Having `Box<dyn Widget>` implement the `Widget` trait is a crutch that
makes a bunch of things more complicated.
It leads to double-boxing in cases when the `dyn Widget` is itself a
`Box<dyn Widget>` (especially since the arena's current implementation
boxes all widgets by default), makes it harder to reason about
downcasting, and ends up producing a lot of code to handle the edge
cases.
On the xilem side, `Box<dyn Widget>` is slightly redundant with
`DynWidget`.
This PR still leaves a lot of boxing. On the long term, we'd like for
the arena to pack arbitrary widgets efficiently using some kind of
archetype scheme, but in the meantime, boxing will have to do.
Changes in this PR:
- New `FromDynWidget` trait that maybe-downcasts widgets to a
maybe-sized `Widget` type.
- Most places that accept `Widget` now accept `Widget + ?Sized`.
- Remove `impl Widget for Box<dyn Widget>`.
- Replace all instances of `WidgetPod<Box<dyn Widget>>` with
`WidgetPod<dyn Widget>`.
- Replace all instances of `xilem::Pod<Box<dyn Widget>>` with
`xilem::Pod<dyn Widget>`.
- Rename WidgetPod to WidgetBox in xilem_core example to avoid
ambiguity.
This is part of the "Pass Specification" RFC:
https://github.com/linebender/rfcs/pull/7
Rename WidgetCtx to MutateCtx.
Add a mutate pass.
Add a `mutate_later` context method to trigger that pass.
Refactor `edit_root_widget` to use a version of that pass.
Add a separate constructor for the synthetic WidgetState created in
RenderRoot.
---------
Co-authored-by: Philipp Mildenberger <philipp@mildenberger.me>
Co-authored-by: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Takes ideas from #235 (in particular the masonry side).
This implements support for explicit spacers in the `Flex` view and flex
parameters for views (see examples `flex` and `mason` for more details).
It also adds a way (`AnyFlexChild`) to dynamically switch between
spacers and widgets (with optional flex parameters).
`masonry::widget::Flex::layout` is also updated to be in sync with
current druid.
---------
Co-authored-by: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Olivier FAURE