[Qgis-user] Canvas larger than viewport is rendered/drawn for vector layers, but not for raster layers

[Nyall Dawson]

On Thu, 16 Nov 2023, 2:40 am Thomas Larsen Wessel via QGIS-User, <
qgis-user at lists.osgeo.org> wrote:

> This screen capture demonstrates much better than words:
> https://imgur.com/5LSEsiY.
>
> Is there any way I can make it prerender the raster data as well?
>
> What I have already tried:
> * setting almost infinite cache size
> * all the relevant QGIS options/settings I could find
> * both local (gpkg) and remote WMS raster data
> * both Windows and Linux
> * QGIS 3.22 and 3.30
> * different CRS for layer
>
> Some of my tests did make the rendering speed up, but no matter what it
> always renders the raster data only for the canvas inside the view port,
> and does not render anything outside of the view port, whereas vector data
> is always rendered for an area that extends outside the view port.
>

There's a few parts to the logic defining whether a layer will be included
in the outside-visible-extent preview:

- WMS layers are **never** included. This is by design, to reduce
unnecessary server load
- when a layer is drawn the time taken to render it is recorded. If this
time exceeds a certain threshold, then the layer is marked as too expensive
to render in these optional out-of-canvas areas.

(You can check the new renderer profile option available in the F12
debugging tools panel in 3.34 for more detailed information about layer
render times)

Nyall



> Sincerely, Thomas
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