Add retained paints and shared text selection

core/src/primitive/color.rs

@@ -1,171 +1,518 @@
-use std::marker::Destruct;
+use crate::util::{Dirty, RefCounter};
+use std::{
+    cell::RefCell,
+    fmt,
+    rc::Rc,
+    sync::mpsc::{Receiver, Sender, channel},
+};
 
+/// Encoded, straight-alpha sRGB at an input boundary.
+///
+/// Palette literals, decoded images and colour glyph bitmaps use this
+/// convention. A solid paint is converted to linear light when it enters the
+/// paint table; the renderer never performs colour arithmetic on these bytes.
 #[repr(C)]
-#[derive(Clone, Copy, Hash, PartialEq, Eq, bytemuck::Zeroable, Debug)]
-pub struct Color<T> {
-    pub r: T,
-    pub g: T,
-    pub b: T,
-    pub a: T,
+#[derive(Clone, Copy, Debug, Hash, PartialEq, Eq, bytemuck::Pod, bytemuck::Zeroable)]
+pub struct Srgba8 {
+    pub r: u8,
+    pub g: u8,
+    pub b: u8,
+    pub a: u8,
 }
 
-/// Required by parley's `Brush`, which every text style is generic over. Opaque
-/// black rather than transparent: a brush that was never set should be visible
-/// and obviously unstyled, not invisible.
-impl<T: ColorNum> Default for Color<T> {
+impl Srgba8 {
+    pub const BLACK: Self = Self::rgb(0, 0, 0);
+    pub const WHITE: Self = Self::rgb(255, 255, 255);
+    pub const GRAY: Self = Self::rgb(127, 127, 127);
+    pub const RED: Self = Self::rgb(255, 0, 0);
+    pub const ORANGE: Self = Self::rgb(255, 127, 0);
+    pub const YELLOW: Self = Self::rgb(255, 255, 0);
+    pub const LIME: Self = Self::rgb(127, 255, 0);
+    pub const GREEN: Self = Self::rgb(0, 255, 0);
+    pub const TURQUOISE: Self = Self::rgb(0, 255, 127);
+    pub const CYAN: Self = Self::rgb(0, 255, 255);
+    pub const SKY: Self = Self::rgb(0, 127, 255);
+    pub const BLUE: Self = Self::rgb(0, 0, 255);
+    pub const PURPLE: Self = Self::rgb(127, 0, 255);
+    pub const MAGENTA: Self = Self::rgb(255, 0, 255);
+    pub const NONE: Self = Self::new(0, 0, 0, 0);
+
+    pub const fn new(r: u8, g: u8, b: u8, a: u8) -> Self {
+        Self { r, g, b, a }
+    }
+
+    pub const fn rgb(r: u8, g: u8, b: u8) -> Self {
+        Self::new(r, g, b, 255)
+    }
+
+    pub fn to_linear(self) -> LinearRgba {
+        LinearRgba::new(
+            srgb_to_linear(self.r as f32 / 255.0),
+            srgb_to_linear(self.g as f32 / 255.0),
+            srgb_to_linear(self.b as f32 / 255.0),
+            self.a as f32 / 255.0,
+        )
+    }
+}
+
+/// Straight-alpha RGBA in linear-light sRGB primaries.
+///
+/// This is Iris's working representation: manipulate and interpolate colours
+/// here, then put the result in [`Paints`]. The GPU paint buffer stores this
+/// exact layout as `vec4<f32>`.
+#[repr(C)]
+#[derive(Clone, Copy, Debug, PartialEq, bytemuck::Pod, bytemuck::Zeroable)]
+pub struct LinearRgba {
+    pub r: f32,
+    pub g: f32,
+    pub b: f32,
+    pub a: f32,
+}
+
+impl LinearRgba {
+    pub const BLACK: Self = Self::rgb(0.0, 0.0, 0.0);
+    pub const WHITE: Self = Self::rgb(1.0, 1.0, 1.0);
+    pub const NONE: Self = Self::new(0.0, 0.0, 0.0, 0.0);
+
+    pub const fn new(r: f32, g: f32, b: f32, a: f32) -> Self {
+        Self { r, g, b, a }
+    }
+
+    pub const fn rgb(r: f32, g: f32, b: f32) -> Self {
+        Self::new(r, g, b, 1.0)
+    }
+
+    pub fn mul_rgb(self, amount: f32) -> Self {
+        Self::new(self.r * amount, self.g * amount, self.b * amount, self.a)
+    }
+
+    pub fn darker(self, amount: f32) -> Self {
+        self.mul_rgb(1.0 - amount)
+    }
+
+    pub fn brighter(self, amount: f32) -> Self {
+        Self::new(
+            self.r + (1.0 - self.r) * amount,
+            self.g + (1.0 - self.g) * amount,
+            self.b + (1.0 - self.b) * amount,
+            self.a,
+        )
+    }
+
+    pub fn to_wgpu(self) -> wgpu::Color {
+        wgpu::Color {
+            r: self.r as f64,
+            g: self.g as f64,
+            b: self.b as f64,
+            a: self.a as f64,
+        }
+    }
+}
+
+fn srgb_to_linear(value: f32) -> f32 {
+    if value <= 0.04045 {
+        value / 12.92
+    } else {
+        ((value + 0.055) / 1.055).powf(2.4)
+    }
+}
+
+/// A description that can be registered in Iris's paint table.
+///
+/// Only solid paints exist today. Keeping registration behind this trait and
+/// making primitives carry [`PaintId`] leaves one place to add gradient or
+/// texture paint records later.
+pub trait Paint: private::Sealed + 'static {
+    #[doc(hidden)]
+    fn add_to(&self, paints: &mut Paints) -> PaintId;
+
+    #[doc(hidden)]
+    fn replace(&self, paints: &mut Paints, slot: u32);
+
+    /// Erases this definition so a widget can register it lazily on its
+    /// first draw. [`PaintId`] overrides this to stay a direct handle.
+    #[doc(hidden)]
+    fn into_value(self) -> PaintValue
+    where
+        Self: Sized,
+    {
+        PaintValue::pending(self)
+    }
+}
+
+impl Paint for Srgba8 {
+    fn add_to(&self, paints: &mut Paints) -> PaintId {
+        paints.add_linear(self.to_linear())
+    }
+
+    fn replace(&self, paints: &mut Paints, slot: u32) {
+        paints.replace_linear(slot, self.to_linear());
+    }
+}
+
+impl Paint for LinearRgba {
+    fn add_to(&self, paints: &mut Paints) -> PaintId {
+        paints.add_linear(*self)
+    }
+
+    fn replace(&self, paints: &mut Paints, slot: u32) {
+        paints.replace_linear(slot, *self);
+    }
+}
+
+mod private {
+    pub trait Sealed {}
+    impl Sealed for super::Srgba8 {}
+    impl Sealed for super::LinearRgba {}
+    impl Sealed for super::PaintId {}
+}
+
+#[derive(Debug)]
+struct PaintLease {
+    slot: u32,
+    counter: RefCounter,
+    send: Sender<u32>,
+}
+
+impl Clone for PaintLease {
+    fn clone(&self) -> Self {
+        Self {
+            slot: self.slot,
+            counter: self.counter.clone(),
+            send: self.send.clone(),
+        }
+    }
+}
+
+impl Drop for PaintLease {
+    fn drop(&mut self) {
+        if self.counter.drop() {
+            let _ = self.send.send(self.slot);
+        }
+    }
+}
+
+/// A stable reference to one entry in a UI's paint table.
+///
+/// Built-in IDs name the same reserved entries in every [`Paints`]. IDs
+/// returned by [`Paints::add`] retain their slot until the last clone held by a
+/// widget, shaped text or retained draw is dropped.
+#[derive(Clone, Debug)]
+pub struct PaintId {
+    slot: u32,
+    lease: Option<PaintLease>,
+}
+
+impl PaintId {
+    pub const BLACK: Self = Self::builtin(0);
+    pub const WHITE: Self = Self::builtin(1);
+    pub const GRAY: Self = Self::builtin(2);
+    pub const RED: Self = Self::builtin(3);
+    pub const ORANGE: Self = Self::builtin(4);
+    pub const YELLOW: Self = Self::builtin(5);
+    pub const LIME: Self = Self::builtin(6);
+    pub const GREEN: Self = Self::builtin(7);
+    pub const TURQUOISE: Self = Self::builtin(8);
+    pub const CYAN: Self = Self::builtin(9);
+    pub const SKY: Self = Self::builtin(10);
+    pub const BLUE: Self = Self::builtin(11);
+    pub const PURPLE: Self = Self::builtin(12);
+    pub const MAGENTA: Self = Self::builtin(13);
+    pub const NONE: Self = Self::builtin(14);
+
+    const fn builtin(slot: u32) -> Self {
+        Self { slot, lease: None }
+    }
+
+    pub(crate) fn slot(&self) -> u32 {
+        self.slot
+    }
+
+    fn is_managed(&self) -> bool {
+        self.lease.is_some()
+    }
+}
+
+impl Default for PaintId {
     fn default() -> Self {
         Self::BLACK
     }
 }
 
-impl<T: ColorNum> Color<T> {
-    pub const BLACK: Self = Self::rgb(T::MIN, T::MIN, T::MIN);
-    pub const WHITE: Self = Self::rgb(T::MAX, T::MAX, T::MAX);
-    pub const GRAY: Self = Self::rgb(T::MID, T::MID, T::MID);
-
-    pub const RED: Self = Self::rgb(T::MAX, T::MIN, T::MIN);
-    pub const ORANGE: Self = Self::rgb(T::MAX, T::MID, T::MIN);
-    pub const YELLOW: Self = Self::rgb(T::MAX, T::MAX, T::MIN);
-    pub const LIME: Self = Self::rgb(T::MID, T::MAX, T::MIN);
-    pub const GREEN: Self = Self::rgb(T::MIN, T::MAX, T::MIN);
-    pub const TURQUOISE: Self = Self::rgb(T::MIN, T::MAX, T::MID);
-    pub const CYAN: Self = Self::rgb(T::MIN, T::MAX, T::MAX);
-    pub const SKY: Self = Self::rgb(T::MIN, T::MID, T::MAX);
-    pub const BLUE: Self = Self::rgb(T::MIN, T::MIN, T::MAX);
-    pub const PURPLE: Self = Self::rgb(T::MID, T::MIN, T::MAX);
-    pub const MAGENTA: Self = Self::rgb(T::MAX, T::MIN, T::MAX);
-
-    pub const NONE: Self = Self::new(T::MIN, T::MIN, T::MIN, T::MIN);
-
-    pub const fn new(r: T, g: T, b: T, a: T) -> Self {
-        Self { r, g, b, a }
-    }
-    pub const fn rgb(r: T, g: T, b: T) -> Self {
-        Self { r, g, b, a: T::MAX }
-    }
-    pub fn alpha(mut self, a: T) -> Self {
-        self.a = a;
-        self
-    }
-
-    pub fn as_arr(self) -> [T; 4] {
-        [self.r, self.g, self.b, self.a]
+impl PartialEq for PaintId {
+    fn eq(&self, other: &Self) -> bool {
+        self.slot == other.slot
     }
 }
 
-pub const trait F32Conversion {
-    fn to(self) -> f32;
-    fn from(x: f32) -> Self;
+impl Eq for PaintId {}
+
+impl Paint for PaintId {
+    fn add_to(&self, _paints: &mut Paints) -> PaintId {
+        self.clone()
+    }
+
+    fn replace(&self, paints: &mut Paints, slot: u32) {
+        let value = paints.entries[self.slot as usize];
+        paints.replace_linear(slot, value);
+    }
+
+    fn into_value(self) -> PaintValue {
+        PaintValue(PaintValueInner::Id(self))
+    }
 }
 
-pub trait ColorNum {
-    const MIN: Self;
-    const MID: Self;
-    const MAX: Self;
+struct PendingPaint {
+    definition: Box<dyn Paint>,
+    resolved: RefCell<Option<PaintId>>,
 }
 
-macro_rules! map_rgb {
-    ($x:ident,$self:ident, $e:tt) => {
-        #[allow(unused_braces)]
-        Self {
-            r: {
-                let $x = $self.r;
-                $e
-            },
-            g: {
-                let $x = $self.g;
-                $e
-            },
-            b: {
-                let $x = $self.b;
-                $e
-            },
-            a: $self.a,
+#[derive(Clone)]
+enum PaintValueInner {
+    Id(PaintId),
+    Pending(Rc<PendingPaint>),
+}
+
+/// A widget property containing either an existing paint-table ID or a paint
+/// definition that will receive an ID the first time it is drawn.
+///
+/// Pending definitions are shared across clones and registered only once.
+/// Each property replaces its own pending variant with the resulting direct
+/// ID after that first resolution, so later draws take the direct path.
+#[derive(Clone)]
+pub struct PaintValue(PaintValueInner);
+
+impl PaintValue {
+    fn pending(paint: impl Paint) -> Self {
+        Self(PaintValueInner::Pending(Rc::new(PendingPaint {
+            definition: Box::new(paint),
+            resolved: RefCell::new(None),
+        })))
+    }
+
+    pub fn resolve(&mut self, paints: &mut Paints) -> &PaintId {
+        if let PaintValueInner::Pending(pending) = &self.0 {
+            let resolved = pending.resolved.borrow().clone();
+            let id = match resolved {
+                Some(id) => id,
+                None => {
+                    let id = pending.definition.add_to(paints);
+                    *pending.resolved.borrow_mut() = Some(id.clone());
+                    id
+                }
+            };
+            self.0 = PaintValueInner::Id(id);
         }
-    };
-}
-
-impl<T: ColorNum + const F32Conversion> Color<T>
-where
-    Self: const Destruct,
-{
-    pub const fn mul_rgb(self, amt: impl const F32Conversion) -> Self {
-        let amt = amt.to();
-        map_rgb!(x, self, { T::from(x.to() * amt) })
+        let PaintValueInner::Id(id) = &self.0 else {
+            unreachable!()
+        };
+        id
     }
 
-    pub const fn add_rgb(self, amt: impl const F32Conversion) -> Self {
-        let amt = amt.to();
-        map_rgb!(x, self, { T::from(x.to() + amt) })
-    }
-
-    pub const fn darker(self, amt: f32) -> Self {
-        self.mul_rgb(1.0 - amt)
-    }
-
-    pub const fn brighter(self, amt: f32) -> Self {
-        map_rgb!(x, self, {
-            let x = x.to();
-            T::from(x + (1.0 - x) * amt)
-        })
-    }
-
-    pub fn map_rgb(self, f: impl Fn(T) -> T) -> Self {
-        Self {
-            r: f(self.r),
-            g: f(self.g),
-            b: f(self.b),
-            a: self.a,
-        }
-    }
-
-    pub fn srgb(r: T, g: T, b: T) -> Self {
-        Self {
-            r: s_to_l(r),
-            g: s_to_l(g),
-            b: s_to_l(b),
-            a: T::MAX,
+    pub fn is(&self, id: &PaintId) -> bool {
+        match &self.0 {
+            PaintValueInner::Id(current) => current == id,
+            PaintValueInner::Pending(pending) => pending.resolved.borrow().as_ref() == Some(id),
         }
     }
 }
 
-fn s_to_l<T: F32Conversion>(x: T) -> T {
-    let x = x.to();
-    T::from(if x <= 0.0405 {
-        x / 12.92
-    } else {
-        ((x + 0.055) / 1.055).powf(2.4)
-    })
-}
-
-impl ColorNum for u8 {
-    const MIN: Self = u8::MIN;
-    const MID: Self = u8::MAX / 2;
-    const MAX: Self = u8::MAX;
-}
-
-impl ColorNum for f32 {
-    const MIN: Self = 0.0;
-    const MID: Self = 0.5;
-    const MAX: Self = 1.0;
-}
-
-unsafe impl bytemuck::Pod for Color<u8> {}
-
-const impl F32Conversion for f32 {
-    fn to(self) -> f32 {
-        self
-    }
-    fn from(x: f32) -> Self {
-        x
+impl fmt::Debug for PaintValue {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match &self.0 {
+            PaintValueInner::Id(id) => f.debug_tuple("PaintValue").field(id).finish(),
+            PaintValueInner::Pending(_) => f.write_str("PaintValue(Pending)"),
+        }
     }
 }
 
-const impl F32Conversion for u8 {
-    fn to(self) -> f32 {
-        self as f32 / 255.0
+const BUILTIN_PAINTS: [Srgba8; 15] = [
+    Srgba8::BLACK,
+    Srgba8::WHITE,
+    Srgba8::GRAY,
+    Srgba8::RED,
+    Srgba8::ORANGE,
+    Srgba8::YELLOW,
+    Srgba8::LIME,
+    Srgba8::GREEN,
+    Srgba8::TURQUOISE,
+    Srgba8::CYAN,
+    Srgba8::SKY,
+    Srgba8::BLUE,
+    Srgba8::PURPLE,
+    Srgba8::MAGENTA,
+    Srgba8::NONE,
+];
+
+/// CPU-side paint table and the dirty set for its GPU mirror.
+pub struct Paints {
+    entries: Vec<LinearRgba>,
+    free: Vec<u32>,
+    dirty: Dirty,
+    send: Sender<u32>,
+    recv: Receiver<u32>,
+}
+
+impl Paints {
+    pub fn new() -> Self {
+        let (send, recv) = channel();
+        Self {
+            entries: BUILTIN_PAINTS.map(Srgba8::to_linear).to_vec(),
+            free: Vec::new(),
+            dirty: Dirty::new_all(),
+            send,
+            recv,
+        }
     }
-    fn from(x: f32) -> Self {
-        (x * 255.0).clamp(0.0, 255.0) as Self
+
+    pub fn add(&mut self, paint: impl Paint) -> PaintId {
+        paint.add_to(self)
+    }
+
+    fn add_linear(&mut self, value: LinearRgba) -> PaintId {
+        self.free_released();
+        let slot = if let Some(slot) = self.free.pop() {
+            self.entries[slot as usize] = value;
+            self.dirty.mark(slot as usize);
+            slot
+        } else {
+            let slot = self.entries.len() as u32;
+            self.entries.push(value);
+            self.dirty.mark(slot as usize);
+            slot
+        };
+        PaintId {
+            slot,
+            lease: Some(PaintLease {
+                slot,
+                counter: RefCounter::new(),
+                send: self.send.clone(),
+            }),
+        }
+    }
+
+    /// Replaces one managed paint in place. Every primitive keeps the same
+    /// index, so a theme change dirties this table and no primitive buffer.
+    pub fn set(&mut self, id: &PaintId, paint: impl Paint) {
+        assert!(
+            id.is_managed(),
+            "a reserved built-in paint cannot be replaced; allocate a theme slot with Paints::add"
+        );
+        paint.replace(self, id.slot);
+    }
+
+    fn replace_linear(&mut self, slot: u32, value: LinearRgba) {
+        self.entries[slot as usize] = value;
+        self.dirty.mark(slot as usize);
+    }
+
+    pub fn get(&self, id: &PaintId) -> LinearRgba {
+        self.entries[id.slot as usize]
+    }
+
+    pub fn free_released(&mut self) {
+        for slot in self.recv.try_iter() {
+            self.entries[slot as usize] = LinearRgba::NONE;
+            self.dirty.mark(slot as usize);
+            self.free.push(slot);
+        }
+    }
+
+    /// A new GPU device has no copy of this table even when the CPU-side UI
+    /// and its paint IDs survived an Android surface recreation.
+    pub fn reupload(&mut self) {
+        self.dirty.mark_all();
+    }
+
+    pub fn for_upload(&mut self) -> (&[LinearRgba], &mut Dirty) {
+        (&self.entries, &mut self.dirty)
+    }
+}
+
+impl Default for Paints {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn srgb_bytes_become_linear_without_transforming_alpha() {
+        let got = Srgba8::new(17, 127, 255, 64).to_linear();
+        assert!((got.r - 0.005605).abs() < 0.000001);
+        assert!((got.g - 0.212231).abs() < 0.000001);
+        assert_eq!(got.b, 1.0);
+        assert!((got.a - 64.0 / 255.0).abs() < f32::EPSILON);
+    }
+
+    #[test]
+    fn changing_a_paint_keeps_its_id_and_dirties_only_its_slot() {
+        let mut paints = Paints::new();
+        let id = paints.add(Srgba8::rgb(17, 17, 27));
+        let slot = id.slot();
+        let (_, dirty) = paints.for_upload();
+        dirty.clear();
+
+        paints.set(&id, Srgba8::rgb(205, 214, 244));
+        let (_, dirty) = paints.for_upload();
+        assert!(dirty.contains(slot as usize));
+        assert_eq!(id.slot(), slot);
+    }
+
+    #[test]
+    fn a_released_paint_slot_is_reused_only_after_the_last_clone() {
+        let mut paints = Paints::new();
+        let id = paints.add(Srgba8::RED);
+        let slot = id.slot();
+        let held = id.clone();
+        drop(id);
+        paints.free_released();
+        let other = paints.add(Srgba8::GREEN);
+        assert_ne!(other.slot(), slot);
+
+        drop(held);
+        paints.free_released();
+        let reused = paints.add(Srgba8::BLUE);
+        assert_eq!(reused.slot(), slot);
+    }
+
+    #[test]
+    fn cloned_pending_paints_register_once_and_then_become_direct_ids() {
+        let mut paints = Paints::new();
+        let mut first = Srgba8::rgb(17, 17, 27).into_value();
+        let mut second = first.clone();
+        let before = paints.entries.len();
+
+        let first_id = first.resolve(&mut paints).clone();
+        let second_id = second.resolve(&mut paints).clone();
+
+        assert_eq!(first_id, second_id);
+        assert_eq!(paints.entries.len(), before + 1);
+        assert!(first.is(&first_id));
+        assert!(second.is(&first_id));
+    }
+
+    #[test]
+    fn independently_constructed_inline_solids_get_independent_slots() {
+        let mut paints = Paints::new();
+        let mut first = Srgba8::rgb(23, 42, 71).into_value();
+        let mut second = Srgba8::rgb(23, 42, 71).into_value();
+        let before = paints.entries.len();
+
+        let first_id = first.resolve(&mut paints).clone();
+        let second_id = second.resolve(&mut paints).clone();
+        assert_ne!(first_id, second_id);
+        assert_eq!(paints.entries.len(), before + 2);
+    }
+
+    #[test]
+    fn explicit_theme_paints_with_equal_values_remain_independent() {
+        let mut paints = Paints::new();
+        let first = paints.add(Srgba8::rgb(23, 42, 71));
+        let second = paints.add(Srgba8::rgb(23, 42, 71));
+        assert_ne!(first.slot(), second.slot());
     }
 }

core/src/primitive/text.rs

@@ -1,4 +1,4 @@
-use crate::{Align, GlyphAtlas, GlyphKey, PlacedGlyph, RegionAlign, Textures, UiColor, util::Vec2};
+use crate::{Align, GlyphAtlas, GlyphKey, PaintId, PlacedGlyph, RegionAlign, Textures, util::Vec2};
 use parley::{
     Alignment, AlignmentOptions, FontContext, FontFamily, FontFamilyName, FontStyle, FontWeight,
     GenericFamily, Layout, LayoutContext, LineHeight, PositionedLayoutItem, StyleProperty,
@@ -32,7 +32,7 @@ pub struct FontDiagnostics {
 
 pub struct TextData {
     pub font_cx: FontContext,
-    pub layout_cx: LayoutContext<UiColor>,
+    pub layout_cx: LayoutContext<PaintId>,
     scale_cx: ScaleContext,
     pub atlas: GlyphAtlas,
     /// Physical pixels per dp -- a second copy of
@@ -240,8 +240,13 @@ impl TextData {
         }
     }
 
-    pub fn place(&mut self, buffer: &TextBuffer, textures: &mut Textures) -> Vec<PlacedGlyph> {
+    pub fn place(
+        &mut self,
+        buffer: &TextBuffer,
+        textures: &mut Textures,
+    ) -> (Vec<PlacedGlyph>, Vec<PaintId>) {
         let mut placed = Vec::new();
+        let mut paints = Vec::new();
         for line in buffer.layout.lines() {
             for item in line.items() {
                 let PositionedLayoutItem::GlyphRun(run) = item else {
@@ -250,7 +255,10 @@ impl TextData {
                 let font = run.run().font();
                 let font_size = run.run().font_size();
                 let coords = run.run().normalized_coords();
-                let run_color = run.style().brush;
+                let run_color = run.style().brush.clone();
+                if !paints.contains(&run_color) {
+                    paints.push(run_color.clone());
+                }
                 let Some(font_ref) = FontRef::from_index(font.data.as_ref(), font.index as usize)
                 else {
                     continue;
@@ -301,12 +309,12 @@ impl TextData {
                             glyph.x.floor() + entry.left as f32,
                             glyph.y.floor() - entry.top as f32,
                         ),
-                        color: run_color,
+                        paint: run_color.slot(),
                     });
                 }
             }
         }
-        placed
+        (placed, paints)
     }
 
     pub fn render(
@@ -318,11 +326,12 @@ impl TextData {
         density: f32,
     ) -> RenderedText {
         buffer.shape(self, attrs, width, density);
-        let glyphs = self.place(buffer, textures);
+        let (glyphs, paints) = self.place(buffer, textures);
         RenderedText {
             glyphs: std::sync::Arc::new(glyphs),
+            paints: std::sync::Arc::new(paints),
             size: buffer.size(),
-            color: attrs.color,
+            color: attrs.color.clone(),
             generation: self.atlas.generation(),
         }
     }
@@ -359,7 +368,7 @@ impl Family {
 #[derive(Clone, PartialEq)]
 pub struct SpanStyle {
     pub range: Range<usize>,
-    pub color: Option<UiColor>,
+    pub color: Option<PaintId>,
     pub family: Option<Family>,
     pub font_size: Option<f32>,
     pub bold: bool,
@@ -379,7 +388,7 @@ impl SpanStyle {
             underline: false,
         }
     }
-    pub fn color(mut self, color: UiColor) -> Self {
+    pub fn color(mut self, color: PaintId) -> Self {
         self.color = Some(color);
         self
     }
@@ -407,7 +416,7 @@ impl SpanStyle {
 
 #[derive(Clone, PartialEq)]
 pub struct TextAttrs {
-    pub color: UiColor,
+    pub color: PaintId,
     pub font_size: f32,
     pub line_height: f32,
     pub family: Family,
@@ -421,7 +430,7 @@ impl Default for TextAttrs {
     fn default() -> Self {
         let size = 16.0;
         Self {
-            color: UiColor::WHITE,
+            color: PaintId::WHITE,
             font_size: size,
             line_height: size * LINE_HEIGHT_MULT,
             family: Family::SansSerif,
@@ -436,7 +445,7 @@ impl Default for TextAttrs {
 /// them apart is how they get out of step.
 pub struct TextBuffer {
     text: String,
-    layout: Layout<UiColor>,
+    layout: Layout<PaintId>,
     spans: Vec<SpanStyle>,
     shaped: Option<(TextAttrs, Option<f32>, f32)>,
 }
@@ -464,7 +473,7 @@ impl TextBuffer {
         &self.text
     }
 
-    pub fn layout(&self) -> &Layout<UiColor> {
+    pub fn layout(&self) -> &Layout<PaintId> {
         &self.layout
     }
 
@@ -515,11 +524,11 @@ impl TextBuffer {
         builder.push_default(StyleProperty::LineHeight(LineHeight::Absolute(
             attrs.line_height * density,
         )));
-        builder.push_default(StyleProperty::Brush(attrs.color));
+        builder.push_default(StyleProperty::Brush(attrs.color.clone()));
         for (span, family) in self.spans.iter().zip(&span_families) {
             let range = span.range.clone();
-            if let Some(color) = span.color {
-                builder.push(StyleProperty::Brush(color), range.clone());
+            if let Some(color) = &span.color {
+                builder.push(StyleProperty::Brush(color.clone()), range.clone());
             }
             if let Some(family) = family {
                 builder.push(StyleProperty::FontFamily(family.family()), range.clone());
@@ -563,8 +572,10 @@ fn hash_coords(coords: &[i16]) -> u64 {
 #[derive(Clone)]
 pub struct RenderedText {
     pub glyphs: std::sync::Arc<Vec<PlacedGlyph>>,
+    /// The unique handles whose compact slots the glyphs above carry.
+    pub paints: std::sync::Arc<Vec<PaintId>>,
     pub size: Vec2,
-    pub color: UiColor,
+    pub color: PaintId,
     /// The [`GlyphAtlas::generation`] the glyphs above were placed against.
     /// A holder must re-render rather than re-emit these quads once the
     /// atlas has moved on (`GlyphAtlas::clear`'s doc says what happens