Merge pull request #94682 from zeux/lod-uv-mirror

Fix LOD generation for meshes with tangents & mirrored UVs

scene/resources/3d/importer_mesh.cpp

@@ -295,6 +295,7 @@ void ImporterMesh::generate_lods(float p_normal_merge_angle, float p_normal_spli
 		Vector<Vector3> vertices = surfaces[i].arrays[RS::ARRAY_VERTEX];
 		PackedInt32Array indices = surfaces[i].arrays[RS::ARRAY_INDEX];
 		Vector<Vector3> normals = surfaces[i].arrays[RS::ARRAY_NORMAL];
+		Vector<float> tangents = surfaces[i].arrays[RS::ARRAY_TANGENT];
 		Vector<Vector2> uvs = surfaces[i].arrays[RS::ARRAY_TEX_UV];
 		Vector<Vector2> uv2s = surfaces[i].arrays[RS::ARRAY_TEX_UV2];
 		Vector<int> bones = surfaces[i].arrays[RS::ARRAY_BONES];
@@ -354,6 +355,7 @@ void ImporterMesh::generate_lods(float p_normal_merge_angle, float p_normal_spli
 		LocalVector<int> merged_normals_counts;
 		const Vector2 *uvs_ptr = uvs.ptr();
 		const Vector2 *uv2s_ptr = uv2s.ptr();
+		const float *tangents_ptr = tangents.ptr();
 
 		for (unsigned int j = 0; j < vertex_count; j++) {
 			const Vector3 &v = vertices_ptr[j];
@@ -368,9 +370,10 @@ void ImporterMesh::generate_lods(float p_normal_merge_angle, float p_normal_spli
 				for (const Pair<int, int> &idx : close_verts) {
 					bool is_uvs_close = (!uvs_ptr || uvs_ptr[j].distance_squared_to(uvs_ptr[idx.second]) < CMP_EPSILON2);
 					bool is_uv2s_close = (!uv2s_ptr || uv2s_ptr[j].distance_squared_to(uv2s_ptr[idx.second]) < CMP_EPSILON2);
+					bool is_tang_aligned = !tangents_ptr || (tangents_ptr[j * 4 + 3] < 0) == (tangents_ptr[idx.second * 4 + 3] < 0);
 					ERR_FAIL_INDEX(idx.second, normals.size());
 					bool is_normals_close = normals[idx.second].dot(n) > normal_merge_threshold;
-					if (is_uvs_close && is_uv2s_close && is_normals_close) {
+					if (is_uvs_close && is_uv2s_close && is_normals_close && is_tang_aligned) {
 						vertex_remap.push_back(idx.first);
 						merged_normals[idx.first] += normals[idx.second];
 						merged_normals_counts[idx.first]++;