Multiple fields in custom visual

Hi,

I have gone through many tutorials, and they all have on thing in common: they only work with one single input field for the visual.

What I want to achieve is some kind of a targeted waterfall diagram, similar to the "Line with stacked column chart": One input field containing the planned (target) value for scaling the y axis and one input field containing the actual value for building the stair steps. Nice to have would also be a category to build a legend (i.e. color separation inside a step).

It seems there is no way of creating a visual that accepts more than one data field, and table or matrix values don't seem to work anyway.

Can anyone make a tutorial that shows how to work with multiple input fields?

Thank you.