Calculation on custom view field created by plugin

Problem/Motivation

On custom views field, created with plugin, and rendered with render function, the calculation is not done on the custom value (the which one that comes from the plugin) but on the raw value from database.

Steps to reproduce

Just create a custom view plugin field, that has a value overrided by render function. Then create a view with views_aggregator and check.

Proposed resolution

Maybe I just have to change the views field plugin to alter the data itself, and not just the render function.