Paint Devices and Backends

Widget

The QWidget class is the base class of user interface elements in the Qt Widgets module. It receives mouse, keyboard and other events from the window system, and paints a representation of itself on the screen.

Image

The https:// class provides a hardware-independent image representation which is designed and optimized for I/O, and for direct pixel access and manipulation. https:// supports several image formats including monochrome, 8-bit, 32-bit and alpha-blended images.

One advantage of using https:// as a paint device is that it is possible to guarantee the pixel exactness of any drawing operation in a platform-independent way. Another benefit is that the painting can be performed in another thread than the current GUI thread.

Pixmap

The https:// class is an off-screen image representation which is designed and optimized for showing images on screen. Unlike https://, the pixel data in a pixmap is internal and is managed by the underlying window system, i.e. pixels can only be accessed through https:// functions or by converting the https:// to a https://.

To optimize drawing with https://, Qt provides the https:// class which can be used to store temporary pixmaps that are expensive to generate without using more storage space than the cache limit.

Qt also provides the https:// convenience class, inheriting https://. https:// guarantees monochrome (1-bit depth) pixmaps, and is mainly used for creating custom https:// and https:// objects, constructing https:// objects.

OpenGL Paint Device

As mentioned previously, Qt is offering classes that makes it easy to use OpenGL in Qt applications. For example, the QOpenGLPaintDevice enables the OpenGL API for rendering with https://.

Picture

The https:// class is a paint device that records and replays https:// commands. A picture serializes painter commands to an IO device in a platform-independent format. https:// is also resolution independent, i.e. a https:// can be displayed on different devices (for example svg, pdf, ps, printer and screen) looking the same.

Qt provides the https://() and https://() functions as well as streaming operators for loading and saving pictures.

Custom Backends

Support for a new backend can be implemented by deriving from the https:// class and reimplementing the virtual https://() function to tell https:// which paint engine should be used to draw on this particular device. To actually be able to draw on the device, this paint engine must be a custom paint engine created by deriving from the https:// class.