- Qt 6.9
- Qt GUI
- Paint System
- Qt 6.9.3 Reference Documentation

Qt GUI Overview ◦ Paint Devices and Backends

# 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
QBrush | Defines the fill pattern of shapes drawn by QPainter
QColor | Colors based on RGB, HSV or CMYK values
QColorSpace | Color space abstraction
QColorTransform | Transformation between color spaces
QColormap | Maps device independent QColors to device dependent pixel values
QConicalGradient | Used in combination with QBrush to specify a conical gradient brush
QFont | Specifies a query for a font used for drawing text
QFontMetrics | Font metrics information
QFontMetricsF | Font metrics information
QGenericMatrix | Template class that represents a NxM transformation matrix with N columns and M rows
QGradient | Used in combination with QBrush to specify gradient fills
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
QLine | Two-dimensional vector using integer precision
QLineF | Two-dimensional vector using floating point precision
QLinearGradient | Used in combination with QBrush to specify a linear gradient brush
QMargins | Defines the four margins of a rectangle
QMarginsF | Defines the four margins of a rectangle
QPageRanges | Represents a collection of page ranges
QPagedPaintDevice | Represents a paint device 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
QPainterStateGuard | RAII convenience class for balanced QPainter::save() and QPainter::restore() calls
QPdfOutputIntent
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
QPixmap | Off-screen image representation that can be used as a paint device
QPoint | Defines a point in the plane using integer precision
QPointF | Defines a point in the plane using floating point precision
QPolygon | List of points using integer precision
QPolygonF | List of points using floating point precision
QRadialGradient | Used in combination with QBrush to specify a radial gradient brush
QRect | Defines a rectangle in the plane using integer precision
QRectF | Defines a finite rectangle in the plane using floating point precision
QRegion | Specifies a clip region for a painter
QRgba64 | Struct contains a 64-bit RGB color
QRgbaFloat | Struct contains a four part RGBA floating-point color
QSize | Defines the size of a two-dimensional object using integer point precision
QSizeF | Defines the size of a two-dimensional object using floating point precision
QStylePainter | Convenience class for drawing QStyle elements inside a widget
QSupportedWritingSystems | Used when registering fonts with the internal Qt fontdatabase
QTransform | Specifies 2D transformations of a coordinate system
QVector2D | Represents a vector or vertex in 2D space