Emacs redraws sometimes partially while scrolling in X.org on VMWare or VirtualBox. I tested only on Windows host OS.
Following error messages are output in /var/log/Xorg.0.log when this problem occurs.
I confirmed it happens even in one CPU configuration.
There are several workarounds I tried.
Emacs 25 supports Cairo by configure --with-cario. This workaround does not hide the problem completely. This makes it less frequently.
This makes Emacs somewhat slow.
Using compiz solves the problem. Unfortunately, compiz makes painting slow.
Xephyr also solve the problem. On the other hand, Xnest doesn’t help.
This triggers repainting whole scrren every seconds.
Press Alt-Tab and Alt-Tab to switch window to repaint.
The following API are called frequently during scroll.
I created a test program and filed a bug report.
This is the install steps for Fedora.
Create /etc/X11/xorg.conf with the following content.
Log out and log in (lightdm restarts X server).
See the log /var/log/Xorg.0.log to check your driver is loaded.