to set this property, as a way of synchronizing the basis rotation with a rotation that was set in some other way, for example by another handler. If you set this property directly, activeRotation does not change, and rotationChanged(0) is emitted.


persistentScale : real

The scale factor that will automatically be set on the target if it is not null. Otherwise, bindings can be used to do arbitrary things with this value. While the pinch gesture is being performed, it is continuously multiplied by activeScale; after the gesture ends, it stays the same; and when the next pinch gesture begins, it begins to be multiplied by activeScale again.

It's possible to set this property, as a way of synchronizing the basis scale with a scale that was set in some other way, for example by another handler. If you set this property directly, activeScale does not change, and scaleChanged(1) is emitted.


persistentTranslation : QPointF

The translation to be applied to the target if it is not null. Otherwise, bindings can be used to do arbitrary things with this value. While the pinch gesture is being performed, activeTranslation is continuously added to it; after the gesture ends, it stays the same.

It's possible to set this property, as a way of synchronizing the basis translation with a translation that was set in some other way, for example by another handler. If you set this property directly, activeTranslation does not change, and translationChanged({0, 0}) is emitted.

Note: On some touchpads, such as on a macOS trackpad, native gestures do not generate any translation values, and this property stays at (0, 0).


[read-only] rotation : QVector2D

\readonly \deprecated [6.5] Use activeRotation


rotationAxis group

[read-only] rotationAxis.activeValue : real

rotationAxis.enabled : bool

rotationAxis.maximum : real

rotationAxis.minimum : real

rotationAxis controls the constraints for setting the rotation of the target item according to the rotation of the group of touchpoints.

minimum is the minimum acceptable rotation. maximum is the maximum acceptable rotation. If enabled is true, rotation is allowed. activeValue is the same as QtQuick::PinchHandler::activeRotation.

The activeValueChanged signal is emitted when activeValue changes, to provide the increment by which it changed. This is intended for incrementally adjusting one property via multiple handlers.

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

Note: The snippet is contrived: PinchHandler already knows how to move, scale and rotate its parent item, but this code achieves different behavior in a less-declarative way, to illustrate how to use activeValueChanged in special cases.


[read-only] scale : QVector2D

\readonly \deprecated [6.5] Use persistentScale


scaleAxis group

[read-only] scaleAxis.activeValue : real

scaleAxis.enabled : bool

scaleAxis.maximum : real

scaleAxis.minimum : real

scaleAxis controls the constraints for setting the scale of the target item according to the distance between the touchpoints.

minimum is the minimum acceptable scale. maximum is the maximum acceptable scale. If enabled is true, scaling is allowed. activeValue is the same as QtQuick::PinchHandler::activeScale.

The activeValueChanged signal is emitted when activeValue changes, to provide the multiplier for the incremental change. This is intended for incrementally adjusting one property via multiple handlers.

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

Note: The snippet is contrived: PinchHandler already knows how to move, scale and rotate its parent item, but this code achieves different behavior in a less-declarative way, to illustrate how to use activeValueChanged in special cases.


[read-only] translation : QVector2D

\readonly \deprecated [6.5] Use activeTranslation


xAxis group

[read-only] xAxis.activeValue : real

xAxis.enabled : bool

xAxis.maximum : real

xAxis.minimum : real

xAxis controls the constraints for horizontal translation of the target item.

minimum is the minimum acceptable x coordinate of the translation. maximum is the maximum acceptable x coordinate of the translation. If enabled is true, horizontal dragging is allowed.

The activeValueChanged signal is emitted when activeValue changes, to provide the increment by which it changed. This is intended for incrementally adjusting one property via multiple handlers.

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

Note: The snippet is contrived: PinchHandler already knows how to move, scale and rotate its parent item, but this code achieves different behavior in a less-declarative way, to illustrate how to use activeValueChanged in special cases.


yAxis group

[read-only] yAxis.activeValue : real

yAxis.enabled : bool

yAxis.maximum : real

yAxis.minimum : real

yAxis controls the constraints for vertical translation of the target item.

minimum is the minimum acceptable y coordinate of the translation. maximum is the maximum acceptable y coordinate of the translation. If enabled is true, vertical dragging is allowed.

The activeValueChanged signal is emitted when activeValue changes, to provide the increment by which it changed. This is intended for incrementally adjusting one property via multiple handlers.

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"; antialiasing: true

     PinchHandler {
         id: handler
         target: null
         xAxis.onActiveValueChanged: (delta) => parent.radius -= delta
         yAxis.onActiveValueChanged: (delta) => parent.border.width += delta
         rotationAxis.onActiveValueChanged: (delta) => parent.rotation += delta // add
         scaleAxis.onActiveValueChanged: (delta) => parent.scale *= delta // multiply
     }

     WheelHandler {
         acceptedModifiers: Qt.NoModifier
         property: "rotation"
     }

     WheelHandler {
         acceptedModifiers: Qt.ControlModifier
         property: "scale"
     }
 }

Note: The snippet is contrived: PinchHandler already knows how to move, scale and rotate its parent item, but this code achieves different behavior in a less-declarative way, to illustrate how to use activeValueChanged in special cases.


Signal Documentation

rotationChanged(qreal delta)

The rotationChanged signal is emitted when activeRotation (and therefore persistentRotation) changes. The delta value gives the additive change in rotation. For example, if the user moves fingers to change the pinch distance so that activeRotation changes from 10 to 30 degrees, rotationChanged(20) will be emitted. You can use that to incrementally change the rotation of an item:

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"

     PinchHandler {
         id: handler
         target: null
         onRotationChanged: (delta) => parent.rotation += delta // add
         onScaleChanged: (delta) => parent.scale *= delta // multiply
     }
 }

Note: If you set the persistentRotation property directly, delta is 0.

Note: The corresponding handler is onRotationChanged.


scaleChanged(qreal delta)

The scaleChanged signal is emitted when activeScale (and therefore persistentScale) changes. The delta value gives the multiplicative change in scale. For example, if the user moves fingers to change the pinch distance so that activeScale changes from 2 to 2.5, scaleChanged(1.25) will be emitted. You can use that to incrementally change the scale of an item:

 import QtQuick

 Rectangle {
     width: 100; height: 100
     color: "lightsteelblue"

     PinchHandler {
         id: handler
         target: null
         onRotationChanged: (delta) => parent.rotation += delta // add
         onScaleChanged: (delta) => parent.scale *= delta // multiply
     }
 }

Note: If you set the persistentScale property directly, delta is 1.

Note: The corresponding handler is onScaleChanged.


translationChanged(QVector2D delta)

The translationChanged signal is emitted when activeTranslation (and therefore persistentTranslation) changes. The delta vector gives the change in translation. You can use that to incrementally change the position of an item:

 import QtQuick

 Window {
     width: 320; height: 240
     visible: true
     title: handler.persistentRotation.toFixed(1) + "° " +
            handler.persistentTranslation.x.toFixed(1) + ", " +
            handler.persistentTranslation.y.toFixed(1) + " " +
            (handler.persistentScale * 100).toFixed(1) + "%"

     PinchHandler {
         id: handler
         target: null
         persistentScale: 0.25
         onTranslationChanged: (delta) => {
             image.x -= delta.x
             image.y -= delta.y
         }
     }

     Image {
         id: image
         source: "images/album-cover.jpg"
         scale: handler.persistentScale
         x: -600; y: -450
     }
 }

Note: If you set the persistentTranslation property directly, delta is 0, 0.

Note: The corresponding handler is onTranslationChanged.