* The basic idea here is to have a reasonable middleground between
ResizeToContents and Stretch. We want to show at *least* enough for
the contents, but the remaining space should be shared between the
columns according to some proportions.
* That way you don't end up with one huge column and several tiny ones
that are just big enough but no more, but all data is still visible.
* This prevents a feedback loop where the label resizes wider to make
room for the margins, then the margins get bigger to keep the image
centred/scaled properly, etc.
* This is used primarily for the buffer/mesh viewer to be able to pin
the index/element column to the left side, group columns together with
a noticeable separator, and other minor tweaks.
* Unfortunately due to tight private coupling and lack of virtual
functions in the QTableView and QHeaderView, a few unrelated functions
have to be re-implemented to point to our own header.
* This means that e.g. right clicking on an item in a list/tree widget
will make sure it's selected before trying to display a context menu
or anything.
There are a few places where the logical 'and' operator
was used to check if a given flag is enabled however
that is not the correct operator.
The binary 'and' operator should be used where
the enum acts as a flag.
* Annoyingly although Qt has an internal bool allowUserMoveOfSection0
which does exactly what we want allowing the tree column to be
movable, we can't enable it because it's private. So instead we have
to re-implement section moving ourselves.
* Minor tweak - also made RDTreeWidgets non-movable by default since
usually we don't want to allow it.
* There's a messy order-of-operations thing to deal with various
different themes, as well as a couple of minor problems, but at least
the highlight and selection bars draw fairly consistently and don't
leave an ugly gap over the branches.
* This still isn't perfect with some custom style stuff but it's next
to impossible to get working right. In theory we should manually
draw PE_PanelItemViewItem in the gap in drawRow() or so to make sure
we also draw any on-hover highlight over objects, but that doesn't
seem to work.
* We add our own custom item model to handle the cases we need. We can
also make a few assumptions and optimisations around things we can
safely assume like e.g. nodel columns won't really change after init.
* This lets us have full control over batching updates, which was the
main motivation, but it makes it easier to extend in future (e.g.
adding single per-item tags instead of the heavyweight Qt::UserRole
data elements).
baldurk