On Thu, 30 Aug 2018 15:47:34 -0700, Thiago Macieira wrote: > You can always just use QPainter on a QPixmap and paint that pixmap on > your QSGPaintedItem. It won't be particularly fast, but it will work and > do what you asked.
After some conversation with Denis: the use case of this thread is a oscilloscope - drawing a polyline with ~400 points, 10 times a second. It is possible to reduce the CPU load from 100% to 50% simply by using a QOpenGLWidget as plot canvas. With raster we probably never reached 10 frames, so all we know is that the improvement is more than by factor 2. The rest seems to be related to the grid lines, and updating the tick labels on the axis. Updating the tick labels 10 times a second does not make much sense as nobody can read this. So I would consider this being an issue, that has to be solved on application side. But the grid lines are responsible for ~30% of the remaining CPU load, so let's spend some thoughts on this: drawing them requires a sequence of QPainter::drawLine calls ( maybe 10-20 ) with a pen width of 1 in Qt::DotLine style. Changing the style to Qt::SolidLine makes this part of the CPU load disappear - actually the CPU load becomes the same as when not drawing the grid at all. So I would guess that the CPU cycles are related to calculating the dots for each line before forwarding it to some OpenGL call. > If you want faster, redesign with OpenGL in mind. What does that mean for a task like drawing a dotted line and why do you consider application code being more effective in finding a fast implementation for this ? I would expect the author/maintainer of the OpenGL paint engine being an expert in how to use OpenGL in the most effective way and the job of this module should be to keep away those details from the application code. And what would be the benefit of Qt/Quick for drawing dotted lines ? How would it be different/superior compared to writing pure OpenGL code - f.e in QOpenGLWidget::paintGL ? And why should Denis use Qt at all if he is supposed to break down basic primitives to pure OpenGL himself ? Uwe _______________________________________________ Development mailing list Development@qt-project.org http://lists.qt-project.org/mailman/listinfo/development
