Inverting the tree turns all of the innermost stack frames into roots,
allowing them to accumulate their total sample counts with other
instances of the same frame being innermost. This is an essential
feature of any cool profiler, and now we have it. :^)
Instead of fetching these from JSON in every paint event, we now have a
separate "SampleData" vector that can be iterated.
This optimization was made possible by profiling ProfileViewer and then
analyzing the profile with ProfileViewer! :^)
You can now select the time range you want on the profile timeline.
The tree view will update automatically as you alter the range.
Unfortunately this causes the treeview to collapse all of its nodes.
It would be nice to solve this somehow in the future so that nodes
can stay open.
We begin with a simple treeview that shows a recorded profile.
To record and view a profile of a process with <PID>, simply do this:
$ profile <PID> on
... wait while PID does something interesting ...
$ profile <PID> off
$ cat /proc/profile > my-profile.prof
$ ProfileViewer my-profile.prof
