[Qgis-user] Selecting displaced symbols

[Nyall Dawson]

On 30 May 2017 at 19:11, Neumann, Andreas <a.neumann at carto.net> wrote:
> Hi Martin,
>
> As far as I know, picking is totally independent of the rendering. So the
> "Info tool" doesn't know about the displacement renderer. I know it is not
> ideal, but it is a technical limitation and there are no known workarounds.

Well - there's this half finished commit I wrote but never merged:
https://github.com/nyalldawson/QGIS/commit/2405c9cc2c9d07bd0975d60ce36db5c5e8d8b612

I can't remember exactly why I didn't complete this. I think it was
written during feature freeze once and I never got around to verifying
that it didn't cause regressions in the rendering speed after freeze
was lifted. From memory it worked well for info tool and rotate point
symbol tool.

>From the commit message:

"Register rendered point features into a spatial index so that we can
later retrieve features by their actual rendered location.
(The rendered location may be different in numerous circumstances, eg
when using the displacement renderer, or when marker symbols
have an offset set)
This index could then be used to later retrieve the features for a
specific canvas coordinate, for use eg in identify tool, rotate point
symbols, etc."

Theoretically this could be cleaned up, finished off and tested, and
then later extended to apply to selections also.

Nyall