options should be available for certain model outputs and script
algorithm outputs
We do this by swapping the test for non-file based output support
from checking only the algorithm's provider to instead checking
on a parameter-by-parameter basis.
This is done in order to support models. For models, depending
on what child algorithm a model output is based off, an individual
model may or may not have support for non-file based outputs. E.g
a model may generate outputs from a native qgis alg (supporting
these outputs) AND an output from a GDAL alg (with no support
for these outputs). In this case we need to enable or disable
the ui controls for non-file based outputs on an individual
output basis.
For scripts (for now) we blindly just say all outputs support
non-file based formats. This is going to be the case most of
the time, since scripts will usually be written using PyQGIS
API. For the exceptions (e.g. scripts which call other algs
like GDAL algs) we probably should add some way for the script
to indicate whether an individual output supports this, but
for now we just say they all do.
Fixes#17949
initAlgorithm() method
This allows 2 benefits:
- algorithms can be subclassed and have subclasses add additional
parameters/outputs to the algorithm. With the previous approach
of declaring parameters/outputs in the constructor, it's not
possible to call virtual methods to add additional parameters/
outputs (since you can't call virtual methods from a constructor).
- initAlgorithm takes a variant map argument, allowing the algorithm
to dynamically adjust its declared parameters and outputs according
to this configuration map. This potentially allows model algorithms which
can be configured to have variable numbers of parameters and
outputs at run time. E.g. a "router" algorithm which directs
features to one of any number of output sinks depending on some
user configured criteria.
and pure virtual createInstance
Allows us to add logic which always need applying within
create(), leaving createInstance() free to just return a
raw new instance of the class
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.
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.
