[QGIS-Developer] Some initial OpenCL feedback

[Alessandro Pasotti]

On Tue, Sep 4, 2018 at 2:21 PM Andreas Neumann <a.neumann at carto.net> wrote:

> Hi Alessandro,
>
> I just tested if the hardware acceleration (OpenCL) helps in the live
> hillshade renderer.
>


Hi Andreas,

thanks a lot for your feedback, I honestly am a little worried about the
possible problems on different platforms, graphic cards and driver
versions, I choose to stay on the safe side and there is a safeguard that
disables the OpenCL support at the first issue in the renderer.

The processing algs looks generally more stable (never got a single crash
myself).


The good news is that it works stable so far and substantially improves
> rendering time of the live hillshade renderer. My notebook on my workplace
> is rather slow. Without hardware acceleration it renders the hillshade in
> approx 8 seconds (large window on two screens). With OpenCL acceleration
> set to on, it renders in about 1 second or even less. I assume quite some
> time is also spent on reading the file. This with resampling on (average
> for zooming out and bilinear for zooming in beyond native resolution).
>

Yes some time is spent on reading the file and some time is spend on I/O
tranferring data to/from the graphic card, this means that the performance
gain is usually higher on larger images than on smaller images.

Hardware is an Intel HD Graphics 4600. The CPU is also listed as supported.
>

Can you also try the CPU? I'm curious about the performances.


> Visually, with or without HW accelation on, there still are some
> rectangular artefacts in both versions.
>

Yes: that does not change, the algorithm is pretty much the same in both
implementations.



> Tested on Windows.
>
> --------------
>
> One more thing: on my machine there is no restart of QGIS necessary for
> the changes (HW acceleration on of off) to be applied. This is contrary to
> the statement in the settings dialogue, which says, that a restart of QGIS
> is necessary.
>

The text can probably be improved: what needs a restart is if you change
the device, enabling and disabling OpenCL support does not require a
restart.


> ---------------
>
> Thanks a lot for your work!
>


Thank you for the feedback!




-- 
Alessandro Pasotti
w3:   www.itopen.it
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