How to use QPainter

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Introduction

QPainter provides standard functions to draw points, lines, ellipses, arcs, Bézier curves, and other primitives. More complex painting operations include support for polygons and vector paths, allowing detailed drawings to be prepared in advance and drawn using a single function call. Text can also be painted directly with a painter or incorporated in a path for later use.

Qt's painting system also provides a number of features to improve overall rendering quality, including alpha blending, Porter-Duff composition modes, anti-aliasing, and linear, radial and conical gradient fills.

First steps

IMPORTANT! QPainter can paint on QWidget only in paintEvent(QPaintEvent*).

Sample code:

void paintEvent(QPaintEvent*)
{
 QPainter painter(this);
 QLineF line(10.0, 80.0, 90.0, 20.0);
 painter.drawLine(line);
}

This snippet will draw black line on the widget. Now we know how to create QPainter object and draw on widgets. But this isn't only supported drawing context. It is also possible to draw on QPrinter, QPicture, QPixmap, QBitmap, QImage, QGLPixelBuffer.

QPen and QBrush

Pens and brushes are fundamental tools for graphic programming with Qt. Without them, you can't do anything. Further information is available at QPen and QBrush.