From 28f3ce479f16bac16e2064c7a5370d7418f30b22 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Wed, 15 Jan 2025 16:07:08 +0000
Subject: [PATCH 1/8] Start work on the transformed view

---
 xilem/src/view/transform.rs | 126 ++++++++++++++++++++++++++++++------
 1 file changed, 108 insertions(+), 18 deletions(-)

diff --git a/xilem/src/view/transform.rs b/xilem/src/view/transform.rs
index 4cd342cd6..479640a0f 100644
--- a/xilem/src/view/transform.rs
+++ b/xilem/src/view/transform.rs
@@ -1,43 +1,133 @@
 // Copyright 2025 the Xilem Authors
 // SPDX-License-Identifier: Apache-2.0
 
-use crate::Affine;
+use std::marker::PhantomData;
 
-/// An extension trait, to allow common transformations of the views transform.
-pub trait Transformable: Sized {
-    fn transform_mut(&mut self) -> &mut Affine;
+use crate::{
+    core::{DynMessage, View, ViewMarker},
+    Affine, Pod, ViewCtx, WidgetView,
+};
+
+/// A view which transforms the widget created by child.
+///
+/// Each widget can only be transformed once, and using this
+/// function in a nesting pattern may cause panics.
+/// This is due to the efficient way that Xilem calculates field changes,
+/// which is incompatible with composing non-idempotent changes to the same field.
+///
+/// The transform can be set using the methods on the return type.
+/// Transformations apply in order.
+/// That is, calling [`rotate`](Transformed::rotate) then [`translate`](Transformed::translate)
+/// will move the rotated widget.
+pub fn transformed<Child, State, Action>(child: Child) -> Transformed<Child, State, Action>
+where
+    Child: WidgetView<State, Action>,
+{
+    Transformed {
+        child,
+        transform: Affine::IDENTITY,
+        phantom: PhantomData,
+    }
+}
 
+/// The view for [`transformed`].
+pub struct Transformed<V, State, Action> {
+    child: V,
+    transform: Affine,
+    phantom: PhantomData<(State, Action)>,
+}
+
+impl<V, State, Action> Transformed<V, State, Action> {
     #[must_use]
-    fn rotate(mut self, radians: f64) -> Self {
-        let transform = self.transform_mut();
-        *transform = transform.then_rotate(radians);
+    /// Rotate the widget by `radians` radians about the origin of its natural location.
+    pub fn rotate(mut self, radians: f64) -> Self {
+        self.transform = self.transform.then_rotate(radians);
         self
     }
 
+    /// Scale the widget by `uniform` in each axis.
     #[must_use]
-    fn scale(mut self, uniform: f64) -> Self {
-        let transform = self.transform_mut();
-        *transform = transform.then_scale(uniform);
+    pub fn scale(mut self, uniform: f64) -> Self {
+        self.transform = self.transform.then_scale(uniform);
         self
     }
 
     #[must_use]
-    fn scale_non_uniform(mut self, x: f64, y: f64) -> Self {
-        let transform = self.transform_mut();
-        *transform = transform.then_scale_non_uniform(x, y);
+    /// Scale the widget by the given amount in each (2d) axis.
+    pub fn scale_non_uniform(mut self, x: f64, y: f64) -> Self {
+        self.transform = self.transform.then_scale_non_uniform(x, y);
         self
     }
 
     #[must_use]
-    fn translate(mut self, v: impl Into<crate::Vec2>) -> Self {
-        let transform = self.transform_mut();
-        *transform = transform.then_translate(v.into());
+    /// Displace the widget by `v` from its natural location.
+    pub fn translate(mut self, v: impl Into<crate::Vec2>) -> Self {
+        self.transform = self.transform.then_translate(v.into());
         self
     }
 
     #[must_use]
-    fn transform(mut self, v: impl Into<Affine>) -> Self {
-        *self.transform_mut() *= v.into();
+    /// Apply an arbitrary 2d transform to the widget.
+    pub fn transform(mut self, v: impl Into<Affine>) -> Self {
+        self.transform *= v.into();
         self
     }
 }
+
+impl<V, State, Action> ViewMarker for Transformed<V, State, Action> {}
+impl<Child, State, Action> View<State, Action, ViewCtx> for Transformed<Child, State, Action>
+where
+    Child: WidgetView<State, Action>,
+    State: 'static,
+    Action: 'static,
+{
+    type Element = Pod<Child::Widget>;
+    type ViewState = Child::ViewState;
+
+    fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
+        let (mut child_pod, child_state) = self.child.build(ctx);
+        // TODO: Use a marker identity value to detect this more properly
+        if child_pod.transform != Affine::IDENTITY {
+            panic!("Tried to create a `Transformed` with an already controlled Transform");
+        }
+        child_pod.transform = self.transform;
+        (child_pod, child_state)
+    }
+
+    fn rebuild(
+        &self,
+        prev: &Self,
+        view_state: &mut Self::ViewState,
+        ctx: &mut ViewCtx,
+        mut element: xilem_core::Mut<'_, Self::Element>,
+    ) {
+        if self.transform != prev.transform {
+            element.ctx.set_transform(self.transform);
+        }
+        self.child.rebuild(&prev.child, view_state, ctx, element);
+    }
+
+    fn teardown(
+        &self,
+        view_state: &mut Self::ViewState,
+        ctx: &mut ViewCtx,
+        element: xilem_core::Mut<'_, Self::Element>,
+    ) {
+        self.child.teardown(view_state, ctx, element);
+    }
+
+    fn message(
+        &self,
+        view_state: &mut Self::ViewState,
+        id_path: &[xilem_core::ViewId],
+        message: DynMessage,
+        app_state: &mut State,
+    ) -> xilem_core::MessageResult<Action, DynMessage> {
+        self.child.message(view_state, id_path, message, app_state)
+    }
+}
+
+/// An extension trait, to allow common transformations of the views transform.
+pub trait Transformable: Sized {
+    fn transform_mut(&mut self) -> &mut Affine;
+}

From 27626ec9deb518341b7cbe31ce51c91983fa3bd1 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Thu, 16 Jan 2025 11:50:43 +0000
Subject: [PATCH 2/8] Add the new way of handling transforms

---
 xilem/examples/transforms.rs |  3 ++-
 xilem/src/lib.rs             | 29 +++++++++++++++++++++++++----
 xilem/src/view/transform.rs  |  4 ++--
 3 files changed, 29 insertions(+), 7 deletions(-)

diff --git a/xilem/examples/transforms.rs b/xilem/examples/transforms.rs
index 83c7b4665..f5e0a25dd 100644
--- a/xilem/examples/transforms.rs
+++ b/xilem/examples/transforms.rs
@@ -6,7 +6,7 @@
 use std::f64::consts::{PI, TAU};
 
 use winit::error::EventLoopError;
-use xilem::view::{button, grid, label, sized_box, GridExt as _, Transformable as _};
+use xilem::view::{button, grid, label, sized_box, GridExt as _};
 use xilem::{Color, EventLoop, Vec2, WidgetView, Xilem};
 
 struct TransformsGame {
@@ -46,6 +46,7 @@ impl TransformsGame {
         // Note that the order of the transformations is relevant.
         let transformed_status = sized_box(status)
             .background(Color::new(bg_color))
+            .transformed()
             .translate(self.translation)
             .rotate(self.rotation)
             .scale(self.scale);
diff --git a/xilem/src/lib.rs b/xilem/src/lib.rs
index 9972a80fe..6f8d1806c 100644
--- a/xilem/src/lib.rs
+++ b/xilem/src/lib.rs
@@ -45,6 +45,7 @@ use std::sync::Arc;
 use masonry::dpi::LogicalSize;
 use masonry::widget::{RootWidget, WidgetMut};
 use masonry::{event_loop_runner, Widget, WidgetId, WidgetPod};
+use view::{transformed, Transformed};
 use winit::error::EventLoopError;
 use winit::window::{Window, WindowAttributes};
 
@@ -188,7 +189,7 @@ where
 pub struct Pod<W: Widget> {
     pub widget: W,
     pub id: WidgetId,
-    pub transform: Affine,
+    pub transform: Option<Affine>,
 }
 
 impl<W: Widget> Pod<W> {
@@ -200,10 +201,18 @@ impl<W: Widget> Pod<W> {
         }
     }
     fn into_widget_pod(self) -> WidgetPod<W> {
-        WidgetPod::new_with_id_and_transform(self.widget, self.id, self.transform)
+        WidgetPod::new_with_id_and_transform(
+            self.widget,
+            self.id,
+            self.transform.unwrap_or_default(),
+        )
     }
     fn boxed_widget_pod(self) -> WidgetPod<Box<dyn Widget>> {
-        WidgetPod::new_with_id_and_transform(Box::new(self.widget), self.id, self.transform)
+        WidgetPod::new_with_id_and_transform(
+            Box::new(self.widget),
+            self.id,
+            self.transform.unwrap_or_default(),
+        )
     }
     fn boxed(self) -> Pod<Box<dyn Widget>> {
         Pod {
@@ -257,6 +266,18 @@ pub trait WidgetView<State, Action = ()>:
     {
         Box::new(self)
     }
+
+    /// This widget with a 2d transform applied.
+    ///
+    /// The returned view has methods to control individual components of
+    /// the transform, as well as apply an arbitrary transform.
+    /// See [`transformed`] for more details.
+    fn transformed(self) -> Transformed<Self, State, Action>
+    where
+        Self: Sized,
+    {
+        transformed(self)
+    }
 }
 
 impl<V, State, Action, W> WidgetView<State, Action> for V
@@ -323,7 +344,7 @@ impl ViewCtx {
     }
     pub fn new_pod_with_transform<W: Widget>(&mut self, widget: W, transform: Affine) -> Pod<W> {
         let mut pod = Pod::new(widget);
-        pod.transform = transform;
+        pod.transform = Some(transform);
         pod
     }
 
diff --git a/xilem/src/view/transform.rs b/xilem/src/view/transform.rs
index 479640a0f..555468d46 100644
--- a/xilem/src/view/transform.rs
+++ b/xilem/src/view/transform.rs
@@ -87,10 +87,10 @@ where
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
         let (mut child_pod, child_state) = self.child.build(ctx);
         // TODO: Use a marker identity value to detect this more properly
-        if child_pod.transform != Affine::IDENTITY {
+        if child_pod.transform.is_some() {
             panic!("Tried to create a `Transformed` with an already controlled Transform");
         }
-        child_pod.transform = self.transform;
+        child_pod.transform = Some(self.transform);
         (child_pod, child_state)
     }
 

From 04c4650d39746fb61edc5417f77ae6a9ad268f28 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Thu, 16 Jan 2025 12:02:05 +0000
Subject: [PATCH 3/8] Remove existing solution

---
 xilem/src/lib.rs                 |  5 -----
 xilem/src/one_of.rs              | 30 +-----------------------------
 xilem/src/view/button.rs         | 22 ++--------------------
 xilem/src/view/checkbox.rs       | 20 ++------------------
 xilem/src/view/flex.rs           | 17 ++---------------
 xilem/src/view/grid.rs           | 17 ++---------------
 xilem/src/view/image.rs          | 18 ++----------------
 xilem/src/view/label.rs          | 18 ++----------------
 xilem/src/view/portal.rs         | 20 ++------------------
 xilem/src/view/progress_bar.rs   | 23 +++--------------------
 xilem/src/view/prose.rs          | 18 ++----------------
 xilem/src/view/sized_box.rs      | 17 ++---------------
 xilem/src/view/spinner.rs        | 21 +++------------------
 xilem/src/view/textbox.rs        | 17 ++---------------
 xilem/src/view/transform.rs      |  5 -----
 xilem/src/view/variable_label.rs |  8 +-------
 xilem/src/view/zstack.rs         | 18 ++----------------
 17 files changed, 30 insertions(+), 264 deletions(-)

diff --git a/xilem/src/lib.rs b/xilem/src/lib.rs
index 6f8d1806c..94e7ebaad 100644
--- a/xilem/src/lib.rs
+++ b/xilem/src/lib.rs
@@ -342,11 +342,6 @@ impl ViewCtx {
     pub fn new_pod<W: Widget>(&mut self, widget: W) -> Pod<W> {
         Pod::new(widget)
     }
-    pub fn new_pod_with_transform<W: Widget>(&mut self, widget: W, transform: Affine) -> Pod<W> {
-        let mut pod = Pod::new(widget);
-        pod.transform = Some(transform);
-        pod
-    }
 
     pub fn with_leaf_action_widget<E: Widget>(
         &mut self,
diff --git a/xilem/src/one_of.rs b/xilem/src/one_of.rs
index 11ae0d69f..7be2d3455 100644
--- a/xilem/src/one_of.rs
+++ b/xilem/src/one_of.rs
@@ -13,8 +13,7 @@ use vello::Scene;
 
 use crate::core::one_of::OneOf;
 use crate::core::Mut;
-use crate::view::Transformable;
-use crate::{Affine, Pod, ViewCtx};
+use crate::{Pod, ViewCtx};
 
 impl<
         A: Widget,
@@ -143,33 +142,6 @@ impl<
     }
 }
 
-impl<A, B, C, D, E, F, G, H, I> Transformable for OneOf<A, B, C, D, E, F, G, H, I>
-where
-    A: Transformable,
-    B: Transformable,
-    C: Transformable,
-    D: Transformable,
-    E: Transformable,
-    F: Transformable,
-    G: Transformable,
-    H: Transformable,
-    I: Transformable,
-{
-    fn transform_mut(&mut self) -> &mut Affine {
-        match self {
-            Self::A(w) => w.transform_mut(),
-            Self::B(w) => w.transform_mut(),
-            Self::C(w) => w.transform_mut(),
-            Self::D(w) => w.transform_mut(),
-            Self::E(w) => w.transform_mut(),
-            Self::F(w) => w.transform_mut(),
-            Self::G(w) => w.transform_mut(),
-            Self::H(w) => w.transform_mut(),
-            Self::I(w) => w.transform_mut(),
-        }
-    }
-}
-
 impl crate::core::one_of::PhantomElementCtx for ViewCtx {
     type PhantomElement = Pod<Box<dyn Widget>>;
 }
diff --git a/xilem/src/view/button.rs b/xilem/src/view/button.rs
index 987aafaeb..995de654e 100644
--- a/xilem/src/view/button.rs
+++ b/xilem/src/view/button.rs
@@ -7,9 +7,7 @@ use xilem_core::ViewPathTracker;
 
 use crate::core::{DynMessage, Mut, View, ViewMarker};
 use crate::view::Label;
-use crate::{Affine, MessageResult, Pod, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, ViewCtx, ViewId};
 
 /// A button which calls `callback` when the primary mouse button (normally left) is pressed.
 pub fn button<State, Action>(
@@ -19,7 +17,6 @@ pub fn button<State, Action>(
 {
     Button {
         label: label.into(),
-        transform: Affine::IDENTITY,
         callback: move |state: &mut State, button| match button {
             PointerButton::Primary => MessageResult::Action(callback(state)),
             _ => MessageResult::Nop,
@@ -35,7 +32,6 @@ pub fn button_any_pointer<State, Action>(
 {
     Button {
         label: label.into(),
-        transform: Affine::IDENTITY,
         callback: move |state: &mut State, button| MessageResult::Action(callback(state, button)),
     }
 }
@@ -45,16 +41,9 @@ pub struct Button<F> {
     // N.B. This widget is *implemented* to handle any kind of view with an element
     // type of `Label` even though it currently does not do so.
     label: Label,
-    transform: Affine,
     callback: F,
 }
 
-impl<F> Transformable for Button<F> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 const LABEL_VIEW_ID: ViewId = ViewId::new(0);
 
 impl<F> ViewMarker for Button<F> {}
@@ -70,10 +59,7 @@ where
             View::<State, Action, _>::build(&self.label, ctx)
         });
         ctx.with_leaf_action_widget(|ctx| {
-            ctx.new_pod_with_transform(
-                widget::Button::from_label_pod(child.into_widget_pod()),
-                self.transform,
-            )
+            ctx.new_pod(widget::Button::from_label_pod(child.into_widget_pod()))
         })
     }
 
@@ -84,10 +70,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
-
         ctx.with_id(LABEL_VIEW_ID, |ctx| {
             View::<State, Action, _>::rebuild(
                 &self.label,
diff --git a/xilem/src/view/checkbox.rs b/xilem/src/view/checkbox.rs
index 439067e68..e2174e53d 100644
--- a/xilem/src/view/checkbox.rs
+++ b/xilem/src/view/checkbox.rs
@@ -5,9 +5,7 @@ use masonry::text::ArcStr;
 use masonry::widget;
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, MessageResult, Pod, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, View, ViewCtx, ViewId};
 
 pub fn checkbox<F, State, Action>(
     label: impl Into<ArcStr>,
@@ -21,7 +19,6 @@ where
         label: label.into(),
         callback,
         checked,
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -30,13 +27,6 @@ pub struct Checkbox<F> {
     label: ArcStr,
     checked: bool,
     callback: F,
-    transform: Affine,
-}
-
-impl<F> Transformable for Checkbox<F> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
 }
 
 impl<F> ViewMarker for Checkbox<F> {}
@@ -49,10 +39,7 @@ where
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
         ctx.with_leaf_action_widget(|ctx| {
-            ctx.new_pod_with_transform(
-                widget::Checkbox::new(self.checked, self.label.clone()),
-                self.transform,
-            )
+            ctx.new_pod(widget::Checkbox::new(self.checked, self.label.clone()))
         })
     }
 
@@ -63,9 +50,6 @@ where
         _ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.label != self.label {
             widget::Checkbox::set_text(&mut element, self.label.clone());
         }
diff --git a/xilem/src/view/flex.rs b/xilem/src/view/flex.rs
index fdbf8a1de..615d836f7 100644
--- a/xilem/src/view/flex.rs
+++ b/xilem/src/view/flex.rs
@@ -11,7 +11,7 @@ use crate::core::{
     AppendVec, DynMessage, ElementSplice, MessageResult, Mut, SuperElement, View, ViewElement,
     ViewId, ViewMarker, ViewPathTracker, ViewSequence,
 };
-use crate::{Affine, AnyWidgetView, Pod, ViewCtx, WidgetView};
+use crate::{AnyWidgetView, Pod, ViewCtx, WidgetView};
 
 pub fn flex<State, Action, Seq: FlexSequence<State, Action>>(
     sequence: Seq,
@@ -19,7 +19,6 @@ pub fn flex<State, Action, Seq: FlexSequence<State, Action>>(
     Flex {
         sequence,
         axis: Axis::Vertical,
-        transform: Affine::IDENTITY,
         cross_axis_alignment: CrossAxisAlignment::Center,
         main_axis_alignment: MainAxisAlignment::Start,
         fill_major_axis: false,
@@ -32,7 +31,6 @@ pub fn flex<State, Action, Seq: FlexSequence<State, Action>>(
 pub struct Flex<Seq, State, Action = ()> {
     sequence: Seq,
     axis: Axis,
-    transform: Affine,
     cross_axis_alignment: CrossAxisAlignment,
     main_axis_alignment: MainAxisAlignment,
     fill_major_axis: bool,
@@ -87,12 +85,6 @@ impl<Seq, State, Action> Flex<Seq, State, Action> {
     }
 }
 
-impl<Seq, State, Action> Transformable for Flex<Seq, State, Action> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl<Seq, State, Action> ViewMarker for Flex<Seq, State, Action> {}
 impl<State, Action, Seq> View<State, Action, ViewCtx> for Flex<Seq, State, Action>
 where
@@ -121,7 +113,7 @@ where
                 FlexElement::FlexSpacer(flex) => widget.with_flex_spacer(flex),
             }
         }
-        let pod = ctx.new_pod_with_transform(widget, self.transform);
+        let pod = ctx.new_pod(widget);
         (pod, seq_state)
     }
 
@@ -132,9 +124,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.axis != self.axis {
             widget::Flex::set_direction(&mut element, self.axis);
         }
@@ -646,8 +635,6 @@ mod hidden {
 }
 use hidden::AnyFlexChildState;
 
-use super::Transformable;
-
 impl<State, Action> ViewMarker for AnyFlexChild<State, Action> {}
 impl<State, Action> View<State, Action, ViewCtx> for AnyFlexChild<State, Action>
 where
diff --git a/xilem/src/view/grid.rs b/xilem/src/view/grid.rs
index 408dd8423..ffbc01fc5 100644
--- a/xilem/src/view/grid.rs
+++ b/xilem/src/view/grid.rs
@@ -10,9 +10,7 @@ use crate::core::{
     AppendVec, DynMessage, ElementSplice, MessageResult, Mut, SuperElement, View, ViewElement,
     ViewId, ViewMarker, ViewSequence,
 };
-use crate::{Affine, Pod, ViewCtx, WidgetView};
-
-use super::Transformable;
+use crate::{Pod, ViewCtx, WidgetView};
 
 pub fn grid<State, Action, Seq: GridSequence<State, Action>>(
     sequence: Seq,
@@ -25,7 +23,6 @@ pub fn grid<State, Action, Seq: GridSequence<State, Action>>(
         phantom: PhantomData,
         height,
         width,
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -35,7 +32,6 @@ pub struct Grid<Seq, State, Action = ()> {
     spacing: f64,
     width: i32,
     height: i32,
-    transform: Affine,
     /// Used to associate the State and Action in the call to `.grid()` with the State and Action
     /// used in the View implementation, to allow inference to flow backwards, allowing State and
     /// Action to be inferred properly
@@ -54,12 +50,6 @@ impl<Seq, State, Action> Grid<Seq, State, Action> {
     }
 }
 
-impl<Seq, State, Action> Transformable for Grid<Seq, State, Action> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl<Seq, State, Action> ViewMarker for Grid<Seq, State, Action> {}
 
 impl<State, Action, Seq> View<State, Action, ViewCtx> for Grid<Seq, State, Action>
@@ -84,7 +74,7 @@ where
                 }
             }
         }
-        let pod = ctx.new_pod_with_transform(widget, self.transform);
+        let pod = ctx.new_pod(widget);
         (pod, seq_state)
     }
 
@@ -95,9 +85,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.height != self.height {
             widget::Grid::set_height(&mut element, self.height);
         }
diff --git a/xilem/src/view/image.rs b/xilem/src/view/image.rs
index 200b4e65d..4bbc4dfdd 100644
--- a/xilem/src/view/image.rs
+++ b/xilem/src/view/image.rs
@@ -6,9 +6,7 @@
 use masonry::widget::{self, ObjectFit};
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, MessageResult, Pod, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, View, ViewCtx, ViewId};
 
 /// Displays the bitmap `image`.
 ///
@@ -27,7 +25,6 @@ pub fn image(image: &vello::peniko::Image) -> Image {
         // easier than documenting that cloning is cheap.
         image: image.clone(),
         object_fit: ObjectFit::default(),
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -38,7 +35,6 @@ pub fn image(image: &vello::peniko::Image) -> Image {
 pub struct Image {
     image: vello::peniko::Image,
     object_fit: ObjectFit,
-    transform: Affine,
 }
 
 impl Image {
@@ -49,20 +45,13 @@ impl Image {
     }
 }
 
-impl Transformable for Image {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl ViewMarker for Image {}
 impl<State, Action> View<State, Action, ViewCtx> for Image {
     type Element = Pod<widget::Image>;
     type ViewState = ();
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
-        let pod =
-            ctx.new_pod_with_transform(widget::Image::new(self.image.clone()), self.transform);
+        let pod = ctx.new_pod(widget::Image::new(self.image.clone()));
         (pod, ())
     }
 
@@ -73,9 +62,6 @@ impl<State, Action> View<State, Action, ViewCtx> for Image {
         _: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.object_fit != self.object_fit {
             widget::Image::set_fit_mode(&mut element, self.object_fit);
         }
diff --git a/xilem/src/view/label.rs b/xilem/src/view/label.rs
index ee6705d4d..cafd59d74 100644
--- a/xilem/src/view/label.rs
+++ b/xilem/src/view/label.rs
@@ -7,9 +7,7 @@ use masonry::widget::{self, LineBreaking};
 use vello::peniko::Brush;
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, Color, MessageResult, Pod, TextAlignment, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{Color, MessageResult, Pod, TextAlignment, View, ViewCtx, ViewId};
 
 pub fn label(label: impl Into<ArcStr>) -> Label {
     Label {
@@ -20,7 +18,6 @@ pub fn label(label: impl Into<ArcStr>) -> Label {
         weight: FontWeight::NORMAL,
         font: FontStack::List(std::borrow::Cow::Borrowed(&[])),
         line_break_mode: LineBreaking::Overflow,
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -33,7 +30,6 @@ pub struct Label {
     weight: FontWeight,
     font: FontStack<'static>,
     line_break_mode: LineBreaking, // TODO: add more attributes of `masonry::widget::Label`
-    transform: Affine,
 }
 
 impl Label {
@@ -75,12 +71,6 @@ impl Label {
     }
 }
 
-impl Transformable for Label {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl<T> From<T> for Label
 where
     T: Into<ArcStr>,
@@ -96,7 +86,7 @@ impl<State, Action> View<State, Action, ViewCtx> for Label {
     type ViewState = ();
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
-        let widget_pod = ctx.new_pod_with_transform(
+        let widget_pod = ctx.new_pod(
             widget::Label::new(self.label.clone())
                 .with_brush(self.text_brush.clone())
                 .with_alignment(self.alignment)
@@ -104,7 +94,6 @@ impl<State, Action> View<State, Action, ViewCtx> for Label {
                 .with_style(StyleProperty::FontWeight(self.weight))
                 .with_style(StyleProperty::FontStack(self.font.clone()))
                 .with_line_break_mode(self.line_break_mode),
-            self.transform,
         );
         (widget_pod, ())
     }
@@ -116,9 +105,6 @@ impl<State, Action> View<State, Action, ViewCtx> for Label {
         _ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.label != self.label {
             widget::Label::set_text(&mut element, self.label.clone());
         }
diff --git a/xilem/src/view/portal.rs b/xilem/src/view/portal.rs
index 2d4531e07..b9763c264 100644
--- a/xilem/src/view/portal.rs
+++ b/xilem/src/view/portal.rs
@@ -6,9 +6,7 @@ use std::marker::PhantomData;
 use masonry::widget;
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, MessageResult, Pod, View, ViewCtx, ViewId, WidgetView};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, View, ViewCtx, ViewId, WidgetView};
 
 /// A view which puts `child` into a scrollable region.
 ///
@@ -19,7 +17,6 @@ where
 {
     Portal {
         child,
-        transform: Affine::IDENTITY,
         phantom: PhantomData,
     }
 }
@@ -27,7 +24,6 @@ where
 #[must_use = "View values do nothing unless provided to Xilem."]
 pub struct Portal<V, State, Action> {
     child: V,
-    transform: Affine,
     phantom: PhantomData<(State, Action)>,
 }
 
@@ -45,10 +41,7 @@ where
         // The Portal `View` doesn't get any messages directly (yet - scroll events?), so doesn't need to
         // use ctx.with_id.
         let (child, child_state) = self.child.build(ctx);
-        let widget_pod = ctx.new_pod_with_transform(
-            widget::Portal::new_pod(child.into_widget_pod()),
-            self.transform,
-        );
+        let widget_pod = ctx.new_pod(widget::Portal::new_pod(child.into_widget_pod()));
         (widget_pod, child_state)
     }
 
@@ -59,9 +52,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         let child_element = widget::Portal::child_mut(&mut element);
         self.child
             .rebuild(&prev.child, view_state, ctx, child_element);
@@ -87,9 +77,3 @@ where
         self.child.message(view_state, id_path, message, app_state)
     }
 }
-
-impl<V, State, Action> Transformable for Portal<V, State, Action> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
diff --git a/xilem/src/view/progress_bar.rs b/xilem/src/view/progress_bar.rs
index ef83c3ecf..7917788b8 100644
--- a/xilem/src/view/progress_bar.rs
+++ b/xilem/src/view/progress_bar.rs
@@ -4,26 +4,14 @@
 use masonry::widget;
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, MessageResult, Pod, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, View, ViewCtx, ViewId};
 
 pub fn progress_bar(progress: Option<f64>) -> ProgressBar {
-    ProgressBar {
-        progress,
-        transform: Affine::IDENTITY,
-    }
+    ProgressBar { progress }
 }
 
 pub struct ProgressBar {
     progress: Option<f64>,
-    transform: Affine,
-}
-
-impl Transformable for ProgressBar {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
 }
 
 impl ViewMarker for ProgressBar {}
@@ -32,9 +20,7 @@ impl<State, Action> View<State, Action, ViewCtx> for ProgressBar {
     type ViewState = ();
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
-        ctx.with_leaf_action_widget(|ctx| {
-            ctx.new_pod_with_transform(widget::ProgressBar::new(self.progress), self.transform)
-        })
+        ctx.with_leaf_action_widget(|ctx| ctx.new_pod(widget::ProgressBar::new(self.progress)))
     }
 
     fn rebuild(
@@ -44,9 +30,6 @@ impl<State, Action> View<State, Action, ViewCtx> for ProgressBar {
         _ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.progress != self.progress {
             widget::ProgressBar::set_progress(&mut element, self.progress);
         }
diff --git a/xilem/src/view/prose.rs b/xilem/src/view/prose.rs
index 749ee4f05..191ab4d01 100644
--- a/xilem/src/view/prose.rs
+++ b/xilem/src/view/prose.rs
@@ -6,9 +6,7 @@ use masonry::widget::{self, LineBreaking};
 use vello::peniko::Brush;
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, Color, MessageResult, Pod, TextAlignment, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{Color, MessageResult, Pod, TextAlignment, View, ViewCtx, ViewId};
 
 pub fn prose(content: impl Into<ArcStr>) -> Prose {
     Prose {
@@ -17,7 +15,6 @@ pub fn prose(content: impl Into<ArcStr>) -> Prose {
         alignment: TextAlignment::default(),
         text_size: masonry::theme::TEXT_SIZE_NORMAL,
         line_break_mode: LineBreaking::WordWrap,
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -39,7 +36,6 @@ pub struct Prose {
     alignment: TextAlignment,
     text_size: f32,
     line_break_mode: LineBreaking,
-    transform: Affine,
     // TODO: disabled: bool,
     // TODO: add more attributes of `masonry::widget::Prose`
 }
@@ -71,12 +67,6 @@ fn line_break_clips(linebreaking: LineBreaking) -> bool {
     matches!(linebreaking, LineBreaking::Clip | LineBreaking::WordWrap)
 }
 
-impl Transformable for Prose {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl ViewMarker for Prose {}
 impl<State, Action> View<State, Action, ViewCtx> for Prose {
     type Element = Pod<widget::Prose>;
@@ -88,10 +78,9 @@ impl<State, Action> View<State, Action, ViewCtx> for Prose {
             .with_alignment(self.alignment)
             .with_style(StyleProperty::FontSize(self.text_size))
             .with_word_wrap(self.line_break_mode == LineBreaking::WordWrap);
-        let widget_pod = ctx.new_pod_with_transform(
+        let widget_pod = ctx.new_pod(
             widget::Prose::from_text_area(text_area)
                 .with_clip(line_break_clips(self.line_break_mode)),
-            self.transform,
         );
         (widget_pod, ())
     }
@@ -103,9 +92,6 @@ impl<State, Action> View<State, Action, ViewCtx> for Prose {
         _ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         let mut text_area = widget::Prose::text_mut(&mut element);
         if prev.content != self.content {
             widget::TextArea::reset_text(&mut text_area, &self.content);
diff --git a/xilem/src/view/sized_box.rs b/xilem/src/view/sized_box.rs
index a1b33a6dd..829d3f2a1 100644
--- a/xilem/src/view/sized_box.rs
+++ b/xilem/src/view/sized_box.rs
@@ -9,9 +9,7 @@ use vello::kurbo::RoundedRectRadii;
 use vello::peniko::Brush;
 
 use crate::core::{DynMessage, Mut, View, ViewId, ViewMarker};
-use crate::{Affine, Pod, ViewCtx, WidgetView};
-
-use super::Transformable;
+use crate::{Pod, ViewCtx, WidgetView};
 
 /// A widget with predefined size.
 ///
@@ -31,7 +29,6 @@ where
         corner_radius: RoundedRectRadii::from_single_radius(0.0),
         padding: Padding::ZERO,
         phantom: PhantomData,
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -45,7 +42,6 @@ pub struct SizedBox<V, State, Action = ()> {
     corner_radius: RoundedRectRadii,
     padding: Padding,
     phantom: PhantomData<fn() -> (State, Action)>,
-    transform: Affine,
 }
 
 impl<V, State, Action> SizedBox<V, State, Action> {
@@ -125,12 +121,6 @@ impl<V, State, Action> SizedBox<V, State, Action> {
     }
 }
 
-impl<V, State, Action> Transformable for SizedBox<V, State, Action> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl<V, State, Action> ViewMarker for SizedBox<V, State, Action> {}
 impl<V, State, Action> View<State, Action, ViewCtx> for SizedBox<V, State, Action>
 where
@@ -154,7 +144,7 @@ where
         if let Some(border) = &self.border {
             widget = widget.border(border.brush.clone(), border.width);
         }
-        let pod = ctx.new_pod_with_transform(widget, self.transform);
+        let pod = ctx.new_pod(widget);
         (pod, child_state)
     }
 
@@ -165,9 +155,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if self.width != prev.width {
             match self.width {
                 Some(width) => widget::SizedBox::set_width(&mut element, width),
diff --git a/xilem/src/view/spinner.rs b/xilem/src/view/spinner.rs
index d2319f8f1..ddf983c0e 100644
--- a/xilem/src/view/spinner.rs
+++ b/xilem/src/view/spinner.rs
@@ -4,9 +4,7 @@
 use masonry::{widget, Color};
 
 use crate::core::{DynMessage, Mut, ViewMarker};
-use crate::{Affine, MessageResult, Pod, View, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{MessageResult, Pod, View, ViewCtx, ViewId};
 
 /// An indefinite spinner.
 ///
@@ -34,10 +32,7 @@ use super::Transformable;
 /// }
 /// ```
 pub fn spinner() -> Spinner {
-    Spinner {
-        color: None,
-        transform: Affine::IDENTITY,
-    }
+    Spinner { color: None }
 }
 
 /// The [`View`] created by [`spinner`].
@@ -46,7 +41,6 @@ pub fn spinner() -> Spinner {
 #[must_use = "View values do nothing unless provided to Xilem."]
 pub struct Spinner {
     color: Option<Color>,
-    transform: Affine,
 }
 
 impl Spinner {
@@ -57,19 +51,13 @@ impl Spinner {
     }
 }
 
-impl Transformable for Spinner {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl ViewMarker for Spinner {}
 impl<State, Action> View<State, Action, ViewCtx> for Spinner {
     type Element = Pod<widget::Spinner>;
     type ViewState = ();
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
-        let pod = ctx.new_pod_with_transform(widget::Spinner::new(), self.transform);
+        let pod = ctx.new_pod(widget::Spinner::new());
         (pod, ())
     }
 
@@ -80,9 +68,6 @@ impl<State, Action> View<State, Action, ViewCtx> for Spinner {
         _: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         if prev.color != self.color {
             match self.color {
                 Some(color) => widget::Spinner::set_color(&mut element, color),
diff --git a/xilem/src/view/textbox.rs b/xilem/src/view/textbox.rs
index 8ce8f8c2a..03b9472ed 100644
--- a/xilem/src/view/textbox.rs
+++ b/xilem/src/view/textbox.rs
@@ -5,9 +5,7 @@ use masonry::widget;
 use vello::peniko::Brush;
 
 use crate::core::{DynMessage, Mut, View, ViewMarker};
-use crate::{Affine, Color, MessageResult, Pod, TextAlignment, ViewCtx, ViewId};
-
-use super::Transformable;
+use crate::{Color, MessageResult, Pod, TextAlignment, ViewCtx, ViewId};
 
 // FIXME - A major problem of the current approach (always setting the textbox contents)
 // is that if the user forgets to hook up the modify the state's contents in the callback,
@@ -26,7 +24,6 @@ where
         on_enter: None,
         text_brush: Color::WHITE.into(),
         alignment: TextAlignment::default(),
-        transform: Affine::IDENTITY,
         // TODO?: disabled: false,
     }
 }
@@ -38,7 +35,6 @@ pub struct Textbox<State, Action> {
     on_enter: Option<Callback<State, Action>>,
     text_brush: Brush,
     alignment: TextAlignment,
-    transform: Affine,
     // TODO: add more attributes of `masonry::widget::TextBox`
 }
 
@@ -63,12 +59,6 @@ impl<State, Action> Textbox<State, Action> {
     }
 }
 
-impl<State, Action> Transformable for Textbox<State, Action> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 impl<State, Action> ViewMarker for Textbox<State, Action> {}
 impl<State: 'static, Action: 'static> View<State, Action, ViewCtx> for Textbox<State, Action> {
     type Element = Pod<widget::Textbox>;
@@ -84,7 +74,7 @@ impl<State: 'static, Action: 'static> View<State, Action, ViewCtx> for Textbox<S
         // Ensure that the actions from the *inner* TextArea get routed correctly.
         let id = textbox.area_pod().id();
         ctx.record_action(id);
-        let widget_pod = ctx.new_pod_with_transform(textbox, self.transform);
+        let widget_pod = ctx.new_pod(textbox);
         (widget_pod, ())
     }
 
@@ -95,9 +85,6 @@ impl<State: 'static, Action: 'static> View<State, Action, ViewCtx> for Textbox<S
         _ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if prev.transform != self.transform {
-            element.set_transform(self.transform);
-        }
         let mut text_area = widget::Textbox::text_mut(&mut element);
 
         // Unlike the other properties, we don't compare to the previous value;
diff --git a/xilem/src/view/transform.rs b/xilem/src/view/transform.rs
index 555468d46..054b6f60c 100644
--- a/xilem/src/view/transform.rs
+++ b/xilem/src/view/transform.rs
@@ -126,8 +126,3 @@ where
         self.child.message(view_state, id_path, message, app_state)
     }
 }
-
-/// An extension trait, to allow common transformations of the views transform.
-pub trait Transformable: Sized {
-    fn transform_mut(&mut self) -> &mut Affine;
-}
diff --git a/xilem/src/view/variable_label.rs b/xilem/src/view/variable_label.rs
index e2a73c1c6..1c8b697ee 100644
--- a/xilem/src/view/variable_label.rs
+++ b/xilem/src/view/variable_label.rs
@@ -10,7 +10,7 @@ use xilem_core::ViewPathTracker;
 use crate::core::{DynMessage, Mut, ViewMarker};
 use crate::{MessageResult, Pod, View, ViewCtx, ViewId};
 
-use super::{label, Label, Transformable};
+use super::{label, Label};
 
 /// A view for displaying non-editable text, with a variable [weight](masonry::parley::style::FontWeight).
 pub fn variable_label(text: impl Into<ArcStr>) -> VariableLabel {
@@ -81,12 +81,6 @@ impl VariableLabel {
     }
 }
 
-impl Transformable for VariableLabel {
-    fn transform_mut(&mut self) -> &mut crate::Affine {
-        self.label.transform_mut()
-    }
-}
-
 impl ViewMarker for VariableLabel {}
 impl<State, Action> View<State, Action, ViewCtx> for VariableLabel {
     type Element = Pod<widget::VariableLabel>;
diff --git a/xilem/src/view/zstack.rs b/xilem/src/view/zstack.rs
index e2f48d90e..160a4dd8b 100644
--- a/xilem/src/view/zstack.rs
+++ b/xilem/src/view/zstack.rs
@@ -10,7 +10,7 @@ use crate::{
         AppendVec, DynMessage, ElementSplice, Mut, SuperElement, View, ViewElement, ViewMarker,
         ViewSequence,
     },
-    Affine, Pod, ViewCtx, WidgetView,
+    Pod, ViewCtx, WidgetView,
 };
 use masonry::{
     widget::{self, Alignment, ChildAlignment, WidgetMut},
@@ -18,8 +18,6 @@ use masonry::{
 };
 use xilem_core::{MessageResult, ViewId};
 
-use super::Transformable;
-
 /// A widget that lays out its children on top of each other.
 /// The children are laid out back to front.
 ///
@@ -42,7 +40,6 @@ pub fn zstack<State, Action, Seq: ZStackSequence<State, Action>>(sequence: Seq)
     ZStack {
         sequence,
         alignment: Alignment::default(),
-        transform: Affine::IDENTITY,
     }
 }
 
@@ -53,7 +50,6 @@ pub fn zstack<State, Action, Seq: ZStackSequence<State, Action>>(sequence: Seq)
 pub struct ZStack<Seq> {
     sequence: Seq,
     alignment: Alignment,
-    transform: Affine,
 }
 
 impl<Seq> ZStack<Seq> {
@@ -82,7 +78,7 @@ where
         for child in elements.into_inner() {
             widget = widget.with_child_pod(child.widget.into_widget_pod(), child.alignment);
         }
-        let pod = ctx.new_pod_with_transform(widget, self.transform);
+        let pod = ctx.new_pod(widget);
         (pod, seq_state)
     }
 
@@ -93,10 +89,6 @@ where
         ctx: &mut ViewCtx,
         mut element: Mut<Self::Element>,
     ) {
-        if self.transform != prev.transform {
-            element.set_transform(self.transform);
-        }
-
         if self.alignment != prev.alignment {
             widget::ZStack::set_alignment(&mut element, self.alignment);
         }
@@ -130,12 +122,6 @@ where
     }
 }
 
-impl<Seq> Transformable for ZStack<Seq> {
-    fn transform_mut(&mut self) -> &mut Affine {
-        &mut self.transform
-    }
-}
-
 // --- MARK: ZStackExt ---
 
 /// A trait that extends a [`WidgetView`] with methods to provide parameters for a parent [`ZStack`].

From fe95af704c602113e02099eab2f0e869ae693d09 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Jan 2025 09:00:36 +0000
Subject: [PATCH 4/8] Make `Transformed` support nesting

---
 masonry/src/contexts.rs     |  5 ++++
 xilem/src/lib.rs            | 19 +++++-------
 xilem/src/view/transform.rs | 59 +++++++++++++++++++++++++++++--------
 3 files changed, 60 insertions(+), 23 deletions(-)

diff --git a/masonry/src/contexts.rs b/masonry/src/contexts.rs
index ae6c25ab7..1a4d8efd4 100644
--- a/masonry/src/contexts.rs
+++ b/masonry/src/contexts.rs
@@ -163,6 +163,11 @@ impl_context_method!(
                 .expect("get_child_state: child not found");
             child_state_ref.item
         }
+
+        /// The current (local) transform of this widget.
+        pub fn transform(&self) -> Affine {
+            self.widget_state.transform
+        }
     }
 );
 
diff --git a/xilem/src/lib.rs b/xilem/src/lib.rs
index 94e7ebaad..67e55c8a4 100644
--- a/xilem/src/lib.rs
+++ b/xilem/src/lib.rs
@@ -189,7 +189,12 @@ where
 pub struct Pod<W: Widget> {
     pub widget: W,
     pub id: WidgetId,
-    pub transform: Option<Affine>,
+    /// The transform the widget will be created with.
+    ///
+    /// If changing transforms of widgets, prefer to use [`WidgetView::transformed`].
+    /// This has a protocol to ensure that multiple views changing the
+    /// transform interoperate successfully.
+    pub transform: Affine,
 }
 
 impl<W: Widget> Pod<W> {
@@ -201,18 +206,10 @@ impl<W: Widget> Pod<W> {
         }
     }
     fn into_widget_pod(self) -> WidgetPod<W> {
-        WidgetPod::new_with_id_and_transform(
-            self.widget,
-            self.id,
-            self.transform.unwrap_or_default(),
-        )
+        WidgetPod::new_with_id_and_transform(self.widget, self.id, self.transform)
     }
     fn boxed_widget_pod(self) -> WidgetPod<Box<dyn Widget>> {
-        WidgetPod::new_with_id_and_transform(
-            Box::new(self.widget),
-            self.id,
-            self.transform.unwrap_or_default(),
-        )
+        WidgetPod::new_with_id_and_transform(Box::new(self.widget), self.id, self.transform)
     }
     fn boxed(self) -> Pod<Box<dyn Widget>> {
         Pod {
diff --git a/xilem/src/view/transform.rs b/xilem/src/view/transform.rs
index 054b6f60c..5af650f86 100644
--- a/xilem/src/view/transform.rs
+++ b/xilem/src/view/transform.rs
@@ -74,6 +74,20 @@ impl<V, State, Action> Transformed<V, State, Action> {
     }
 }
 
+mod private {
+    use crate::Affine;
+
+    /// The View state for the [Transformed](super::Transformed)
+    #[expect(
+        unnameable_types,
+        reason = "This type has no public API, and is only public due to trait visibility rules"
+    )]
+    pub struct TransformedState<ChildState> {
+        pub(super) child: ChildState,
+        pub(super) previous_transform: Affine,
+    }
+}
+
 impl<V, State, Action> ViewMarker for Transformed<V, State, Action> {}
 impl<Child, State, Action> View<State, Action, ViewCtx> for Transformed<Child, State, Action>
 where
@@ -82,16 +96,16 @@ where
     Action: 'static,
 {
     type Element = Pod<Child::Widget>;
-    type ViewState = Child::ViewState;
+    type ViewState = private::TransformedState<Child::ViewState>;
 
     fn build(&self, ctx: &mut ViewCtx) -> (Self::Element, Self::ViewState) {
         let (mut child_pod, child_state) = self.child.build(ctx);
-        // TODO: Use a marker identity value to detect this more properly
-        if child_pod.transform.is_some() {
-            panic!("Tried to create a `Transformed` with an already controlled Transform");
-        }
-        child_pod.transform = Some(self.transform);
-        (child_pod, child_state)
+        let state = private::TransformedState {
+            child: child_state,
+            previous_transform: child_pod.transform,
+        };
+        child_pod.transform = self.transform * state.previous_transform;
+        (child_pod, state)
     }
 
     fn rebuild(
@@ -101,10 +115,30 @@ where
         ctx: &mut ViewCtx,
         mut element: xilem_core::Mut<'_, Self::Element>,
     ) {
-        if self.transform != prev.transform {
-            element.ctx.set_transform(self.transform);
+        let initial_transform = element.ctx.transform();
+        self.child.rebuild(
+            &prev.child,
+            &mut view_state.child,
+            ctx,
+            element.reborrow_mut(),
+        );
+        let transform_changed = element.ctx.transform() != initial_transform;
+        // We detect a child view changing the transform by comparing the
+        // resulting transform before and after the child view runs.
+        if transform_changed {
+            // If it has changed the transform, then we know that it will only be due to effects
+            // "below us" (that is, it will have restarted from scratch).
+            // We update our stored understanding of the transforms below us
+            view_state.previous_transform = element.ctx.transform();
+            // This is a convention used to communicate with ourselves, which could
+            // break down if any other view handles transforms differently.
+            // However, we document against this in `Pod::transform`.
+        }
+        if self.transform != prev.transform || transform_changed {
+            element
+                .ctx
+                .set_transform(self.transform * view_state.previous_transform);
         }
-        self.child.rebuild(&prev.child, view_state, ctx, element);
     }
 
     fn teardown(
@@ -113,7 +147,7 @@ where
         ctx: &mut ViewCtx,
         element: xilem_core::Mut<'_, Self::Element>,
     ) {
-        self.child.teardown(view_state, ctx, element);
+        self.child.teardown(&mut view_state.child, ctx, element);
     }
 
     fn message(
@@ -123,6 +157,7 @@ where
         message: DynMessage,
         app_state: &mut State,
     ) -> xilem_core::MessageResult<Action, DynMessage> {
-        self.child.message(view_state, id_path, message, app_state)
+        self.child
+            .message(&mut view_state.child, id_path, message, app_state)
     }
 }

From 70e8efd74e7545ca381dba0527c204c563348cfa Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Jan 2025 09:15:58 +0000
Subject: [PATCH 5/8] "Test" the new ability

---
 xilem/examples/transforms.rs | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xilem/examples/transforms.rs b/xilem/examples/transforms.rs
index f5e0a25dd..c088d07f5 100644
--- a/xilem/examples/transforms.rs
+++ b/xilem/examples/transforms.rs
@@ -48,7 +48,12 @@ impl TransformsGame {
             .background(Color::new(bg_color))
             .transformed()
             .translate(self.translation)
+            // In an actual app, you wouldn't use `.transformed` here.
+            // This is here to validate that Xilem's support for nested `Transformed`
+            // values works as expected.
+            .transformed()
             .rotate(self.rotation)
+            .transformed()
             .scale(self.scale);
 
         let controls = (

From 05190d6b591dab0187edcbe8f54c1c83d9276278 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Jan 2025 16:26:40 +0000
Subject: [PATCH 6/8] Expose `transform_has_changed` and use that instead

---
 masonry/src/contexts.rs     | 9 +++++++++
 xilem/src/view/transform.rs | 6 ++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/masonry/src/contexts.rs b/masonry/src/contexts.rs
index 1a4d8efd4..3d9dbcfc0 100644
--- a/masonry/src/contexts.rs
+++ b/masonry/src/contexts.rs
@@ -236,6 +236,15 @@ impl MutateCtx<'_> {
             widget_children: self.widget_children.reborrow_mut(),
         }
     }
+
+    /// Whether the (local) transform of this widget has been modified since
+    /// the last time this widget's transformation was resolved.
+    ///
+    /// This is exposed for Xilem, and is more likely to change or be removed
+    /// in major releases of Masonry.
+    pub fn transform_has_changed(&self) -> bool {
+        self.widget_state.transform_changed
+    }
 }
 
 // --- MARK: WIDGET_REF ---
diff --git a/xilem/src/view/transform.rs b/xilem/src/view/transform.rs
index 5af650f86..8a2e974eb 100644
--- a/xilem/src/view/transform.rs
+++ b/xilem/src/view/transform.rs
@@ -115,16 +115,14 @@ where
         ctx: &mut ViewCtx,
         mut element: xilem_core::Mut<'_, Self::Element>,
     ) {
-        let initial_transform = element.ctx.transform();
         self.child.rebuild(
             &prev.child,
             &mut view_state.child,
             ctx,
             element.reborrow_mut(),
         );
-        let transform_changed = element.ctx.transform() != initial_transform;
-        // We detect a child view changing the transform by comparing the
-        // resulting transform before and after the child view runs.
+        let transform_changed = element.ctx.transform_has_changed();
+        // If the child view changed the transform, we know we're out of date.
         if transform_changed {
             // If it has changed the transform, then we know that it will only be due to effects
             // "below us" (that is, it will have restarted from scratch).

From 77aebb4e484dffe342811c12f62c23ab9b8b8be6 Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Jan 2025 17:28:47 +0000
Subject: [PATCH 7/8] Make extension method `.transform`

---
 xilem/examples/transforms.rs | 20 +++++++++-----------
 xilem/src/lib.rs             | 10 +++++-----
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/xilem/examples/transforms.rs b/xilem/examples/transforms.rs
index c088d07f5..edfc8648e 100644
--- a/xilem/examples/transforms.rs
+++ b/xilem/examples/transforms.rs
@@ -6,8 +6,8 @@
 use std::f64::consts::{PI, TAU};
 
 use winit::error::EventLoopError;
-use xilem::view::{button, grid, label, sized_box, GridExt as _};
-use xilem::{Color, EventLoop, Vec2, WidgetView, Xilem};
+use xilem::view::{button, grid, label, sized_box, transformed, GridExt as _};
+use xilem::{Affine, Color, EventLoop, Vec2, WidgetView, Xilem};
 
 struct TransformsGame {
     rotation: f64,
@@ -41,20 +41,18 @@ impl TransformsGame {
             [1.0, 0.0, 0.0, 0.2]
         };
 
+        let status = sized_box(status).background(Color::new(bg_color));
         // Every view can be transformed similar as with CSS transforms in the web.
         // Currently only 2D transforms are supported.
         // Note that the order of the transformations is relevant.
-        let transformed_status = sized_box(status)
-            .background(Color::new(bg_color))
-            .transformed()
-            .translate(self.translation)
-            // In an actual app, you wouldn't use `.transformed` here.
+        let transformed_status = transformed(
+            // In an actual app, you wouldn't use both `transformed` and `.transform`.
             // This is here to validate that Xilem's support for nested `Transformed`
             // values works as expected.
-            .transformed()
-            .rotate(self.rotation)
-            .transformed()
-            .scale(self.scale);
+            status.transform(Affine::translate(self.translation)),
+        )
+        .rotate(self.rotation)
+        .scale(self.scale);
 
         let controls = (
             button("↶", |this: &mut Self| {
diff --git a/xilem/src/lib.rs b/xilem/src/lib.rs
index 67e55c8a4..949217693 100644
--- a/xilem/src/lib.rs
+++ b/xilem/src/lib.rs
@@ -266,14 +266,14 @@ pub trait WidgetView<State, Action = ()>:
 
     /// This widget with a 2d transform applied.
     ///
-    /// The returned view has methods to control individual components of
-    /// the transform, as well as apply an arbitrary transform.
-    /// See [`transformed`] for more details.
-    fn transformed(self) -> Transformed<Self, State, Action>
+    /// See [`transformed`] for similar functionality with a builder-API using this.
+    /// The return type is the same as for `transformed`, and so also has these
+    /// builder methods.
+    fn transform(self, by: Affine) -> Transformed<Self, State, Action>
     where
         Self: Sized,
     {
-        transformed(self)
+        transformed(self).transform(by)
     }
 }
 

From 8eda8fbbf904e8f2dca69ef499fbb503826847cb Mon Sep 17 00:00:00 2001
From: Daniel McNab <36049421+DJMcNab@users.noreply.github.com>
Date: Fri, 17 Jan 2025 17:37:45 +0000
Subject: [PATCH 8/8] Fixup docs

---
 xilem/src/lib.rs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/xilem/src/lib.rs b/xilem/src/lib.rs
index 949217693..f5f554a7f 100644
--- a/xilem/src/lib.rs
+++ b/xilem/src/lib.rs
@@ -191,7 +191,8 @@ pub struct Pod<W: Widget> {
     pub id: WidgetId,
     /// The transform the widget will be created with.
     ///
-    /// If changing transforms of widgets, prefer to use [`WidgetView::transformed`].
+    /// If changing transforms of widgets, prefer to use [`transformed`]
+    /// (or [`WidgetView::transform`]).
     /// This has a protocol to ensure that multiple views changing the
     /// transform interoperate successfully.
     pub transform: Affine,