About the efficiency issus of Qt Graphics View Framework when there are vast items

Question

Recently, i develop a new visualization software using the QT Grapohics View Framework. In the software, we need show a lot of items, include the point and line, about ten thousand above. But, in the process of display , there are pool efficiency and often no response. When we want to zoom it or remove the position of scene, we must wait a span and it hard to bear. so, i want to know whether it is normal and how to improve the efficiency about the situation. Thanks .

Answer 1

I use Graphics View Framework to draw geographical map (large polygons with thousands of points). And it does it very well.

In Qt-4.6 there were delays when zooming and moving around. With antialiasing enabled dealys were so long that it was better to kill the application. So try to use the latest version of Qt.

Also if you use custom QGraphicsItem-s check this article: Qt: Improving QGraphicsView Performance.

Answer 2

I fixed my most serious problems with performance by:

• disabling the scrool bars (it helped a lot when zooming in/out and scrolling),
• ploting points with painter->drawPoints(pointCloud.constData(), pointCloud.size());
• disable indexing in case of moving items or enable indexing but avoiding some operations
• use cosmetic pen, 0 width or Qt::NoPen always that possible
• setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
• setViewportUpdateMode(FullViewportUpdate);