[QGIS-Developer] Vertex tool and cache invalidation

Martin Dobias wonder.sk at gmail.com
Wed Jan 23 14:02:28 PST 2019

Hi Hugo

(finally coming back to the earlier thread now)

On Mon, Jan 7, 2019 at 4:14 PM Hugo Mercier <hugo.mercier at oslandia.com> wrote:
> >
> > Are the issues you mentioned solved now by your PR
> > https://github.com/qgis/QGIS/pull/8724 or that was some other separate
> > issue?
> Unfortunately, this only solves a very small part of the problem. The
> overall issue of wrong cache synchronization is still there.

So what are the missing pieces of the puzzle? With data dependencies
defined in QGIS, I would expect that edit of a geometry in a layer
should trigger dataChanged() signal, so any piece of QGIS that caches
any data is notified that caches should be invalidated... isn't this
the case?

> > For your open question with "click first" behavior of vertex tool as
> > an option - I don't know. There has been some interest to address some
> > ergonomic issues in the new implementation, but I am not sure yet what
> > we would end up doing...
> I understand. I am still looking for a solution here.
> So instead of resurrecting the old vertex tool, would it be possible to
> make it work without index/cache ?
> I understand a cache has been introduced to allow for edition when lots
> of geometries are displayed on the current extent. But usually geometry
> editions are made at a high level of details, when a few geometry
> features are visible. Is a cache still needed if we somehow enforce the
> edition to be allowed only at small scale ?

I am not sure I understand what is the problem with cache... attribute
table has its cache, vector joins have caches, snapping has its cache,
so vertex tool has its cache too to make things faster. As long as we
can detect that the cache needs to be invalidated, there should not be
a problem. Could you please shed some light where is the source of the
troubles you are having?


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