feat: multi-lumières directionnelles + ponctuelles (Étape 12, Phase 4.2)

- Light (48 o) + MAX_LIGHTS=8 ; FrameUniforms étendu (ambient, lights[8], compteurs, _pad)
- resources/lights.rs : Lights (1 dir +Z par défaut, non-régression) + into_frame_array
- Scene : API déclarative add_directional_light / add_point_light / set_ambient / clear_lights
- Renderer::write_frame_uniforms upload les lumières/ambiant de la scène
- standard_shader.wgsl : struct Light + boucles d'accumulation (dir + ponctuelles, atténuation linéaire)
- exemple cube : 1 lumière ponctuelle chaude
- Docs : shaders/resources README, README roadmap, ROADMAP (item coché + Spot notée futur)
- Build/test/fmt OK ; non-régression par défaut (1 dir +Z + ambiant blanc)

README.md

@@ -186,3 +186,4 @@ The architecture docs live in `docs/tech/` and are written in **French**. Each d
 7. ✅ **CPU geometry storage (Étape 8)** — `Mesh` retains a shared `Arc<Geometry>` (CPU source of truth with colors) alongside its GPU buffers; meshes are declared from a `Geometry` via `Mesh::from_geometry`/`Scene::create_mesh(id, geometry, material)` instead of raw `&[Vertex]` arrays. (Done 2026-09-18; `transform` stays on `Entity` — deviation D3.)
 8. ✅ **Diffuse textures (Étape 10, Phase 4.1)** — `resources::Texture` (GPU image: device+view+sampler, `Rgba8UnormSrgb`, loaders `from_rgba8`/`from_bytes`/`from_file`) attached to a `Material` as diffuse texture. The `standard` shader samples it via bind group **@2** (shared layout: sampler+texture); UVs are forwarded as vertex attribute location 2. Without a texture the material uses a shared 1×1 white placeholder so lit and unlit rendering are unchanged (no regression). The `cube` example now uses a procedural checkerboard texture. (Done 2026-09-18.)
 9. ✅ **Window resize (Étape 11, Phase 4.4)** — `App::resize` reconfigures the surface (`Context::configure`) and recreates the depth texture (`Renderer::resize_depth`) together on each `WindowEvent::Resized`, so color and depth attachments always match. Guards against 0×0 (minimize). The surface format is re-synced to the Renderer and Scene if it ever changes. (Done 2026-09-18; verified at runtime on the `cube` example.)
+10. ✅ **Multi-lighting (Étape 12, Phase 4.2)** — the scene now carries a global light list (directional + point) with a white ambient, uploaded into the per-frame `FrameUniforms` array each frame. `Scene::add_directional_light` / `add_point_light` / `set_ambient` / `clear_lights` configure it; `FrameUniforms::default()` (one white directional along +Z + white ambient) reproduces the pre-multi-light look exactly. The `standard` fragment accumulates ambient + all lights; the `cube` example adds a warm point light on top of the default directional. (Done 2026-09-18.)

docs/DRAFT.md

@@ -1,15 +1,4 @@
 # DRAFT — Étape suivante
 
-> 📅 **Document vidé le 2026-09-18** (fin de l'Étape 11, Resize — Phase 4.4, bilan archivé
-> dans l'historique git). Ce fichier accueillera le plan de l'étape suivante.
->
-> **Étape 11 (2026-09-18) : Gestion du Resize (Surface + Depth) — FAIT & vérifié.**
-> `App::resize(w,h)` (`lib/src/app.rs`) reconfigure la surface via `Context::configure` et
-> recrée la depth texture via `Renderer::resize_depth` (+ `set_format`), avec re-synchronisation
-> de la Scene si le format change (D4). `AppRunner::window_event` branche `WindowEvent::Resized`
-> (garde 0×0, D3) et `RedrawRequested` (garde taille nulle, D6).
-> Vérifié : `cargo build`/`test` workspace + compilation des exemples OK, et **au runtime**
-> (exemple `cube`) le resize (agrandir + rétrécir) ne produit ni crash, ni artefact — rendu
-> correct à la nouvelle taille, aspect non déformé.
->
-> Source de vérité = code + README.md. Ce document est vidé à la complétion de chaque étape.
+> DRAFT vide. L'Étape 12 (Phase 4.2 — multi-lumières) est terminée et son bilan est archivé dans l'historique git
+> (commit correspondant). Préparer le plan de l'étape suivante ici.

docs/ROADMAP.md

@@ -139,7 +139,8 @@ generated: { by: human:jerome, at: 2026-07-31T00:00:00Z }
 
 ### 4.2 Éclairage avancé
 - [x] Lumières hémisphériques *(déjà dans le `standard_shader` : mélange hémisphérique, Étape 2)*
-- [ ] Support multi-lumières (directionnelles, ponctuelles)
+- [x] Support multi-lumières (directionnelles, ponctuelles) *(Étape 12, 2026-09-18 : liste globale dans la `Scene`, tableau `FrameUniforms.lights[8]`, shader accumule ambiant + directionnelles + ponctuelles, `MAX_LIGHTS = 8`)*
+- [ ] Lumières spot (cône + angle) *(futur, post-Étape 12 — hors périmètre du multi-lumières initial ; extension triviale : même struct `Light` + champ d'angle/orientation et boucle d'accumulation dédiée)*
 - [ ] Shadows (optionnel)
 
 ### 4.3 Optimisations

lib/examples/cube.rs

@@ -10,7 +10,7 @@
 //! la texture est générée *procéduralement* (damier RGBA 8×8) pour rester autonome, sans asset sur disque.
 //! La caméra active par défaut (`Scene::default`, position (0,0,3), fov 45°) cadre le cube, et
 //! `AppHandler::update` fait tourner l'entité via `set_entity_transform` chaque frame.
-use glam::Quat;
+use glam::{Quat, Vec3};
 use wsg_lib::AppHandler;
 use wsg_lib::app::AppBuilder;
 use wsg_lib::resources::{Geometry, Texture};
@@ -123,6 +123,18 @@ impl AppHandler for Cube {
             .create_mesh("cube_mesh", cube_geometry(), Some("cube_material"))
             .unwrap();
         app.scene.add_entity("cube", "cube_mesh").unwrap();
+
+        // Étape 12 (Phase 4.2) : en plus de la lumière directionnelle par défaut (+Z), on ajoute
+        // une lumière **ponctuelle** chaude devant le cube. Son halo (atténuation linéaire dans le
+        // rayon) est visible sur la face proche du cube, en superposition à l'éclairage directionnel.
+        app.scene
+            .add_point_light(
+                Vec3::new(1.0, 0.5, 1.5), // position monde, devant/droite du cube
+                [1.0, 0.7, 0.3],          // teinte chaude
+                1.0,                      // intensité
+                3.0,                      // rayon d'atténuation
+            )
+            .unwrap();
     }
 
     fn update(&mut self, app: &mut wsg_lib::App) {

lib/src/core/renderer.rs

@@ -23,7 +23,7 @@ use crate::core::Frame;
 use crate::math::Transform;
 use crate::pipeline::{DEPTH_FORMAT, create_uniform_bind_group_layouts};
 use crate::resources::uniform::{FRAME_UNIFORMS_SIZE, OBJECT_UNIFORM_SIZE};
-use crate::resources::{Camera, FrameUniforms, Material, Mesh, ObjectUniform};
+use crate::resources::{Camera, FrameUniforms, Lights, Material, Mesh, ObjectUniform};
 use crate::scene::Scene;
 use glam::Vec4;
 use std::cell::RefCell;
@@ -184,20 +184,31 @@ impl Renderer {
         self.format = format;
     }
 
-    /// Rewrites the shared per-frame uniform buffer from the scene's active camera and the current
-    /// viewport aspect, then returns the frame bind group wired to that buffer. Called at the start of
-    /// every `render_scene` so the GPU sees the latest camera matrices and camera position (Étape 4.3).
+    /// Rewrites the shared per-frame uniform buffer from the scene's active camera, its global
+    /// light list, its ambient color, and the current viewport aspect, then returns the frame bind
+    /// group wired to that buffer. Called at the start of every `render_scene` so the GPU sees the
+    /// latest camera matrices, camera position, and lighting (Étape 4.3, Étape 12).
     ///
-    /// The directional light stays at the `FrameUniforms::default()` values (white, along +Z) — scene
-    /// lighting configuration is a later step; only the camera-driven fields are derived from `camera`.
-    /// Inputs: camera (the scene's active camera), aspect (viewport width / height).
-    fn write_frame_uniforms(&self, camera: &Camera, aspect: f32) {
+    /// The light array is packed via `Lights::into_frame_array` (directionals first, then point
+    /// lights). Inputs: camera (the scene's active camera), lights (the scene's global light list),
+    /// ambient (the scene's ambient hemisphere color, rgb), aspect (viewport width / height).
+    fn write_frame_uniforms(
+        &self,
+        camera: &Camera,
+        lights: &Lights,
+        ambient: [f32; 3],
+        aspect: f32,
+    ) {
+        let (light_array, num_directional, num_point) = lights.into_frame_array();
         let frame = FrameUniforms {
             view: camera.view_matrix(),
             proj: camera.projection_matrix(aspect),
             cam_pos: camera.position.extend(1.0),
-            light_dir: Vec4::new(0.0, 0.0, 1.0, 0.0),
-            light_color: Vec4::ONE,
+            ambient: Vec4::new(ambient[0], ambient[1], ambient[2], 1.0),
+            lights: light_array,
+            num_directional,
+            num_point,
+            _pad: [0, 0],
             options: [if self.unlit { 1 } else { 0 }, 0, 0, 0],
         };
         self.queue
@@ -268,7 +279,7 @@ impl Renderer {
     /// Before drawing, the shared frame uniform buffer is rewritten from `scene.camera()` so the GPU
     /// receives the active camera's view/projection matrices and position for this frame (Étape 4.3).
     pub fn render_scene(&self, view: &wgpu::TextureView, scene: &Scene, aspect: f32) {
-        self.write_frame_uniforms(scene.camera(), aspect);
+        self.write_frame_uniforms(scene.camera(), scene.lights(), scene.ambient(), aspect);
 
         let mut encoder = self
             .device

lib/src/resources/README.md

@@ -10,6 +10,8 @@ The `resources` module defines three immutable data types that flow through the
 | **mesh** | Mesh struct — persistent GPU geometry container with retained CPU `geometry: Arc<Geometry>` (Étape 8), vertex_buffer (wgpu::Buffer), optional index_buffer, and draw call counters. Created via Mesh::from_geometry() which derives Vertex arrays from the Geometry and uploads them to GPU buffers. |
 | **material** | Material struct — lightweight appearance descriptor pairing shader_id with a shared RenderPipeline Arc. Multiple Materials referencing the same shader_id point to the identical compiled GPU pipeline. Optionally holds a diffuse `Texture` (Étape 10) plus its texture bind group. |
 | **texture** | Texture struct *(Étape 10)* — GPU 2D image (device, view, sampler) in `Rgba8UnormSrgb`. Constructors: `from_rgba8` (raw bytes), `from_bytes` (encoded, via the `image` crate: png/jpeg/...), `from_file`, and `white_placeholder` (1x1 white used when no texture is attached). Sampler is linear-filtered with repeat addressing. |
+| **uniform** | `FrameUniforms` (per-frame uniforms: camera, ambient, global light list, options — 576 B, `Pod`) and `ObjectUniform` (per-entity model matrix — 64 B). Also `Light` (48 B) and `MAX_LIGHTS` (Phase 4.2, Étape 12). |
+| **lights** | `Lights` — the scene's CPU-side global light list (directional + point) and its `into_frame_array` packing (Phase 4.2, Étape 12). |
 
 ## Interaction with Other Modules
 

lib/src/resources/lights.rs

@@ -0,0 +1,132 @@
+//! # Lights Module — CPU-side Global Light List (Phase 4.2, Étape 12)
+//!
+//! Holds the scene's global light list — directional + point lights — in a CPU-side [`Lights`]
+//! group. The list is uploaded into the per-frame [`FrameUniforms`] uniform array each frame by
+//! `Renderer::write_frame_uniforms`. Lights are **global to the scene**: every entity is lit by
+//! the same list (per-material lights are out of scope, a later performance/feature step).
+//!
+//! ## Rangement (no type flag)
+//! Directional lights occupy indices `0..num_directional`; point lights occupy
+//! `num_directional..num_directional + num_point`. The index alone disambiguates the type in the
+//! fragment shader, so no type field is stored in [`Light`].
+//!
+//! ## Non-régression
+//! [`Lights::default()`] = one white directional light along +Z, which (combined with a white
+//! ambient) reproduces exactly the pre-multi-light rendering of `standard_shader.wgsl`.
+
+use crate::resources::uniform::{Light, MAX_LIGHTS};
+use glam::{Vec3, Vec4};
+
+/// The scene's global light list: directional lights (first) and point lights (after).
+/// Total capacity is bounded by `MAX_LIGHTS`; adding beyond it is rejected by the `Scene` API.
+#[derive(Clone, PartialEq)]
+pub struct Lights {
+    /// Directional lights (indices `0..len` in the frame array).
+    pub directional: Vec<Light>,
+    /// Point lights (indices `num_directional..` in the frame array).
+    pub point: Vec<Light>,
+}
+
+impl Lights {
+    /// Default = one white directional light along +Z (from surface toward light), no point lights.
+    /// This reproduces the historical single-light look when combined with a white ambient.
+    pub fn new() -> Self {
+        Self {
+            directional: vec![Light {
+                position_dir: Vec4::new(0.0, 0.0, 1.0, 0.0), // from surface toward light = +Z
+                color: Vec4::ONE,
+                radius: Vec4::ZERO,
+            }],
+            point: Vec::new(),
+        }
+    }
+
+    /// Total number of lights (directional + point).
+    pub fn len(&self) -> usize {
+        self.directional.len() + self.point.len()
+    }
+
+    /// `true` when there are no lights at all.
+    pub fn is_empty(&self) -> bool {
+        self.len() == 0
+    }
+
+    /// Packs the lights into the GPU frame array: directionals first (`0..num_directional`),
+    /// then point lights. The tail is zero-filled. Returns `(array, num_directional, num_point)`.
+    /// Caller must ensure `len() <= MAX_LIGHTS` (the `Scene` API validates capacity).
+    pub fn into_frame_array(&self) -> ([Light; MAX_LIGHTS], u32, u32) {
+        let empty = Light {
+            position_dir: Vec4::ZERO,
+            color: Vec4::ZERO,
+            radius: Vec4::ZERO,
+        };
+        let mut array = [empty; MAX_LIGHTS];
+        for (i, l) in self.directional.iter().enumerate() {
+            array[i] = *l;
+        }
+        let n_dir = self.directional.len();
+        for (i, l) in self.point.iter().enumerate() {
+            array[n_dir + i] = *l;
+        }
+        (array, n_dir as u32, self.point.len() as u32)
+    }
+}
+
+impl Default for Lights {
+    /// `Lights::new()` — one white directional light along +Z (non-regression default).
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+/// Builds a directional [`Light`] from a direction (from surface toward the light), a color and
+/// an intensity multiplier. Used by `Scene::add_directional_light`.
+pub fn directional_light(dir: Vec3, color: [f32; 3], intensity: f32) -> Light {
+    Light {
+        position_dir: dir.extend(0.0),
+        color: Vec4::new(color[0], color[1], color[2], intensity),
+        radius: Vec4::ZERO,
+    }
+}
+
+/// Builds a point [`Light`] from a world position, a color, an intensity multiplier and an
+/// attenuation radius (linear falloff to zero at the radius). Used by `Scene::add_point_light`.
+pub fn point_light(pos: Vec3, color: [f32; 3], intensity: f32, radius: f32) -> Light {
+    Light {
+        position_dir: pos.extend(0.0),
+        color: Vec4::new(color[0], color[1], color[2], intensity),
+        radius: Vec4::new(radius, 0.0, 0.0, 0.0),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn default_has_one_directional() {
+        let lights = Lights::new();
+        assert_eq!(lights.directional.len(), 1);
+        assert_eq!(lights.point.len(), 0);
+        assert_eq!(lights.len(), 1);
+    }
+
+    #[test]
+    fn into_frame_array_packs_directional_then_point() {
+        let mut lights = Lights::new(); // 1 directional
+        lights
+            .point
+            .push(point_light(Vec3::ONE, [1.0, 0.0, 0.0], 1.0, 2.0));
+        let (array, n_dir, n_point) = lights.into_frame_array();
+        assert_eq!(n_dir, 1);
+        assert_eq!(n_point, 1);
+        // Directional first, point after.
+        assert_eq!(array[0].color, Vec4::ONE);
+        assert_eq!(array[1].color, Vec4::new(1.0, 0.0, 0.0, 1.0));
+    }
+
+    #[test]
+    fn capacity_bounded_by_max_lights() {
+        assert!(MAX_LIGHTS >= 1);
+    }
+}

lib/src/resources/mod.rs

@@ -13,6 +13,7 @@
 //! - `material::new()` requests RenderPipelines from PipelineCache during scene initialization.
 
 pub mod camera;
+pub mod lights;
 pub mod material;
 pub mod mesh;
 pub mod texture;
@@ -21,10 +22,11 @@ pub mod vertex;
 
 // Re-exports
 pub use camera::Camera;
+pub use lights::Lights;
 pub use material::Material;
 pub use mesh::Mesh;
 pub use texture::{Texture, TextureError};
-pub use uniform::{FrameUniforms, ObjectUniform};
+pub use uniform::{FrameUniforms, Light, MAX_LIGHTS, ObjectUniform};
 pub use vertex::Vertex;
 
 // Convenience re-export of `math::Geometry` (Étape 8, D2) so examples can build meshes

lib/src/resources/uniform.rs

@@ -21,10 +21,32 @@ 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.
+/// Maximum number of lights stored in the per-frame uniform buffer.
+/// Bounded capacity: adding more than this returns `WsgError` (no dynamic UBO allocation).
+pub const MAX_LIGHTS: usize = 8;
+
+/// A single light, stored in the per-frame uniform array. One struct serves both types; the
+/// *position in the array* disambiguates: indices `0..num_directional` are directional
+/// (`position_dir.xyz` = direction **from the surface toward the light**), indices
+/// `num_directional..` are point (`position_dir.xyz` = world position). No type flag in the struct.
+///
+/// 3 × Vec4 = 48 bytes, 16-byte aligned (std140-compatible with the WGSL `struct Light`).
+#[repr(C)]
+#[derive(Clone, Copy, Pod, Zeroable, PartialEq)]
+pub struct Light {
+    /// xyz = direction from surface toward the light (directional) or world position (point); w = 0.
+    pub position_dir: Vec4,
+    /// rgb = color; a = intensity (multiplier).
+    pub color: Vec4,
+    /// x = attenuation radius (point lights); 0 for directional.
+    pub radius: Vec4,
+}
+
+/// Per-frame GPU uniforms : camera matrices + ambient + global light list + 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.
+/// 192 + 48·MAX_LIGHTS bytes (16-byte aligned) — `Pod` for direct `bytes_of` upload. The bind-group
+/// layout uses `min_binding_size: None`, so extending this struct is transparent (no relayout).
 #[repr(C)]
 #[derive(Clone, Copy, Pod, Zeroable)]
 pub struct FrameUniforms {
@@ -34,23 +56,38 @@ pub struct FrameUniforms {
     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.
+    /// Ambient hemisphere color (`.rgb` used). Offset 144.
+    pub ambient: Vec4,
+    /// Global light list: `0..num_directional` directional, then `num_point` point. Offset 160.
+    pub lights: [Light; MAX_LIGHTS],
+    /// Number of active directional lights (indices `0..num_directional`). Offset 160 + 48·MAX_LIGHTS.
+    pub num_directional: u32,
+    /// Number of active point lights (indices after the directionals).
+    pub num_point: u32,
+    /// Padding so `options` lands on a 16-byte boundary — matching the WGSL `vec4<u32>`
+    /// (alignment 16), which Rust's `repr(C)` would otherwise place at offset 552.
+    pub _pad: [u32; 2],
+    /// Options. `options[0]` = unlit flag (1 → flat color, no lighting).
     pub options: [u32; 4],
 }
 
 impl Default for FrameUniforms {
-    /// Sensible defaults : identity camera, white light along +Z, *lit* mode.
+    /// Sensible defaults : identity camera, white ambient, a single white directional light along
+    /// +Z (from surface toward light), *lit* mode — reproduces the pre-multi-light look exactly.
     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,
+            ambient: Vec4::ONE,
+            lights: [Light {
+                position_dir: Vec4::new(0.0, 0.0, 1.0, 0.0), // from surface toward light = +Z
+                color: Vec4::ONE,
+                radius: Vec4::ZERO,
+            }; MAX_LIGHTS],
+            num_directional: 1,
+            num_point: 0,
+            _pad: [0, 0],
             options: [0, 0, 0, 0],
         }
     }
@@ -75,18 +112,29 @@ mod tests {
     #[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);
+        // Header (view..ambient) = 160, lights = 48·MAX_LIGHTS, then counters(8) + pad(8) +
+        // options(16) = 32. Total = 160 + 48·MAX_LIGHTS + 32 = 576 bytes.
+        assert_eq!(size_of::<FrameUniforms>(), 160 + 48 * MAX_LIGHTS + 32);
         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!(offset_of!(FrameUniforms, ambient), 144);
+        assert_eq!(offset_of!(FrameUniforms, lights), 160);
+        assert_eq!(
+            offset_of!(FrameUniforms, num_directional),
+            160 + 48 * MAX_LIGHTS
+        );
+        assert_eq!(
+            offset_of!(FrameUniforms, options),
+            160 + 48 * MAX_LIGHTS + 16
+        );
+        // Default is lit mode (unlit flag cleared), one directional light, no point lights.
         assert_eq!(f.options[0], 0);
+        assert_eq!(f.num_directional, 1);
+        assert_eq!(f.num_point, 0);
     }
 
     #[test]

lib/src/scene/scene.rs

@@ -17,8 +17,9 @@
 
 use crate::math::{Geometry, Transform};
 use crate::pipeline::PipelineCache;
-use crate::resources::{Camera, Material, Mesh, Texture};
+use crate::resources::{Camera, Lights, Material, Mesh, Texture};
 use crate::scene::Entity;
+use glam::Vec3;
 use std::cell::RefCell;
 use std::collections::HashMap;
 use std::sync::Arc;
@@ -58,6 +59,11 @@ pub struct Scene {
     /// Lazily-built default `standard` material, cached so `default_material` costs O(1) after the
     /// first call. Interior-mutable so it can be filled from an immutable `&Scene` (used by the Renderer).
     default_material: RefCell<Option<Arc<Material>>>,
+    /// Global light list (directional + point), uploaded into the frame uniforms each frame
+    /// (Phase 4.2, Étape 12). Default = one white directional light along +Z (non-regression).
+    lights: Lights,
+    /// Ambient hemisphere color (rgb) used by the `standard` shader. Default = white.
+    ambient: [f32; 3],
 }
 
 impl Scene {
@@ -74,6 +80,8 @@ impl Scene {
             camera: Camera::default(),
             gpu: None,
             default_material: RefCell::new(None),
+            lights: Lights::new(),
+            ambient: [1.0, 1.0, 1.0],
         }
     }
 
@@ -248,6 +256,86 @@ impl Scene {
         &self.camera
     }
 
+    /// Adds a directional light (direction **from the surface toward the light**, color, intensity).
+    /// Lights are global to the scene and uploaded into the frame uniforms each frame (Phase 4.2,
+    /// Étape 12). Returns `Err` if the scene would exceed `MAX_LIGHTS` (capacity is bounded; no
+    /// dynamic UBO allocation). Inputs: dir (direction toward the light source), color (rgb),
+    /// intensity (multiplier).
+    pub fn add_directional_light(
+        &mut self,
+        dir: Vec3,
+        color: [f32; 3],
+        intensity: f32,
+    ) -> Result<(), String> {
+        if self.lights.len() >= crate::resources::MAX_LIGHTS {
+            return Err(format!(
+                "Cannot add another light: MAX_LIGHTS ({}) reached.",
+                crate::resources::MAX_LIGHTS
+            ));
+        }
+        self.lights
+            .directional
+            .push(crate::resources::lights::directional_light(
+                dir, color, intensity,
+            ));
+        Ok(())
+    }
+
+    /// Adds a point light (world position, color, intensity, attenuation radius).
+    /// Returns `Err` if the scene would exceed `MAX_LIGHTS`. Inputs: pos (world position of the
+    /// light), color (rgb), intensity (multiplier), radius (linear falloff to zero at this distance).
+    pub fn add_point_light(
+        &mut self,
+        pos: Vec3,
+        color: [f32; 3],
+        intensity: f32,
+        radius: f32,
+    ) -> Result<(), String> {
+        if self.lights.len() >= crate::resources::MAX_LIGHTS {
+            return Err(format!(
+                "Cannot add another light: MAX_LIGHTS ({}) reached.",
+                crate::resources::MAX_LIGHTS
+            ));
+        }
+        self.lights
+            .point
+            .push(crate::resources::lights::point_light(
+                pos, color, intensity, radius,
+            ));
+        Ok(())
+    }
+
+    /// Replaces the scene's global light list. The `Scene` keeps ownership; the list is uploaded
+    /// into the frame uniforms each frame. Used to reset or bulk-configure lighting.
+    pub fn set_lights(&mut self, lights: Lights) {
+        self.lights = lights;
+    }
+
+    /// Returns a reference to the scene's global light list (directional + point).
+    /// Read by `Renderer::render_scene` each frame to upload the light array.
+    pub fn lights(&self) -> &Lights {
+        &self.lights
+    }
+
+    /// Removes all lights (neither directional nor point). The fragment shader then contributes
+    /// only the ambient term. Useful for flat look without toggling `unlit`.
+    pub fn clear_lights(&mut self) {
+        self.lights = Lights {
+            directional: Vec::new(),
+            point: Vec::new(),
+        };
+    }
+
+    /// Sets the ambient hemisphere color (rgb). Default is white.
+    pub fn set_ambient(&mut self, color: [f32; 3]) {
+        self.ambient = color;
+    }
+
+    /// Returns the scene's ambient hemisphere color (rgb).
+    pub fn ambient(&self) -> [f32; 3] {
+        self.ambient
+    }
+
     /// Registers a Mesh in the scene under a unique identifier.
     /// Inputs: id (unique key), mesh (Arc-wrapped Mesh instance). Returns Ok(id) on success or Err(String) if already exists.
     /// Called during scene initialization when building the resource depot.

lib/src/shaders/README.md

@@ -14,7 +14,7 @@ unlit** de `standard` (décision actée dans le DRAFT : « 2D ⊂ 3D »).
 
 | File | Purpose |
 |------|---------|
-| **standard_shader.wgsl** | Standard (Phong) vertex/fragment shader — ambient + directional diffuse with an explicit unlit mode. Carries the full uniform contract (frame @group(0) + object @group(1)). |
+| **standard_shader.wgsl** | Standard (Phong) vertex/fragment shader — ambient + multi-light (directional + point) diffuse with an explicit unlit mode. Carries the full uniform contract (frame @group(0) + object @group(1) + texture @group(2)). |
 
 ## Shader Contract (standard_shader.wgsl)
 
@@ -34,14 +34,18 @@ par tout matériau (Étape 3 : un seul layout pour tous).
 
 | Group / Binding | Struct | Contenu |
 |-----------------|--------|---------|
-| `@group(0) @binding(0)` | `FrameUniforms` (192 B) | `view`, `proj`, `cam_pos`, `light_dir`, `light_color`, `options` (.x = unlit flag) |
+| `@group(0) @binding(0)` | `FrameUniforms` (576 B) | `view`, `proj`, `cam_pos`, `ambient`, `lights[8]`, `num_directional`, `num_point`, `options` (.x = unlit flag) |
 | `@group(1) @binding(0)` | `ObjectUniform` (64 B) | `model` (matrice modèle de l'entité) |
 
-`light_dir` pointe de la surface vers la lumière ; le fragment shader l'inverse pour le terme N·L.
+`FrameUniforms` porte une **liste de lumières globales** (Étape 12, Phase 4.2) : `lights[0..num_directional]`
+sont des lumières **directionnelles** (`position_dir.xyz` = direction de la surface vers la lumière), et
+`lights[num_directional..]` des lumières **ponctuelles** (`position_dir.xyz` = position monde, `radius.x` =
+rayon d'atténuation linéaire). L'index disambiguise le type — pas de drapeau. `ambient` est la couleur du
+terme ambiant hémisphérique.
 
 ### Mode unlit
 
-Un flag `options.x != 0` neutralise la directionnelle et renvoie la couleur du vertex telle quelle
+Un flag `options.x != 0` neutralise **toutes les lumières** et renvoie la couleur du vertex telle quelle
 (couleur plate). Côté API, `Renderer::set_unlit(true)` (ou `app.renderer_mut().set_unlit(true)`)
 positionne ce flag dans les frame uniforms. Ainsi le rendu 2D plat est un **cas particulier** de la 3D
 éclairée.

lib/src/shaders/standard_shader.wgsl

@@ -8,24 +8,27 @@
 //!
 //! ## Uniform Contract
 //! Three bind groups, shared by every material (one single pipeline layout — voir Étape 3) :
-//! - `@group(0) @binding(0)` : `FrameUniforms` (per-frame, camera + lights)   [192 bytes]
+//! - `@group(0) @binding(0)` : `FrameUniforms` (per-frame, camera + lights)   [192 + 48·MAX_LIGHTS bytes]
 //! - `@group(1) @binding(0)` : `ObjectUniform` (per-entity model matrix)      [64 bytes]
 //! - `@group(2) @binding(0)` : `texture_sampler` (sampler) — diffuse        (Étape 10)
 //! - `@group(2) @binding(1)` : `diffuse_texture` (texture_2d<f32>)          (Étape 10)
 //!
-//! `FrameUniforms` layout (std140 — each element 16-byte aligned, no padding) :
-//! | Offset | Field        | Type      | Meaning                           |
-//! |--------|--------------|-----------|-----------------------------------|
-//! | 0      | view         | mat4x4<f32> | Camera view matrix                |
-//! | 64     | proj         | mat4x4<f32> | Camera projection matrix          |
-//! | 128    | cam_pos      | vec4<f32>  | Camera world position (.xyz)      |
-//! | 144    | light_dir    | vec4<f32>  | Light direction (see below)       |
-//! | 160    | light_color  | vec4<f32>  | Light color (.rgb)                |
-//! | 176    | options      | vec4<u32>  | x = unlit flag (1 => flat color)  |
-//! | 192    | total        |            |                                   |
+//! `FrameUniforms` layout (std140 — each element 16-byte aligned) :
+//! | Offset                | Field          | Type          | Meaning                          |
+//! |-----------------------|----------------|---------------|----------------------------------|
+//! | 0                     | view           | mat4x4<f32>   | Camera view matrix               |
+//! | 64                    | proj           | mat4x4<f32>   | Camera projection matrix         |
+//! | 128                   | cam_pos        | vec4<f32>     | Camera world position (.xyz)     |
+//! | 144                   | ambient        | vec4<f32>     | Ambient hemisphere color (.rgb)  |
+//! | 160                   | lights[0..MAX] | array<Light>  | Global light list                |
+//! | 160 + 48·MAX_LIGHTS   | num_directional| u32           | # directional (indices 0..n)     |
+//! |                       | num_point      | u32           | # point (indices n..)            |
+//! |                       | options        | vec4<u32>     | x = unlit flag (1 => flat color) |
 //!
-//! `light_dir` convention : vector pointing **from the surface toward the light**.
-//! The fragment shader negates it to obtain the light direction for the N·L term.
+//! `MAX_LIGHTS = 8`. `struct Light` is 48 bytes (3 × vec4). Directional lights occupy
+//! `lights[0..num_directional]` (`position_dir.xyz` = direction **from the surface toward the
+//! light**); point lights occupy `lights[num_directional..]` (`position_dir.xyz` = world position,
+//! `radius.x` = linear attenuation radius). No type flag — the index disambiguates (Étape 12).
 //!
 //! ## Texturing (Étape 10, D2)
 //! The fragment samples `diffuse_texture` **unconditionally**. A texture-less `Material` binds the
@@ -52,13 +55,28 @@ struct VertexInput {
     @location(3) color: vec4<f32>,
 };
 
+// Étape 12 (Phase 4.2) : maximum number of lights in the per-frame array. Must match
+// `wsg_lib::resources::MAX_LIGHTS`.
+const MAX_LIGHTS: u32 = 8u;
+
+// A single light (48 bytes = 3 × vec4). Directional: `position_dir.xyz` = direction from the
+// surface toward the light. Point: `position_dir.xyz` = world position, `radius.x` = linear
+// attenuation radius. The array index disambiguates the type (no flag stored).
+struct Light {
+    position_dir: vec4<f32>,
+    color: vec4<f32>,   // rgb = color; a = intensity
+    radius: vec4<f32>,  // x = point-light attenuation radius
+};
+
 struct FrameUniforms {
     view: mat4x4<f32>,
     proj: mat4x4<f32>,
     cam_pos: vec4<f32>,
-    light_dir: vec4<f32>,
-    light_color: vec4<f32>,
-    options: vec4<u32>, // .x : unlit flag (1 = flat color, no directional lighting)
+    ambient: vec4<f32>,                    // .rgb = ambient hemisphere color
+    lights: array<Light, MAX_LIGHTS>,     // [0..num_directional] directional, then point
+    num_directional: u32,
+    num_point: u32,
+    options: vec4<u32>, // .x : unlit flag (1 = flat color, no lighting)
 };
 
 struct ObjectUniform {
@@ -115,16 +133,32 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
     }
 
     let n = normalize(in.normal);
-    // light_dir pointe de la surface vers la lumière ; on inverse pour le terme N·L.
-    let l = normalize(-frame.light_dir.xyz);
-    let ndotl = max(dot(n, l), 0.0);
 
-    // Ambient hémisphérique : dépend de la composante verticale de la normale.
+    // Ambient hémisphérique : dépend de la composante verticale de la normale (couleur venue
+    // de frame.ambient, Étape 12 — était codée en dur via la couleur de la lumière avant).
     let sky = max(n.y, 0.0);
-    let ambient = frame.light_color.rgb * (0.3 + 0.4 * sky);
+    let ambient = frame.ambient.rgb * (0.3 + 0.4 * sky);
 
-    // Diffuse directionnel classique.
-    let diffuse = frame.light_color.rgb * ndotl;
+    var diffuse = vec3<f32>(0.0);
+
+    // Lumières directionnelles (indices 0..num_directional). `position_dir` pointe de la surface
+    // vers la lumière ; on l'inverse pour le terme N·L.
+    for (var i = 0u; i < frame.num_directional; i++) {
+        let l = normalize(-frame.lights[i].position_dir.xyz);
+        let ndotl = max(dot(n, l), 0.0);
+        diffuse += frame.lights[i].color.rgb * frame.lights[i].color.a * ndotl;
+    }
+
+    // Lumières ponctuelles (indices num_directional..num_directional + num_point). Atténuation
+    // linéaire dans le rayon (zéro au-delà).
+    for (var i = frame.num_directional; i < frame.num_directional + frame.num_point; i++) {
+        let to_light = frame.lights[i].position_dir.xyz - in.world_pos;
+        let dist = length(to_light);
+        let l = to_light / max(dist, 1e-4);
+        let ndotl = max(dot(n, l), 0.0);
+        let falloff = clamp(1.0 - dist / max(frame.lights[i].radius.x, 1e-4), 0.0, 1.0);
+        diffuse += frame.lights[i].color.rgb * frame.lights[i].color.a * ndotl * falloff;
+    }
 
     let lit = base * (ambient + diffuse);
     return vec4<f32>(lit, in.color.a);