Instead of showing the progress reports for each child algorithm
individually, which leads to repeated 0->100% progress for every
step of a model, we proxy the progress reports and account for the
overall progress through a model as well. This means that
the progress accounts for both the progress within the current
model step AND the total number of steps left to execute.
This allows optional outputs (such as null geometry features detected
by the Remove Null Geometries algorithm) to be skipped by default
when desirable.
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
