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src/shaders/mesh.wgsl

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+// 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);
+}