animation.qdoc

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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
/*!
    \group animation
    \brief Provides an easy way for creating animated GUIs.
    \title Animation Framework
 
    This page lists classes belonging to \l{Qt Core}'s
    \l{The Animation Framework}{animation framework}.
 
*/
 
/*!
    \page animation-overview.html
    \title The Animation Framework
    \ingroup qt-gui-concepts
 
    \brief An overview of the Animation Framework
 
    \ingroup frameworks-technologies
 
    \keyword Animation
 
    The animation framework provides an easy way to animate your GUI elements.
    It enables you to animate a Qt property value of a widget or QObject.
    Most of the features offered by the framework are also available in
    \l{Qt Quick}, where it's possible to define animations in a declarative way.
 
    This overview explains the framework's architecture, with examples that
    demonstrate the common techniques used for animating QObject and
    GUI elements.
 
    \tableofcontents
 
    \section1 The Animation architecture
 
    The following diagram shows the most important classes provided by the
    framework:
 
    \image animations-architecture.png
 
    It includes the QAbstractAnimation class, which provides the
    necessary foundation for animations. This class defines the
    generic properties for all animations supported by the framework.
    For example, the ability to start, stop, and pause an animation. The
    class also receives the time change notifications.
 
    The framework further provides the QVariantAnimation and
    QAnimationGroup classes, which build on their base case, QAbstractAnimation.
    Next in the hierarchy is QPropertyAnimation, which is derived from
    QVariantAnmiation, and it lets you animate a Qt property of a widget or
    QObject. The class performs interpolation on the property value using an
    easing curve. With these in place, you just need a QObject class with a
    Qt property value that you can animate.
 
    \note It is required that the target object you are animating is a QObject
    or its subclass. This is necessary as the animation framework depends on the
    \l{Meta-Object System}{meta-object system} for all the information about the
    object it is animating.
 
    Complex animations can be constructed by building a tree structure
    of \l{QAbstractAnimation}s, where the tree is a QAnimationGroup that
    contains other animations. These animation groups can also contain
    subgroups representing different groups or animations, such as
    QParallelAnimationGroup and QSequentialAnimationGroup.
 
    Behind the scenes, all animations are controlled by a global
    timer, which sends \l{QAbstractAnimation::updateCurrentTime()}{updates} about
    all animations that are running.
 
    For detailed information of these individual classes' and their roles in
    the framework, refer to their documentation.
 
    \section1 Classes offered by the framework
 
    These classes provide the necessary infrastructure to create both simple and
    complex animations.
 
    \annotatedlist animation
 
    \section1 Animating Qt properties
 
    As the QPropertyAnimation class can interpolate on Qt properties, it is
    used often. In fact, its superclass---QVariantAnimation---provides an
    abstract implementation of \l{QVariantAnimation::}{updateCurrentValue()},
    which does not change any value unless you change it on the
    \l{QVariantAnimation::valueChanged()}{valueChanged signal}.
 
    The framework lets you animate the Qt properties of the existing
    classes in Qt. For example, the QWidget class---can be embedded in
    a QGraphicsView---has properties for its bounds, colors, and so on.
    The following example demonstrates how you can animate a QPushButton
    widget:
 
    \snippet code/src_corelib_animation_qpropertyanimation.cpp 0
 
    The example animates the \c pos Qt property of a QPushButton, to move
    it from the top--left corner of the screen to the end position (250, 250),
    in 10 seconds (10000 milliseconds).
 
    It uses the linear interpolation method to control the speed of
    animation between the start and end values. Try adding another value
    in--between the start and end value to see how they are interpolated.
    This time use the QPropertyAnimation::setKeyValueAt function to add
    these values:
 
    \code
        ...
        anim->setDuration(10000);
        anim->setKeyValueAt(0, QPoint(0, 0));
        anim->setKeyValueAt(0.8, QPoint(250, 250));
        anim->setKeyValueAt(1, QPoint(0, 0));
        ...
    \endcode
 
    In this example, the animation moves the button to
    (250, 250) in 8 seconds, and moves it back to its original position in
    the remaining 2 seconds. The button's movement is linear-interpolated
    between these points.
 
    You can also animate a QObject's value that is not declared as a Qt
    property, if the value has a setter method. In such cases, derive
    a new class from the class that contains the value, and add a Qt property
    for that value with the setter.
 
    \note Each Qt property requires a getter also, so you should provide a
    getter if that is not defined.
 
    \code
        class MyGraphicsRectItem : public QObject, public QGraphicsRectItem
        {
            Q_OBJECT
            Q_PROPERTY(QPointF pos READ pos WRITE setPos)
        };
    \endcode
 
    In this example, the \c MyGraphicsRectItem derives from
    QGraphicsRectItem and QObject, and defines the \c pos property. You can
    animate the item's \c pos even if QGraphicsRectItem does not provide
    the \c pos property.
 
    For a general introduction to the Qt property system, refer to
    \l{Qt's Property System}.
 
    \section1 Animations and the Graphics View Framework
 
    QPropertyAnimation can also be used to animate a QGraphicsItem, which does
    not inherit QObject. In such cases, you derive a class from the graphics
    item that you want to animate. This derived class should also inherit form
    QObject to enable using QPropertyAnimation on a QGraphicsItem. The
    following example shows how this is done:
 
    \code
        class Pixmap : public QObject, public QGraphicsPixmapItem
        {
            Q_OBJECT
            Q_PROPERTY(QPointF pos READ pos WRITE setPos)
            ...
        }
    \endcode
 
    \note You can also derive from QGraphicsWidget, which already is a
    QObject.
 
    As described in the previous section, you need to define
    properties that you want to animate. The derived class must inherit
    from QObject first as the meta-object system requires it.
 
    \section1 Easing curves
 
    A QPropertyAnimation performs linear interpolation
    between the start and end property values. In addition to adding more key
    values to the animation, you can also choose an easing curve to control the
    speed of interpolation between 0 and 1, without changing the
    path.
 
 
    \snippet code/src_corelib_animation_qpropertyanimation.cpp easing-curve
 
    In this example, the animation follows a curve that makes the
    \c button bounce like a ball. QEasingCurve offers a large collection of curves
    to choose from the QEasingCurve::Type enum. If you want
    to use another curve that is not available, implement one yourself and
    register it with QEasingCurve.
 
    \section1 Grouping animations
 
    An application often contains more than one animation. For
    example, it wants to move more than one graphics item
    simultaneously or move them in sequence after each other.
 
    The subclasses of QAnimationGroup---QSequentialAnimationGroup and
    QParallelAnimationGroup---are containers for other animations so
    that these animations can be animated either in sequence or
    parallel. The QAnimationGroup does not animate properties, but it
    gets notified of time changes periodically. This enables it to
    forward those time changes to the animation groups, which control when
    their animations are played.
 
    The two following examples demonstrate the use of both
    QSequentialAnimationGroup and QParallelAnimationGroup:
 
    \snippet code/src_corelib_animation_qpropertyanimation.cpp animation-group1
 
    A parallel group plays more than one animation at the same time.
    Its \l{QAbstractAnimation::}{start()} function starts all
    animations that are part of the group.
 
    \snippet code/src_corelib_animation_qpropertyanimation.cpp animation-group2
 
    As the name suggests, a QSequentialAnimationGroup plays
    its animations in sequence. It starts the next animation in
    the list after the previous finishes.
 
    A group is an animation itself, so you can add
    it to another group. This way, building an animation tree, which define
    when the animations are played in relation to each other.
 
    \section1 Object ownership
 
    A QPropertyAnimation should always have a parent that controls
    its lifespan. A typical application may include several animations that
    are grouped, where the animation group takes ownership of those animations.
    An independent QProperyAnimation must be explicitly assigned a parent to
    control its lifespan. In the following example, you can see that an
    independent QPropertyAnimation has the QApplication instance as its
    parent:
 
    \snippet code/src_corelib_animation_qpropertyanimation.cpp 0
 
    \note You can also control the animation's lifespan by choosing a
    \l{QAbstractAnimation::DeletionPolicy}{delete policy} while starting it.
*/