QPixmap

QPixmap is a class in the Qt framework used to handle images that are intended for on-screen display. It is part of the QtGui module and is commonly employed when rendering images in widgets or during custom painting with QPainter.

QPixmap represents a platform-dependent image representation that is optimized for fast display. On most platforms, it interacts with the window system to store native pixmap resources. The class uses implicit sharing (copy-on-write), so copying a QPixmap is inexpensive; modifications trigger a detach. QPixmap is generally not thread-safe; GUI work should be done in the main thread, while image processing can be done with QImage in worker threads.

Creating and loading: You can construct an empty pixmap with a given size, or load from a file or resource using load() or from a file path. QPixmap can be created from a QImage via QPixmap::fromImage, and can be converted to a QImage with toImage(). It can be drawn with QPainter, saved to disk with save(), and optimized using QPixmapCache for repeated usage.

Usage patterns: To render, create a QPainter, then drawPixmap or drawImage; you can scale or transform pixmaps with QPainter. For caching, QPixmapCache::insert or a per-widget cache improves performance for reusable images.

Relation to QImage vs QPixmap: QImage is device-independent and intended for image manipulation or format conversion; QPixmap is optimized for display and platform-specific rendering. If an image needs processing, convert to QImage; when displaying, use QPixmap.