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// Copyright 2018 The Druid Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
use std::num::NonZeroU64;
use std::ops::{Deref, DerefMut};
use super::prelude::*;
use crate::debug_state::DebugState;
use crate::widget::Axis;
/// A unique identifier for a single [`Widget`].
///
/// `WidgetId`s are generated automatically for all widgets that participate
/// in layout. More specifically, each [`WidgetPod`] has a unique `WidgetId`.
///
/// These ids are used internally to route events, and can be used to communicate
/// between widgets, by submitting a command (as with [`EventCtx::submit_command`])
/// and passing a `WidgetId` as the [`Target`].
///
/// A widget can retrieve its id via methods on the various contexts, such as
/// [`LifeCycleCtx::widget_id`].
///
/// ## Explicit `WidgetId`s.
///
/// Sometimes, you may want to know a widget's id when constructing the widget.
/// You can give a widget an _explicit_ id by wrapping it in an [`IdentityWrapper`]
/// widget, or by using the [`WidgetExt::with_id`] convenience method.
///
/// If you set a `WidgetId` directly, you are responsible for ensuring that it
/// is unique in time. That is: only one widget can exist with a given id at a
/// given time.
///
/// [`Target`]: crate::Target
/// [`WidgetPod`]: crate::WidgetPod
/// [`WidgetExt::with_id`]: super::WidgetExt::with_id
/// [`IdentityWrapper`]: super::IdentityWrapper
// this is NonZeroU64 because we regularly store Option<WidgetId>
#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq)]
pub struct WidgetId(NonZeroU64);
/// The trait implemented by all widgets.
///
/// All appearance and behavior for a widget is encapsulated in an
/// object that implements this trait.
///
/// The trait is parametrized by a type (`T`) for associated data.
/// All trait methods are provided with access to this data, and
/// in the case of [`event`] the reference is mutable, so that events
/// can directly update the data.
///
/// Whenever the application data changes, the framework traverses
/// the widget hierarchy with an [`update`] method. The framework
/// needs to know whether the data has actually changed or not, which
/// is why `T` has a [`Data`] bound.
///
/// All the trait methods are provided with a corresponding context.
/// The widget can request things and cause actions by calling methods
/// on that context.
///
/// In addition, all trait methods are provided with an environment
/// ([`Env`]).
///
/// Container widgets will generally not call `Widget` methods directly
/// on their child widgets, but rather will own their widget wrapped in
/// a [`WidgetPod`], and call the corresponding method on that. The
/// `WidgetPod` contains state and logic for these traversals. On the
/// other hand, particularly light-weight containers might contain their
/// child `Widget` directly (when no layout or event flow logic is
/// needed), and in those cases will call these methods.
///
/// As a general pattern, container widgets will call the corresponding
/// `WidgetPod` method on all their children. The `WidgetPod` applies
/// logic to determine whether to recurse, as needed.
///
/// [`event`]: Widget::event
/// [`update`]: Widget::update
/// [`WidgetPod`]: crate::WidgetPod
pub trait Widget<T> {
/// Handle an event.
///
/// A number of different events (in the [`Event`] enum) are handled in this
/// method call. A widget can handle these events in a number of ways:
/// requesting things from the [`EventCtx`], mutating the data, or submitting
/// a [`Command`].
///
/// [`Command`]: crate::Command
fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env);
/// Handle a life cycle notification.
///
/// This method is called to notify your widget of certain special events,
/// (available in the [`LifeCycle`] enum) that are generally related to
/// changes in the widget graph or in the state of your specific widget.
///
/// A widget is not expected to mutate the application state in response
/// to these events, but only to update its own internal state as required;
/// if a widget needs to mutate data, it can submit a [`Command`] that will
/// be executed at the next opportunity.
///
/// [`Command`]: crate::Command
fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env);
/// Update the widget's appearance in response to a change in the app's
/// [`Data`] or [`Env`].
///
/// This method is called whenever the data or environment changes.
/// When the appearance of the widget needs to be updated in response to
/// these changes, you can call [`request_paint`] or [`request_layout`] on
/// the provided [`UpdateCtx`] to schedule calls to [`paint`] and [`layout`]
/// as required.
///
/// The previous value of the data is provided in case the widget wants to
/// compute a fine-grained delta; you should try to only request a new
/// layout or paint pass if it is actually required.
///
/// To determine if the [`Env`] has changed, you can call [`env_changed`]
/// on the provided [`UpdateCtx`]; you can then call [`env_key_changed`]
/// with any keys that are used in your widget, to see if they have changed;
/// you can then request layout or paint as needed.
///
/// [`env_changed`]: UpdateCtx::env_changed
/// [`env_key_changed`]: UpdateCtx::env_key_changed
/// [`request_paint`]: UpdateCtx::request_paint
/// [`request_layout`]: UpdateCtx::request_layout
/// [`layout`]: Widget::layout
/// [`paint`]: Widget::paint
fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env);
/// Compute layout.
///
/// A leaf widget should determine its size (subject to the provided
/// constraints) and return it.
///
/// A container widget will recursively call [`WidgetPod::layout`] on its
/// child widgets, providing each of them an appropriate box constraint,
/// compute layout, then call [`set_origin`] on each of its children.
/// Finally, it should return the size of the container. The container
/// can recurse in any order, which can be helpful to, for example, compute
/// the size of non-flex widgets first, to determine the amount of space
/// available for the flex widgets.
///
/// For efficiency, a container should only invoke layout of a child widget
/// once, though there is nothing enforcing this.
///
/// The layout strategy is strongly inspired by Flutter.
///
/// [`WidgetPod::layout`]: crate::WidgetPod::layout
/// [`set_origin`]: crate::WidgetPod::set_origin
fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size;
/// Paint the widget appearance.
///
/// The [`PaintCtx`] derefs to something that implements the [`RenderContext`]
/// trait, which exposes various methods that the widget can use to paint
/// its appearance.
///
/// Container widgets can paint a background before recursing to their
/// children, or annotations (for example, scrollbars) by painting
/// afterwards. In addition, they can apply masks and transforms on
/// the render context, which is especially useful for scrolling.
fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env);
#[doc(hidden)]
/// Get the identity of the widget; this is basically only implemented by
/// `IdentityWrapper`. Widgets should not implement this on their own.
fn id(&self) -> Option<WidgetId> {
None
}
#[doc(hidden)]
/// Get the (verbose) type name of the widget for debugging purposes.
/// You should not override this method.
fn type_name(&self) -> &'static str {
std::any::type_name::<Self>()
}
#[doc(hidden)]
/// Get the (abridged) type name of the widget for debugging purposes.
/// You should not override this method.
fn short_type_name(&self) -> &'static str {
let name = self.type_name();
name.split('<')
.next()
.unwrap_or(name)
.split("::")
.last()
.unwrap_or(name)
}
#[doc(hidden)]
/// From the current data, get a best-effort description of the state of
/// this widget and its children for debugging purposes.
fn debug_state(&self, data: &T) -> DebugState {
#![allow(unused_variables)]
DebugState {
display_name: self.short_type_name().to_string(),
..Default::default()
}
}
/// Computes max intrinsic/preferred dimension of a widget on the provided axis.
///
/// Max intrinsic/preferred dimension is the dimension the widget could take, provided infinite
/// constraint on that axis.
///
/// If axis == Axis::Horizontal, widget is being asked to calculate max intrinsic width.
/// If axis == Axis::Vertical, widget is being asked to calculate max intrinsic height.
///
/// Box constraints must be honored in intrinsics computation.
///
/// AspectRatioBox is an example where constraints are honored. If height is finite, max intrinsic
/// width is *height * ratio*.
/// Only when height is infinite, child's max intrinsic width is calculated.
///
/// Intrinsic is a *could-be* value. It's the value a widget *could* have given infinite constraints.
/// This does not mean the value returned by layout() would be the same.
///
/// This method **must** return a finite value.
fn compute_max_intrinsic(
&mut self,
axis: Axis,
ctx: &mut LayoutCtx,
bc: &BoxConstraints,
data: &T,
env: &Env,
) -> f64 {
match axis {
Axis::Horizontal => self.layout(ctx, bc, data, env).width,
Axis::Vertical => self.layout(ctx, bc, data, env).height,
}
}
}
impl WidgetId {
/// Allocate a new, unique `WidgetId`.
///
/// All widgets are assigned ids automatically; you should only create
/// an explicit id if you need to know it ahead of time, for instance
/// if you want two sibling widgets to know each others' ids.
///
/// You must ensure that a given `WidgetId` is only ever used for one
/// widget at a time.
pub fn next() -> WidgetId {
use crate::shell::Counter;
static WIDGET_ID_COUNTER: Counter = Counter::new();
WidgetId(WIDGET_ID_COUNTER.next_nonzero())
}
/// Create a reserved `WidgetId`, suitable for reuse.
///
/// The caller is responsible for ensuring that this ID is in fact assigned
/// to a single widget at any time, or your code may become haunted.
///
/// The actual inner representation of the returned `WidgetId` will not
/// be the same as the raw value that is passed in; it will be
/// `u64::max_value() - raw`.
#[allow(unsafe_code)]
pub const fn reserved(raw: u16) -> WidgetId {
let id = u64::max_value() - raw as u64;
// safety: by construction this can never be zero.
WidgetId(unsafe { std::num::NonZeroU64::new_unchecked(id) })
}
pub(crate) fn to_raw(self) -> u64 {
self.0.into()
}
}
impl<T> Widget<T> for Box<dyn Widget<T>> {
fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
self.deref_mut().event(ctx, event, data, env)
}
fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env) {
self.deref_mut().lifecycle(ctx, event, data, env);
}
fn update(&mut self, ctx: &mut UpdateCtx, old_data: &T, data: &T, env: &Env) {
self.deref_mut().update(ctx, old_data, data, env);
}
fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size {
self.deref_mut().layout(ctx, bc, data, env)
}
fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env) {
self.deref_mut().paint(ctx, data, env);
}
fn id(&self) -> Option<WidgetId> {
self.deref().id()
}
fn type_name(&self) -> &'static str {
self.deref().type_name()
}
fn debug_state(&self, data: &T) -> DebugState {
self.deref().debug_state(data)
}
fn compute_max_intrinsic(
&mut self,
axis: Axis,
ctx: &mut LayoutCtx,
bc: &BoxConstraints,
data: &T,
env: &Env,
) -> f64 {
self.deref_mut()
.compute_max_intrinsic(axis, ctx, bc, data, env)
}
}