From cabd84823e10f6aef031788eeb607ff90e096216 Mon Sep 17 00:00:00 2001
From: viktorstrate <viktorstrate@gmail.com>
Date: Sun, 10 Nov 2024 17:10:56 +0100
Subject: [PATCH] Add ZStack widget and view

---
 masonry/src/widget/mod.rs                     |   2 +
 ...k__tests__zstack_with_button_and_label.png |   3 +
 ...__tests__zstack_with_button_and_label.snap |  10 +
 masonry/src/widget/zstack.rs                  | 135 ++++++++++++
 xilem/src/view/mod.rs                         |   3 +
 xilem/src/view/zstack.rs                      | 200 ++++++++++++++++++
 6 files changed, 353 insertions(+)
 create mode 100644 masonry/src/widget/screenshots/masonry__widget__zstack__tests__zstack_with_button_and_label.png
 create mode 100644 masonry/src/widget/snapshots/masonry__widget__zstack__tests__zstack_with_button_and_label.snap
 create mode 100644 masonry/src/widget/zstack.rs
 create mode 100644 xilem/src/view/zstack.rs

diff --git a/masonry/src/widget/mod.rs b/masonry/src/widget/mod.rs
index ec41bf3c6..e1e693340 100644
--- a/masonry/src/widget/mod.rs
+++ b/masonry/src/widget/mod.rs
@@ -31,6 +31,7 @@ mod split;
 mod textbox;
 mod variable_label;
 mod widget_arena;
+mod zstack;
 
 pub use self::image::Image;
 pub use align::Align;
@@ -52,6 +53,7 @@ pub use variable_label::VariableLabel;
 pub use widget_mut::WidgetMut;
 pub use widget_pod::WidgetPod;
 pub use widget_ref::WidgetRef;
+pub use zstack::ZStack;
 
 pub(crate) use widget_arena::WidgetArena;
 pub(crate) use widget_state::WidgetState;
diff --git a/masonry/src/widget/screenshots/masonry__widget__zstack__tests__zstack_with_button_and_label.png b/masonry/src/widget/screenshots/masonry__widget__zstack__tests__zstack_with_button_and_label.png
new file mode 100644
index 000000000..faaec6255
--- /dev/null
+++ b/masonry/src/widget/screenshots/masonry__widget__zstack__tests__zstack_with_button_and_label.png
@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:bf58dc4e5466d5d47250aca4e4086743bd96b0a09ac43d68340777afb40cb277
+size 6284
diff --git a/masonry/src/widget/snapshots/masonry__widget__zstack__tests__zstack_with_button_and_label.snap b/masonry/src/widget/snapshots/masonry__widget__zstack__tests__zstack_with_button_and_label.snap
new file mode 100644
index 000000000..9cde1bf98
--- /dev/null
+++ b/masonry/src/widget/snapshots/masonry__widget__zstack__tests__zstack_with_button_and_label.snap
@@ -0,0 +1,10 @@
+---
+source: masonry/src/widget/zstack.rs
+expression: harness.root_widget()
+---
+ZStack(
+    Button(
+        Label<Button>,
+    ),
+    Label<Label>,
+)
diff --git a/masonry/src/widget/zstack.rs b/masonry/src/widget/zstack.rs
new file mode 100644
index 000000000..658217d26
--- /dev/null
+++ b/masonry/src/widget/zstack.rs
@@ -0,0 +1,135 @@
+use crate::{
+    vello::Scene, widget::WidgetMut, AccessCtx, BoxConstraints, LayoutCtx, PaintCtx, Point,
+    RegisterCtx, Size, Widget, WidgetId, WidgetPod,
+};
+use accesskit::{NodeBuilder, Role};
+use smallvec::SmallVec;
+use tracing::trace_span;
+
+struct Child {
+    widget: WidgetPod<Box<dyn Widget>>,
+}
+
+pub struct ZStack {
+    children: Vec<Child>,
+}
+
+// --- MARK: IMPL ZSTACK ---
+impl ZStack {
+    pub fn new() -> Self {
+        ZStack {
+            children: Vec::new(),
+        }
+    }
+
+    pub fn with_child(self, child: impl Widget) -> Self {
+        self.with_child_pod(WidgetPod::new(Box::new(child)))
+    }
+
+    pub fn with_child_id(self, child: impl Widget, id: WidgetId) -> Self {
+        self.with_child_pod(WidgetPod::new_with_id(Box::new(child), id))
+    }
+
+    pub fn with_child_pod(mut self, child: WidgetPod<Box<dyn Widget>>) -> Self {
+        let child = Child { widget: child };
+        self.children.push(child);
+        self
+    }
+}
+
+// --- MARK: WIDGETMUT---
+impl ZStack {
+    pub fn add_child(this: &mut WidgetMut<'_, Self>, child: impl Widget) {
+        let child_pod: WidgetPod<Box<dyn Widget>> = WidgetPod::new(Box::new(child));
+        Self::insert_child_pod(this, child_pod);
+    }
+
+    pub fn add_child_id(this: &mut WidgetMut<'_, Self>, child: impl Widget, id: WidgetId) {
+        let child_pod: WidgetPod<Box<dyn Widget>> = WidgetPod::new_with_id(Box::new(child), id);
+        Self::insert_child_pod(this, child_pod);
+    }
+
+    pub fn insert_child_pod(this: &mut WidgetMut<'_, Self>, widget: WidgetPod<Box<dyn Widget>>) {
+        let child = Child { widget };
+        this.widget.children.push(child);
+        this.ctx.children_changed();
+        this.ctx.request_layout();
+    }
+
+    pub fn remove_child(this: &mut WidgetMut<'_, Self>, idx: usize) {
+        let child = this.widget.children.remove(idx);
+        this.ctx.remove_child(child.widget);
+        this.ctx.request_layout();
+    }
+
+    pub fn child_mut<'t>(
+        this: &'t mut WidgetMut<'_, Self>,
+        idx: usize,
+    ) -> Option<WidgetMut<'t, Box<dyn Widget>>> {
+        let child = &mut this.widget.children[idx].widget;
+        Some(this.ctx.get_mut(child))
+    }
+}
+
+// --- MARK: IMPL WIDGET---
+impl Widget for ZStack {
+    fn layout(&mut self, ctx: &mut LayoutCtx, bc: &BoxConstraints) -> Size {
+        let total_size = bc.max();
+
+        for child in &mut self.children {
+            let _child_size = ctx.run_layout(&mut child.widget, bc);
+            ctx.place_child(&mut child.widget, Point::ZERO);
+        }
+
+        total_size
+    }
+
+    fn paint(&mut self, _ctx: &mut PaintCtx, _scene: &mut Scene) {}
+
+    fn register_children(&mut self, ctx: &mut RegisterCtx) {
+        for child in self.children.iter_mut().map(|x| &mut x.widget) {
+            ctx.register_child(child);
+        }
+    }
+
+    fn children_ids(&self) -> SmallVec<[WidgetId; 16]> {
+        self.children
+            .iter()
+            .map(|child| &child.widget)
+            .map(|widget_pod| widget_pod.id())
+            .collect()
+    }
+
+    fn accessibility_role(&self) -> Role {
+        Role::GenericContainer
+    }
+
+    fn accessibility(&mut self, _ctx: &mut AccessCtx, _node: &mut NodeBuilder) {}
+
+    fn make_trace_span(&self) -> tracing::Span {
+        trace_span!("ZStack")
+    }
+}
+
+// --- MARK: TESTS ---
+#[cfg(test)]
+mod tests {
+    use insta::assert_debug_snapshot;
+
+    use super::*;
+    use crate::assert_render_snapshot;
+    use crate::testing::TestHarness;
+    use crate::widget::{Button, Label};
+
+    #[test]
+    fn zstack_with_button_and_label() {
+        let widget = ZStack::new()
+            .with_child(Button::new("Button"))
+            .with_child(Label::new("Label"));
+
+        let mut harness = TestHarness::create(widget);
+
+        assert_debug_snapshot!(harness.root_widget());
+        assert_render_snapshot!(harness, "zstack_with_button_and_label");
+    }
+}
diff --git a/xilem/src/view/mod.rs b/xilem/src/view/mod.rs
index b879de45f..fd8e39eeb 100644
--- a/xilem/src/view/mod.rs
+++ b/xilem/src/view/mod.rs
@@ -47,3 +47,6 @@ pub use textbox::*;
 
 mod portal;
 pub use portal::*;
+
+mod zstack;
+pub use zstack::*;
diff --git a/xilem/src/view/zstack.rs b/xilem/src/view/zstack.rs
new file mode 100644
index 000000000..fdaebce9f
--- /dev/null
+++ b/xilem/src/view/zstack.rs
@@ -0,0 +1,200 @@
+use crate::{
+    core::{
+        AppendVec, DynMessage, ElementSplice, Mut, SuperElement, View, ViewElement, ViewMarker,
+        ViewSequence,
+    },
+    Pod, ViewCtx,
+};
+use masonry::{
+    widget::{self, WidgetMut},
+    Widget,
+};
+
+pub fn zstack<State, Action, Seq: ZStackSequence<State, Action>>(sequence: Seq) -> Stack<Seq> {
+    Stack { sequence }
+}
+
+pub struct Stack<Seq> {
+    sequence: Seq,
+}
+
+impl<Seq> ViewMarker for Stack<Seq> {}
+impl<State, Action, Seq> View<State, Action, ViewCtx> for Stack<Seq>
+where
+    State: 'static,
+    Action: 'static,
+    Seq: ZStackSequence<State, Action>,
+{
+    type Element = Pod<widget::ZStack>;
+
+    type ViewState = Seq::SeqState;
+
+    fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
+        let mut elements = AppendVec::default();
+        let mut widget = widget::ZStack::new();
+        let seq_state = self.sequence.seq_build(ctx, &mut elements);
+        for child in elements.into_inner() {
+            widget = widget.with_child_pod(child.0.inner);
+        }
+        (ctx.new_pod(widget), seq_state)
+    }
+
+    fn rebuild(
+        &self,
+        prev: &Self,
+        view_state: &mut Self::ViewState,
+        ctx: &mut ViewCtx,
+        element: crate::core::Mut<Self::Element>,
+    ) {
+        let mut splice = StackSplice::new(element);
+        self.sequence
+            .seq_rebuild(&prev.sequence, view_state, ctx, &mut splice);
+        debug_assert!(splice.scratch.is_empty());
+    }
+
+    fn teardown(
+        &self,
+        view_state: &mut Self::ViewState,
+        ctx: &mut ViewCtx,
+        element: crate::core::Mut<Self::Element>,
+    ) {
+        let mut splice = StackSplice::new(element);
+        self.sequence.seq_teardown(view_state, ctx, &mut splice);
+        debug_assert!(splice.scratch.into_inner().is_empty());
+    }
+
+    fn message(
+        &self,
+        view_state: &mut Self::ViewState,
+        id_path: &[crate::core::ViewId],
+        message: DynMessage,
+        app_state: &mut State,
+    ) -> crate::core::MessageResult<Action, DynMessage> {
+        self.sequence
+            .seq_message(view_state, id_path, message, app_state)
+    }
+}
+
+// MARK: ZStackElement
+pub struct ZStackElement(Pod<Box<dyn Widget>>);
+
+pub struct ZStackElementMut<'w> {
+    parent: WidgetMut<'w, widget::ZStack>,
+    idx: usize,
+}
+
+impl ViewElement for ZStackElement {
+    type Mut<'a> = ZStackElementMut<'a>;
+}
+
+impl SuperElement<ZStackElement, ViewCtx> for ZStackElement {
+    fn upcast(ctx: &mut ViewCtx, child: ZStackElement) -> Self {
+        child
+    }
+
+    fn with_downcast_val<R>(
+        mut this: crate::core::Mut<Self>,
+        f: impl FnOnce(crate::core::Mut<ZStackElement>) -> R,
+    ) -> (Self::Mut<'_>, R) {
+        let r = {
+            let parent = this.parent.reborrow_mut();
+            let reborrow = ZStackElementMut {
+                idx: this.idx,
+                parent,
+            };
+            f(reborrow)
+        };
+        (this, r)
+    }
+}
+
+impl<W: Widget> SuperElement<Pod<W>, ViewCtx> for ZStackElement {
+    fn upcast(ctx: &mut ViewCtx, child: Pod<W>) -> Self {
+        ZStackElement(ctx.boxed_pod(child))
+    }
+
+    fn with_downcast_val<R>(
+        mut this: crate::core::Mut<Self>,
+        f: impl FnOnce(crate::core::Mut<Pod<W>>) -> R,
+    ) -> (Self::Mut<'_>, R) {
+        let ret = {
+            let mut child = widget::ZStack::child_mut(&mut this.parent, this.idx)
+                .expect("This is supposed to be a widget");
+            let downcast = child.downcast();
+            f(downcast)
+        };
+
+        (this, ret)
+    }
+}
+
+// MARK: Sequence
+pub trait ZStackSequence<State, Action = ()>:
+    ViewSequence<State, Action, ViewCtx, ZStackElement>
+{
+}
+
+impl<Seq, State, Action> ZStackSequence<State, Action> for Seq where
+    Seq: ViewSequence<State, Action, ViewCtx, ZStackElement>
+{
+}
+
+// MARK: Splice
+
+pub struct StackSplice<'w> {
+    idx: usize,
+    element: WidgetMut<'w, widget::ZStack>,
+    scratch: AppendVec<ZStackElement>,
+}
+
+impl<'w> StackSplice<'w> {
+    fn new(element: WidgetMut<'w, widget::ZStack>) -> Self {
+        Self {
+            idx: 0,
+            element,
+            scratch: AppendVec::default(),
+        }
+    }
+}
+
+impl ElementSplice<ZStackElement> for StackSplice<'_> {
+    fn with_scratch<R>(&mut self, f: impl FnOnce(&mut AppendVec<ZStackElement>) -> R) -> R {
+        let ret = f(&mut self.scratch);
+        for element in self.scratch.drain() {
+            widget::ZStack::insert_child_pod(&mut self.element, element.0.inner);
+            self.idx += 1;
+        }
+        ret
+    }
+
+    fn insert(&mut self, element: ZStackElement) {
+        widget::ZStack::insert_child_pod(&mut self.element, element.0.inner);
+        self.idx += 1;
+    }
+
+    fn mutate<R>(&mut self, f: impl FnOnce(Mut<ZStackElement>) -> R) -> R {
+        let child = ZStackElementMut {
+            parent: self.element.reborrow_mut(),
+            idx: self.idx,
+        };
+        let ret = f(child);
+        self.idx += 1;
+        ret
+    }
+
+    fn skip(&mut self, n: usize) {
+        self.idx += n;
+    }
+
+    fn delete<R>(&mut self, f: impl FnOnce(Mut<ZStackElement>) -> R) -> R {
+        let ret = {
+            let child = ZStackElementMut {
+                parent: self.element.reborrow_mut(),
+                idx: self.idx,
+            };
+            f(child)
+        };
+        widget::ZStack::remove_child(&mut self.element, self.idx);
+        ret
+    }
+}