How to calculate the total duration of a state during an interval

For each consecutive point for which the expression evaluates as true, the state duration ist incremented by the duration between points.
When a point evaluates as false, the state duration is reset.
My problem is that i want to get the total duration of a state without reseting it for each batch.
Any simple solutions for that ?

The issue names no files, tests, or entry points. Start by reading Kapacitor's state-duration and batch-processing documentation or implementation to determine whether duration can persist across batches; done should be a documented, supported way to calculate the total duration without resetting it.

Written by the indexing model from the issue text.