QRegion

QRegion is a class in the Qt framework that represents a geometric region used for clipping, hit testing, and region operations. A QRegion can describe a single rectangle or a complex area composed of multiple rectangles. It can be constructed from a QRect, from a QBitmap, or by combining other regions. Internally it stores the region as a set of rectangles, but it can also utilize the operating system's native region representation to speed up operations on the target platform.

The class supports boolean operations such as union, intersection, subtraction, and symmetric difference with other regions. It provides methods to translate a region, query its bounding rectangle, and test containment of points. The operators |, &, -, and ^ are commonly used to combine regions, with corresponding member functions like united(), intersected(), subtracted(), and symmetricDifference().

In practice, QRegion is widely used for clipping in painting code. A region can be supplied to QPainter via setClipRegion to constrain drawing to complex shapes, or used for hit-testing in custom widgets. It is also useful for optimizing redraw regions in windowing code.

QRegion relies on native platform representations where available to improve performance, and remains a core part of Qt’s geometry utilities across its supported versions. See also QPainter, QBitmap, and related region operations.