The shadow pass was correct but the demo light was much too steep (52°
elevation), so the blocker's shadow fell in a ~0.5-unit sliver tight against
the cube's base and was invisible against the bright ground (offscreen pixel
probe found a single dark pixel). Verified with an offscreen probe using the
real Renderer::render_scene + shadow path:
- steep front light (0.6,1.1,0.6) -> 1 dark pixel (no visible shadow)
- shallow side light (1.0,0.3,0.0) -> 17 107 pixels (shadow pipeline OK)
- tuned front-right (1.0,0.5,0.0) -> 16 979 pixels (clear visible shadow)
The azimuth matters most: from the elevated front-right camera, a shadow cast
toward -z falls behind the cube and is occluded; one cast toward -x runs across
the ground to the left of the cube and reads clearly. Tuned light therefore sits
front-right and low (toward_light (1.0,0.5,0.0)), keeping the front faces lit
while casting a clearly visible PCF-softened shadow.
Also reapply the LessEqual comparison sampler fix (commit 39167ee had set it,
but was later reverted to GreaterEqual by 9a51ff7 while debugging; the probe
confirms LessEqual is the correct, non-inverted test). Correct 'rotating cube'
to 'cube' in README/ROADMAP (shadow_test scene is static).
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.
Jérôme Bousquié