# Shadow Rendering Analysis

## Issue
In `test_mesh` (and the engine generally), shadows cast by `ObjectType::MESH` objects onto the floor (or other objects) appear as simple bounding boxes, not matching the mesh geometry.

## Root Cause
The engine uses **Hybrid Rendering**:
1.  **Visibility**: Meshes are rasterized using the GPU graphics pipeline (`mesh_render.wgsl`).
2.  **Shadows**: Shadows are calculated using **SDF Raymarching** in the fragment shader (`calc_shadow` in `shadows.wgsl`).

To calculate shadows, the shader needs to query the distance to every object in the scene (`map_scene`).
For SDF primitives (Sphere, Box, Torus), we have exact mathematical distance functions.
For arbitrary Meshes, calculating the exact Signed Distance Field (SDF) in the shader is computationally expensive and complex (requires BVH in shader or 3D texture).

Current implementation in `assets/final/shaders/render/scene_query.wgsl`:
```wgsl
fn get_dist(p: vec3<f32>, obj_params: vec4<f32>) -> f32 {
    // ...
    if (obj_type == 5.0) { return sdBox(p, obj_params.yzw); } // MESH AABB
    return 100.0;
}
```
`obj_params.yzw` contains the local extents (half-size) of the mesh's AABB.
Thus, **all meshes are approximated as Boxes in the shadow/SDF pass.**

## Implications
- **Shadow Casting**: Meshes cast box-shaped shadows.
- **Shadow Receiving**: Meshes receive shadows correctly (from other objects' SDFs).
- **Self-Shadowing**: Disabled via `skip_idx` to prevent the mesh from being shadowed by its own proxy box.

## Potential Solutions

### 1. Shadow Mapping (Recommended for future)
Render the scene depth from the light's perspective into a texture.
- **Pros**: Exact shadows for rasterized geometry; handles self-shadowing naturally.
- **Cons**: Requires additional render pass, potential bias artifacts, doesn't integrate perfectly with soft SDF shadows (though can be combined).
- **Status**: Tracked as **Task #40**.

### 2. Mesh SDF Baking
Pre-calculate a 3D texture containing the SDF of the mesh and sample it in the shader.
- **Pros**: Accurate soft shadows, integrates with existing SDF system.
- **Cons**: High memory usage (3D textures), requires tooling to bake SDFs (e.g. `mesh_to_sdf` tool).

### 3. Analytic Proxies
Manually assign a better proxy shape (e.g. combination of spheres/boxes) for specific meshes.
- **Pros**: Cheap, better than box.
- **Cons**: Manual labor, limited fidelity.

## Conclusion
The current "bounding box shadow" behavior is a known limitation of using an AABB as the SDF proxy for meshes. It is not a bug in the code, but a simplified implementation choice for the 64k intro constraints. Accurate shadows require implementing Shadow Mapping (Task #40).