Implement shadow mapping for directional lights:
- Scene::set_shadow_caster(Option<usize>) selects the shadow-casting light
by packed frame-array index (None disables; point lights rejected at render).
- Lights::get(index) resolves a packed index across the directional/point/spot lists.
- Renderer allocates a shadow depth map, comparison sampler, group-3 bind groups,
shadow uniform buffer and shadow pipeline; render_scene does a depth-only
shadow pass before the main pass; compute_shadow_light_view_proj builds an
orthographic light-space frustum from the scene radius.
- standard_shader: shadow_light_index/light_view_proj/shadow_params uniforms,
@group(3) depth map + comparison sampler, 3x3 PCF compute_shadow().
- shadow_shader: path/vertex shader with attribute layout matching the shared
vertex buffer (only position consumed).
- shadow_test example: directional shadow caster casts a PCF-softened shadow
onto a ground slab; documented in examples README.
Étape 2 du plan 3D+Phong : nouveau shader unifié, non encore branché à un
pipeline (Étape 3 : infra uniforms).
- shaders/standard_shader.wgsl : contrat vertex complet (position/normal/uv/color,
56 octets, corrige la défaut latente du basic) ; 2 bind groups formative frame
(view/proj/cam_pos/light_dir/light_color/options) + object (model) ; éclairage
hemisphérique ambient + diffuse directionnel; mode unlit (options.x) pour que la
2D plate soit un cas partticulier de la 3D.
- utils/conf.rs : constantes STANDARD_SHADER_PATH + STANDARD_SHADER (include_str!).
- tests/wgsl_validate.rs : validation hors-ligne naga (via wgpu::naga, aucune
nouvelle dépendance) tant que le shader n'est pas compilé par un pipeline.
- shaders/README.md : documente le contrat standard et le statut du basic.
- Erreur WGSL corrigée en validation: cast mat4x4->mat3x3 non supporte, remplacé
par construction explicite de la sous-matrice 3x3.
- Validation: cargo test (naga OK), check workspace+examples 0 warning, doc OK, fmt OK.
Jérôme Bousquié