[Interest] Slow animations/video playback with Qt Quick 2 on some hardware platforms

Benjamin Federau benjamin.federau at basyskom.com
Tue Feb 11 16:06:08 CET 2014


In a larger QML application I face some performance issue(?) with Qt Quick 2 and animations/video playback.
I broke this down to a simple QML test application that shows the issue.

I see this on different platforms and Qt 5 versions. 

The OS is Ubuntu 12.04.  with X and matchbox or OpenBox as window managers.
The hardware and Qt 5 versions are:

* Intel Atom N270 (single core, 1GB RAM), Qt 5.2.0, x86
* Freescale i.MX6q (quad core, 1GB RAM), Qt 5.1.1, armhf
* Intel Atom CedarTrail (dual core, 2GB RAM), Qt 5.2.0, x86

All Qt versions are built against OpenGL ES 2.0.

The test app contains one Repeater with 500 Rectangles. This should simulate the amount of elements in my larger QML app. On top of these Rectangles is a black Rectangle and a Canvas Path Animation or a QtMultimedia video player.

The behaviour is the following:

Per default the Rectangles in the Repeater are visible and this leads to a slow animation or video playback. I added a button to trigger the visibility of the Rectangles and as soon as they are set to invisible the speed of the animation or video is ok. Over these repeated Rectangles there is a black Rectangle so all the other Rectangle are not visible for the user right now (but the visible flag of the repeated Rectangles is true). 

What I do not understand is why the animation or video gets slow when the visible flag of the Rectangles in the Repeater is true and on the other hand the speed of the animations is ok when they are set to invisible. 
Could it be that on every animation or video repaint/redraw the Rectangles in the Repeater will be repainted too? 
There isn't a high CPU load at this time so I don't know where the performance drop comes from. Could this be a OpenGL ES 2.0 driver/lib issue?

Btw. I see this behaviour on the N270 and on the Freecsale i.MX6, but not on the CedarTrail hardware.

You can find my QML test application here:  http://pastebin.com/ZAfEvXbq

Any hints are very welcome.

Benjamin Federau

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