[QtComp] Vertical scrolling in Apps scope is jumpy

Isn't this bug actually a duplicate of
https://bugs.launchpad.net/bugs/1338430
which happens in the virgin image ?

I've enabled a setting for Qt's renderer which appears to improve animations like this scrolling (I enabled support for buffer queuing, which means Qt can assume that each frame is displayed a fixed time after the previous - something Mir pretty much guarantees - so it can use fixed animation steps, and has less calculations to perform).

I had this accidentally turned off. The old unity8 arch was enabling the same optimization with QSG_FIXED_ANIMATION_STEP=1), so we know it works.

It hasn't landed in the silo yet. I'll update this bug when it has

One thing to note here is that the scrolling is only slow in those scopes which load local icons. Like the apps scope and the Scopes scope. It is however smooth in Music and Videos scope which generally does not load icons, rather show thumbnails.

It's weird here. Not sure if it's something that happened after image 125, but, for example when switching scopes left-to-right, it goes from buttery-smooth to dropping probably over half of the frames with no obvious reason, then back to full fps again.

It feels like maybe I/O has a much higher impact...

I've optimised the scopes as much as I can for now. The primary change: marking off-screen scopes as "visible: false"

While switching scopes, you'll have 2 scopes being rendered simultaneously, which can cause a slowdown.

The scopes scope is very severe on GPU (lots of UbuntuShapes, uncached, causes over 1500GL calls, compared to apps scope at 700) and CPU (scrolling and generating geometry for those UbuntuShapes), so still exhibits performance issues.

Overall performance has improved though, please check it out!

Duplicate of bug 1336724 I think.