Mouser cursor move around when calling qopenglwidget::update.

[doodle]

platform: imx6q cortex-a9 arm based board
rootfs: fsl-yocto-L4.1.15_2.0.0-ga; fsl-img-qt5
qt version: 5.6.2

The code is very simple, a mainwindow containing a custom widget inherits qopenglwidget, and call the qopenglwidget::update 30 times per second, the strange thing is the cursor will move around randomly, if I don't call the update then everything works right. Qopenglwidget::update will call the override paintgl and I have commented it so it will do nothing. But if I run the code on my pc there is no such issue. So I think the problem might come from the rootfs on the arm board writed by qt.
I have came up with one solution, write a render function calling paintgl, but there will be some work with qopenglcontext and qopenglframebufferobject , how to write

====update====

Or, is there any low level example about how to use qwidget and opengl instead of using qopenglwidget?