diff --git a/TODO b/TODO
new file mode 100644
index 0000000..5dcf131
--- /dev/null
+++ b/TODO
@@ -0,0 +1,6 @@
+images
+text
+ui ctx = ui + app ctx for sensors
+free / delete widgets
+abstract sensors to work with any event, maybe associate data as well?
+make senses orable so you can select multiple
diff --git a/src/core/stack.rs b/src/core/stack.rs
index 855c7ea..994d565 100644
--- a/src/core/stack.rs
+++ b/src/core/stack.rs
@@ -7,7 +7,7 @@ pub struct Stack {
 impl<Ctx> Widget<Ctx> for Stack {
     fn draw(&self, painter: &mut crate::Painter<Ctx>) {
         for child in &self.children {
-            painter.draw(child);
+            painter.draw_within(child, painter.region);
         }
     }
 }
diff --git a/src/layout/id.rs b/src/layout/id.rs
new file mode 100644
index 0000000..65a0cad
--- /dev/null
+++ b/src/layout/id.rs
@@ -0,0 +1,147 @@
+use std::{
+    any::TypeId,
+    marker::PhantomData,
+    sync::{
+        Arc,
+        atomic::{AtomicU32, Ordering},
+        mpsc::Sender,
+    },
+};
+
+use crate::{FnTag, Ui, Widget, WidgetLike, WidgetTag, util::Id};
+
+pub struct AnyWidget;
+
+/// An identifier for a widget that can index a UI to get the associated widget.
+/// It should always remain valid; it keeps a ref count and removes the widget from the UI if all
+/// references are dropped.
+///
+/// W does not need to implement widget so that AnyWidget is valid;
+/// Instead, add generic bounds on methods that take an ID if they need specific data.
+#[repr(C)]
+pub struct WidgetId<W = AnyWidget> {
+    pub(super) ty: TypeId,
+    pub(super) id: Id,
+    pub(super) refcount: Arc<AtomicU32>,
+    pub(super) send: Sender<Id>,
+    _pd: PhantomData<W>,
+}
+
+impl<W> std::fmt::Debug for WidgetId<W> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        self.id.fmt(f)
+    }
+}
+
+impl<W> Clone for WidgetId<W> {
+    fn clone(&self) -> Self {
+        self.refcount.fetch_add(1, Ordering::Release);
+        Self {
+            id: self.id.duplicate(),
+            ty: self.ty,
+            refcount: self.refcount.clone(),
+            send: self.send.clone(),
+            _pd: PhantomData,
+        }
+    }
+}
+
+impl<W> WidgetId<W> {
+    pub(super) fn new(id: Id, ty: TypeId, send: Sender<Id>) -> Self {
+        Self {
+            ty,
+            id,
+            refcount: AtomicU32::new(0).into(),
+            send,
+            _pd: PhantomData,
+        }
+    }
+
+    pub fn erase_type(self) -> WidgetId<AnyWidget> {
+        self.cast_type()
+    }
+
+    pub fn as_any(&self) -> &WidgetId<AnyWidget> {
+        // safety: self is repr(C) and generic only used for phantom data
+        unsafe { std::mem::transmute(self) }
+    }
+
+    pub(super) fn cast_type<W2>(self) -> WidgetId<W2> {
+        unsafe { std::mem::transmute(self) }
+    }
+
+    pub fn refs(&self) -> u32 {
+        self.refcount.load(Ordering::Acquire)
+    }
+}
+
+impl<W> Drop for WidgetId<W> {
+    fn drop(&mut self) {
+        let refs = self.refcount.fetch_sub(1, Ordering::Release);
+        if refs == 0 {
+            let _ = self.send.send(self.id.duplicate());
+        }
+    }
+}
+
+pub struct IdTag;
+
+// pub trait WidgetIdFn<W, Ctx> = FnOnce(&mut Ui<Ctx>) -> WidgetId<W>;
+macro_rules! WidgetIdFnRet {
+    ($W:ty, $Ctx:ty) => {
+        impl FnOnce(&mut $crate::Ui<$Ctx>) -> $crate::WidgetId<$W>
+    };
+    ($W:ty, $Ctx:ty, $($use:tt)*) => {
+        impl FnOnce(&mut $crate::Ui<$Ctx>) -> $crate::WidgetId<$W> + use<$($use)*>
+    };
+}
+pub(crate) use WidgetIdFnRet;
+
+pub trait Idable<Ctx, Tag> {
+    type Widget: Widget<Ctx>;
+    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>);
+    fn id<'a>(
+        self,
+        id: &WidgetId<Self::Widget>,
+    ) -> WidgetIdFnRet!(Self::Widget, Ctx, 'a, Self, Ctx, Tag)
+    where
+        Self: Sized,
+    {
+        let id = id.clone();
+        move |ui| {
+            self.set(ui, &id);
+            id
+        }
+    }
+}
+
+impl<W: Widget<Ctx>, Ctx> Idable<Ctx, WidgetTag> for W {
+    type Widget = W;
+
+    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
+        ui.set(id, self);
+    }
+}
+
+impl<F: FnOnce(&mut Ui<Ctx>) -> W, W: Widget<Ctx>, Ctx> Idable<Ctx, FnTag> for F {
+    type Widget = W;
+
+    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
+        let w = self(ui);
+        ui.set(id, w);
+    }
+}
+
+impl<W: 'static, Ctx> WidgetLike<Ctx, FnTag> for WidgetId<W> {
+    type Widget = W;
+    fn add(self, _: &mut Ui<Ctx>) -> WidgetId<W> {
+        self
+    }
+}
+
+impl<W: 'static, F: FnOnce(&mut Ui<Ctx>) -> WidgetId<W>, Ctx> WidgetLike<Ctx, IdTag> for F {
+    type Widget = W;
+    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
+        self(ui)
+    }
+}
diff --git a/src/layout/mod.rs b/src/layout/mod.rs
index 0d1f9da..4e8f600 100644
--- a/src/layout/mod.rs
+++ b/src/layout/mod.rs
@@ -5,6 +5,7 @@ mod sense;
 mod ui;
 mod vec2;
 mod widget;
+mod id;
 
 pub use color::*;
 pub use painter::*;
@@ -13,5 +14,6 @@ pub use sense::*;
 pub use ui::*;
 pub use vec2::*;
 pub use widget::*;
+pub use id::*;
 
 pub type UiColor = Color<u8>;
diff --git a/src/layout/region.rs b/src/layout/region.rs
index dd6672c..22e0b89 100644
--- a/src/layout/region.rs
+++ b/src/layout/region.rs
@@ -12,27 +12,19 @@ pub struct UiPos {
 }
 
 impl UiPos {
-    pub const fn anchor_offset(anchor_x: f32, anchor_y: f32, offset_x: f32, offset_y: f32) -> Self {
-        Self {
-            anchor: vec2(anchor_x, anchor_y),
-            offset: vec2(offset_x, offset_y),
-        }
-    }
-
     pub const fn center() -> Self {
-        Self::anchor_offset(0.5, 0.5, 0.0, 0.0)
+        Self::anchor(vec2(0.5, 0.5))
     }
 
     pub const fn anchor(anchor: Vec2) -> Self {
-        Self::anchor_offset(anchor.x, anchor.y, 0.0, 0.0)
+        Self {
+            anchor,
+            offset: Vec2::ZERO,
+        }
     }
 
-    pub const fn top_left() -> Self {
-        Self::anchor_offset(0.0, 0.0, 0.0, 0.0)
-    }
-
-    pub const fn bottom_right() -> Self {
-        Self::anchor_offset(1.0, 1.0, 0.0, 0.0)
+    pub const fn corner(corner: Corner) -> Self {
+        Self::anchor(corner.anchor())
     }
 
     pub const fn shift(&mut self, offset: Vec2) {
@@ -126,8 +118,8 @@ pub struct UiRegion {
 impl UiRegion {
     pub const fn full() -> Self {
         Self {
-            top_left: UiPos::top_left(),
-            bot_right: UiPos::bottom_right(),
+            top_left: UiPos::corner(Corner::TopLeft),
+            bot_right: UiPos::corner(Corner::BotRight),
         }
     }
     pub fn center() -> Self {
@@ -178,17 +170,10 @@ impl UiRegion {
         self
     }
 
-    pub fn top_left() -> Self {
+    pub fn corner(corner: Corner) -> Self {
         Self {
-            top_left: UiPos::top_left(),
-            bot_right: UiPos::top_left(),
-        }
-    }
-
-    pub fn bottom_right() -> Self {
-        Self {
-            top_left: UiPos::bottom_right(),
-            bot_right: UiPos::bottom_right(),
+            top_left: UiPos::corner(corner),
+            bot_right: UiPos::corner(corner),
         }
     }
 
@@ -236,3 +221,22 @@ impl UIScalarView<'_> {
         }
     }
 }
+
+#[derive(Clone, Copy, Debug)]
+pub enum Corner {
+    TopLeft,
+    TopRight,
+    BotLeft,
+    BotRight,
+}
+
+impl Corner {
+    pub const fn anchor(&self) -> Vec2 {
+        match self {
+            Corner::TopLeft => vec2(0.0, 0.0),
+            Corner::TopRight => vec2(1.0, 0.0),
+            Corner::BotLeft => vec2(0.0, 1.0),
+            Corner::BotRight => vec2(1.0, 1.0),
+        }
+    }
+}
diff --git a/src/layout/ui.rs b/src/layout/ui.rs
index 64f66cb..d345812 100644
--- a/src/layout/ui.rs
+++ b/src/layout/ui.rs
@@ -6,6 +6,7 @@ use crate::{
 use std::{
     any::{Any, TypeId},
     ops::{Index, IndexMut},
+    sync::mpsc::{Receiver, Sender, channel},
 };
 
 pub struct Ui<Ctx> {
@@ -13,6 +14,8 @@ pub struct Ui<Ctx> {
     base: Option<WidgetId>,
     widgets: Widgets<Ctx>,
     updates: Vec<WidgetId>,
+    del_recv: Receiver<Id>,
+    del_send: Sender<Id>,
     pub(super) active_sensors: ActiveSensors,
     pub(super) sensor_map: SensorMap<Ctx>,
     primitives: Primitives,
@@ -35,9 +38,9 @@ impl<Ctx> Ui<Ctx> {
     }
 
     pub fn push<W: Widget<Ctx>>(&mut self, w: W) -> WidgetId<W> {
-        let id = self.ids.next();
-        self.widgets.insert(id.duplicate(), w);
-        WidgetId::new(id, TypeId::of::<W>())
+        let id = self.id();
+        self.widgets.insert(id.id.duplicate(), w);
+        id
     }
 
     pub fn set<W: Widget<Ctx>>(&mut self, i: &WidgetId<W>, w: W) {
@@ -65,7 +68,7 @@ impl<Ctx> Ui<Ctx> {
     }
 
     pub fn id<W: Widget<Ctx>>(&mut self) -> WidgetId<W> {
-        WidgetId::new(self.ids.next(), TypeId::of::<W>())
+        WidgetId::new(self.ids.next(), TypeId::of::<W>(), self.del_send.clone())
     }
 
     pub fn redraw_all(&mut self, ctx: &mut Ctx)
@@ -89,6 +92,10 @@ impl<Ctx> Ui<Ctx> {
     where
         Ctx: 'static,
     {
+        while let Ok(id) = self.del_recv.try_recv() {
+            self.widgets.delete(id);
+        }
+
         if self.full_redraw {
             self.redraw_all(ctx);
             self.full_redraw = false;
@@ -105,6 +112,10 @@ impl<Ctx> Ui<Ctx> {
     pub fn needs_redraw(&self) -> bool {
         self.full_redraw || !self.updates.is_empty()
     }
+
+    pub fn num_widgets(&self) -> usize {
+        self.widgets.len()
+    }
 }
 
 impl<W: Widget<Ctx>, Ctx> Index<&WidgetId<W>> for Ui<Ctx> {
@@ -146,6 +157,18 @@ impl<Ctx> Widgets<Ctx> {
     pub fn insert_any(&mut self, id: Id, widget: Box<dyn Widget<Ctx>>) {
         self.0.insert(id, widget);
     }
+
+    pub fn delete(&mut self, id: Id) {
+        self.0.remove(&id);
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
 }
 
 impl<Ctx> dyn Widget<Ctx> {
@@ -160,6 +183,7 @@ impl<Ctx> dyn Widget<Ctx> {
 
 impl<Ctx: 'static> Default for Ui<Ctx> {
     fn default() -> Self {
+        let (del_send, del_recv) = channel();
         Self {
             ids: Default::default(),
             base: Default::default(),
@@ -169,6 +193,8 @@ impl<Ctx: 'static> Default for Ui<Ctx> {
             full_redraw: false,
             active_sensors: Default::default(),
             sensor_map: Default::default(),
+            del_send,
+            del_recv,
         }
     }
 }
diff --git a/src/layout/widget.rs b/src/layout/widget.rs
index 6be44d2..26388ab 100644
--- a/src/layout/widget.rs
+++ b/src/layout/widget.rs
@@ -1,72 +1,12 @@
-use std::{
-    any::{Any, TypeId},
-    marker::PhantomData,
-};
-
-use crate::{Painter, Ui, util::Id};
+use crate::{Painter, Ui, WidgetId, WidgetIdFnRet};
+use std::{any::Any, marker::PhantomData};
 
 pub trait Widget<Ctx>: Any {
     fn draw(&self, painter: &mut Painter<Ctx>);
 }
 
-pub struct AnyWidget;
-
-/// An identifier for a widget.
-/// Can index a UI to get the associated widget.
-///
-/// W does not need to implement widget so that AnyWidget is valid;
-/// Instead, add generic bounds on methods that take an ID if they need specific data.
-#[repr(C)]
-#[derive(Eq, Hash, PartialEq)]
-pub struct WidgetId<W = AnyWidget> {
-    pub(super) ty: TypeId,
-    pub(super) id: Id,
-    _pd: PhantomData<W>,
-}
-
-impl<W> std::fmt::Debug for WidgetId<W> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        self.id.fmt(f)
-    }
-}
-
-// TODO: temp
-impl<W> Clone for WidgetId<W> {
-    fn clone(&self) -> Self {
-        Self::new(self.id.duplicate(), self.ty)
-    }
-}
-
-impl<W> WidgetId<W> {
-    pub(super) fn new(id: Id, ty: TypeId) -> Self {
-        Self {
-            ty,
-            id,
-            _pd: PhantomData,
-        }
-    }
-
-    pub fn erase_type(self) -> WidgetId<AnyWidget> {
-        self.cast_type()
-    }
-
-    pub fn as_any(&self) -> &WidgetId<AnyWidget> {
-        // safety: self is repr(C) and generic only used for phantom data
-        unsafe { std::mem::transmute(self) }
-    }
-
-    fn cast_type<W2>(self) -> WidgetId<W2> {
-        WidgetId {
-            ty: self.ty,
-            id: self.id,
-            _pd: PhantomData,
-        }
-    }
-}
-
 pub struct WidgetTag;
 pub struct FnTag;
-pub struct IdTag;
 
 pub trait WidgetLike<Ctx, Tag> {
     type Widget: 'static;
@@ -85,63 +25,18 @@ pub trait WidgetLike<Ctx, Tag> {
     }
 }
 
-// A function that returns a widget given a UI.
-// Useful for defining trait functions on widgets that create a parent widget so that the children
-// don't need to be IDs yet
 // pub trait WidgetFn<W: Widget<Ctx>, Ctx> = FnOnce(&mut Ui<Ctx>) -> W;
-// pub trait WidgetIdFn<W, Ctx> = FnOnce(&mut Ui<Ctx>) -> WidgetId<W>;
 
-// copium for rust analyzer
+/// A function that returns a widget given a UI.
+/// Useful for defining trait functions on widgets that create a parent widget so that the children
+/// don't need to be IDs yet
+/// currently a macro for rust analyzer (doesn't support trait aliases atm)
 macro_rules! WidgetFnRet {
     ($W:ty, $Ctx:ty) => {
         impl FnOnce(&mut $crate::Ui<$Ctx>) -> $W
     };
 }
 pub(crate) use WidgetFnRet;
-macro_rules! WidgetIdFnRet {
-    ($W:ty, $Ctx:ty) => {
-        impl FnOnce(&mut $crate::Ui<$Ctx>) -> $crate::WidgetId<$W>
-    };
-    ($W:ty, $Ctx:ty, $($use:tt)*) => {
-        impl FnOnce(&mut $crate::Ui<$Ctx>) -> $crate::WidgetId<$W> + use<$($use)*>
-    };
-}
-pub(crate) use WidgetIdFnRet;
-
-pub trait Idable<Ctx, Tag> {
-    type Widget: Widget<Ctx>;
-    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>);
-    fn id<'a>(
-        self,
-        id: &WidgetId<Self::Widget>,
-    ) -> WidgetIdFnRet!(Self::Widget, Ctx, 'a, Self, Ctx, Tag)
-    where
-        Self: Sized,
-    {
-        let id = id.clone();
-        move |ui| {
-            self.set(ui, &id);
-            id
-        }
-    }
-}
-
-impl<W: Widget<Ctx>, Ctx> Idable<Ctx, WidgetTag> for W {
-    type Widget = W;
-
-    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
-        ui.set(id, self);
-    }
-}
-
-impl<F: FnOnce(&mut Ui<Ctx>) -> W, W: Widget<Ctx>, Ctx> Idable<Ctx, FnTag> for F {
-    type Widget = W;
-
-    fn set(self, ui: &mut Ui<Ctx>, id: &WidgetId<Self::Widget>) {
-        let w = self(ui);
-        ui.set(id, w);
-    }
-}
 
 impl<W: Widget<Ctx>, Ctx, F: FnOnce(&mut Ui<Ctx>) -> W> WidgetLike<Ctx, FnTag> for F {
     type Widget = W;
@@ -151,13 +46,6 @@ impl<W: Widget<Ctx>, Ctx, F: FnOnce(&mut Ui<Ctx>) -> W> WidgetLike<Ctx, FnTag> f
     }
 }
 
-impl<W: 'static, F: FnOnce(&mut Ui<Ctx>) -> WidgetId<W>, Ctx> WidgetLike<Ctx, IdTag> for F {
-    type Widget = W;
-    fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
-        self(ui)
-    }
-}
-
 impl<W: Widget<Ctx>, Ctx> WidgetLike<Ctx, WidgetTag> for W {
     type Widget = W;
     fn add(self, ui: &mut Ui<Ctx>) -> WidgetId<W> {
@@ -165,13 +53,6 @@ impl<W: Widget<Ctx>, Ctx> WidgetLike<Ctx, WidgetTag> for W {
     }
 }
 
-impl<W: 'static, Ctx> WidgetLike<Ctx, FnTag> for WidgetId<W> {
-    type Widget = W;
-    fn add(self, _: &mut Ui<Ctx>) -> WidgetId<W> {
-        self
-    }
-}
-
 pub struct WidgetArr<const LEN: usize, Ws> {
     pub arr: [WidgetId; LEN],
     _pd: PhantomData<Ws>,
diff --git a/src/testing/mod.rs b/src/testing/mod.rs
index 89e76bf..a451058 100644
--- a/src/testing/mod.rs
+++ b/src/testing/mod.rs
@@ -22,13 +22,13 @@ pub struct Client {
 }
 
 pub struct UiIds {
-    test: WidgetId<Span>,
+    span_add: WidgetId<Span>,
 }
 
 impl Client {
     pub fn create_ui() -> (Ui<Self>, UiIds) {
         let mut ui = Ui::new();
-        let test = ui.id();
+        let span_add = ui.id();
         let rect = Rect {
             color: UiColor::WHITE,
             radius: 20.0,
@@ -73,7 +73,7 @@ impl Client {
                     ],
                 ),
         );
-        let span_add_test = ui.add(Span::empty(Dir::RIGHT).id(&test));
+        let span_add_test = ui.add(Span::empty(Dir::RIGHT).id(&span_add));
         let main: WidgetId<Regioned> = ui.id();
 
         fn switch_button<To>(
@@ -100,7 +100,7 @@ impl Client {
                 })
         }
 
-        let buttons = ui.add(
+        let tabs = ui.add(
             (
                 switch_button(UiColor::RED, &main, &pad_test),
                 switch_button(UiColor::GREEN, &main, &span_test),
@@ -108,22 +108,36 @@ impl Client {
             )
                 .span(Dir::RIGHT, [1, 1, 1]),
         );
+        let test_button = Rect::new(Color::PURPLE)
+            .radius(30)
+            .on(Sense::PressStart, move |ui, _| {
+                println!("{}", ui.num_widgets());
+            })
+            .region(
+                UiRegion::corner(Corner::BotRight)
+                    .size((150, 150))
+                    .shifted((-75, -75)),
+            );
+
+        let s = span_add.clone();
+        let del_button = Rect::new(Color::RED)
+            .radius(30)
+            .on(Sense::PressStart, move |ui, _| {
+                ui[&s].children.pop();
+            })
+            .region(
+                UiRegion::corner(Corner::BotLeft)
+                    .size((150, 150))
+                    .shifted((75, -75)),
+            );
         ui.set_base(
             (
-                buttons,
-                (
-                    pad_test.pad(10).id(&main),
-                    Rect::new(Color::PURPLE).radius(30).region(
-                        UiRegion::bottom_right()
-                            .size((150, 150))
-                            .shifted((-75, -75)),
-                    ),
-                )
-                    .stack(),
+                tabs,
+                (pad_test.pad(10).id(&main), test_button, del_button).stack(),
             )
                 .span(Dir::DOWN, [fixed(40), ratio(1)]),
         );
-        (ui, UiIds { test })
+        (ui, UiIds { span_add })
     }
 
     pub fn new(window: Arc<Window>, ui: UiIds) -> Self {
@@ -151,7 +165,7 @@ impl Client {
             WindowEvent::KeyboardInput { event, .. } => {
                 if event.state.is_pressed() {
                     let child = ui.add(Rect::new(Color::YELLOW)).erase_type();
-                    ui[&self.ui.test].children.push((child, fixed(20.0)));
+                    ui[&self.ui.span_add].children.push((child, fixed(20.0)));
                     self.renderer.window().request_redraw();
                 }
             }