[Interest] Qt5 and eglfs, mouse input performance

[Jacob Kroon]

Hi,

I'm using Qt 5.1.1 on a Wandboard, built with OpenEmbeddedCore.

I'm seeing some strange things when using eglfs. If I dont set
QT_QPA_EGLFS_FORCEVSYNC, the mouse cursor reacts slowly to input. If I do
set QT_QPA_EGLFS_FORCEVSYNC=1, the mouse cursor response improves. So this
makes think that since the render thread now waits for vsync, the input
thread (if this is in fact how the work is split up..) now has time to poll
and handle the mouse input events. But this feels wrong, why should vsync
improve mouse reponse ?

Could anyone shed some light on this, and on what could be done to improve
the mouse input latency ?

Regards
Jacob
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