This is useful in some cases when working on a third party app/script
that only uses qgis_core. For example, I am working on qgis 3D project
and it is useful to be able to build QGIS core lib with custom Qt version
without having to spend too much time building what I do not need.
Also may be useful for QField to simplify the build of QGIS as a dependency
(no QScintilla, Qwt) and avoid bits of code in providers that would not
be used anyway.
No real source code changes, just configuration changes, mainly in providers.
Since expressions can be written which convert string values
to numeric, and vice versa, it doesn't make sense to restrict
creation of expression variables to only numeric inputs/outputs.
Instead create variables for all sensible inputs/outputs, since
users may want to use these in expressions which convert the
output to a number....
model execution
And use this function to determine in advance dependencies between
child algorithm parameters with expression based values and
which other child algorithms they depend upon.
Contains variables for model parameters, algorithm results for
other child algorithms which are not dependent on the
algorithm.
Allows removal of final pieces of ModelerAlgorithm code
The expression is evaluated just before the child algorithm is
executed, so can utilise results already calculated by other
children in the model through the use of expression context
functions
converted to QgsMapLayer objects with the ownership transferred
to the Python caller
This should make it super-easy for PyQGIS scripts to run processing
algorithms and immediately utilise the results, even if they
are memory layers. They call processing.run(), and get a dict of
results back which includes those layers ready for adding to the
current project or doing some other processing or operations
with, and if they don't transfer to ownership off then these
layers will be correctly garbaged collected by Python.
- remove temporary layers from context, delete them as soon as they
are finished with
- directly remove features via data provider, instead of selecting
and using edit buffer
- use native geometry methods for splitting to single features
and removing rings
Since it's safe to evaluate parameters in background threads
now, it's usually going to be ok to evaluate everything in
the processAlgorithm step.
This keeps the algorithm code as simple as possible, and will
make porting faster.
Note that the prepare/postProcess virtual methods still exist
and can be used when an algorithm MUST do setup/cleanup work
in the main thread.
