diff --git a/core/src/render/mod.rs b/core/src/render/mod.rs
index 12c5146..8a31049 100644
--- a/core/src/render/mod.rs
+++ b/core/src/render/mod.rs
@@ -364,9 +364,9 @@ impl UiRenderNode {
         })
     }
 
-    /// One list's per-instance data. Per primitive with `stride` stated: a
-    /// `None` minimum is filled in from the first pipeline built against the
-    /// layout, so a shared one would hold every primitive to the largest.
+    /// One list's per-instance data. Each primitive needs its own, stating its
+    /// own `stride`: a `None` minimum takes its value from the first pipeline
+    /// built against the layout, and then holds every later one to that.
     fn data_layout(device: &Device, stride: u64) -> BindGroupLayout {
         device.create_bind_group_layout(&BindGroupLayoutDescriptor {
             entries: &[BindGroupLayoutEntry {
@@ -383,8 +383,7 @@ impl UiRenderNode {
         })
     }
 
-    /// The one image an instance samples. The sampler is shared, so there is
-    /// nothing else in here.
+    /// The image one instance samples.
     fn image_layout(device: &Device) -> BindGroupLayout {
         device.create_bind_group_layout(&BindGroupLayoutDescriptor {
             entries: &[BindGroupLayoutEntry {
diff --git a/core/src/render/primitive.rs b/core/src/render/primitive.rs
index 0f236da..1f43e47 100644
--- a/core/src/render/primitive.rs
+++ b/core/src/render/primitive.rs
@@ -1,7 +1,7 @@
 use std::{any::TypeId, marker::PhantomData};
 
 use crate::{
-    Color, UiRegion, WidgetId,
+    Color, TextureHandle, UiRegion, WidgetId,
     render::data::{MaskIdx, PrimitiveInstance},
     util::{HashMap, Vec2},
 };
@@ -15,13 +15,12 @@ pub trait Primitive: Pod + 'static {
     /// Compiled after `prelude.wgsl`, which states what it declares and what
     /// it is given.
     const WGSL: &'static str;
-    /// Reads the image an instance samples, for a primitive that draws one.
-    /// Each instance is then a draw of its own, bound for it alone.
+    /// Reads the image an instance uses. Each instance is then a draw of its
+    /// own, with that image bound for it alone.
     const TEXTURE: Option<fn(&Self) -> u32> = None;
 }
 
-/// Which registered primitive an instance is. Only `PrimitiveRegistry::kind`
-/// mints one, so holding it is the proof that `P` has a list to go in.
+/// Which registered primitive an instance is.
 pub struct PrimitiveKind<P> {
     id: u32,
     _p: PhantomData<fn(P)>,
@@ -45,6 +44,7 @@ impl<P> Clone for PrimitiveKind<P> {
 impl<P> Copy for PrimitiveKind<P> {}
 
 /// Every primitive a ui can draw, in the order they were first drawn.
+#[derive(Default)]
 pub struct PrimitiveRegistry {
     kinds: Vec<PrimitiveSource>,
     ids: HashMap<TypeId, u32>,
@@ -59,21 +59,6 @@ pub struct PrimitiveSource {
     pub textured: bool,
 }
 
-impl Default for PrimitiveRegistry {
-    /// The built-ins are registered up front rather than on first use, so that
-    /// what a ui happens to draw first cannot decide anything about them.
-    fn default() -> Self {
-        let mut registry = Self {
-            kinds: Vec::new(),
-            ids: HashMap::default(),
-        };
-        registry.kind::<RectPrimitive>();
-        registry.kind::<GlyphPrimitive>();
-        registry.kind::<TexturePrimitive>();
-        registry
-    }
-}
-
 impl PrimitiveRegistry {
     /// Registers `P` if this is the first time it has been drawn.
     pub fn kind<P: Primitive>(&mut self) -> PrimitiveKind<P> {
@@ -354,3 +339,11 @@ impl Primitive for TexturePrimitive {
     const WGSL: &'static str = include_str!("shader/texture.wgsl");
     const TEXTURE: Option<fn(&Self) -> u32> = Some(|texture| texture.slot);
 }
+
+impl From<&TextureHandle> for TexturePrimitive {
+    fn from(handle: &TextureHandle) -> Self {
+        Self {
+            slot: handle.slot(),
+        }
+    }
+}
diff --git a/core/src/render/shader/glyph.wgsl b/core/src/render/shader/glyph.wgsl
index 376b4fd..08029ff 100644
--- a/core/src/render/shader/glyph.wgsl
+++ b/core/src/render/shader/glyph.wgsl
@@ -1,6 +1,12 @@
 // Matches `GlyphEntry::IS_COLORED`.
 const COLORED: u32 = 1u;
 
+// The glyph atlas, whose array layers are its pages.
+@group(0) @binding(2)
+var atlas: texture_2d_array<f32>;
+@group(0) @binding(3)
+var samp: sampler;
+
 struct GlyphInfo {
     uv_min: vec2<f32>,
     uv_max: vec2<f32>,
diff --git a/core/src/render/shader/prelude.wgsl b/core/src/render/shader/prelude.wgsl
index c967a24..013fe4b 100644
--- a/core/src/render/shader/prelude.wgsl
+++ b/core/src/render/shader/prelude.wgsl
@@ -1,17 +1,15 @@
 // Prepended to every primitive's shader, which declares its own instance data
 // as `var<storage> <name>: array<T>` at group 1 binding 0, and an `fs_main`
-// shading one instance of it. A primitive that samples an image of its own
-// takes it at group 2 binding 0; see texture.wgsl.
+// shading one instance of it.
+//
+// The rest of group 0 is bound for every draw but declared by the shaders that
+// read it: the glyph atlas at binding 2 and the ui's sampler at binding 3. A
+// primitive that samples an image of its own takes it at group 2 binding 0.
 
 @group(0) @binding(0)
 var<uniform> window: WindowUniform;
 @group(0) @binding(1)
 var<storage> masks: array<Mask>;
-// The glyph atlas, whose array layers are its pages.
-@group(0) @binding(2)
-var atlas: texture_2d_array<f32>;
-@group(0) @binding(3)
-var samp: sampler;
 
 struct WindowUniform {
     dim: vec2<f32>,
diff --git a/core/src/render/shader/texture.wgsl b/core/src/render/shader/texture.wgsl
index e4e3cec..179d0a3 100644
--- a/core/src/render/shader/texture.wgsl
+++ b/core/src/render/shader/texture.wgsl
@@ -1,6 +1,8 @@
 // The image this instance draws, bound for it alone.
 @group(2) @binding(0)
 var image: texture_2d<f32>;
+@group(0) @binding(3)
+var samp: sampler;
 
 @fragment
 fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
diff --git a/core/src/ui/painter.rs b/core/src/ui/painter.rs
index 11139cb..d0496b5 100644
--- a/core/src/ui/painter.rs
+++ b/core/src/ui/painter.rs
@@ -28,8 +28,7 @@ impl<'a> Painter<'a> {
         self.write(kind, primitive, region);
     }
 
-    /// For a caller with many of one primitive to write, since looking the kind
-    /// up is per type rather than per instance.
+    /// Takes the kind, for a caller writing many of one primitive.
     fn write<P: Primitive>(&mut self, kind: PrimitiveKind<P>, primitive: P, region: UiRegion) {
         let h = self.state.layers.write(
             self.layer,
@@ -98,14 +97,12 @@ impl<'a> Painter<'a> {
         self.texture_at(handle, self.region);
     }
 
+    /// A texture primitive, plus a share of the handle it names -- which a
+    /// `Pod` primitive cannot carry, and without which the slot could be
+    /// freed and reused while still drawn.
     pub fn texture_at(&mut self, handle: &TextureHandle, region: UiRegion) {
         self.textures.push(handle.clone());
-        self.primitive_at(
-            TexturePrimitive {
-                slot: handle.slot(),
-            },
-            region,
-        );
+        self.primitive_at(TexturePrimitive::from(handle), region);
     }
 
     pub fn render_text(