Редактирование: Qt:Документация 4.3.2/graphicsview

{{Qt4.3.2_header}}

=The Graphics View Framework=
<div id="graphics-view"></div>
<div id="graphicsview"></div>
<div id="graphics"></div>
<div id="canvas"></div>
Графическая подсистема Qt представляет собой площадку для размещения  неограниченного числа двумерных графических элементов и взаимодействия с ними, а также виджет для их визуализации с возможностью масштабирования и вращения.

<div id="event-propagation-architecture"></div>
<div id="double-precision"></div>
Подсистема содержит механизм передачи событий, который предоставляет элементам сцены возможность взаимодействовать друг с другом с использованием тонкой подгонки на основе double-арифметики. Элементы сцены могут обрабатывать нажания клавиш, нажатие, перемещение и отпуск мыши, а также двойные щелчки. Кроме того, они могут отслеживать траекторию движения мыши.

Графическая подсистема использует BSP-дерево (дерево двоичного  разбиения области), что значительно ускоряет обработку элементов  сцены, и --- как следствие --- позволяет оборазить в реальном времени даже большую, содержащую миллионы элементов, сцену.

Графическая подсистема введена в Qt 4.2 и заменила своего  предшественника,  класс [[Qt:Документация 4.3.2/porting4#qcanvas | QCanvas]]. О том, как  выполнить перенос кода,  использующего [[Qt:Документация 4.3.2/porting4#qcanvas | QCanvas]], в  подсистему двумерной графики,  см. раздел [[Qt:Документация 4.3.2/graphicsview-porting | «Porting to  Graphics View»]].

Topics:
*[[#the-graphics-view-architecture | Архитектура графической подсистемы]]
**[[#the-scene | Сцена]]
**[[#the-view | Изображение]]
**[[#the-item | Элемент]]
*[[#the-graphics-view-coordinate-system | Система координат]]
**[[#item-coordinates | Координаты элемента]]
**[[#scene-coordinates | Координаты сцены]]
**[[#view-coordinates | Координаты изображения]]
**[[#coordinate-mapping | Отображения координат]]
*[[#key-features | Key Features]]
**[[#zooming-and-rotating | Масштабирование и повороты]]
**[[#printing | Печать]]
**[[#drag-and-drop | Перетаскивание мышью]]
**[[#cursors-and-tooltips | Курсоры и всплывающие подсказки]]
**[[#animation | Анимация]]
**[[#opengl-rendering | Отрисовка при помощи OpenGL]]
**[[#item-groups | Группы элементов]]

<div id="the-graphics-view-architecture"></div>
===Архитектура графической подсистемы===
Графическая подсистема основана на элементно-ориентированном подходе  и структуре «модель–изображение», во многом  похожей на вспомогательные классы   [[Qt:Документация 4.3.2/qtablewidget | QTableWidget]], [[Qt:Документация 4.3.2/qtreewidget | QTreeWidget]]  b [[Qt:Документация 4.3.2/qlistwidget | QListWidget]], используемые в  демонстрационном  примере [[Qt:Документация 4.3.2/demos-interview | InterView]].  Несколько  изображений могут отображать одну и ту же сцену, которая, в свою  очередь, может содержать элементы самой различной геометрической  формы.

<div id="the-scene"></div>
====Сцена====
Класс [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] реализует  ''сцену'' графической подсистемы. Сцена выполняет следующие  функции:

*быстрый интерфейс для управления множеством элементов;
*передачу событий каждому элементу;
*управление состояниями элемента, такими как статус выбранности и  клавиатурный фокус;
*отрисовка без трансформаций --- главным образом, для печати.

The scene serves as a container for [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] objects. Items are added to the scene by calling [[Qt:Документация 4.3.2/qgraphicsscene#addItem | QGraphicsScene::addItem]](), and then retrieved by calling one of the many item discovery functions. [[Qt:Документация 4.3.2/qgraphicsscene#items | QGraphicsScene::items]]() and its overloads return all items contained by or intersecting with a point, a rectangle, a polygon or a general vector path. [[Qt:Документация 4.3.2/qgraphicsscene#itemAt | QGraphicsScene::itemAt]]() returns the topmost item at a particular point. All item discovery functions return the items in descending stacking order (i.e., the first returned item is topmost, and the last item is bottom-most).

<source lang="cpp-qt"> QGraphicsScene scene;
 QGraphicsRectItem *rect = scene.addRect(QRectF(0, 0, 100, 100));

 QGraphicsItem *item = scene.itemAt(50, 50);
 // item == rect</source> 
[[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]]'s event propagation architecture schedules scene events for delivery to items, and also manages propagation between items. If the scene receives a mouse press event at a certain position, the scene passes the event on to whichever item is at that position.

[[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] also manages certain item states, such as item selection and focus. You can select items on the scene by calling [[Qt:Документация 4.3.2/qgraphicsscene#setSelectionArea | QGraphicsScene::setSelectionArea]](), passing an arbitrary shape. This functionality is also used as a basis for rubberband selection in [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]]. To get the list of all currently selected items, call [[Qt:Документация 4.3.2/qgraphicsscene#selectedItems | QGraphicsScene::selectedItems]](). Another state handled by [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] is whether or not an item has keyboard input focus. You can set focus on an item by calling [[Qt:Документация 4.3.2/qgraphicsscene#setFocusItem | QGraphicsScene::setFocusItem]]() or [[Qt:Документация 4.3.2/qgraphicsitem#setFocus | QGraphicsItem::setFocus]](), or get the current focus item by calling [[Qt:Документация 4.3.2/qgraphicsscene#focusItem | QGraphicsScene::focusItem]]().

Finally, [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] allows you to render parts of the scene into a paint device through the [[Qt:Документация 4.3.2/qgraphicsscene#render | QGraphicsScene::render]]() function. You can read more about this in the Printing section later in this document.

<div id="the-view"></div>

====The View====

[[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] provides the view widget, which visualizes the contents of a scene. You can attach several views to the same scene, to provide several viewports into the same data set. The view widget is a scroll area, and provides scroll bars for navigating through large scenes. To enable OpenGL support, you can set a [[Qt:Документация 4.3.2/qglwidget | QGLWidget]] as the viewport by calling [[Qt:Документация 4.3.2/qabstractscrollarea#setViewport | QGraphicsView::setViewport]]().

<source lang="cpp-qt"> QGraphicsScene scene;
 myPopulateScene(&scene);

 QGraphicsView view(&scene);
 view.show();</source> 
The view receives input events from the keyboard and mouse, and translates these to scene events (converting the coordinates used to scene coordinates where appropriate), before sending the events to the visualized scene.

Using its transformation matrix, [[Qt:Документация 4.3.2/qgraphicsview#matrix | QGraphicsView::matrix]](), the view can ''transform'' the scene's coordinate system. This allows advanced navigation features such as zooming and rotation. For convenience, [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] also provides functions for translating between view and scene coordinates: [[Qt:Документация 4.3.2/qgraphicsview#mapToScene | QGraphicsView::mapToScene]]() and [[Qt:Документация 4.3.2/qgraphicsview#mapFromScene | QGraphicsView::mapFromScene]]().

[[Image:graphicsview-view.png|center]]
<div id="the-item"></div>

====The Item====

[[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] is the base class for graphical items in a scene. Graphics View provides several standard items for typical shapes, such as rectangles ([[Qt:Документация 4.3.2/qgraphicsrectitem | QGraphicsRectItem]]), ellipses ([[Qt:Документация 4.3.2/qgraphicsellipseitem | QGraphicsEllipseItem]]) and text items ([[Qt:Документация 4.3.2/qgraphicstextitem | QGraphicsTextItem]]), but the most powerful [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] features are available when you write a custom item. Among other things, [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] supports the following features:


*Mouse press, move, release and double click events, as well as mouse hover events, wheel events, and context menu events.
*Keyboard input focus, and key events
*Drag and drop
*Grouping, both through parent-child relationships, and with [[Qt:Документация 4.3.2/qgraphicsitemgroup | QGraphicsItemGroup]]
*Collision detection



Items live in a local coordinate system, and like [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]], it also provides many functions for mapping coordinates between the item and the scene, and from item to item. Also, like [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]], it can transform its coordinate system using a matrix: [[Qt:Документация 4.3.2/qgraphicsitem-obsolete#matrix | QGraphicsItem::matrix]](). This is useful for rotating and scaling individual items.


Items can contain other items (children). Parent items' transformations are inherited by all its children. Regardless of an item's accumulated transformation, though, all its functions (e.g., [[Qt:Документация 4.3.2/qgraphicsitem#contains | QGraphicsItem::contains]](), [[Qt:Документация 4.3.2/qgraphicsitem#boundingRect | QGraphicsItem::boundingRect]](), QGraphicsItem::collidesWith()) still operate in local coordinates.


[[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] supports collision detection through the [[Qt:Документация 4.3.2/qgraphicsitem#shape | QGraphicsItem::shape]]() function, and QGraphicsItem::collidesWith(), which are both virtual functions. By returning your item's shape as a local coordinate [[Qt:Документация 4.3.2/qpainterpath | QPainterPath]] from [[Qt:Документация 4.3.2/qgraphicsitem#shape | QGraphicsItem::shape]](), [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] will handle all collision detection for you. If you want to provide your own collision detection, however, you can reimplement QGraphicsItem::collidesWith().

[[Image:graphicsview-items.png|center]]
<div id="the-graphics-view-coordinate-system"></div>

===The Graphics View Coordinate System===

Graphics View is based on the Cartesian coordinate system; items' position and geometry on the scene are represented by sets of two numbers: the x-coordinate, and the y-coordinate. When observing a scene using an untransformed view, one unit on the scene is represented by one pixel on the screen.

There are three effective coordinate systems in play in Graphics View: Item coordinates, scene coordinates, and view coordinates. To simplify your implementation, Graphics View provides convenience functions that allow you to map between the three coordinate systems.

When rendering, Graphics View's scene coordinates correspond to [[Qt:Документация 4.3.2/qpainter | QPainter]]'s ''logical'' coordinates, and view coordinates are the same as ''device'' coordinates. In [[Qt:Документация 4.3.2/coordsys | The Coordinate System]], you can read about the relationship between logical coordinates and device coordinates.

[[Image:graphicsview-parentchild.png|center]]
<div id="item-coordinates"></div>

====Item Coordinates====

Items live in their own local coordinate system. Their coordinates are usually centered around its center point (0, 0), and this is also the center for all transformations. Geometric primitives in the item coordinate system are often referred to as item points, item lines, or item rectangles.

When creating a custom item, item coordinates are all you need to worry about; [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] and [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] will perform all transformations for you. This makes it very easy to implement custom items. For example, if you receive a mouse press or a drag enter event, the event position is given in item coordinates. The [[Qt:Документация 4.3.2/qgraphicsitem#contains | QGraphicsItem::contains]]() virtual function, which returns true if a certain point is inside your item, and false otherwise, takes a point argument in item coordinates. Similarly, an item's bounding rect and shape are in item coordinates.

At item's ''position'' is the coordinate of the item's center point in its parent's coordinate system; sometimes referred to as ''parent'' coordinates. The scene is in this sense regarded as all parent-less items' "parent". Top level items' position are in scene coordinates.

Child coordinates are relative to the parent's coordinates. If the child is untransformed, the difference between a child coordinate and a parent coordinate is the same as the distance between the items in parent coordinates. For example: If an untransformed child item is positioned precisely in its parent's center point, then the two items' coordinate systems will be identical. If the child's position is (10, 0), however, the child's (0, 10) point will correspond to its parent's (10, 10) point.

Because items' position and transformation are relative to the parent, child items' coordinates are unaffected by the parent's transformation, although the parent's transformation implicitly transforms the child. In the above example, even if the parent is rotated and scaled, the child's (0, 10) point will still correspond to the parent's (10, 10) point. Relative to the scene, however, the child will follow the parent's transformation and position. If the parent is scaled (2x, 2x), the child's position will be at scene coordinate (20, 0), and its (10, 0) point will correspond to the point (40, 0) on the scene.

With [[Qt:Документация 4.3.2/qgraphicsitem#pos | QGraphicsItem::pos]]() being one of the few exceptions, [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]]'s functions operate in item coordinates, regardless of the item, or any of its parents' transformation. For example, an item's bounding rect (i.e. [[Qt:Документация 4.3.2/qgraphicsitem#boundingRect | QGraphicsItem::boundingRect]]()) is always given in item coordinates.

<div id="scene-coordinates"></div>

====Scene Coordinates====

The scene represents the base coordinate system for all its items. The scene coordinate system describes the position of each top-level item, and also forms the basis for all scene events delivered to the scene from the view. Each item on the scene has a scene position and bounding rectangle ([[Qt:Документация 4.3.2/qgraphicsitem#scenePos | QGraphicsItem::scenePos]](), [[Qt:Документация 4.3.2/qgraphicsitem#sceneBoundingRect | QGraphicsItem::sceneBoundingRect]]()), in addition to its local item pos and bounding rectangle. The scene position describes the item's position in scene coordinates, and its scene bounding rect forms the basis for how [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]] determines what areas of the scene have changed. Changes in the scene are communicated through the [[Qt:Документация 4.3.2/qgraphicsscene#changed | QGraphicsScene::changed]]() signal, and the argument is a list of scene rectangles.

<div id="view-coordinates"></div>

====View Coordinates====

View coordinates are the coordinates of the widget. Each unit in view coordinates corresponds to one pixel. What's special about this coordinate system is that it is relative to the widget, or viewport, and unaffected by the observed scene. The top left corner of [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]]'s viewport is always (0, 0), and the bottom right corner is always (viewport width, viewport height). All mouse events and drag and drop events are originally received as view coordinates, and you need to map these coordinates to the scene in order to interact with items.

<div id="coordinate-mapping"></div>

====Coordinate Mapping====

Often when dealing with items in a scene, it can be useful to map coordinates and arbitrary shapes from the scene to an item, from item to item, or from the view to the scene. For example, when you click your mouse in [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]]'s viewport, you can ask the scene what item is under the cursor by calling [[Qt:Документация 4.3.2/qgraphicsview#mapToScene | QGraphicsView::mapToScene]](), followed by [[Qt:Документация 4.3.2/qgraphicsscene#itemAt | QGraphicsScene::itemAt]](). If you want to know where in the viewport an item is located, you can call [[Qt:Документация 4.3.2/qgraphicsitem#mapToScene | QGraphicsItem::mapToScene]]() on the item, then [[Qt:Документация 4.3.2/qgraphicsview#mapFromScene | QGraphicsView::mapFromScene]]() on the view. Finally, if you use want to find what items are inside a view ellipse, you can pass a [[Qt:Документация 4.3.2/qpainterpath | QPainterPath]] to mapToScene(), and then pass the mapped path to [[Qt:Документация 4.3.2/qgraphicsscene#items | QGraphicsScene::items]]().

You can map coordinates and shapes to and from and item's scene by calling [[Qt:Документация 4.3.2/qgraphicsitem#mapToScene | QGraphicsItem::mapToScene]]() and [[Qt:Документация 4.3.2/qgraphicsitem#mapFromScene | QGraphicsItem::mapFromScene]](). You can also map to an item's parent item by calling [[Qt:Документация 4.3.2/qgraphicsitem#mapToParent | QGraphicsItem::mapToParent]]() and [[Qt:Документация 4.3.2/qgraphicsitem#mapFromParent | QGraphicsItem::mapFromParent]](), or between items by calling [[Qt:Документация 4.3.2/qgraphicsitem#mapToItem | QGraphicsItem::mapToItem]]() and [[Qt:Документация 4.3.2/qgraphicsitem#mapFromItem | QGraphicsItem::mapFromItem]](). All mapping functions can map both points, rectangles, polygons and paths.

The same mapping functions are available in the view, for mapping to and from the scene. [[Qt:Документация 4.3.2/qgraphicsview#mapFromScene | QGraphicsView::mapFromScene]]() and [[Qt:Документация 4.3.2/qgraphicsview#mapToScene | QGraphicsView::mapToScene]](). To map from a view to an item, you first map to the scene, and then map from the scene to the item.

<div id="key-features"></div>

===Key Features===

<div id="zooming-and-rotating"></div>

====Zooming and rotating====

[[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] supports the same affine transformations as [[Qt:Документация 4.3.2/qpainter | QPainter]] does through [[Qt:Документация 4.3.2/qgraphicsview#setMatrix | QGraphicsView::setMatrix]](). By applying a transformation to the view, you can easily add support for common navigation features such as zooming and rotating.

Here is an example of how to implement zoom and rotate slots in a subclass of [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]]:

<source lang="cpp-qt"> class View : public QGraphicsView
 {
 Q_OBJECT
     ...
 public slots:
     void zoomIn() { scale(1.2, 1.2); }
     void zoomOut() { scale(1 / 1.2, 1 / 1.2); }
     void rotateLeft() { rotate(-10); }
     void rotateRight() { rotate(10); }
     ...
 };</source> 
The slots could be connected to [[Qt:Документация 4.3.2/qtoolbutton | QToolButtons]] with [[Qt:Документация 4.3.2/qabstractbutton#autoRepeat-prop | autoRepeat]] enabled.

[[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] keeps the center of the view aligned when you transform the view.

See also the [[Qt:Документация 4.3.2/graphicsview-elasticnodes | Elastic Nodes]] example for code that shows how to implement basic zooming features.

<div id="printing"></div>

====Printing====

Graphics View provides single-line printing through its rendering functions, [[Qt:Документация 4.3.2/qgraphicsscene#render | QGraphicsScene::render]]() and [[Qt:Документация 4.3.2/qgraphicsview#render | QGraphicsView::render]](). The functions provide the same API: You can have the scene or the view render all or parts of their contents into any paint device by passing a [[Qt:Документация 4.3.2/qpainter | QPainter]] to either of the rendering functions. This example shows how to print the whole scene into a full page, using [[Qt:Документация 4.3.2/qprinter | QPrinter]].

<source lang="cpp-qt"> QGraphicsScene scene;
 scene.addRect(QRectF(0, 0, 100, 200), Qt::black, QBrush(Qt::green));

 QPrinter printer;
 if (QPrintDialog(&printer).exec() == QDialog::Accepted) {
     QPainter painter(&printer);
     painter.setRenderHint(QPainter::Antialiasing);
     scene->render(&painter);
 }</source> 
The difference between the scene and view rendering functions is that one operates in scene coordinates, and the other in view coordinates. [[Qt:Документация 4.3.2/qgraphicsscene#render | QGraphicsScene::render]]() is often preferred for printing whole segments of a scene untransformed, such as for plotting geometrical data, or for printing a text document. [[Qt:Документация 4.3.2/qgraphicsview#render | QGraphicsView::render]](), on the other hand, is suitable for taking screenshots; its default behavior is to render the exact contents of the viewport using the provided painter.

<source lang="cpp-qt"> QGraphicsScene scene;
 scene.addRect(QRectF(0, 0, 100, 200), Qt::black, QBrush(Qt::green));

 QPixmap pixmap;
 QPainter painter(&pixmap);
 painter.setRenderHint(QPainter::Antialiasing);
 scene->render(&painter);
 painter.end();

 pixmap.save("scene.png");</source> 
When the source and target areas' sizes do not match, the source contents are stretched to fit into the target area. By passing a [[Qt:Документация 4.3.2/qt#AspectRatioMode-enum | Qt::AspectRatioMode]] to the rendering function you are using, you can choose to maintain or ignore the aspect ratio of the scene when the contents are stretched.

<div id="drag-and-drop"></div>

====Drag and Drop====

Because [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] inherits [[Qt:Документация 4.3.2/qwidget | QWidget]] indirectly, it already provides the same drag and drop functionality that [[Qt:Документация 4.3.2/qwidget | QWidget]] provides. In addition, as a convenience, the Graphics View framework provides drag and drop support for the scene, and for each and every item. As the view receives a drag, it translates the drag and drop events into a [[Qt:Документация 4.3.2/qgraphicsscenedragdropevent | QGraphicsSceneDragDropEvent]], which is then forwarded to the scene. The scene takes over scheduling of this event, and sends it to the first item under the mouse cursor that accepts drops.

To start a drag from an item, create a [[Qt:Документация 4.3.2/qdrag | QDrag]] object, passing a pointer to the widget that starts the drag. Items can be observed by many views at the same time, but only one view can start the drag. Drags are in most cases started as a result of pressing or moving the mouse, so in mousePressEvent() or mouseMoveEvent(), you can get the originating widget pointer from the event. For example:

<source lang="cpp-qt"> void CustomItem::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
     QMimeData *data = new QMimeData;
     data->setColor(Qt::green);

     QDrag *drag = new QDrag(event->widget());
     drag->setMimeData(data);
     drag->start();
 }</source> 
To intercept drag and drop events for the scene, you reimplement [[Qt:Документация 4.3.2/qgraphicsscene#dragEnterEvent | QGraphicsScene::dragEnterEvent]]() and whichever event handlers your particular scene needs, in a [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] subclass. You can read more about drag and drop in Graphics View in the documentation for each of [[Qt:Документация 4.3.2/qgraphicsscene | QGraphicsScene]]'s event handlers.

Items can enable drag and drop support by calling [[Qt:Документация 4.3.2/qgraphicsitem#setAcceptDrops | QGraphicsItem::setAcceptDrops]](). To handle the incoming drag, reimplement [[Qt:Документация 4.3.2/qgraphicsitem#dragEnterEvent | QGraphicsItem::dragEnterEvent]](), [[Qt:Документация 4.3.2/qgraphicsitem#dragMoveEvent | QGraphicsItem::dragMoveEvent]](), [[Qt:Документация 4.3.2/qgraphicsitem#dragLeaveEvent | QGraphicsItem::dragLeaveEvent]](), and [[Qt:Документация 4.3.2/qgraphicsitem#dropEvent | QGraphicsItem::dropEvent]]().

See also the [[Qt:Документация 4.3.2/graphicsview-dragdroprobot | Drag and Drop Robot]] example for a demonstration of Graphics View's support for drag and drop operations.

<div id="cursors-and-tooltips"></div>

====Cursors and Tooltips====

Like [[Qt:Документация 4.3.2/qwidget | QWidget]], [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] also supports cursors ([[Qt:Документация 4.3.2/qgraphicsitem#setCursor | QGraphicsItem::setCursor]]()), and tooltips ([[Qt:Документация 4.3.2/qgraphicsitem#setToolTip | QGraphicsItem::setToolTip]]()). The cursors and tooltips are activated by [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] as the mouse cursor enters the item's area (detected by calling [[Qt:Документация 4.3.2/qgraphicsitem#contains | QGraphicsItem::contains]]()).

You can also set a default cursor directly on the view by calling [[Qt:Документация 4.3.2/qwidget#cursor-prop | QGraphicsView::setCursor]]().

See also the [[Qt:Документация 4.3.2/graphicsview-dragdroprobot | Drag and Drop Robot]] example for code that implements tooltips and cursor shape handling.

<div id="animation"></div>


====Animation====



  Графическая подсистема поддерживает анимацию на нескольких уровнях.
  You can easily assemble
  animation paths by associating a
  [[Qt:Документация 4.3.2/qgraphicsitemanimation | QGraphicsItemAnimation]]
  with your item. This allows timeline controlled animations that operate at
  a steady speed on all platforms (although the frame rate may vary depending
  on the platform's performance).
  [[Qt:Документация 4.3.2/qgraphicsitemanimation | QGraphicsItemAnimation]] allows you
  to create a path for an item's position, rotation, scale, shear and
  translation. The animation can be controlled by a
  [[Qt:Документация 4.3.2/qslider | QSlider]], or more commonly by
  [[Qt:Документация 4.3.2/qtimeline | QTimeLine]].



Another option is to create a custom item that inherits from [[Qt:Документация 4.3.2/qobject | QObject]] and [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]]. The item can the set up its own timers, and control animations with incremental steps in [[Qt:Документация 4.3.2/qobject#timerEvent | QObject::timerEvent]]().


A third option, which is mostly available for compatibility with [[Qt:Документация 4.3.2/porting4#qcanvas | QCanvas]] in Qt 3, is to ''advance'' the scene by calling [[Qt:Документация 4.3.2/qgraphicsscene#advance | QGraphicsScene::advance]](), which in turn calls [[Qt:Документация 4.3.2/qgraphicsitem#advance | QGraphicsItem::advance]]().


See also the [[Qt:Документация 4.3.2/graphicsview-dragdroprobot | Drag and Drop Robot]] example for an illustration of timeline-based animation techniques.

<div id="opengl-rendering"></div>

====OpenGL Rendering====

To enable OpenGL rendering, you simply set a new [[Qt:Документация 4.3.2/qglwidget | QGLWidget]] as the viewport of [[Qt:Документация 4.3.2/qgraphicsview | QGraphicsView]] by calling [[Qt:Документация 4.3.2/qabstractscrollarea#setViewport | QGraphicsView::setViewport]](). If you want OpenGL with antialiasing, you need OpenGL sample buffer support (see [[Qt:Документация 4.3.2/qglformat#sampleBuffers | QGLFormat::sampleBuffers]]()).

Example:

<source lang="cpp-qt"> QGraphicsView view(&scene);
 view.setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));</source> 
<div id="item-groups"></div>

====Item Groups====

By making an item a child of another, you can achieve the most essential feature of item grouping: the items will move together, and all transformations are propagated from parent to child. [[Qt:Документация 4.3.2/qgraphicsitem | QGraphicsItem]] can also handle all events for its children (see [[Qt:Документация 4.3.2/qgraphicsitem#setHandlesChildEvents | QGraphicsItem::setHandlesChildEvents]]()). This allows the parent item to act on behalf of its children, effectively treating all items as one.

In addition, [[Qt:Документация 4.3.2/qgraphicsitemgroup | QGraphicsItemGroup]] is a special item that combines child event handling with a useful interface for adding and removing items to and from a group. Adding an item to a [[Qt:Документация 4.3.2/qgraphicsitemgroup | QGraphicsItemGroup]] will keep the item's original position and transformation, whereas reparenting items in general will cause the child to reposition itself relative to its new parent. For convenience, you can create [[Qt:Документация 4.3.2/qgraphicsitemgroup | QGraphicsItemGroup]]s through the scene by calling [[Qt:Документация 4.3.2/qgraphicsscene#createItemGroup | QGraphicsScene::createItemGroup]]().

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