We are trying to use Qt 4.8.5 for some Linux-based embedded medical devices in our company. I need to plot measured data and update them very often (20-30fps). The system is ARM based, 400Mhz, have no GPU and no FPU. I subclassed QWidget and overridden the paintEvent(). I have WA_OpaquePaintEvent and WA_StaticContents set. For testing, my paint event is empty, and I call the update() function of the widget form a timer set to 50ms. My problem is that the empty update is eating up 30% of the CPU. The amount varies with the area of the widget, so I think QT may redraw something in the background. I read many posts but I cannot find the solution for my problem. If I comment out the update call, the CPU usage drops to ~1% (even if I generate a sine in the timer for testing the widget, which should be much more complex than an empty function call). My widget is rectangular, is not transparent and I want to handle the full drawing procedure from the paint event.

Is it possible to reduce this overhead, and handle the whole painting process by my own?

Thank You
Robert Csordas