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Diffstat (limited to 'examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc')
| -rw-r--r-- | examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc | 56 |
1 files changed, 44 insertions, 12 deletions
diff --git a/examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc b/examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc index 1b0406037c..07acef6b4d 100644 --- a/examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc +++ b/examples/widgets/gestures/imagegestures/doc/src/imagegestures.qdoc @@ -83,18 +83,50 @@ QGesture subclass. To illustrate how a standard gesture can be interpreted by an application, we - show the implementation of the \c swipeTriggered() function, which handles the - gesture associated with a brushing or swiping motion on the user's display or + show the implementation of the \c pinchTriggered() function, which handles the + pinch gesture when the user moves two fingers around on the display or input device: - \snippet gestures/imagegestures/imagewidget.cpp swipe function - - The QSwipeGesture class provides specialized functions and defines a enum - to make it more convenient for developers to discover which direction, if - any, the user swiped the display. Here, we simply navigate to the previous - image in the collection if the user swiped upwards or to the left; otherwise - we navigate to the next image in the collection. - - The other gestures are also handled by special purpose functions, but use - the values of properties held by the QGesture object passed to them. + \snippet gestures/imagegestures/imagewidget.cpp pinch function + + The QPinchGesture class provides properties to interpret the changing + distance between the two touch points as a zoom factor, and the angle delta + as a rotation to be applied to the image. The center point between the + touch points could be used to drag the image, but in this example we use + the pan gesture for that purpose. + + The \c scaleFactor() is a relative value representing how much the zoom + should change from one event to the next, whereas \c totalScaleFactor() + provides the amount of zoom that has been expressed since the gesture + began. When the touch points are released and another gesture begins, + \c totalScaleFactor() will begin again at 1.0. In this case we store + \c totalScaleFactor() into the \c currentStepScaleFactor variable so that + it can be used in \c paintEvent() to scale the image. Alternatively it would + be possible to simply multiply the stored total scale factor by + \c scaleFactor() here in the pinch handler. + + In contrast, \c rotationAngle() represents the amount of rotation since the + pinch gesture began, while \c lastRotationAngle() provides the previous + value. So it is necessary to subtract in order to get an incremental delta. + When the user begins a new pinch gesture, \c rotationAngle() will start + from zero, and we want the image to begin to rotate from its current angle. + This is achieved by adding the delta to the stored \c rotationAngle (which + will be applied in \c paintEvent()). If we simply assigned + \c totalRotationAngle() to the stored \c rotationAngle, a new gesture would + cause the image to reset to a right-side-up orientation before beginning to + rotate again. But it would be possible to store the rotation angle since the + gesture began and add it to \c rotationAngle in \c paintEvent(), just as + we store the amount of zoom since the gesture began. + + The pan and swipe gestures in this example are also handled in separate + functions, and use the values of properties from the QGesture objects + passed to them. + + \snippet gestures/imagegestures/imagewidget.cpp paint method + + In \c paintEvent(), scaleFactor represents the zoom level before the pinch + gesture began, while currentStepScaleFactor represents the additional zoom + factor while a pinch gesture is in progress. But for rotation, only the + current rotationAngle is stored. The horizontal and vertical offsets + represent the distance that the image has been dragged by the pan gesture. */ |