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
parameters in models
There's not a 1:1 correlation here - vector layers can be used
as inputs for sources, but sources cannot be used when a
full vector layer is required.
in processing toolbox
Helps aid in user discoverability of these algorithms, and
indicates to users that these should generally be the
preferred algorithm choices if duplicates exist from other
providers.
Also fix some UX issues with the panel in folder, such as
correctly remembering/restoring last used folders, defaulting
to home dir, don't clear value when canceling while browsing
require all input layers to be in the same CRS
The default behaviour is to assume that algorithms are well behaved
and can handle multi-CRS inputs, but algs have the option to
flag that they do not allow this and require the input CRS check.
Those algs should document that they require all inputs to have
matching CRS - processing 3.0 behaviour is to assume that algs
can handle this.
This adds a lot of flexibility to algorithms, as it makes output
sinks truely optional. For instance, the various "Extract by..."
algorithms could add a new optional sink for features which
'fail' the extraction criteria. This effectively allows these
algorithms to become feature 'routers', directing features onto
other parts of a model depending on whether they pass or fail
the test.
But in this situation we don't always care about these failing
features, and we don't want to force them to always be fetched
from the provider. By making the outputs truely optional,
the algorithm can tweak its logic to either fetch all features
and send them to the correct output, or only fetch
matching features from the provider in the first place (a big
speed boost).
