[Interest] Qt5 performance on imx6 with full hd

[Jacob Kroon]

Hi,

I'm experimenting with a Qt application running on the Wandboards,
at full hd resolution, 1920x1080x32. I have a static background image, and
some small animated Qml-elements on the screen. I'm not entirely satisfied
with the resulting performance, and I think it is because of the background
image being constantly fully redrawn in each frame. I've experimented with

* setClearBeforeRendering(false), since the background will be drawn
anyway, there is no point in clearing before rendering. This seemed to have
little impact on performance though.

* Letting Qt5 render into /dev/fb1 overlay on the imx6, with no background
image, but instead write the background image manually into /dev/fb0. In
this way, the IPU will blend the result onto the display. This seemed to be
even worse than letting the GPU render the background.

Can the scenegraph be smart enough in such a way that it will only "clear"
dirty rectangles with a user supplied background image ? Or are there any
other tricks I am not aware of ?

Regards Jacob
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