// Mesh shader — renders triangle meshes (truck Shell/Solid tessellation).
//
// Vertex layout: position [f32;3], normal [f32;3], color [f32;4]  (40 bytes)
//
// Lighting: simple half-Lambert with a fixed directional light so solids look
// solid regardless of camera angle.  Selection highlight overrides color.

struct Uniforms {
    view_proj:   mat4x4<f32>,
    viewport:    vec2<f32>,
    _pad:        vec2<f32>,
};

@group(0) @binding(0)
var<uniform> u: Uniforms;

struct VertexIn {
    @location(0) position: vec3<f32>,
    @location(1) normal:   vec3<f32>,
    @location(2) color:    vec4<f32>,
};

struct VertexOut {
    @builtin(position) clip_pos: vec4<f32>,
    @location(0)       color:    vec4<f32>,
    @location(1)       normal:   vec3<f32>,
};

@vertex
fn vs_main(v: VertexIn) -> VertexOut {
    var out: VertexOut;
    out.clip_pos = u.view_proj * vec4<f32>(v.position, 1.0);
    out.color    = v.color;
    out.normal   = v.normal;
    return out;
}

@fragment
fn fs_main(in: VertexOut) -> @location(0) vec4<f32> {
    // Fixed directional light (world space, tilted toward the viewer).
    let light_dir = normalize(vec3<f32>(0.4, 0.8, 0.6));
    let n = normalize(in.normal);
    // Half-Lambert: [0.5, 1.0] so the dark side isn't fully black.
    let diff = clamp(dot(n, light_dir), 0.0, 1.0) * 0.5 + 0.5;
    let rgb  = in.color.rgb * diff;
    return vec4<f32>(rgb, in.color.a);
}