Make a texture a registered primitive like any other

`write_texture` differed from `write` by one argument, which is what the
generic parameter was already for, so textures register as a primitive
with a `TexturePrimitive` holding the slot. `write_texture`,
`InstanceKind` and the layer's separate texture list are gone;
`DrawLayers` is back to `write` and `free`, with the kind carried in
`PrimitiveInst` as it carries everything else.

What differs between a texture and a rect is only what it samples, so
that is what registration says: `PrimitiveTexture::Atlas` binds the
shared atlas once for the layer, `PerInstance` binds the texture its own
data names and draws one instance at a time. One loop over a layer's
lists, one match on that.

`Pod` is back to being a supertrait of `Primitive` rather than the bound
itself. The guarantee is that a `PrimitiveKind<P>` is only minted by
`register::<P>` and `write` takes the kind and the value together, so a
primitive always has a list of its own to go in and the write does not
check anything: a list takes its stride from the type it was made for
instead of inferring it from the first write and asserting on the rest.

Also from reviewing this: a layer's lists and their buffers are created
only when that layer draws that primitive, so a primitive nobody uses no
longer costs two buffers in every layer -- which matters more now the set
is open-ended. `ListBuffers::update` takes the two things it uses rather
than the whole pipeline.

Verified again over all five cases: an image alone in a layer, three
images added and one deleted, the masked text-edit tab, the text-layout
tab and the default tab.

core/src/primitive/layer.rs

@@ -1,8 +1,7 @@
 use std::ops::{Index, IndexMut};
 
 use crate::{
-    UiRegion, WidgetId,
-    render::{LayerDraws, MaskIdx, PrimitiveHandle, PrimitiveKind},
+    render::{LayerDraws, MaskIdx, Primitive, PrimitiveHandle, PrimitiveInst},
     util::to_mut,
 };
 
@@ -121,32 +120,17 @@ impl<T: Default> Layers<T> {
 }
 
 impl DrawLayers {
-    pub fn write<P: bytemuck::Pod>(
+    pub fn write<P: Primitive>(
         &mut self,
         layer: LayerId,
-        kind: PrimitiveKind<P>,
-        id: WidgetId,
-        primitive: P,
-        region: UiRegion,
-        mask_idx: MaskIdx,
+        info: PrimitiveInst<P>,
     ) -> PrimitiveHandle {
-        self[layer].write(layer, kind, id, primitive, region, mask_idx)
+        self[layer].write(layer, info)
     }
 
     pub fn free(&mut self, h: &PrimitiveHandle) -> MaskIdx {
         self[h.layer].free(h)
     }
-
-    pub fn write_texture(
-        &mut self,
-        layer: LayerId,
-        id: WidgetId,
-        texture: u32,
-        region: UiRegion,
-        mask_idx: MaskIdx,
-    ) -> PrimitiveHandle {
-        self[layer].write_texture(layer, id, texture, region, mask_idx)
-    }
 }
 
 impl<T: Default> Default for Layers<T> {

core/src/render/mod.rs

@@ -26,19 +26,15 @@ pub use data::{Mask, MaskIdx};
 pub use primitive::*;
 
 const PRELUDE: &str = include_str!("./shader/prelude.wgsl");
-const TEXTURE_SHADER: &str = include_str!("./shader/texture.wgsl");
 
 pub struct UiRenderNode {
     shared_layout: BindGroupLayout,
     shared_group: BindGroup,
-    texture_data_layout: BindGroupLayout,
     texture_layout: BindGroupLayout,
     format: TextureFormat,
 
-    /// One per registered primitive, in id order. The texture pipeline is
-    /// apart because a texture binds group 2 per instance, not per draw.
+    /// One per registered primitive, in id order.
     primitives: Vec<PrimitivePipeline>,
-    texture_pipeline: RenderPipeline,
 
     layers: HashMap<usize, RenderLayer>,
     active: Vec<usize>,
@@ -50,11 +46,10 @@ pub struct UiRenderNode {
 }
 
 struct RenderLayer {
-    /// One per registered primitive, in id order, matching `LayerDraws`.
-    primitives: Vec<ListBuffers>,
-    textures: ListBuffers,
-    /// Which texture each entry of `textures` samples, in the same order.
-    texture_slots: Vec<u32>,
+    /// One per registered primitive, in id order, matching `LayerDraws` --
+    /// `None` where this layer draws none, so a primitive nobody uses costs no
+    /// buffers per layer.
+    primitives: Vec<Option<ListBuffers>>,
 }
 
 /// What draws one registered primitive. The group 1 layout is its own rather
@@ -62,6 +57,7 @@ struct RenderLayer {
 struct PrimitivePipeline {
     data_layout: BindGroupLayout,
     pipeline: RenderPipeline,
+    texture: PrimitiveTexture,
 }
 
 /// One list's vertex buffer and the data its shader reads at group 1.
@@ -69,6 +65,8 @@ struct ListBuffers {
     instance: ArrBuf<PrimitiveInstance>,
     data: ArrBuf<u8>,
     group: Option<BindGroup>,
+    /// For a `PerInstance` primitive, the texture each instance binds.
+    slots: Vec<u32>,
 }
 
 impl UiRenderNode {
@@ -80,36 +78,37 @@ impl UiRenderNode {
             // under a texture. Ordering beyond that is what `Layers` is for --
             // freeing an instance swaps another into its place.
             for (id, list) in layer.primitives.iter().enumerate() {
+                let Some(list) = list else {
+                    continue;
+                };
                 let Some(group) = &list.group else {
                     continue;
                 };
-                pass.set_pipeline(&self.primitives[id].pipeline);
-                // Both after the pipeline: each primitive has its own pipeline
-                // layout, and a change drops the groups from where they differ.
+                let primitive = &self.primitives[id];
+                pass.set_pipeline(&primitive.pipeline);
+                // Both groups after the pipeline: each primitive has its own
+                // pipeline layout, and a change drops the groups from where
+                // the two layouts differ.
                 pass.set_bind_group(1, group, &[]);
-                pass.set_bind_group(2, self.pages.group(), &[]);
                 pass.set_vertex_buffer(0, list.instance.buffer.slice(..));
+                match primitive.texture {
+                    PrimitiveTexture::Atlas => {
+                        pass.set_bind_group(2, self.pages.group(), &[]);
                         pass.draw(0..4, 0..list.instance.len() as u32);
                     }
-            if !layer.texture_slots.is_empty() {
-                // Group 1 too, unread as it is: a layer holding only an image
-                // never ran the loop above, so nothing is bound there.
-                let Some(data) = &layer.textures.group else {
+                    PrimitiveTexture::PerInstance => {
+                        for (i, &slot) in list.slots.iter().enumerate() {
+                            let Some(texture) = self.textures.group(slot) else {
                                 continue;
                             };
-                pass.set_pipeline(&self.texture_pipeline);
-                pass.set_bind_group(1, data, &[]);
-                pass.set_vertex_buffer(0, layer.textures.instance.buffer.slice(..));
-                for (i, &slot) in layer.texture_slots.iter().enumerate() {
-                    let Some(group) = self.textures.group(slot) else {
-                        continue;
-                    };
-                    pass.set_bind_group(2, group, &[]);
+                            pass.set_bind_group(2, texture, &[]);
                             pass.draw(0..4, i as u32..i as u32 + 1);
                         }
                     }
                 }
             }
+        }
+    }
 
     pub fn update(
         &mut self,
@@ -135,35 +134,33 @@ impl UiRenderNode {
                     }
                 }
             }
-            let rlayer = self
-                .layers
-                .entry(i)
-                .or_insert_with(|| RenderLayer::new(device));
+            let rlayer = self.layers.entry(i).or_insert_with(RenderLayer::new);
             if draws.updated {
                 rlayer
                     .primitives
-                    .resize_with(draws.primitives().len(), || ListBuffers::new(device));
-                for (id, (list, draws)) in rlayer
+                    .resize_with(draws.primitives().len(), || None);
+                for (id, (buffers, list)) in rlayer
                     .primitives
                     .iter_mut()
                     .zip(draws.primitives())
                     .enumerate()
                 {
+                    let Some(list) = list else {
+                        continue;
+                    };
                     // Indexed, not zipped: a missing pipeline should say so
                     // rather than quietly leave the list unbuilt.
-                    let layout = &self.primitives[id].data_layout;
-                    list.update(device, queue, layout, draws);
+                    let primitive = &self.primitives[id];
+                    buffers
+                        .get_or_insert_with(|| ListBuffers::new(device))
+                        .update(
+                            device,
+                            queue,
+                            primitive.texture,
+                            &primitive.data_layout,
+                            list,
+                        );
                 }
-                rlayer
-                    .textures
-                    .update(device, queue, &self.texture_data_layout, &draws.textures);
-                rlayer.texture_slots.clear();
-                // Read rather than cast: the payload is a byte vec, so it
-                // carries no alignment a `u32` slice could borrow.
-                let slots = draws.textures.data().as_chunks::<4>().0;
-                rlayer
-                    .texture_slots
-                    .extend(slots.iter().copied().map(u32::from_ne_bytes));
                 draws.updated = false;
             }
         }
@@ -218,30 +215,12 @@ impl UiRenderNode {
         let pages = GpuPages::new(device, queue, &texture_layout, &sampler);
         let textures = GpuTextures::new(device, queue);
 
-        // A texture instance's data is the slot it binds, which its shader
-        // never reads -- but group 1 is in the layout, so it is bound anyway.
-        let texture_data_layout = Self::data_layout(device, size_of::<u32>() as u64);
-        let texture_pipeline = Self::pipeline(
-            device,
-            &Self::pipeline_layout(
-                device,
-                &shared_layout,
-                &texture_data_layout,
-                &texture_layout,
-            ),
-            config.format,
-            TEXTURE_SHADER,
-            "texture",
-        );
-
         Self {
             shared_layout,
             shared_group,
-            texture_data_layout,
             texture_layout,
             format: config.format,
             primitives: Vec::new(),
-            texture_pipeline,
             window_buffer,
             layers: HashMap::default(),
             active: Vec::new(),
@@ -267,6 +246,7 @@ impl UiRenderNode {
             self.primitives.push(PrimitivePipeline {
                 data_layout,
                 pipeline,
+                texture: source.texture,
             });
         }
     }
@@ -438,11 +418,9 @@ impl UiRenderNode {
 }
 
 impl RenderLayer {
-    fn new(device: &Device) -> Self {
+    fn new() -> Self {
         Self {
             primitives: Vec::new(),
-            textures: ListBuffers::new(device),
-            texture_slots: Vec::new(),
         }
     }
 }
@@ -461,6 +439,7 @@ impl ListBuffers {
                 "primitive data",
             ),
             group: None,
+            slots: Vec::new(),
         }
     }
 
@@ -468,9 +447,18 @@ impl ListBuffers {
         &mut self,
         device: &Device,
         queue: &Queue,
+        texture: PrimitiveTexture,
         layout: &BindGroupLayout,
         list: &InstanceList,
     ) {
+        if texture == PrimitiveTexture::PerInstance {
+            self.slots.clear();
+            // Read rather than cast: the payload is a byte vec, so it carries
+            // no alignment a `u32` slice could borrow.
+            let slots = list.data().as_chunks::<4>().0;
+            self.slots
+                .extend(slots.iter().copied().map(u32::from_ne_bytes));
+        }
         self.instance.update(device, queue, list.instances());
         let resized = self.data.update(device, queue, list.data());
         // An empty list has no buffer big enough for one entry, and nothing

core/src/render/primitive.rs

@@ -7,6 +7,14 @@ use crate::{
 };
 use bytemuck::Pod;
 
+/// One instance of a registered primitive, laid out as the struct that
+/// primitive's shader reads at `@group(1) @binding(0)`.
+///
+/// A `PrimitiveKind<P>` is only minted by `register::<P>`, and `write` takes
+/// the kind and the value together, so holding one is the proof that `P` has a
+/// list of its own to go in and a write needs no check.
+pub trait Primitive: Pod {}
+
 /// Which registered primitive an instance is, and so which list it lives in
 /// and which pipeline draws it. The type ties a `write` to what its shader reads.
 pub struct PrimitiveKind<P> {
@@ -37,6 +45,7 @@ impl<P> Copy for PrimitiveKind<P> {}
 
 pub const RECT: PrimitiveKind<RectPrimitive> = PrimitiveKind::new(0);
 pub const GLYPH: PrimitiveKind<GlyphPrimitive> = PrimitiveKind::new(1);
+pub const TEXTURE: PrimitiveKind<TexturePrimitive> = PrimitiveKind::new(2);
 
 /// Every primitive a ui can draw, in id order. Registering one is all the
 /// wiring it needs: its list, buffers, free list and pipeline follow, and
@@ -44,6 +53,9 @@ pub const GLYPH: PrimitiveKind<GlyphPrimitive> = PrimitiveKind::new(1);
 ///
 /// A source is compiled after `prelude.wgsl` and supplies its data at
 /// `@group(1) @binding(0)` and an `fs_main` shading one instance.
+///
+/// Order is draw order within a layer, so a primitive registered later is
+/// drawn over one registered earlier.
 pub struct PrimitiveRegistry {
     kinds: Vec<PrimitiveSource>,
 }
@@ -54,30 +66,55 @@ pub struct PrimitiveSource {
     /// Size of one instance's entry, which the renderer states as the group 1
     /// binding's minimum rather than leaving it to be inferred.
     pub stride: u64,
+    pub texture: PrimitiveTexture,
+}
+
+/// What a primitive samples at group 2, which is the whole of why some of them
+/// cannot share one instanced draw.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum PrimitiveTexture {
+    /// The shared glyph atlas, bound once for the layer.
+    Atlas,
+    /// The `Textures` slot in the first four bytes of its own data, bound for
+    /// that instance alone -- so one draw call each.
+    PerInstance,
 }
 
 impl Default for PrimitiveRegistry {
     fn default() -> Self {
+        use PrimitiveTexture::*;
         let mut registry = Self { kinds: Vec::new() };
-        let rect = registry.register::<RectPrimitive>(include_str!("shader/rect.wgsl"), "rect");
-        let glyph = registry.register::<GlyphPrimitive>(include_str!("shader/glyph.wgsl"), "glyph");
+        let rect =
+            registry.register::<RectPrimitive>(include_str!("shader/rect.wgsl"), "rect", Atlas);
+        let glyph =
+            registry.register::<GlyphPrimitive>(include_str!("shader/glyph.wgsl"), "glyph", Atlas);
+        let texture = registry.register::<TexturePrimitive>(
+            include_str!("shader/texture.wgsl"),
+            "texture",
+            PerInstance,
+        );
         // The built-ins have constant ids so a widget can name one without the
         // registry; registering them first is what makes those constants true.
-        assert_eq!((rect.id(), glyph.id()), (RECT.id(), GLYPH.id()));
+        assert_eq!(
+            (rect.id(), glyph.id(), texture.id()),
+            (RECT.id(), GLYPH.id(), TEXTURE.id())
+        );
         registry
     }
 }
 
 impl PrimitiveRegistry {
-    pub fn register<P: Pod>(
+    pub fn register<P: Primitive>(
         &mut self,
         wgsl: &'static str,
         label: &'static str,
+        texture: PrimitiveTexture,
     ) -> PrimitiveKind<P> {
         self.kinds.push(PrimitiveSource {
             wgsl,
             label,
             stride: size_of::<P>() as u64,
+            texture,
         });
         PrimitiveKind::new(self.kinds.len() as u32 - 1)
     }
@@ -87,21 +124,13 @@ impl PrimitiveRegistry {
     }
 }
 
-/// Which of a layer's lists an instance is in. They index independently, so a
-/// handle or a renumbering naming only a position would be ambiguous.
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub enum InstanceKind {
-    Primitive(u32),
-    Texture,
-}
-
-/// Instances, the widget each belongs to, the slots waiting to be reused, and
-/// `stride` bytes of data per instance at the same index.
+/// One registered primitive's instances in one layer: the instances, the
+/// widget each belongs to, the slots waiting to be reused, and `stride` bytes
+/// of that primitive's data per instance at the same index.
 ///
-/// That data is the struct a primitive's shader reads, or the slot a texture
-/// binds. Keeping both here is what holds them in step through a
-/// `swap_remove`.
-#[derive(Default)]
+/// `stride` comes from the type the list was made for, so a write is never
+/// checked against it. The data rides here rather than beside the list so the
+/// two stay in step through a `swap_remove`.
 pub struct InstanceList {
     instances: Vec<PrimitiveInstance>,
     assoc: Vec<WidgetId>,
@@ -111,6 +140,16 @@ pub struct InstanceList {
 }
 
 impl InstanceList {
+    fn new<P: Primitive>() -> Self {
+        Self {
+            instances: Vec::new(),
+            assoc: Vec::new(),
+            free: Vec::new(),
+            data: Vec::new(),
+            stride: size_of::<P>(),
+        }
+    }
+
     pub fn instances(&self) -> &[PrimitiveInstance] {
         &self.instances
     }
@@ -120,14 +159,6 @@ impl InstanceList {
     }
 
     fn push(&mut self, id: WidgetId, inst: PrimitiveInstance, data: &[u8]) -> usize {
-        if self.instances.is_empty() {
-            self.stride = data.len();
-        }
-        debug_assert_eq!(
-            data.len(),
-            self.stride,
-            "primitive written to the wrong list"
-        );
         if let Some(i) = self.free.pop() {
             self.instances[i] = inst;
             self.assoc[i] = id;
@@ -147,7 +178,7 @@ impl InstanceList {
         self.instances[i].mask_idx
     }
 
-    fn apply_free(&mut self, kind: InstanceKind) -> impl Iterator<Item = PrimitiveChange> {
+    fn apply_free(&mut self, kind: u32) -> impl Iterator<Item = PrimitiveChange> {
         self.free.sort_by(|a, b| b.cmp(a));
         let instances = &mut self.instances;
         let assoc = &mut self.assoc;
@@ -173,11 +204,13 @@ impl InstanceList {
     }
 }
 
-/// Everything one layer draws. A texture binds its own group 2, so it draws on
-/// its own and cannot join the instanced draw a primitive gets.
+/// Everything one layer draws, one list per registered primitive. They index
+/// independently, so a handle or a renumbering naming only a position would be
+/// ambiguous between them.
 pub struct LayerDraws {
-    primitives: Vec<InstanceList>,
-    pub textures: InstanceList,
+    /// `None` until this layer draws that primitive, because only the write
+    /// knows the type the list is for.
+    primitives: Vec<Option<InstanceList>>,
     pub updated: bool,
 }
 
@@ -185,99 +218,85 @@ impl Default for LayerDraws {
     fn default() -> Self {
         Self {
             primitives: Vec::new(),
-            textures: InstanceList::default(),
             updated: true,
         }
     }
 }
 
 impl LayerDraws {
-    pub fn write<P: Pod>(
+    pub fn write<P: Primitive>(
         &mut self,
         layer: usize,
-        kind: PrimitiveKind<P>,
-        id: WidgetId,
-        primitive: P,
-        region: UiRegion,
-        mask_idx: MaskIdx,
+        PrimitiveInst {
+            kind,
+            id,
+            primitive,
+            region,
+            mask_idx,
+        }: PrimitiveInst<P>,
     ) -> PrimitiveHandle {
         self.updated = true;
+        // Grown on first use rather than sized from the registry, which a
+        // layer cannot see.
         if self.primitives.len() <= kind.id as usize {
-            self.primitives
-                .resize_with(kind.id as usize + 1, Default::default);
+            self.primitives.resize_with(kind.id as usize + 1, || None);
         }
-        let inst_idx = self.primitives[kind.id as usize].push(
+        let inst_idx = self.primitives[kind.id as usize]
+            .get_or_insert_with(InstanceList::new::<P>)
+            .push(
                 id,
                 PrimitiveInstance { region, mask_idx },
                 bytemuck::bytes_of(&primitive),
             );
         PrimitiveHandle {
             layer,
-            kind: InstanceKind::Primitive(kind.id),
+            kind: kind.id,
             inst_idx,
         }
     }
 
-    /// Writes an instance that samples the texture in slot `texture`, which is
-    /// bound for it alone rather than read from a buffer.
-    pub fn write_texture(
-        &mut self,
-        layer: usize,
-        id: WidgetId,
-        texture: u32,
-        region: UiRegion,
-        mask_idx: MaskIdx,
-    ) -> PrimitiveHandle {
-        self.updated = true;
-        PrimitiveHandle {
-            layer,
-            kind: InstanceKind::Texture,
-            inst_idx: self.textures.push(
-                id,
-                PrimitiveInstance { region, mask_idx },
-                bytemuck::bytes_of(&texture),
-            ),
-        }
-    }
-
-    pub fn primitives(&self) -> &[InstanceList] {
+    pub fn primitives(&self) -> &[Option<InstanceList>] {
         &self.primitives
     }
 
     pub fn apply_free(&mut self) -> impl Iterator<Item = PrimitiveChange> {
-        let Self {
-            primitives,
-            textures,
-            ..
-        } = self;
-        primitives
+        self.primitives
             .iter_mut()
             .enumerate()
-            .flat_map(|(i, list)| list.apply_free(InstanceKind::Primitive(i as u32)))
-            .chain(textures.apply_free(InstanceKind::Texture))
+            .filter_map(|(kind, list)| Some((kind as u32, list.as_mut()?)))
+            .flat_map(|(kind, list)| list.apply_free(kind))
     }
 
     pub fn free(&mut self, h: &PrimitiveHandle) -> MaskIdx {
         self.updated = true;
-        self.list_mut(h.kind).free(h.inst_idx)
+        self.list(h).free(h.inst_idx)
     }
 
     pub fn region_mut(&mut self, h: &PrimitiveHandle) -> &mut UiRegion {
         self.updated = true;
-        &mut self.list_mut(h.kind).instances[h.inst_idx].region
+        &mut self.list(h).instances[h.inst_idx].region
     }
 
-    fn list_mut(&mut self, kind: InstanceKind) -> &mut InstanceList {
-        match kind {
-            InstanceKind::Primitive(i) => &mut self.primitives[i as usize],
-            InstanceKind::Texture => &mut self.textures,
-        }
+    /// A handle is only ever made by `write`, which is what created the list.
+    fn list(&mut self, h: &PrimitiveHandle) -> &mut InstanceList {
+        self.primitives[h.kind as usize]
+            .as_mut()
+            .expect("handle names a primitive this layer never drew")
     }
 }
 
+pub struct PrimitiveInst<P> {
+    pub kind: PrimitiveKind<P>,
+    pub id: WidgetId,
+    pub primitive: P,
+    pub region: UiRegion,
+    pub mask_idx: MaskIdx,
+}
+
 pub struct PrimitiveChange {
     pub id: WidgetId,
-    pub kind: InstanceKind,
+    /// Which registered primitive's list moved, since they index separately.
+    pub kind: u32,
     pub old: usize,
     pub new: usize,
 }
@@ -285,7 +304,7 @@ pub struct PrimitiveChange {
 #[derive(Debug)]
 pub struct PrimitiveHandle {
     pub layer: usize,
-    pub kind: InstanceKind,
+    pub kind: u32,
     pub inst_idx: usize,
 }
 
@@ -300,6 +319,7 @@ pub struct RectPrimitive {
 
 unsafe impl bytemuck::Pod for RectPrimitive {}
 unsafe impl bytemuck::Zeroable for RectPrimitive {}
+impl Primitive for RectPrimitive {}
 
 impl RectPrimitive {
     pub fn color(color: Color<u8>) -> Self {
@@ -327,3 +347,16 @@ pub struct GlyphPrimitive {
 
 unsafe impl bytemuck::Pod for GlyphPrimitive {}
 unsafe impl bytemuck::Zeroable for GlyphPrimitive {}
+impl Primitive for GlyphPrimitive {}
+
+/// One drawn image. Its shader reads nothing: the slot names the texture bound
+/// for this instance alone, which is what `PrimitiveTexture::PerInstance` does.
+#[repr(C)]
+#[derive(Debug, Copy, Clone)]
+pub struct TexturePrimitive {
+    pub slot: u32,
+}
+
+unsafe impl bytemuck::Pod for TexturePrimitive {}
+unsafe impl bytemuck::Zeroable for TexturePrimitive {}
+impl Primitive for TexturePrimitive {}

core/src/ui/painter.rs

@@ -1,9 +1,10 @@
-use bytemuck::Pod;
-
 use crate::{
     Axis, Len, RenderedText, Size, SizeCtx, StrongWidget, TextAttrs, TextBuffer, TextData,
     TextureHandle, UiRegion, UiRenderState, UiRsc, UiScalar, UiVec2, Widget, WidgetId,
-    render::{GLYPH, GlyphPrimitive, Mask, MaskIdx, PrimitiveHandle, PrimitiveKind},
+    render::{
+        GLYPH, GlyphPrimitive, Mask, MaskIdx, Primitive, PrimitiveHandle, PrimitiveInst,
+        PrimitiveKind, TEXTURE, TexturePrimitive,
+    },
     util::Vec2,
 };
 
@@ -22,11 +23,22 @@ pub struct Painter<'a> {
 }
 
 impl<'a> Painter<'a> {
-    fn primitive_at<P: Pod>(&mut self, kind: PrimitiveKind<P>, primitive: P, region: UiRegion) {
-        let h = self
-            .state
-            .layers
-            .write(self.layer, kind, self.id, primitive, region, self.mask);
+    fn primitive_at<P: Primitive>(
+        &mut self,
+        kind: PrimitiveKind<P>,
+        primitive: P,
+        region: UiRegion,
+    ) {
+        let h = self.state.layers.write(
+            self.layer,
+            PrimitiveInst {
+                kind,
+                id: self.id,
+                primitive,
+                region,
+                mask_idx: self.mask,
+            },
+        );
         self.push_primitive(h);
     }
 
@@ -39,11 +51,11 @@ impl<'a> Painter<'a> {
     }
 
     /// Writes a primitive to be rendered
-    pub fn primitive<P: Pod>(&mut self, kind: PrimitiveKind<P>, primitive: P) {
+    pub fn primitive<P: Primitive>(&mut self, kind: PrimitiveKind<P>, primitive: P) {
         self.primitive_at(kind, primitive, self.region)
     }
 
-    pub fn primitive_within<P: Pod>(
+    pub fn primitive_within<P: Primitive>(
         &mut self,
         kind: PrimitiveKind<P>,
         primitive: P,
@@ -91,11 +103,13 @@ impl<'a> Painter<'a> {
 
     pub fn texture_at(&mut self, handle: &TextureHandle, region: UiRegion) {
         self.textures.push(handle.clone());
-        let h =
-            self.state
-                .layers
-                .write_texture(self.layer, self.id, handle.slot(), region, self.mask);
-        self.push_primitive(h);
+        self.primitive_at(
+            TEXTURE,
+            TexturePrimitive {
+                slot: handle.slot(),
+            },
+            region,
+        );
     }
 
     pub fn render_text(

core/src/ui/render_state.rs

@@ -245,9 +245,12 @@ impl UiRenderState {
     pub fn debug_layers(&self) {
         for ((idx, depth), draws) in self.layers.iter_depth() {
             let indent = " ".repeat(depth * 2);
-            let primitives: usize = draws.primitives().iter().map(|l| l.instances().len()).sum();
-            let textures = draws.textures.instances().len();
-            println!("{indent}{idx}: {primitives} primitives, {textures} textures");
+            let counts: Vec<String> = draws
+                .primitives()
+                .iter()
+                .map(|l| l.as_ref().map_or(0, |l| l.instances().len()).to_string())
+                .collect();
+            println!("{indent}{idx}: [{}]", counts.join(", "));
         }
     }