Offers the same functionality as the Random points inside polygons
algorithm, and in addition it includes (possible to opt-out) the attributes
from the containing polygon and the ability to specify a seed for the random
number generator.
Could replace the Python algorithm Random points inside polygons, but
this C++ implementation only supports "Points count" ("number of points
for each feature") directly, while "Points density" is supported by allowing the
point count to be data defined (using the polygon area to calculate the
number of points).
Instead, only store references to the algorithm id string, and
use this to retrieve algorithms when the actions are triggered.
This avoids errors caused by the algorithm instances being
removed, e.g. due to plugin removal or reload of providers
(e.g. by opening options dialog).
Fixes#19070
Ensure that dialogs are always correctly deleted when appropriate.
Also, if an algorithm is running in a background task and hits
an error, we automatically re-show the algorithm dialog and the
associated log for debugging.
Fixes#16858
The dialogs are parented to the main window, which means sip
transfers the ownership to the main window - and they are
never deleted as a result. This results in various error
messages caused by the widgets hanging around forever
and listening out for various signals they are connected to.
This somewhat changes the meaning of outputs from processing 2.x.
In 2.x processing outputs were used both as a method of specifying
inputs to algorithms (file paths to destination layers created
by the algorithm) AND pure outputs (such as statistics calculated
by the algorithm).
This is now split. The old input-type-outputs (destination layers)
are now input parameters (since the parameter value IS an input to the
algorithm). To differentiate them from parameters indicating pure
input layers a new "isDestination()" method was added to
QgsProcessingParameterDefinition.
Output definitions are now purely indications of values CREATED
by the algorithms. Suitable candidates are the existing calculated
stats and actual file path/URI of any layers created by the algorithm.
Moving forward we should ensure all algorithms output as much
useful information as possible - e.g. number of features processed,
number of skipped features, count null geometries encountered, etc...
