Allow rearranging columns by dragging, in the same
way the treeview does.
We add the "dnd" style class to the header while
it is dragged, and we move the header of the dragged
column to the end of its parents children, so that
it gets drawn on top.
Add helper functions that let us temporarily give
a different allocation to headers. These will be
used to implement interactive column reordering
in GtkColumnView.
The listview inside always thinks it gets its full size,
and updates its horizontal adjustment accordingly.
So keep our own adjustment, and update it when allocating.
Tweak the behavior slightly. We don't show
a scrollbar as long as we have at least
min-size available, but we still give the
entire size to the child, up to nat-size.
This matches how viewports handle scroll-minimum.
Since it's a type with sub-classes, we need to use GTypeInstance (at the
very least), otherwise we won't be able to address each sub-class as
such.
This is similar to how GskRenderNode and GdkEvent are handled, with the
added difficulty that GtkExpression is meant to be used in properties,
in order to be deserialised by GtkBuilder. This requires adding a
GParamSpec sub-class that we can match on from within GtkBuilder,
alongside some convenience API for storing a GtkExpression inside a
GValue.
We're printing out the file we're testing once we succeed, but it's hard
to know which file caused a failure. Let's add a g_test_message()
directive so we can look in our logs.
The print backends do some complicated dispose handling
where the implementations call gtk_print_backend_destroy().
Our tests (in particular, the templates test) trigger
situations where we use print backends after dispose,
and they can't handle the printers listmodel being
NULL at that time. So just remove the printers in
dispose, keep the empty liststore until finalize.
Scroll events do not have a position, so they shouldn't implement the
GdkEventClass.get_position() virtual function; nor they should have an x
and y fields that never get updated.
When we run the frameclock RUN_FLUSH_IDLE idle before the paint,
then gdk_frame_clock_flush_idle() sets
```
priv->phase = GDK_FRAME_CLOCK_PHASE_BEFORE_PAINT
```
at the end if there is a paint comming.
But, before doing the paint cycle it may handle other X events, and
during that time the phase is set to BEFORE_PAINT. This means that the
current check on whether we're inside a paint is wrong:
```
if (priv->phase != GDK_FRAME_CLOCK_PHASE_NONE &&
priv->phase != GDK_FRAME_CLOCK_PHASE_FLUSH_EVENTS)
return priv->smoothed_frame_time_base;
```
This caused us to sometimes use this smoothed_frame_time_base even
though we previously reported a later value during PHASE_NONE, thus
being non-monotonic.
We can't just additionally check for the BEGIN_PAINT phase though,
becasue if we are in the paint loop actually doing that phase we
should use the time base. Instead we check for `!(BEFORE_PAINT &&
in_paint_idle)`.
