[QGIS-Developer] processing temporal animation export in parallel

[Tim Sutton]

Hi

If you want to try some python, you could make a variant of this (1) to
export in parallel (thanks Nyall for most of the key rendering logic
there). Note teh complete plugin shown there is not functional yet, and you
would need to adapt it to temporal based rendering.


(1)
https://github.com/timlinux/QGISAnimationWorkbench/blob/main/animation_workbench.py#L211


Regards

Tim

On Tue, Feb 22, 2022 at 7:02 PM Richard Duivenvoorde <rdmailings at duif.net>
wrote:

> Hi Dolf,
>
> I hope others can confirm/falsify, but I do not think you can do parallel
> painting, as QGIS has just one MapCanvas, and for what I know QGIS first
> paints the map on that MapCanvas (given your layers, styles, temporal
> filter etc etc), and then 'just' creates an image from that?
> But maybe I'm wrong in this.
>
> Slow (as in Hours?) that would be a huge map or very complex styling, OR a
> lot of timesteps/frames?
> Also: how does QGIS itself render your map if you step through it using
> the temporal controller? Can you maybe set (spatial/temporal) indexes on
> your data?
>
> Regards,
>
> Richard Duivenvoorde
>
> On 2/22/22 10:06, Dolf Andringa wrote:
> > Hi all,
> >
> > The temporal animation functionality of QGIS is great. I am currently
> playing with it, probably a little out-of-scope, to make a travel animation
> on a map. Everything works great, except that at high frame rates and high
> resolution, exporting the animation to images is very slow (hours).
> >
> > I dug into the code a little, and in bool
> QgsTemporalUtils::exportAnimation
> > I see:
> >
> > while ( currentFrame < totalFrames )
> > {
> >      ...
> >      QPainter p( &img );
> >      QgsMapRendererCustomPainterJob job( ms, &p );
> >      job.start();
> >      job.waitForFinished();
> >      ...
> > }
> >
> > Which renders each image in sequence. I am new to QGIS development
> specifically, so forgive my ignorance, but could the jobs system be used to
> render them in parallel instead? Could this potentially speed up the
> process significantly? If this is feasible, I'd gladly make a feature
> request, and it also looks like a nice PR I could contribute myself
> potentially? I'd love to hear your thoughts.
> > Cheers,
> >
> > Dolf.
> >
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Tim Sutton
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Tim is a member of the QGIS Project Steering Committee
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