gltf: Vertex attribute は UnsignedInt に対応していないので修正 (#351)

- 以下に従い、UnsignedIntをFloatに変更
-
https://github.com/CesiumGS/glTF/blob/proposal-EXT_mesh_features/extensions/2.0/Vendor/EXT_mesh_features/README.md#feature-id-by-vertex

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **機能変更**
-
メッシュプリミティブが`UnsignedInt`をサポートしていないため、`feature_id`を`u32`から`f32`へ変換しました。これにより、バイナリコンテンツの書き込みとアクセサコンポーネントのタイプが影響を受けます。

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

demo/cesium/examples/ext_structural_metadata/tileset.json

@@ -1,23 +1,27 @@
 {
-	"asset": {
-		"version": "1.1"
-	},
-	"geometricError": 1e100,
-	"root": {
-		"boundingVolume": {
-			"region": [
-				2.423545352784276, 0.6126113632476141, 2.423568686412357,
-				0.6126530152363875, 48.27812072424482, 61.914851977799785
-			]
-		},
-		"geometricError": 0.0,
-		"contents": [
-			{
-				"uri": "PlantCover.glb"
-			},
-			{
-				"uri": "SolitaryVegetationObject.glb"
-			}
-		]
-	}
-}
+  "asset": {
+    "version": "1.1"
+  },
+  "geometricError": 1e100,
+  "root": {
+    "boundingVolume": {
+      "region": [
+        2.423545352784276,
+        0.6126113632476141,
+        2.423568686412357,
+        0.6126530152363875,
+        48.27812072424482,
+        61.914851977799785
+      ]
+    },
+    "geometricError": 0.0,
+    "contents": [
+      {
+        "uri": "PlantCover.glb"
+      },
+      {
+        "uri": "SolitaryVegetationObject.glb"
+      }
+    ]
+  }
+}

nusamai/src/sink/gltf/gltf_writer.rs

@@ -134,9 +134,10 @@ pub fn build_base_gltf(class_name: &str, buffer: &Buffers, translation: [f64; 3]
     let feature_ids_offset = bin_content.len();
     let mut feature_ids_count = 0;
     for vertex in buffer.vertices.clone() {
-        bin_content
-            .write_all(&vertex.feature_id.to_le_bytes())
-            .unwrap();
+        // UnsignedInt cannot be used as vertix attributes in MeshPrimitive
+        // https://github.com/CesiumGS/glTF/blob/proposal-EXT_mesh_features/extensions/2.0/Vendor/EXT_mesh_features/README.md#feature-id-by-vertex
+        let vertex = vertex.feature_id as f32;
+        bin_content.write_all(&vertex.to_le_bytes()).unwrap();
         feature_ids_count += 1;
     }
     let feature_ids_len = bin_content.len() - feature_ids_offset;
@@ -154,7 +155,7 @@ pub fn build_base_gltf(class_name: &str, buffer: &Buffers, translation: [f64; 3]
     let feature_id_max = buffer.vertices.iter().map(|v| v.feature_id).max().unwrap();
     let accessor = Accessor {
         buffer_view: Some(buffer_view_length),
-        component_type: ComponentType::UnsignedInt,
+        component_type: ComponentType::Float,
         count: feature_ids_count,
         type_: AccessorType::Scalar,
         min: Some(vec![feature_id_min as f64]),