Stan wrote:
> I guess it's the concept of changing things "yourself" that I'm
> trying to get my mind around. Can I conclude that init_sizes()
> needs to be called (only) after calling resize (or one of its cousins)
> on a group member, from outside the execution context of the group's
> resize method?
Right.
> For instance, suppose I've derived MyGroup from Fl_Group,
> and implemented its resize() method.
Hmm, if you're redefining the resize behavior
of the group, then it's your option to either:
a) completely redefine the resize behavior,
and never call Fl_Group::resize(),
in which case calling init_sizes() becomes moot.
- or -
b) 'slightly modify' the resize behavior,
while still depending on Fl_Group::resize()'s
algorithm to manage the child positions.
In the case of (a), calling init_sizes() becomes
totally moot; init_sizes() takes a "snapshot" of the
children's current widget positions. This snapshot
is used by Fl_Group::resize()'s algorithm to calculate
the new widget positions when the group is scaled up
and down.
If you never call Fl_Group::resize(), then the snapshot
that init_sizes() grabs will never be used.
In the case of (b), you probably would want to call
init_sizes() after moving things around, so that if
you later call Fl_Group::resize(), its scaling algorithm
will take into account the new position tweaks you made.
This is how I visualize it:
init_sizes() and Fl_Group's default resize behavior
work together; init_sizes() "snapshots" the widget layout,
'caching' all the children's new positions in an internal array
so that later, when the group is resized, Fl_Group's scaling
algorithm can use those cached values to scale the widget's
positions up and down, without accumulating precision loss.
Consider the extreme case where the Fl_Group is scaled
all the way down to a single pixel, such that all the
children have their x/y/w/h values scaled to a single value.
When the group is scaled back up, if not for the snapshot
of the original widget positions, there'd be no way
to recover the original widget layout.
> Now, for MyGroup* my_group, my_group->child(0)->size(..)
> should be followed by my_group->init_sizes(),
..only if you want the new position to be updated
in the snapshot so that Fl_Group's automatic resize
algorithm can take it into account.
You may or might not want that, depends on what
you're doing.
> but my_group->resize(..) should not be,
Yes, I don't think you'd want to follow a call to
the group's resize() with init_sizes(), otherwise you'd
be defeating the purpose of the single layout snapshot,
and promoting the accumulation of precision loss.
The above described 'extreme case' becomes relevant here;
when the group is scaled down to a single pixel, if you
then call init_sizes(), you've now lost the widget's original
layout completely. When the group is scaled back up, there's
no way to recover the original layout; the widgets would all
remain crunched together.
HTH.
_______________________________________________
fltk mailing list
[email protected]
http://lists.easysw.com/mailman/listinfo/fltk
