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// Copyright 2022 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.
//! A ZStack widget.
use crate::{
BoxConstraints, Data, Env, Event, EventCtx, InternalEvent, LayoutCtx, LifeCycle, LifeCycleCtx,
PaintCtx, Point, Rect, Size, UnitPoint, UpdateCtx, Vec2, Widget, WidgetExt, WidgetPod,
};
/// A container that stacks its children on top of each other.
///
/// The container has a baselayer which has the lowest z-index and determines the size of the
/// container.
pub struct ZStack<T> {
layers: Vec<ZChild<T>>,
}
struct ZChild<T> {
child: WidgetPod<T, Box<dyn Widget<T>>>,
relative_size: Vec2,
absolute_size: Vec2,
position: UnitPoint,
offset: Vec2,
}
impl<T: Data> ZStack<T> {
/// Creates a new ZStack with a baselayer.
///
/// The baselayer is used by the ZStack to determine its own size.
pub fn new(base_layer: impl Widget<T> + 'static) -> Self {
Self {
layers: vec![ZChild {
child: WidgetPod::new(base_layer.boxed()),
relative_size: Vec2::new(1.0, 1.0),
absolute_size: Vec2::ZERO,
position: UnitPoint::CENTER,
offset: Vec2::ZERO,
}],
}
}
/// Builder-style method to add a new child to the Z-Stack.
///
/// The child is added directly above the base layer.
///
/// `relative_size` is the space the child is allowed to take up relative to its parent. The
/// values are between 0 and 1.
/// `absolute_size` is a fixed amount of pixels added to `relative_size`.
///
/// `position` is the alignment of the child inside the remaining space of its parent.
///
/// `offset` is a fixed amount of pixels added to `position`.
pub fn with_child(
mut self,
child: impl Widget<T> + 'static,
relative_size: Vec2,
absolute_size: Vec2,
position: UnitPoint,
offset: Vec2,
) -> Self {
let next_index = self.layers.len() - 1;
self.layers.insert(
next_index,
ZChild {
child: WidgetPod::new(child.boxed()),
relative_size,
absolute_size,
position,
offset,
},
);
self
}
/// Builder-style method to add a new child to the Z-Stack.
///
/// The child is added directly above the base layer, is positioned in the center and has no
/// size constraints.
pub fn with_centered_child(self, child: impl Widget<T> + 'static) -> Self {
self.with_aligned_child(child, UnitPoint::CENTER)
}
/// Builder-style method to add a new child to the Z-Stack.
///
/// The child is added directly above the base layer, uses the given alignment and has no
/// size constraints.
pub fn with_aligned_child(self, child: impl Widget<T> + 'static, alignment: UnitPoint) -> Self {
self.with_child(
child,
Vec2::new(1.0, 1.0),
Vec2::ZERO,
alignment,
Vec2::ZERO,
)
}
}
impl<T: Data> Widget<T> for ZStack<T> {
fn event(&mut self, ctx: &mut EventCtx, event: &Event, data: &mut T, env: &Env) {
let mut previous_hot = false;
for layer in self.layers.iter_mut() {
if event.is_pointer_event() && previous_hot {
if layer.child.is_active() {
ctx.set_handled();
layer.child.event(ctx, event, data, env);
} else {
layer
.child
.event(ctx, &Event::Internal(InternalEvent::MouseLeave), data, env);
}
} else {
layer.child.event(ctx, event, data, env);
}
previous_hot |= layer.child.is_hot();
}
}
fn lifecycle(&mut self, ctx: &mut LifeCycleCtx, event: &LifeCycle, data: &T, env: &Env) {
let mut previous_hot = false;
for layer in self.layers.iter_mut() {
let inner_event = event.ignore_hot(previous_hot);
layer.child.lifecycle(ctx, &inner_event, data, env);
previous_hot |= layer.child.is_hot();
}
}
fn update(&mut self, ctx: &mut UpdateCtx, _: &T, data: &T, env: &Env) {
for layer in self.layers.iter_mut().rev() {
layer.child.update(ctx, data, env);
}
}
fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints, data: &T, env: &Env) -> Size {
//Layout base layer
let base_layer = self.layers.last_mut().unwrap();
let base_size = base_layer.child.layout(ctx, bc, data, env);
//Layout other layers
let other_layers = self.layers.len() - 1;
for layer in self.layers.iter_mut().take(other_layers) {
let max_size = layer.resolve_max_size(base_size);
layer
.child
.layout(ctx, &BoxConstraints::new(Size::ZERO, max_size), data, env);
}
//Set origin for all Layers and calculate paint insets
let mut paint_rect = Rect::ZERO;
for layer in self.layers.iter_mut() {
let remaining = base_size - layer.child.layout_rect().size();
let origin = layer.resolve_point(remaining);
layer.child.set_origin(ctx, origin);
paint_rect = paint_rect.union(layer.child.paint_rect());
}
ctx.set_paint_insets(paint_rect - base_size.to_rect());
ctx.set_baseline_offset(self.layers.last().unwrap().child.baseline_offset());
base_size
}
fn paint(&mut self, ctx: &mut PaintCtx, data: &T, env: &Env) {
//Painters algorithm (Painting back to front)
for layer in self.layers.iter_mut().rev() {
layer.child.paint(ctx, data, env);
}
}
}
impl<T: Data> ZChild<T> {
fn resolve_max_size(&self, availible: Size) -> Size {
self.absolute_size.to_size()
+ Size::new(
availible.width * self.relative_size.x,
availible.height * self.relative_size.y,
)
}
fn resolve_point(&self, remaining_space: Size) -> Point {
(self.position.resolve(remaining_space.to_rect()).to_vec2() + self.offset).to_point()
}
}