10、将osg的Geometry转换为虚幻引擎的UStaticMesh-Toy模板网

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将osg::Geometry转换为FMeshDescription，通过FMeshDescription即可构建UStaticMesh，下面这段代码主要是为了转换倾斜摄影的osgb数据，但是倾斜摄影数据中本身不携带法线数据，也不需要计算法线，因此如果要转换其他携带或需要计算法线的osg::Geometry的数据，请另行将法线信息补充到FMeshDescription中文章来源地址https://www.toymoban.com/news/detail-859001.html

FMeshDescription ConvertOsgGeometryToMeshDescription(osg::ref_ptr<osg::Geometry> InGeometry)
{
	FMeshDescription result;
	//顶点
	osg::MixinVector<osg::Vec3f>* vertices = dynamic_cast<osg::MixinVector<osg::Vec3f>*>(InGeometry->getVertexArray());
	if (!vertices)
		return result;
	//纹理坐标
	osg::MixinVector<osg::Vec2f>* texCoords = dynamic_cast<osg::MixinVector<osg::Vec2f>*>(InGeometry->getTexCoordArray(0));
	assert(vertices->size() == texCoords->size());

	//法线，倾斜摄影数据没有法线，其实不需要
	osg::MixinVector<osg::Vec3f>* normals = dynamic_cast<osg::MixinVector<osg::Vec3f>*>(InGeometry->getNormalArray());
	//索引
	osg::MixinVector<unsigned int>* indices = dynamic_cast<osg::MixinVector<unsigned int>*>(InGeometry->getPrimitiveSet(0));
	if (!indices)
		return result;
	assert(indices->size() / 3 == 0);

	FStaticMeshAttributes attributes(result);
	//注册默认的静态模型属性
	attributes.Register();

	//FMeshDescriptionBuilder用于设置顶点、法线、UV坐标等信息
	FMeshDescriptionBuilder meshDescBuilder;
	meshDescBuilder.SetMeshDescription(&result);
	//允许使用多边形组
	meshDescBuilder.EnablePolyGroups();
	//设置UV坐标的级数为1
	meshDescBuilder.SetNumUVLayers(1);
	FPolygonGroupID GroupId = meshDescBuilder.AppendPolygonGroup();

	const uint32 vertexCount = vertices->size();
	TArray<FVertexID> vertexIDs;
	vertexIDs.SetNum(vertices->size());
	const float unit = 100.0;
	// 定义一个Lambda表达式，用于将OSG坐标转换为UE坐标
	auto ConvertOSGToUE = [&unit](const osg::Vec3f& OSGCoordinate) -> FVector
		{
			float X = OSGCoordinate.x() * unit;
			float Y = -OSGCoordinate.y() * unit; 
			float Z = OSGCoordinate.z() * unit; 

			return FVector(X, Y, Z);
		};
	for (uint32 i = 0; i < vertexCount; ++i) {
		const osg::Vec3f vertex = vertices->at(i);
		vertexIDs[i] = meshDescBuilder.AppendVertex(ConvertOSGToUE(vertex));
	}

	const uint32 indiceCount = indices->size();
	assert(indiceCount / 3 == 0);
	const uint32 triangleCount = indiceCount / 3;
	for (uint32 i = 0; i < triangleCount; ++i) {
		const uint32 indice1 = indices->at(i * 3);
		const FVertexInstanceID vertexInstanceId1 = meshDescBuilder.AppendInstance(vertexIDs[indice1]);
		const osg::Vec2f texCoord1 = texCoords->at(indice1);
		meshDescBuilder.SetInstanceUV(vertexInstanceId1, FVector2D(texCoord1.x(), 1 - texCoord1.y()), 0);

		const uint32 indice2 = indices->at(i * 3 + 1);
		const FVertexInstanceID vertexInstanceId2 = meshDescBuilder.AppendInstance(vertexIDs[indice2]);
		const osg::Vec2f texCoord2 = texCoords->at(indice2);
		meshDescBuilder.SetInstanceUV(vertexInstanceId2, FVector2D(texCoord2.x(), 1 - texCoord2.y()), 0);

		const uint32 indice3 = indices->at(i * 3 + 2);
		const FVertexInstanceID vertexInstanceId3 = meshDescBuilder.AppendInstance(vertexIDs[indice3]);
		const osg::Vec2f texCoord3 = texCoords->at(indice3);
		meshDescBuilder.SetInstanceUV(vertexInstanceId3, FVector2D(texCoord3.x(), 1 - texCoord3.y()), 0);

		meshDescBuilder.AppendTriangle(vertexInstanceId1, vertexInstanceId2, vertexInstanceId3, GroupId);

	}

	//FStaticMeshOperations::ComputeTriangleTangentsAndNormals(result);//倾斜摄影数据没有法线，不必计算
	return result;
}