[Qgis-user] variables in postgis filters

[Sandro Santilli]

On Mon, Apr 04, 2016 at 10:25:35AM +1000, Nyall Dawson wrote:
> On 3 April 2016 at 01:27, Sandro Santilli <strk at keybit.net> wrote:

> > Being able to use canvas-dependent variables (extent and scale,
> > mostly) would help a lot with speeding up some kind of query
> > layers (TopoGeometry ones, for example).
> 
> Be aware that this would not be possible in a vector layer filter.
> Expressions at the vector layer level will only have access to global,
> project and layer variables. Think about it this way - if the project
> has multiple maps in various composers, which extent and scale would
> be used when fetching features from the layer for something which
> isn't specific to an individual map (Eg the attribute table).

How's the current support for "simplify at the provider side" done ?
It seems to have the exact same constraints of the ones you're
mentioning (yes, I've seen the recent thread about $area parameter
changing value across zoom levels, which seems to be one of those
side-effects).

--strk;