Hi Alessandro,
Thanks for the clarification that only the change of the OpenCL-device
needs a restart.
I tried both - acceleration in CPU and in GPU. I had the impression that
the acceleration in the CPU was slightly faster than in the CPU - but
not a lot faster. Maybe the GPU (Intel HD Graphics 4600) is not too
powerful. It is a ThinkPad notebook, not a desktop.
Greetings,
Andreas
On 2018-09-04 15:56, Alessandro Pasotti wrote:
> On Tue, Sep 4, 2018 at 2:21 PM Andreas Neumann <[email protected]> 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 [1]
Links:
------
[1] http://www.itopen.it
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