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    <p>We need to know more, what does not happen? Does the window appear at all? Are the lines not drawn? In the meantime try out this sample code if you want :) Edit: updated to show updating.</p> <pre><code>#include ... class QUpdatingPathItem : public QGraphicsPathItem { void advance(int phase) { if (phase == 0) return; int x = abs(rand()) % 100; int y = abs(rand()) % 100; QPainterPath p = path(); p.lineTo(x, y); setPath(p); } }; int main(int argc, char *argv[]) { QApplication a(argc, argv); QGraphicsScene s; QGraphicsView v(&amp;s); QUpdatingPathItem item; item.setPen(QPen(QColor("red"))); s.addItem(&amp;item); v.show(); QTimer *timer = new QTimer(&amp;s); timer-&gt;connect(timer, SIGNAL(timeout()), &amp;s, SLOT(advance())); timer-&gt;start(1000); return a.exec(); } </code></pre> <p>You should get something like this:</p> <p><img src="https://imgur.com/6kC2Y.png" alt="meh..."></p> <p>The path in any <code>QGraphicsPathItem</code> can of course be updated later. You might want to keep the original painter path somewhere to avoid performance hit caused by all the path copying (I'm not sure if QPainterPath is implicitly shared...)</p> <pre><code>QPainterPath p = gPath.path(); p.lineTo(0, 42); gPath.setPath(p); </code></pre> <h1>Animation</h1> <p>It seems that you're trying to do some sort of animation/on-the-fly updating. There is entire framework for this in Qt. In the simplest form you can subclass QGraphicsPathItem, reimplement its advance() slot to automatically fetch next point from motion. The only thing left to do then would be calling s.advance() with the required frequency.</p> <p><a href="http://doc.trolltech.com/4.5/qgraphicsscene.html#advance" rel="nofollow noreferrer">http://doc.trolltech.com/4.5/qgraphicsscene.html#advance</a> </p>
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    1. COThe window appears. Lines are not drawn. If I add them before call to scene.addPath(), they appears, but (as in your example) GraphicsView doens't update, if I change path (new lines doesn't appear).
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    2. COOh, I think I figured out the bug... The combo board_path_item = new QGraphicsPathItem(); scene.addPath(nature_path_item->path(), nature_pen); Doen't track changes. Thanks to your sample
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    3. COBut the task about clipping is still open...
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