Allows easy insertion of map layer IDs and relation IDs into
expressions. Numerous expression functions now utilise these,
so it makes sense to allow them to be easily inserted.
Fix#11680, #16879
Sponsored by Andreas Neumann
This commit adds an epoch() function to the expression engine which
returns the interval in milliseconds between the unix epoch and a
given date value.
This adds a new item_variables expression function when expressions
are used inside a composition context.
The function takes a single argument, the id for an item inside
the composition, and returns a map of variable name to value
for that item.
This allows you to do things like insert text in a label fetching
properties of another item in the composition, eg
Insert scale of map into a label:
map_get( item_variables( 'map'),'map_scale')
Insert x coordinate of map center into a label:
x(map_get( item_variables( 'map'),'map_extent_center'))
- support negative start value (e.g. substr('hello',-2) returns 'lo')
- support negative length value (e.g. substr('hello',3,-1) returns 'll')
- length parameter now optional, defaults to end of string
(e.g. substr('hello world',7) returns 'world')
The new function returns an array of strings captured by capturing
groups in a supplied regular expression. For e.g., the following
expression: regexp_matches('qgis=>rocks','(.*)=>(.*)')
will return the following array: 'qgis', 'rocks'.
* is_selected() returns if the current feature is selected
* num_selected() returns the number of selected features on the current layer
* is_selected(layer, feature) returns if the "feature" is selected. "feature"
must be on "layer".
* num_selected(layer) returns the number of selected features on "layer"
The Expression LIKE binary operator does not care about escape % and _ char.
No-one has already open an issue about it but in the OGC element PropertyIsLike the user can defined is own wild and single char. This mean that QGIS has to escape % and _ if they are not used as wild and single char.
Exposes simplification and smoothing algorithms to expression
engine, via:
- simplify(): applies Douglas-Peucker geometry simplification
- simplify_vw(): applies Visvalingam-Whyatt geometry simplification
- smooth(): smoothes a geometry
Carto tip: use smooth along with geometry generators to minimise
the typical "GIS" noded look of rendered geometries!
