Qt 5.7 | Qt GUI | Paint System

Qt 5.7.1 Reference Documentation

# Paint System

Qt's paint system enables painting on screen and print devices using the same API, and is primarily based on the QPainter, QPaintDevice, and QPaintEngine classes.

QPainter is used to perform drawing operations, QPaintDevice is an abstraction of a two-dimensional space that can be painted on using a QPainter, and QPaintEngine provides the interface that the painter uses to draw onto different types of devices. The QPaintEngine class is used internally by QPainter and QPaintDevice, and is hidden from application programmers unless they create their own device type.

The main benefit of this approach is that all painting follows the same painting pipeline making it easy to add support for new features and providing default implementations for unsupported ones.

## Topics

- Classes for Painting
- Paint Devices and Backends
- Drawing and Filling
- Coordinate System
- Reading and Writing Image Files

## Classes for Painting

These classes provide support for painting onto a paint device.

QBitmap | Monochrome (1-bit depth) pixmaps
QIcon | Scalable icons in different modes and states
QIconEngine | Abstract base class for QIcon renderers
QImage | Hardware-independent image representation that allows direct access to the pixel data, and can be used as a paint device
QImageReader | Format independent interface for reading images from files or other devices
QImageWriter | Format independent interface for writing images to files or other devices
QPixmap | Off-screen image representation that can be used as a paint device
QGenericMatrix | Template class that represents a NxM transformation matrix with N columns and M rows
QVector2D | Represents a vector or vertex in 2D space
QBrush | Defines the fill pattern of shapes drawn by QPainter
QConicalGradient | Used in combination with QBrush to specify a conical gradient brush
QGradient | Used in combination with QBrush to specify gradient fills
QLinearGradient | Used in combination with QBrush to specify a linear gradient brush
QRadialGradient | Used in combination with QBrush to specify a radial gradient brush
QColor | Colors based on RGB, HSV or CMYK values
QPagedPaintDevice | Represents a paintdevice that supports multiple pages
QPaintDevice | The base class of objects that can be painted on with QPainter
QPaintEngine | Abstract definition of how QPainter draws to a given device on a given platform
QPainter | Performs low-level painting on widgets and other paint devices
QPainterPath | Container for painting operations, enabling graphical shapes to be constructed and reused
QPainterPathStroker | Used to generate fillable outlines for a given painter path
QPdfWriter | Class to generate PDFs that can be used as a paint device
QPen | Defines how a QPainter should draw lines and outlines of shapes
QPolygon | Vector of points using integer precision
QPolygonF | Vector of points using floating point precision
QRegion | Specifies a clip region for a painter
QRgba64 | Struct contains a 64-bit RGB color
QTransform | Specifies 2D transformations of a coordinate system
QFont | Specifies a font used for drawing text
QFontMetrics | Font metrics information
QFontMetricsF | Font metrics information
QPlatformFontDatabase | Makes it possible to customize how fonts are discovered and how they are rendered
QSupportedWritingSystems | Used when registering fonts with the internal Qt fontdatabase