feat(renderer): uniform bind groups infrastructure (Étape 3 + 4.1/4.2/4.4)

Étape 3 (infrastructure uniforms) + le câblage minimal d'Étape 4 pour garder
les exemples exécutables (wgpu requiert que tous les bind groups du layout
pipeline soient posés au draw) :

- resources/uniform.rs : types bytemuck Pod FrameUniforms (192 B) et
  ObjectUniform (64 B), alignés 16 octets sans padding; offsets vérifiés par un
  test unitaire contre le contrat du shader. glam feature bytemuck activé.
- pipeline_cache: create_uniform_bind_group_layouts() expose les 2 layouts
  (frame @0 Vertex|Fragment + object @1 Vertex); build_pipeline les attache à
  TOUT pipeline (un seul layout pour tous, décision actée).
- Renderer: alloue le buffer frame partagé + BindGroup(0) (défaut identité,
  mode lit) et un object identité partagé pour le chemin bas-niveau; cache
  RefCell<HashMap<label,(buffer,bindgroup)>> par entité, model réécrit chaque
  frame depuis transform.to_matrix(); draw_entity pose groupes 0+1.

4.3 (caméra active + aspect) non implémenté: simple/manual restent exécutables
car basic ignore ces uniforms. Documentation DRAFT mise à jour.

Validation: check workspace+examples 0 warning, doc 0 warning, test (Pod+wgsl)
OK, fmt propre.

Cargo.lock

@@ -488,6 +488,9 @@ name = "glam"
 version = "0.33.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "7f22fb22f065b308be0d8724e3706c7fa3fc2a6c7d6899df4cad7860e7a75436"
+dependencies = [
+ "bytemuck",
+]
 
 [[package]]
 name = "glow"

docs/DRAFT.md

@@ -70,34 +70,37 @@ toucher au rendu (pure façade de données, validable par compilation).
 
 **But** : permettre aux pipelines de recevoir des uniforms (bind groups) au lieu de `bind_group_layouts: &[]`.
 
-- [ ] 3.1 **Types bytemuck `Pod`** (nouveau `lib/src/resources/uniform.rs`, ou `math/uniform.rs`) :
-  - `#[repr(C)] #[derive(Pod, Zeroable, Copy, Clone)] FrameUniforms` (voir 2.1)
-  - `#[repr(C)] #[derive(...)] ObjectUniform { model: Mat4 }`
-  - (alignement 16 octets : utiliser `Vec4`/tableaux pour éviter le padding). Exporter via le `mod.rs` concerné.
-- [ ] 3.2 **Bind group layouts** : dans `build_pipeline`, créer 2 `BindGroupLayout`
-  (frame @0 + object @1, chacun avec un buffer uniform `Vertex`/`Fragment`/`Vertex|Fragment` selon usage) et les
-  passer dans `PipelineLayoutDescriptor.bind_group_layouts`. `immediate_size` reste 0 (pas de `var<immediate>`).
-- [ ] 3.3 **Acté : un seul layout pour tous** (option A). `build_pipeline` attache **toujours** les 2 bind groups
-  (frame @0 + object @1). Plus de famille `basic` au layout vide : tout matériau partage le même layout
-  uniformisé. `manual`/quad plat migrent (Étape 5).
-- [ ] **Validation** : `cargo check` 0 warning ; `cargo doc` 0 warning (types documentés, `missing_docs` actif).
+- [X] 3.1 **Types bytemuck `Pod`** (nouveau `lib/src/resources/uniform.rs`) : `FrameUniforms` (192 B) et
+  `ObjectUniform` (64 B), `#[repr(C)]`, 16-byte alignés, sans padding — offset vérifiés par un test
+  unitaire contre la table du shader. Exports via `resources/mod.rs`. *(fait — 2026-09-16. Au passage,
+  `glam` feature `bytemuck` activé pour que `Mat4`/`Vec4` implémentent `Pod`/`Zeroable`.)*
+- [X] 3.2 **Bind group layouts** : nouveau `create_uniform_bind_group_layouts(device)` (dans
+  `pipeline_cache.rs`, exporté) → frame @0 (`Uniform`, `Vertex|Fragment`) + object @1 (`Uniform`, `Vertex`).
+  `build_pipeline` les passe dans le `PipelineLayoutDescriptor`. `immediate_size` reste 0.
+  *(fait — 2026-09-16)*
+- [X] 3.3 **Acté : un seul layout pour tous** (option A). `build_pipeline` attache **toujours** les 2 bind
+  groups (frame @0 + object @1), même si le shader ne les lit pas (validation wgpu : layout╱bind group).
+  *(fait — 2026-09-16)*
+- [X] **Validation** : `cargo check --workspace --examples` 0 warning ; `cargo doc --no-deps` 0 warning ;
+  `cargo test` (types Pod + wgsl naga) OK ; `cargo fmt` propre. *(fait — 2026-09-16)*
 
 ## Étape 4 — Rendu 3D dans le `Renderer`
 
 **But** : `render_scene` applique matrices + éclairage par entité.
 
-- [ ] 4.1 **Buffers frame partagés** : créer le `wgpu::Buffer` `FrameUniforms` + `BindGroup(0)` dans
-  `Renderer::new` (ou à la 1re frame). Écrire chaque frame : view/proj (caméra active) + lumière.
-- [ ] 4.2 **Buffers object par entité** : `Renderer` maintient un cache
-  `RefCell<HashMap<String, (wgpu::Buffer, wgpu::BindGroup)>>` clefé par label d'entité (créé à la 1re rencontre),
-  car `render_scene(&self, &Scene)` est immuable. Chaque frame : écrire `ObjectUniform.world = entity.transform.to_matrix()` + `set_bind_group(1, ...)`.
-- [ ] 4.3 **Caméra active** : ajouter `scene.set_active_camera(Camera)` / `scene.active_camera() -> Option<&Camera>`.
-  Calcul du `proj` avec l'aspect de la fenêtre (`window.inner_size()` accessible via `App.window`).
-- [ ] 4.4 **`draw_entity` étendu** : `set_bind_group(0, frame_bg)` + `set_bind_group(1, object_bg)` avant le draw,
-  pour **tout** matériau (layout unique). Le chemin bas-niveau `Renderer::render` pose aussi les 2 bind groups
-  (frame partagé + object du mesh appelant).
-- [ ] **Validation** : `cargo check` 0 warning ; exécution `simple` (sans panique, boucle active) ;
-  `manual` non-régressif (chemin bas-niveau).
+- [X] 4.1 **Buffers frame partagés** : le `Renderer::new` crée le `wgpu::Buffer` `FrameUniforms` + `BindGroup(0)`
+  (défaut : caméra identité + lumière blanche + mode lit). *(fait — 2026-09-16)*
+- [X] 4.2 **Buffers object par entité** : le `Renderer` maintient un cache
+  `RefCell<HashMap<String,(wgpu::Buffer, wgpu::BindGroup)>>` clefé par label d'entité ; chaque frame il
+  écrit `ObjectUniform.world = entity.transform.to_matrix()` (via `object_bind_group_for`). *(fait — 2026-09-16)*
+- [ ] 4.3 **Caméra active** : ajouter `scene.set_active_camera(Camera)` / `scene.active_camera() -> Option<&Camera>` ;
+  écrire view/proj (avec aspect de la fenêtre) dans le buffer frame chaque frame. *(non fait — laisse le
+  `FrameUniforms::default()` : simple/manual tournent toujours via `basic` qui ignore ces uniforms)*
+- [X] 4.4 **`draw_entity` étendu** : pose `set_bind_group(0, frame_bg)` + `set_bind_group(1, object_bg)` avant le
+  draw (groupes requis par le layout unique) ; le chemin bas-niveau `Renderer::render` pose aussi les 2 bind
+  groups (frame partagé + object identité partagé). *(fait — 2026-09-16)*
+- [ ] **Validation** : `cargo check` 0 warning ; exécution `simple` (sans panique, boucle active). *(une partie :
+  `simple` reste exécutable car `basic` ignore les uniforms ; le rendu 3D réel attend 4.3)*
 
 ## Étape 5 — Exemple 3D (cube éclairé)
 

lib/Cargo.toml

@@ -11,5 +11,5 @@ wgpu = "30.0.0" # Vérifiez la version la plus récente
 winit = "0.30.13"  # For window management — pinned to match examples
 thiserror = "2"
 bytemuck = { version = "1.25.0", features = ["derive"] }
-glam = "0.33"
+glam = { version = "0.33", features = ["bytemuck"] } # feature requis pour Pod/Zeroable sur Mat4/Vec4 (uniform.rs)
 pollster = { version="1.0.1", features = ["macro"] }

lib/src/core/renderer.rs

@@ -20,12 +20,20 @@
 
 use crate::core::Context;
 use crate::core::Frame;
-use crate::resources::{Material, Mesh};
+use crate::math::Transform;
+use crate::pipeline::create_uniform_bind_group_layouts;
+use crate::resources::uniform::{FRAME_UNIFORMS_SIZE, OBJECT_UNIFORM_SIZE};
+use crate::resources::{FrameUniforms, Material, Mesh, ObjectUniform};
 use crate::scene::Scene;
+use std::cell::RefCell;
+use std::collections::HashMap;
 
 /// The Executor layer of the architecture. Holds shared references to Device and Queue from Context,
 /// plus the surface texture format. Executes WGPU rendering commands by binding Materials and Meshes
 /// into RenderPasses during each frame. Does not own raw hardware resources (they are Arc-cloned from Context).
+///
+/// Since Étape 3 every pipeline declares the two uniform bind groups (frame @0 + object @1), the
+/// Renderer owns the matching GPU buffers and `BindGroup`s and binds them around every draw call.
 pub struct Renderer {
     /// GPU command submission queue — holds an Arc clone from Context; shared with other Context users.
     queue: wgpu::Queue,
@@ -33,19 +41,78 @@ pub struct Renderer {
     device: wgpu::Device,
     /// Surface texture output format — stored here so it can be passed to PipelineCache on Material creation.
     format: wgpu::TextureFormat,
+    /// Bind group layout for the per-object uniforms (group 1) — must match every pipeline layout.
+    object_layout: wgpu::BindGroupLayout,
+    /// Shared per-frame uniform buffer + bind group (camera + lights). Written each frame (`render_scene`).
+    frame_bind_group: wgpu::BindGroup,
+    /// Shared per-object bind group (identity model) used by the low-level `render` path.
+    shared_object_bind_group: wgpu::BindGroup,
+    /// Per-entity object uniform buffers + bind groups, lazily created on first encounter and keyed by
+    /// entity label. Needed because `render_scene(&self, &Scene)` is immutable; the model matrix is
+    /// rewritten each frame for every entity.
+    object_cache: RefCell<HashMap<String, (wgpu::Buffer, wgpu::BindGroup)>>,
 }
 
 impl Renderer {
-    /// Creates a Renderer by cloning Device and Queue Arc references from the Context, plus capturing the surface format.
+    /// Creates a Renderer by cloning Device and Queue Arc references from the Context, plus capturing
+    /// the surface format, and allocates the shared frame + object uniform buffers and their bind groups.
     /// Inputs: context (borrowed reference to Context providing GPU resource handles), format (surface texture format).
     /// Returns a new Renderer instance sharing the same underlying GPU resources as Context.
     /// Called once at application startup during scene setup. The Renderer shares these resources via Arc;
     /// Context retains ownership and can continue using them after this call.
     pub fn new(context: &Context, format: wgpu::TextureFormat) -> Self {
+        let queue: wgpu::Queue = context.queue.clone();
+        let device: wgpu::Device = context.device.clone();
+        let [frame_layout, object_layout] = create_uniform_bind_group_layouts(&device);
+
+        // Shared frame uniforms: identity camera + white directional light, lit mode by default.
+        // Values become meaningful once an active camera is wired (Étape 4.3); for now the default
+        // is a coherent scene when a shader actually reads them, and irrelevant to shaders that don't.
+        let default_frame = FrameUniforms::default();
+        let frame_buffer = device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some("frame uniform buffer"),
+            size: FRAME_UNIFORMS_SIZE,
+            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+            mapped_at_creation: false,
+        });
+        queue.write_buffer(&frame_buffer, 0, bytemuck::bytes_of(&default_frame));
+        let frame_bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
+            label: Some("frame bind group"),
+            layout: &frame_layout,
+            entries: &[wgpu::BindGroupEntry {
+                binding: 0,
+                resource: frame_buffer.as_entire_binding(),
+            }],
+        });
+
+        // Shared per-object bind group (identity model) for the low-level `render` path.
+        let object_buffer = device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some("shared object uniform buffer"),
+            size: OBJECT_UNIFORM_SIZE,
+            usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+            mapped_at_creation: false,
+        });
+        let identity_object = ObjectUniform {
+            model: glam::Mat4::IDENTITY,
+        };
+        queue.write_buffer(&object_buffer, 0, bytemuck::bytes_of(&identity_object));
+        let shared_object_bind_group = device.create_bind_group(&wgpu::BindGroupDescriptor {
+            label: Some("shared object bind group"),
+            layout: &object_layout,
+            entries: &[wgpu::BindGroupEntry {
+                binding: 0,
+                resource: object_buffer.as_entire_binding(),
+            }],
+        });
+
         Self {
-            queue: context.queue.clone(),
-            device: context.device.clone(),
+            queue,
+            device,
             format,
+            object_layout,
+            frame_bind_group,
+            shared_object_bind_group,
+            object_cache: RefCell::new(HashMap::new()),
         }
     }
 
@@ -81,7 +148,13 @@ impl Renderer {
                 ..Default::default()
             });
 
-            draw_entity(&mut render_pass, mesh, material);
+            draw_entity(
+                &mut render_pass,
+                mesh,
+                material,
+                &self.frame_bind_group,
+                &self.shared_object_bind_group,
+            );
         }
         self.queue.submit(std::iter::once(encoder.finish()));
     }
@@ -113,8 +186,15 @@ impl Renderer {
                 ..Default::default()
             });
 
-            for (_label, mesh, material, _transform) in scene.iter_entities() {
-                draw_entity(&mut render_pass, mesh, material);
+            for (label, mesh, material, transform) in scene.iter_entities() {
+                let object_bind_group = self.object_bind_group_for(label, transform);
+                draw_entity(
+                    &mut render_pass,
+                    mesh,
+                    material,
+                    &self.frame_bind_group,
+                    &object_bind_group,
+                );
             }
         }
         self.queue.submit(std::iter::once(encoder.finish()));
@@ -138,18 +218,62 @@ impl Renderer {
     pub fn format(&self) -> wgpu::TextureFormat {
         self.format
     }
+
+    /// Returns the per-entity object bind group for `label`, creating its uniform buffer on first
+    /// encounter and rewriting the model matrix each call. Since `render_scene(&self)` is immutable,
+    /// the lazily-populated cache is interior-mutable (`RefCell`). Étape 4.2.
+    /// Inputs: label (entity identifier used as cache key), transform (world placement to upload).
+    /// Returns an owned (cheaply Arc-cloned) reference handle to the object bind group (group 1).
+    fn object_bind_group_for(&self, label: &str, transform: &Transform) -> wgpu::BindGroup {
+        let mut cache = self.object_cache.borrow_mut();
+        let (buffer, bind_group) = cache.entry(label.to_string()).or_insert_with(|| {
+            let buffer = self.device.create_buffer(&wgpu::BufferDescriptor {
+                label: Some("object uniform buffer"),
+                size: OBJECT_UNIFORM_SIZE,
+                usage: wgpu::BufferUsages::UNIFORM | wgpu::BufferUsages::COPY_DST,
+                mapped_at_creation: false,
+            });
+            let bind_group = self.device.create_bind_group(&wgpu::BindGroupDescriptor {
+                label: Some("object bind group"),
+                layout: &self.object_layout,
+                entries: &[wgpu::BindGroupEntry {
+                    binding: 0,
+                    resource: buffer.as_entire_binding(),
+                }],
+            });
+            (buffer, bind_group)
+        });
+        // Rewrite the model matrix every frame so entity transforms can update (e.g. rotation).
+        let object_uniforms = ObjectUniform {
+            model: transform.to_matrix(),
+        };
+        self.queue
+            .write_buffer(buffer, 0, bytemuck::bytes_of(&object_uniforms));
+        bind_group.clone()
+    }
 }
 
-/// Binds a Material pipeline and Mesh buffers into an active render pass and issues the draw call.
-/// Shared by `Renderer::render` and `Renderer::render_scene` to avoid duplicated draw logic.
+/// Binds a Material pipeline, the two uniform bind groups, and Mesh buffers into an active render
+/// pass and issues the draw call. Shared by `Renderer::render` and `Renderer::render_scene`.
+/// The frame (group 0) and object (group 1) bind groups are **required** by every pipeline layout
+/// (Étape 3 : un seul layout pour tous) — they must be bound even if the shader does not read them.
 /// Draws indexed geometry when an index buffer exists, otherwise falls back to a non-indexed draw.
-/// Inputs: pass (active render pass), mesh (geometry to draw), material (pipeline to bind).
-fn draw_entity(pass: &mut wgpu::RenderPass<'_>, mesh: &Mesh, material: &Material) {
+/// Inputs: pass (active render pass), mesh (geometry to draw), material (pipeline to bind),
+/// frame_bind_group (shared per-frame uniforms), object_bind_group (per-entity/identity model).
+fn draw_entity(
+    pass: &mut wgpu::RenderPass<'_>,
+    mesh: &Mesh,
+    material: &Material,
+    frame_bind_group: &wgpu::BindGroup,
+    object_bind_group: &wgpu::BindGroup,
+) {
     if mesh.num_vertices == 0 {
         // No vertices — nothing to render.
         return;
     }
     pass.set_pipeline(&material.pipeline);
+    pass.set_bind_group(0, frame_bind_group, &[]);
+    pass.set_bind_group(1, object_bind_group, &[]);
     pass.set_vertex_buffer(0, mesh.vertex_buffer.slice(..));
     if let Some(index_buffer) = &mesh.index_buffer {
         pass.set_index_buffer(index_buffer.slice(..), wgpu::IndexFormat::Uint16);

lib/src/pipeline/mod.rs

@@ -11,4 +11,4 @@
 
 pub mod pipeline_cache;
 // Re-exports
-pub use pipeline_cache::PipelineCache;
+pub use pipeline_cache::{PipelineCache, create_uniform_bind_group_layouts};

lib/src/pipeline/pipeline_cache.rs

@@ -21,6 +21,44 @@ use crate::utils::BASIC_SHADER;
 use std::collections::HashMap;
 use std::sync::Arc;
 
+/// Creates the two bind group layouts shared by **every** pipeline (Étape 3 — décision actée
+/// « un seul layout pour tous »). Both buffers are `Uniform`, 16-byte aligned, no dynamic offset.
+/// Matching CPU types: `FrameUniforms` (192 B) and `ObjectUniform` (64 B) in `resources::uniform`.
+/// Returns `[frame_layout, object_layout]` in renderer binding order.
+///
+/// - `index 0` : per-frame uniforms (view/proj/light/options), visible in both shader stages.
+/// - `index 1` : per-object uniforms (model matrix), visible in the vertex stage only.
+pub fn create_uniform_bind_group_layouts(device: &wgpu::Device) -> [wgpu::BindGroupLayout; 2] {
+    [
+        device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+            label: Some("frame_uniform_layout"),
+            entries: &[wgpu::BindGroupLayoutEntry {
+                binding: 0,
+                visibility: wgpu::ShaderStages::VERTEX_FRAGMENT,
+                ty: wgpu::BindingType::Buffer {
+                    ty: wgpu::BufferBindingType::Uniform,
+                    has_dynamic_offset: false,
+                    min_binding_size: None,
+                },
+                count: None,
+            }],
+        }),
+        device.create_bind_group_layout(&wgpu::BindGroupLayoutDescriptor {
+            label: Some("object_uniform_layout"),
+            entries: &[wgpu::BindGroupLayoutEntry {
+                binding: 0,
+                visibility: wgpu::ShaderStages::VERTEX,
+                ty: wgpu::BindingType::Buffer {
+                    ty: wgpu::BufferBindingType::Uniform,
+                    has_dynamic_offset: false,
+                    min_binding_size: None,
+                },
+                count: None,
+            }],
+        }),
+    ]
+}
+
 /// Shader pipeline cache: maps (shader_id, format) keys to compiled RenderPipelines.
 /// Ensures each unique shader+format combination is compiled at most once; subsequent requests return cached instances.
 pub struct PipelineCache {
@@ -156,12 +194,16 @@ impl PipelineCache {
             ],
         };
 
-        // Pipeline layout — defines bind group bindings (empty here; no uniform buffers used).
-        // wgpu 30: `immediate_size` replaces `push_constant_ranges`.
+        // Pipeline layout — the two uniform bind groups (frame @0 + object @1) are attached
+        // to EVERY pipeline (Étape 3, décision actée « un seul layout pour tous »), even if a
+        // given shader does not read them. `immediate_size` stays 0 (no var<immediate> used).
+        let bind_group_layouts = create_uniform_bind_group_layouts(device);
+        let layout_refs: Vec<Option<&wgpu::BindGroupLayout>> =
+            bind_group_layouts.iter().map(Some).collect();
         let render_pipeline_layout =
             device.create_pipeline_layout(&wgpu::PipelineLayoutDescriptor {
                 label: Some("render_pipeline_layout"),
-                bind_group_layouts: &[],
+                bind_group_layouts: &layout_refs,
                 immediate_size: 0, // no var<immediate> used
             });
 

lib/src/resources/mod.rs

@@ -13,10 +13,12 @@
 pub mod camera;
 pub mod material;
 pub mod mesh;
+pub mod uniform;
 pub mod vertex;
 
 // Re-exports
 pub use camera::Camera;
 pub use material::Material;
 pub use mesh::Mesh;
+pub use uniform::{FrameUniforms, ObjectUniform};
 pub use vertex::Vertex;

lib/src/resources/uniform.rs

@@ -0,0 +1,98 @@
+//! # Uniform Module — GPU Buffer Data Types
+//!
+//! Defines the CPU-side `Pod` (plain old data) structs that are uploaded to GPU uniform buffers.
+//! Their memory layout must match **exactly** the WGSL uniforms declared in `standard_shader.wgsl`
+//! (see the "Uniform Contract" section of that file) — 16-byte alignment (std140), no padding.
+//!
+//! Two bind groups are shared by every pipeline (single-layout decision, Étape 3) :
+//! - `@group(0) @binding(0)` : `FrameUniforms` (per-frame : camera + lights) → 192 bytes
+//! - `@group(1) @binding(0)` : `ObjectUniform` (per-entity model matrix) → 64 bytes
+//!
+//! ## Interaction with Other Modules
+//! - `pipeline_cache::build_pipeline()` creates the two bind group layouts matching these types.
+//! - `Renderer` allocates the buffers and `BindGroup`s from these types and writes them each frame.
+//! - `standard_shader.wgsl` consumes them (layout identical to these structs).
+
+use bytemuck::{Pod, Zeroable};
+use glam::{Mat4, Vec4};
+
+/// Byte size of the per-frame uniform buffer (`FrameUniforms`).
+pub const FRAME_UNIFORMS_SIZE: u64 = std::mem::size_of::<FrameUniforms>() as u64;
+/// Byte size of the per-object uniform buffer (`ObjectUniform`).
+pub const OBJECT_UNIFORM_SIZE: u64 = std::mem::size_of::<ObjectUniform>() as u64;
+
+/// Per-frame GPU uniforms : camera matrices + directional light + options.
+///
+/// Mirrors the WGSL `FrameUniforms` struct in `standard_shader.wgsl` (offset table there).
+/// 192 bytes, 16-byte aligned, no padding — `Pod` for direct `bytes_of` upload.
+#[repr(C)]
+#[derive(Clone, Copy, Pod, Zeroable)]
+pub struct FrameUniforms {
+    /// Camera view matrix (world → view space). Offset 0.
+    pub view: Mat4,
+    /// Camera projection matrix (view → clip space). Offset 64.
+    pub proj: Mat4,
+    /// Camera world position (`.xyz` used). Offset 128.
+    pub cam_pos: Vec4,
+    /// Directional light direction : points **from the surface toward the light**. Offset 144.
+    pub light_dir: Vec4,
+    /// Directional light color (`.rgb` used). Offset 160.
+    pub light_color: Vec4,
+    /// Options. `options[0]` = unlit flag (1 → flat color, no directional lighting). Offset 176.
+    pub options: [u32; 4],
+}
+
+impl Default for FrameUniforms {
+    /// Sensible defaults : identity camera, white light along +Z, *lit* mode.
+    fn default() -> Self {
+        Self {
+            view: Mat4::IDENTITY,
+            proj: Mat4::IDENTITY,
+            cam_pos: Vec4::ZERO,
+            light_dir: Vec4::new(0.0, 0.0, 1.0, 0.0),
+            light_color: Vec4::ONE,
+            options: [0, 0, 0, 0],
+        }
+    }
+}
+
+/// Per-object GPU uniforms : the entity's world-space model matrix.
+///
+/// Mirrors the WGSL `ObjectUniform` struct. 64 bytes, `Pod`.
+#[repr(C)]
+#[derive(Clone, Copy, Pod, Zeroable, Default)]
+pub struct ObjectUniform {
+    /// Model matrix (object → world space). Offset 0.
+    pub model: Mat4,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::mem::offset_of;
+    use std::mem::{align_of, size_of};
+
+    #[test]
+    fn frame_uniforms_layout_matches_wgsl() {
+        // The offsets below must match the offset table in standard_shader.wgsl.
+        assert_eq!(size_of::<FrameUniforms>(), 192);
+        assert_eq!(align_of::<FrameUniforms>(), 16);
+
+        let f = FrameUniforms::default();
+        assert_eq!(offset_of!(FrameUniforms, view), 0);
+        assert_eq!(offset_of!(FrameUniforms, proj), 64);
+        assert_eq!(offset_of!(FrameUniforms, cam_pos), 128);
+        assert_eq!(offset_of!(FrameUniforms, light_dir), 144);
+        assert_eq!(offset_of!(FrameUniforms, light_color), 160);
+        assert_eq!(offset_of!(FrameUniforms, options), 176);
+        // Default is lit mode (unlit flag cleared).
+        assert_eq!(f.options[0], 0);
+    }
+
+    #[test]
+    fn object_uniform_layout_matches_wgsl() {
+        assert_eq!(size_of::<ObjectUniform>(), 64);
+        assert_eq!(align_of::<ObjectUniform>(), 16);
+        assert_eq!(offset_of!(ObjectUniform, model), 0);
+    }
+}