IFC提取转换成GLTF的逻辑在Builder类中，
Builder.BuildInstancedScene():该函数包含主要的转换逻辑，对应于我们在第二章中最后提出的转换算法流程，但是此处源代码并没有按照原本IFC中对象的组织形式将构件导出，而是按照扁平化的方式，将所有的构件一起导出，所以导出的GLTF中没有保留原来对象的空间组织关系。在此先分析源代码，然后我将给大家展示我修改后的代码。
//model：已打开的IFC实例，exclude：不导出的类型，EntityLabels：导出的构件ID
public gltf.Gltf BuildInstancedScene(IModel model, List<Type> exclude = null, HashSet<int> EntityLebels = null) { Init(); Dictionary<int, ShapeComponentIds> geometries = new Dictionary<int, ShapeComponentIds>(); // this needs a previously meshed xbim file. //设置定时器 var s = new Stopwatch(); s.Start(); int iCnt = 0; Random r = new Random();
//获取不导出的类型 var excludedTypes = DefaultExclusions(model, exclude);
//geomstore保存了该模型的几何信息，通过BeginRead()函数返回的Reader访问 using (var geomStore = model.GeometryStore) using (var geomReader = geomStore.BeginRead()) { // process the materials and styles var sstyleIds = geomReader.StyleIds; foreach (var styleId in sstyleIds) { PrepareStyleMaterial(model, styleId); }
// TODO: 无效代码 int productLabel = 0;
//获取需要渲染的Shape，shape是真正的几何图元信息 var shapeInstances = GetShapeInstancesToRender(geomReader, excludedTypes, EntityLebels); // foreach (var shapeInstance in shapeInstances.OrderBy(x=>x.IfcProductLabel)) gltf.Mesh targetMesh = null;
//遍历每一个shape，IFC中的一个shape对应于gltf的一个mesh foreach (var shapeInstance in shapeInstances.OrderBy(x => x.IfcProductLabel)) { if (CustomFilter != null) { var skip = CustomFilter(shapeInstance.IfcProductLabel, model); if (skip) continue; } // we start with a shape instance and then load its geometry. // a product (e.g. wall or window) in the scene returns: // - a node // - pointing to a mesh, with a transform // - 1 mesh // - with as many mesh primitives as needed to render the different parts // - pointers to the a material and accessors as needed // - 3 accessors per primitive // - vertices, normals, indices // - bufferviews can be reused by different accessors // - data in the buffer, of course if (productLabel != shapeInstance.IfcProductLabel) { // need new product // create node
//_nodes数组保存着已经创建的node，所以新node的索引为数组的大小 var nodeIndex = _nodes.Count; var entity = model.Instances[shapeInstance.IfcProductLabel] as IIfcProduct; if (entity == null) { // fire error here. } var tnode = new gltf.Node(); tnode.Name = entity.Name + $" #{entity.EntityLabel}";
//获取node的转换矩阵 tnode.Matrix = GetTransformInMeters(model, shapeInstance); // create mesh var meshIndex = _meshes.Count; targetMesh = new gltf.Mesh { Name = $"Instance {productLabel}" }; // link node to mesh
//使node指向mesh tnode.Mesh = meshIndex; // add all to lists _nodes.Add(tnode); _meshes.Add(targetMesh);
//此时mesh还未包含具体的图元信息，在此之前只做了node和mesh的关联 } // now the geometry //填充mesh IXbimShapeGeometryData shapeGeom = geomReader.ShapeGeometry(shapeInstance.ShapeGeometryLabel); if (shapeGeom.Format != (byte)XbimGeometryType.PolyhedronBinary) continue;
//处理style // work out colour id; // the colour is associated with the instance, not the geometry. // positives are styles, negatives are types var colId = shapeInstance.StyleLabel > 0 ? shapeInstance.StyleLabel : shapeInstance.IfcTypeId * -1; //处理material int materialIndex; if (!styleDic.TryGetValue(colId, out materialIndex)) { // if the style is not available we build one by ExpressType materialIndex = PrepareTypeMaterial(model, shapeInstance.IfcTypeId); styleDic.Add(colId, materialIndex); } // note: at a first investigation it looks like the shapeInstance.Transformation is the same for all shapes of the same product //一个shape（mesh）可以被多个构件（node）所引用
//TODO: 经测试，以下的代码存在BUG if (shapeGeom.ReferenceCount > 1) { // retain the information to reuse the map multiple times // // if g is not found in the dictionary then build it and add it ShapeComponentIds components; if (!geometries.TryGetValue(shapeGeom.ShapeLabel, out components)) { // mesh
//XbimMesher类可以理解为geometry的容器，它保存几何图元的顶点，法向量和索引等信息 var xbimMesher = new XbimMesher(); xbimMesher.AddMesh(shapeGeom.ShapeData); components = AddGeom( xbimMesher.PositionsAsSingleList(model.ModelFactors.OneMeter), xbimMesher.Indices, xbimMesher.NormalsAsSingleList() ); geometries.Add(shapeGeom.ShapeLabel, components); } if (components != null) { var arr = GetTransformInMeters(model, shapeInstance); AddComponentsToMesh(targetMesh, components, materialIndex); } } else { // repeat the geometry only once // var xbimMesher = new XbimMesher(); xbimMesher.AddMesh(shapeGeom.ShapeData); var trsf = GetTransformInMeters(model, shapeInstance); var components = AddGeom( xbimMesher.PositionsAsSingleList(model.ModelFactors.OneMeter), xbimMesher.Indices, xbimMesher.NormalsAsSingleList() ); AddComponentsToMesh(targetMesh, components, materialIndex); } iCnt++; if (iCnt % 100 == 0) Debug.WriteLine($"added {iCnt} elements in {s.ElapsedMilliseconds}ms."); } } Debug.WriteLine($"added {iCnt} elements in {s.ElapsedMilliseconds}ms.");
//构造GLTF，并返回 return Build(); }
修改后的Builder.BuildInstancedScene()，按照原本IFC中对象树的组织方式，访问IFC对象，同时导出GLTF对象，因此导出的GLTF是树状组织结构。
/// <param name="model">The model needs to have the geometry meshes already cached</param> /// <param name="exclude">The types of elements that are going to be omitted (e.g. ifcSpaces).</param> /// <param name="EntityLebels">Only entities in the collection are exported; if null exports the whole model</param> /// <returns>GLTF, containing all message about the model</returns> public gltf.Gltf BuildInstancedScene(IModel model, List<Type> exclude = null, HashSet<int> EntityLabels = null) { //TODO: 需要确保context已经建立？ using (var geomStore = model.GeometryStore) using (var geomReader = geomStore.BeginRead()) { // process the materials and styles //保存material和style到builder类成员（内存中） var sstyleIds = geomReader.StyleIds; foreach (var styleId in sstyleIds) { PrepareStyleMaterial(model, styleId); } Dictionary<int, ShapeComponentIds> geometries = new Dictionary<int, ShapeComponentIds>(); Dictionary<int, int> shapes = new Dictionary<int, int>(); HashSet<int> visitedLabels = new HashSet<int>(); // this needs a previously meshed xbim file. var excludedTypes = DefaultExclusions(model, exclude); //获取根节点 var projects = model.Instances.OfType<IIfcProject>(); if (projects.Count() != 1) { Debug.WriteLine("Projects more than one."); } var project = projects.First(); var projectRelations = project.IsDecomposedBy; Queue<IIfcObjectDefinition> objectQueue = new Queue<IIfcObjectDefinition>(); Queue<int> nodeIndexQueue = new Queue<int>(); //添加根节点 var rootNode = new gltf.Node(); rootNode.Name = project.Name + $"#{project.EntityLabel}"; rootNode.Matrix = new[] { 1.0f, 0.0f, 0.0f, 0.0f, //右手坐标系下相对坐标原点绕X轴旋转90度(pi/4) 0.0f, 0.0f, -1.0f, 0.0f, 0.0f, 1.0f, 0.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f }; _nodes.Add(rootNode); List<int> rootSon = new List<int>(); foreach (var rel in projectRelations) { foreach (var relatedObject in rel.RelatedObjects) { var tnode = new gltf.Node(); var tnodeIndex = _nodes.Count; _nodes.Add(tnode); rootSon.Add(tnodeIndex); nodeIndexQueue.Enqueue(tnodeIndex); objectQueue.Enqueue(relatedObject); } } rootNode.Children = rootSon.ToArray(); //遍历IFC节点树，用参数队列和节点队列模拟递归顺序访问节点树 while (objectQueue.Count > 0) { //当前待处理的节点 var obj = objectQueue.Dequeue(); var nodeIndex = nodeIndexQueue.Dequeue(); if (visitedLabels.Contains(obj.EntityLabel)) continue; visitedLabels.Add(obj.EntityLabel); List<int> sonNodes = new List<int>(); //处理当前节点包含的子节点，只有为IfcSpatialElement时才有relContained关系 var spatialElement = obj as IIfcSpatialElement; if (spatialElement != null) { var containRelations = spatialElement.ContainsElements; foreach (var containRelation in containRelations) { var containObjects = containRelation.RelatedElements; foreach (var containObject in containObjects) { var tnode = new gltf.Node(); var tnodeIndex = _nodes.Count; _nodes.Add(tnode); sonNodes.Add(tnodeIndex); nodeIndexQueue.Enqueue(tnodeIndex); objectQueue.Enqueue(containObject); } } } //处理当前节点聚合的子节点 var aggregateRelations = obj.IsDecomposedBy; foreach (var aggregateRelation in aggregateRelations) { var aggregateObjects = aggregateRelation.RelatedObjects; foreach (var aggregateObject in aggregateObjects) { var tnode = new gltf.Node(); var tnodeIndex = _nodes.Count; _nodes.Add(tnode); sonNodes.Add(tnodeIndex); nodeIndexQueue.Enqueue(tnodeIndex); objectQueue.Enqueue(aggregateObject); } } //处理当前节点 var parentNode = _nodes.ElementAt(nodeIndex); parentNode.Name = obj.Name + $" #{obj.EntityLabel}"; if (typeof(IIfcProduct).IsInstanceOfType(obj)) { //#endregion //遍历每一个shape var shapeInstances = GetShapeInstancesToRender(geomReader, excludedTypes, new HashSet<int> { obj.EntityLabel }); foreach (var shapeInstance in shapeInstances.OrderBy(x => x.IfcProductLabel)) { if (CustomFilter != null) { //TODO: 此处是productlabel，但是过滤器中的是ifc label,有何区别 var skip = CustomFilter(shapeInstance.IfcProductLabel, model); if (skip) continue; } //instanceLabel 全为-1 //entityLabel 和 productLabel 全都一样，都是一个产品的label，如一个椅子，有自己的entityLabel=ProductLabel。同时，相同外观的椅子的label不一样 //shapeGeometryLabel是产品构件的label，如一张椅子多个腿，每个腿有自己的shapeGeometryLabel，但是不同椅子有相同腿脚，它们的shapeGeometryLabel相同，所以不能用作筛选 //相同模型数据的节点只添加node，node包含转换矩阵，然后返回，不添加数据 //A mesh is instantiated by node.mesh property. //The same mesh could be used by many nodes, //which could have different transformations // now the geometry //提取对应label的图形几何信息 //只要以二进制存储的几何多边形 IXbimShapeGeometryData shapeGeom = geomReader.ShapeGeometry(shapeInstance.ShapeGeometryLabel); var entity = model.Instances[shapeInstance.IfcProductLabel] as IIfcProduct; //Instance是模型的所有实例，一个PRODUCT(ENTITY)可以对应多个实例 if (entity == null) { // fire error here. } var tnode = new gltf.Node(); tnode.Name = entity.Name + $" #{entity.EntityLabel} #{shapeGeom.IfcShapeLabel}"; tnode.Matrix = GetTransformInMeters(model, shapeInstance); // create mesh var meshIndex = _meshes.Count; var tnodeIndex = _nodes.Count; sonNodes.Add(tnodeIndex); if (shapes.TryGetValue(shapeInstance.ShapeGeometryLabel, out meshIndex)) { tnode.Mesh = meshIndex; _nodes.Add(tnode); continue; } meshIndex = _meshes.Count; var targetMesh = new gltf.Mesh { Name = $"Instance {shapeInstance.IfcProductLabel}" //经过测试，produceLabel似乎和entityLabel一样 }; // link node to mesh tnode.Mesh = meshIndex; // add all to lists _nodes.Add(tnode); _meshes.Add(targetMesh); shapes.Add(shapeInstance.ShapeGeometryLabel, meshIndex); if (shapeGeom.Format != (byte)XbimGeometryType.PolyhedronBinary) continue; // work out colour id; // the colour is associated with the instance, not the geometry. // positives are styles, negatives are types //存储并获取material var colId = shapeInstance.StyleLabel > 0 ? shapeInstance.StyleLabel : shapeInstance.IfcTypeId * -1; int materialIndex; if (!styleDic.TryGetValue(colId, out materialIndex)) { // if the style is not available we build one by ExpressType materialIndex = PrepareTypeMaterial(model, shapeInstance.IfcTypeId); styleDic.Add(colId, materialIndex); } // note: at a first investigation it looks like the shapeInstance.Transformation is the same for all shapes of the same product //如果这个shape被引用的次数大于1(只要被product引用了，就至少为1，即最小值为1)，那么这个shape可能在之前已经被添加过了 if (shapeGeom.ReferenceCount > 1) { // retain the information to reuse the map multiple times // // if g is not found in the dictionary then build it and add it ShapeComponentIds components; if (!geometries.TryGetValue(shapeGeom.ShapeLabel, out components)) { // mesh var xbimMesher = new XbimMesher(); xbimMesher.AddMesh(shapeGeom.ShapeData); components = AddGeom( xbimMesher.PositionsAsSingleList(model.ModelFactors.OneMeter), xbimMesher.Indices, xbimMesher.NormalsAsSingleList() ); geometries.Add(shapeGeom.ShapeLabel, components); } //添加顶点等信息（primitive）到mesh中 if (components != null) { var arr = GetTransformInMeters(model, shapeInstance); //TODO: ???unused AddComponentsToMesh(targetMesh, components, materialIndex); //此处添加了实际的mesh } //不应该这样做，应该不添加mesh，只在node中添加同样mesh的索引即可 } else//这个shape的被引用次数小于等于一，那么这个shape在此之前肯定还没有被添加，直接添加即可。 { //TODO： ？？？ 这两段if-else代码似乎没有区别呀！ // repeat the geometry only once var xbimMesher = new XbimMesher(); xbimMesher.AddMesh(shapeGeom.ShapeData); var trsf = GetTransformInMeters(model, shapeInstance); var components = AddGeom( xbimMesher.PositionsAsSingleList(model.ModelFactors.OneMeter), xbimMesher.Indices, xbimMesher.NormalsAsSingleList() ); AddComponentsToMesh(targetMesh, components, materialIndex); } } } //为当前节点（gltf.node）添加子节点（node.children），建立起父子关系 if (sonNodes.Count > 0) parentNode.Children = sonNodes.ToArray(); else Debug.WriteLine(obj.GetType()); } } return Build(); }