Note that for historical reasons the return value of the QRect::right() and QRect::bottom() functions deviate from the true bottom-right corner of the rectangle. The size (width and height) of a graphics primitive always correspond to its mathematical model, ignoring the width of the pen it is rendered with: QPainter also supports coordinate transformations (e.g. The logical and physical coordinate systems coincide by default. The mapping of the logical QPainter coordinates to the physical QPaintDevice coordinates are handled by QPainter's transformation matrix, viewport and 'window'. The default unit is one pixel on pixel-based devices and one point (1/72 of an inch) on printers. The x values increase to the right and the y values increase downwards. The default coordinate system of a paint device has its origin at the top-left corner. The QPaintDevice class is the base class of objects that can be painted: Its drawing capabilities are inherited by the QWidget, QImage, QPixmap, QPicture, and QOpenGLPaintDevice 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.

Together with the QPaintDevice and QPaintEngine classes, QPainter form the basis of Qt's painting system, Arthur. The coordinate system is controlled by the QPainter class.

Pixel grid on paint 3d