[QGIS-Developer] QGIS Server does not wait for remote SVG before rendering

[Nyall Dawson]

On Thu, 4 Jul 2019 at 23:08, René-Luc Dhont <rldhont at gmail.com> wrote:
>
> Hi devs,
>
> We encountered a strange issue with QGIS Server, a point layer with a
> simple style using a remote SVG.
>
> At the first GetMap request to this layer, QGIS Server rendered an image
> with missing symbol, the ?.
>
> At the second same GetMap Request, QGIS Server rendered an image with
> the remote SVG.
>
> And sometimes the remote SVG is not drawn and replaced by the  ?.
>
> Do you know if the renderer or the styler has a timer to wait for SVG ?
> Is It configurable ? or the context can be configured to wait for svg or
> an error ?

On the desktop it's done in a background thread, and the svg/raster
image caches fire a signal when the image is downloaded, triggering a
canvas refresh.

I'm not sure how you could address this with server. Maybe either:
1. (ugly) push some flag via the render context to force the renderer
to wait until a required svg is downloaded, and push this flag into
the svg/ raster image caches.
2. (out of the box) use https://github.com/qgis/QGIS/pull/30522 to
check in advance for any remote svg/images required in a project, and
prefetch all these on server startup BEFORE any rendering operation is
requested.

Nyall

>
> Regards,
> René-Luc
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