QGraphicsView

QGraphicsView is a widget in the Qt toolkit that provides a window for viewing and interacting with a QGraphicsScene. It is part of the Graphics View Framework and serves as the visual component that renders the contents of a scene composed of QGraphicsItems. The view manages rendering, coordinate transformations, and user input, such as scrolling, selecting items, and performing drag operations.

QGraphicsView is typically used together with QGraphicsScene and QGraphicsItem. The scene owns the items and defines their logical structure and geometry, while the view presents a portion of the scene on screen and translates user actions into scene coordinates. The view supports features such as item selection, rubber-band selection, panning, and zooming, and can be customized by subclassing or by adjusting its rendering and interaction settings.

Key features include render hints (for anti-aliasing and smooth pixmap transforms), viewport update modes (Full, Minimal, or Smart updates for performance), and drag modes (NoDrag, ScrollHandDrag, or RubberBandDrag for selection). The view can leverage hardware acceleration by using an OpenGL-based viewport. It provides coordinate mapping between view and scene via mapToScene and mapFromScene, and convenience methods such as centerOn, fitInView, and ensureVisible. It also emits signals such as rubberBandChanged to track the selection rectangle.

In practice, a QGraphicsView is created, a QGraphicsScene is assigned with setScene, items are added to the scene, and the view is shown within a window or layout. The combination supports interactive editing, animation, and rendering of complex 2D scenes with consistent coordinate handling and efficient redraw strategies.