How does Qt paint the painter path

Asked Feb 11 '15 at 09:42

Active Dec 15 '17 at 14:15

Viewed 495 times

The hierarchy of classes in Qt (5.4 version) is awesome. I tried to find solution in Qt's sources, but my end point of investigation is the QPaintEngine. This class has member:

virtual void QPaintEngine::drawPath(const QPainterPath &)

This member is simple gap (do nothing). The only derived class is QRasterPaintEngine (implementation for linux), which does not override the drawPath method. Does somebody have ideas?

I want to find way to paint path. I guess that painter path (simplified version (without self intersections)) are converted to polygons. Given polygons are triangulated. I want to see implementation of triangulation.

edited Dec 15 '17 at 14:15

ymoreau

3,402
1
22
60

asked Feb 11 '15 at 09:42

Alex Aparin

4,393
5
25
51

I think it just forwards to the native drawer – ratchet freak Feb 11 '15 at 09:44
Why? for example, qt allows to paint with usage Opengl. ( i guess it uses the above algorithm of painting ) – Alex Aparin Feb 11 '15 at 09:46
There is [`QPaintEngineEx`](https://qt.gitorious.org/qt/qtbase/source/9754e5a03e4444a18ec7ca1525d196326ff4e038:src/gui/painting/qpaintengineex.cpp) which derives from `QPaintEngine`. Might be more, you need to dig deeper. – thuga Feb 11 '15 at 10:25
Thank you, i will try. I guess this class is private implementation. Documentation shows the only class QRasterPaintEngine (or i forgot something). – Alex Aparin Feb 11 '15 at 10:52
Polygon triangulation is a typical technique for 3D rendering, but Qt is much more 2D oriented. I would not assume it uses triangles. – MSalters Feb 11 '15 at 10:55
I do not agree with you. 2D triangulation is common practise for rendering – Alex Aparin Feb 11 '15 at 11:16
but not for lines, there pixel based algorithms are better/faster – ratchet freak Feb 11 '15 at 12:26
Yes, of course)) but I meant rendering of complex shapes)) – Alex Aparin Feb 11 '15 at 12:37
even then, Most of the QPainterPath primitives have efficient pixel based algorithms – ratchet freak Feb 11 '15 at 12:40
I am interesting filling of path offsetting)) – Alex Aparin Feb 11 '15 at 13:07
Have you tried stepping into the source code with the debugger? That would be the best way to see what happens IMO. – sashoalm Feb 11 '15 at 15:09
I tried)) i had some problems - i cannot step into QT source code from my debugger – Alex Aparin Feb 11 '15 at 15:14

How does Qt paint the painter path

0 Answers0