It seems to me that inverting values on a chart prevents the values from being stacked.
Four WAN interfaces on one firewall, plotted on one chart. The positive DCIs seem to be stacked correctly but negatively is not. Alternatively, I might be misunderstanding how stacked graphs should work.
Yes, this is currently a known limitation / issue.
See #859 on bug tracker.
Only non-inverted sources are stacked according to the ticket.
Can you please confirm that is how it behaves (seems so from your screenshots).
I have posted the same graph twice, one with stack enabled, one without and I think it demonstrates two distinct issues.
1) Negative is not stacked.
2) A DCI that I have specified to be inverted but in this dataset happens to be 0 for the entire series [WAN link is down so throughput is 0] is rendered above the positive values rather than at x=0. See the thin green line on the top of nxwanstack.png. Is this worth opening a separate bug for?
Yes, please open a separate ticket for that (issue 2.) :)
How to make a gradient fill line graphs? As performance - Area.