CuraEngine（4）核心SliceDataStorage类和函数sliceModel源码阅读

CuraEngine所有的和模型切片相关的数据都存放在一个叫 SliceDataStorage 的类里面，这个SliceDataStorage类包含了一系列的成员变量，它们各自代表了3D打印切片过程中的不同数据和信息。

SliceDataStorage类

class SliceDataStorage : public NoCopy
{
public:
    size_t print_layer_count; //!< The total number of layers (except the raft and filler layers)

    Point3 model_size, model_min, model_max;
    AABB3D machine_size; //!< The bounding box with the width, height and depth of the printer.
    std::vector<SliceMeshStorage> meshes;

    std::vector<WipeScriptConfig> wipe_config_per_extruder; //!< Wipe configs per extruder.

    std::vector<RetractionConfig> retraction_config_per_extruder; //!< Retraction config per extruder.
    std::vector<RetractionConfig> extruder_switch_retraction_config_per_extruder; //!< Retraction config per extruder for when performing an extruder switch

    SupportStorage support;

    Polygons skirt_brim[MAX_EXTRUDERS]; //!< Skirt and brim polygons per extruder, ordered from inner to outer polygons.
    Polygons raftOutline;               //Storage for the outline of the raft. Will be filled with lines when the GCode is generated.

    int max_print_height_second_to_last_extruder; //!< Used in multi-extrusion: the layer number beyond which all models are printed with the same extruder
    std::vector<int> max_print_height_per_extruder; //!< For each extruder the highest layer number at which it is used.
    std::vector<size_t> max_print_height_order; //!< Ordered indices into max_print_height_per_extruder: back() will return the extruder number with the highest print height.

    std::vector<int> spiralize_seam_vertex_indices; //!< the index of the seam vertex for each layer
    std::vector<Polygons* > spiralize_wall_outlines; //!< the wall outline polygons for each layer

    PrimeTower primeTower;

    std::vector<Polygons> oozeShield;        //oozeShield per layer
    Polygons draft_protection_shield; //!< The polygons for a heightened skirt which protects from warping by gusts of wind and acts as a heated chamber.

    /*!
     * \brief Creates a new slice data storage that stores the slice data of the
     * current mesh group.
     */
    SliceDataStorage();

    ~SliceDataStorage()
    {
    }

下面是对这些成员变量的解释：

print_layer_count: 整数类型，表示除了基础层（raft）和填充层之外的层数总数。

model_size, model_min, model_max: Point3类型（可能是三维的点，包含x、y和z坐标）。分别表示模型的大小、最小边界和最大边界。

machine_size: AABB3D类型（AABB是Axis-Aligned Bounding Box的缩写，即轴对齐的边界框）。它表示打印机的宽度、高度和深度的边界框。

meshes: SliceMeshStorage类型的向量vector，存储了所有网格（三维mesh）的切片数据。这个最重要，后面附有SliceMeshStorage类的定义

wipe_config_per_extruder: WipeScriptConfig类型的向量，存储了每个挤出机的擦拭配置。

retraction_config_per_extruder: RetractionConfig类型的向量，存储了每个挤出机的回抽配置。

extruder_switch_retraction_config_per_extruder: RetractionConfig类型的向量，存储了在挤出机切换时需要使用的回抽配置。

support: SupportStorage类型，可能用于存储打印过程中支撑结构的信息。

skirt_brim: Polygons类型的数组，用于存储每个挤出机的裙边和边缘多边形，从内到外排序。

raftOutline: Polygons类型，用于存储raft（基础层）的轮廓，将在生成G代码时填充线条。

max_print_height_second_to_last_extruder: 整数类型，在多挤出机打印中使用，表示所有模型使用相同挤出机打印的层数界限。

max_print_height_per_extruder: 整数类型的向量，对于每个挤出机，存储了使用它的最高层数。

max_print_height_order: 整数类型的向量，是对max_print_height_per_extruder中元素的排序索引，通过back()方法可以获取具有最高打印高度的挤出机编号。

spiralize_seam_vertex_indices: 整数类型的向量，存储了每层螺旋接缝顶点的索引。

spiralize_wall_outlines: Polygons指针的向量，存储了每层的墙体外轮廓多边形。

primeTower: PrimeTower类型，可能用于存储挤出机引丝塔的信息。

oozeShield: Polygons类型的向量，存储了每层的防漏屏蔽多边形。

draft_protection_shield: Polygons类型，表示一个加高的裙边，用于防止风吹造成的翘曲，并作为加热舱室。

这些成员变量共同构成了3D打印切片过程中的各种数据和配置，包括模型尺寸、挤出机配置、支撑结构、打印高度等关键信息。

FffPolygonGenerator::sliceModel接口

bool FffPolygonGenerator::sliceModel(MeshGroup* meshgroup, TimeKeeper& timeKeeper, SliceDataStorage& storage) /// slices the model
{
    Progress::messageProgressStage(Progress::Stage::SLICING, &timeKeeper);

    storage.model_min = meshgroup->min();
    storage.model_max = meshgroup->max();
    storage.model_size = storage.model_max - storage.model_min;

    log("Slicing model...\n");

    const Settings& mesh_group_settings = Application::getInstance().current_slice->scene.current_mesh_group->settings;

    // regular layers
    int slice_layer_count = 0; //Use signed int because we need to subtract the initial layer in a calculation temporarily.

    // Initial layer height of 0 is not allowed. Negative layer height is nonsense.
    coord_t initial_layer_thickness = mesh_group_settings.get<coord_t>("layer_height_0");
    if (initial_layer_thickness <= 0)
    {
        logError("Initial layer height %i is disallowed.\n", initial_layer_thickness);
        return false;
    }

    // Layer height of 0 is not allowed. Negative layer height is nonsense.
    const coord_t layer_thickness = mesh_group_settings.get<coord_t>("layer_height");
    if(layer_thickness <= 0)
    {
        logError("Layer height %i is disallowed.\n", layer_thickness);
        return false;
    }

    // variable layers
    AdaptiveLayerHeights* adaptive_layer_heights = nullptr;
    const bool use_variable_layer_heights = mesh_group_settings.get<bool>("adaptive_layer_height_enabled");

    if (use_variable_layer_heights)
    {
        // Calculate adaptive layer heights
        const coord_t variable_layer_height_max_variation = mesh_group_settings.get<coord_t>("adaptive_layer_height_variation");
        const coord_t variable_layer_height_variation_step = mesh_group_settings.get<coord_t>("adaptive_layer_height_variation_step");
        const double adaptive_threshold = mesh_group_settings.get<double>("adaptive_layer_height_threshold");
        adaptive_layer_heights = new AdaptiveLayerHeights(layer_thickness, variable_layer_height_max_variation,
                                                          variable_layer_height_variation_step, adaptive_threshold);

        // Get the amount of layers
        slice_layer_count = adaptive_layer_heights->getLayerCount();
    }
    else
    {
        slice_layer_count = (storage.model_max.z - initial_layer_thickness) / layer_thickness + 1;
    }

    // Model is shallower than layer_height_0, so not even the first layer is sliced. Return an empty model then.
    if (slice_layer_count <= 0)
    {
        return true; // This is NOT an error state!
    }

    std::vector<Slicer*> slicerList;
    for(unsigned int mesh_idx = 0; mesh_idx < meshgroup->meshes.size(); mesh_idx++)
    {
        // Check if adaptive layers is populated to prevent accessing a method on NULL
        std::vector<AdaptiveLayer>* adaptive_layer_height_values = {};
        if (adaptive_layer_heights != nullptr)
        {
            adaptive_layer_height_values = adaptive_layer_heights->getLayers();
        }

        Mesh& mesh = meshgroup->meshes[mesh_idx];
        Slicer* slicer = new Slicer(&mesh, layer_thickness, slice_layer_count, use_variable_layer_heights, adaptive_layer_height_values);

        slicerList.push_back(slicer);

        /*
        for(SlicerLayer& layer : slicer->layers)
        {
            //Reporting the outline here slows down the engine quite a bit, so only do so when debugging.
            sendPolygons("outline", layer_nr, layer.z, layer.polygonList);
            sendPolygons("openoutline", layer_nr, layer.openPolygonList);
        }
        */

        Progress::messageProgress(Progress::Stage::SLICING, mesh_idx + 1, meshgroup->meshes.size());
    }

    // Clear the mesh face and vertex data, it is no longer needed after this point, and it saves a lot of memory.
    meshgroup->clear();

    Mold::process(slicerList);

    Scene& scene = Application::getInstance().current_slice->scene;
    for (unsigned int mesh_idx = 0; mesh_idx < slicerList.size(); mesh_idx++)
    {
        Mesh& mesh = scene.current_mesh_group->meshes[mesh_idx];
        if (mesh.settings.get<bool>("conical_overhang_enabled") && !mesh.settings.get<bool>("anti_overhang_mesh"))
        {
            ConicalOverhang::apply(slicerList[mesh_idx], mesh);
        }
    }

    MultiVolumes::carveCuttingMeshes(slicerList, scene.current_mesh_group->meshes);

    Progress::messageProgressStage(Progress::Stage::PARTS, &timeKeeper);

    if (scene.current_mesh_group->settings.get<bool>("carve_multiple_volumes"))
    {
        carveMultipleVolumes(slicerList);
    }

    generateMultipleVolumesOverlap(slicerList);

    storage.print_layer_count = 0;
    for (unsigned int meshIdx = 0; meshIdx < slicerList.size(); meshIdx++)
    {
        Mesh& mesh = scene.current_mesh_group->meshes[meshIdx];
        Slicer* slicer = slicerList[meshIdx];
        if (!mesh.settings.get<bool>("anti_overhang_mesh") && !mesh.settings.get<bool>("infill_mesh") && !mesh.settings.get<bool>("cutting_mesh"))
        {
            storage.print_layer_count = std::max(storage.print_layer_count, slicer->layers.size());
        }
    }
    storage.support.supportLayers.resize(storage.print_layer_count);

    storage.meshes.reserve(slicerList.size()); // causes there to be no resize in meshes so that the pointers in sliceMeshStorage._config to retraction_config don't get invalidated.
    for (unsigned int meshIdx = 0; meshIdx < slicerList.size(); meshIdx++)
    {
        Slicer* slicer = slicerList[meshIdx];
        Mesh& mesh = scene.current_mesh_group->meshes[meshIdx];

        // always make a new SliceMeshStorage, so that they have the same ordering / indexing as meshgroup.meshes
        storage.meshes.emplace_back(&meshgroup->meshes[meshIdx], slicer->layers.size()); // new mesh in storage had settings from the Mesh
        SliceMeshStorage& meshStorage = storage.meshes.back();

        // only create layer parts for normal meshes
        const bool is_support_modifier = AreaSupport::handleSupportModifierMesh(storage, mesh.settings, slicer);
        if (!is_support_modifier)
        {
            createLayerParts(meshStorage, slicer);
        }

        // Do not add and process support _modifier_ meshes further, and ONLY skip support _modifiers_. They have been
        // processed in AreaSupport::handleSupportModifierMesh(), but other helper meshes such as infill meshes are
        // processed in a later stage, except for support mesh itself, so an exception is made for that.
        if (is_support_modifier && ! mesh.settings.get<bool>("support_mesh"))
        {
            storage.meshes.pop_back();
            continue;
        }

        // check one if raft offset is needed
        const bool has_raft = mesh_group_settings.get<EPlatformAdhesion>("adhesion_type") == EPlatformAdhesion::RAFT;

        // calculate the height at which each layer is actually printed (printZ)
        for (unsigned int layer_nr = 0; layer_nr < meshStorage.layers.size(); layer_nr++)
        {
            SliceLayer& layer = meshStorage.layers[layer_nr];

            if (use_variable_layer_heights)
            {
                meshStorage.layers[layer_nr].printZ = adaptive_layer_heights->getLayers()->at(layer_nr).z_position;
                meshStorage.layers[layer_nr].thickness = adaptive_layer_heights->getLayers()->at(layer_nr).layer_height;
            }
            else
            {
                meshStorage.layers[layer_nr].printZ = initial_layer_thickness + (layer_nr * layer_thickness);

                if (layer_nr == 0)
                {
                    meshStorage.layers[layer_nr].thickness = initial_layer_thickness;
                }
                else
                {
                    meshStorage.layers[layer_nr].thickness = layer_thickness;
                }
            }

            // add the raft offset to each layer
            if (has_raft)
            {
                const ExtruderTrain& train = mesh_group_settings.get<ExtruderTrain&>("adhesion_extruder_nr");
                layer.printZ +=
                    Raft::getTotalThickness()
                    + train.settings.get<coord_t>("raft_airgap")
                    - train.settings.get<coord_t>("layer_0_z_overlap"); // shift all layers (except 0) down

                if (layer_nr == 0)
                {
                    layer.printZ += train.settings.get<coord_t>("layer_0_z_overlap"); // undo shifting down of first layer
                }
            }
        }

        delete slicerList[meshIdx];

        Progress::messageProgress(Progress::Stage::PARTS, meshIdx + 1, slicerList.size());
    }
    return true;
}

大致流程

sliceModel函数接收三个参数：一个MeshGroup指针，一个TimeKeeper引用和一个SliceDataStorage引用。函数返回一个布尔值，表示切片操作是否成功。

1、首先计算模型的最小和最大坐标，以及模型的大小。

2、然后根据模型的设置，计算切片的层数slice_layer_count。

3、接下来，函数遍历模型中的每个网格mesh，为每个网格创建一个Slicer对象，并将这些Slicer对象存储在一个列表slicerList中。

4、处理模型的多卷切割和生成多卷重叠部分carveMultipleVolumes和generateMultipleVolumesOverlap。

5、函数遍历每个切片器，为每个切片器创建层部分，并将它们添加到SliceMeshStorage对象中。

6、最后，计算每个切片层的打印高度（printZ）和层厚。

首先根据是否使用可变层高，计算每个切片层的打印高度和层厚。如果使用可变层高，则从自适应层高列表中获取相应的层高信息；否则，根据初始层厚和层厚计算每个切片层的打印高度和层厚。

接下来，如果存在raft（底座），则需要将raft的偏移量添加到每个切片层上。首先获取raft的厚度、空气间隙和第0层的重叠距离等参数，然后将这些参数应用到每个切片层上，除了第0层需要特殊处理。

最后，删去切片器列表中的切片器对象，并更新进度条。整个函数返回true表示切片操作成功。

SliceMeshStorage类定义

class SliceMeshStorage
{
public:
    Settings& settings;
    std::vector<SliceLayer> layers;
    std::string mesh_name;

    LayerIndex layer_nr_max_filled_layer; //!< the layer number of the uppermost layer with content (modified while infill meshes are processed)

    std::vector<AngleDegrees> infill_angles; //!< a list of angle values which is cycled through to determine the infill angle of each layer
    std::vector<AngleDegrees> roofing_angles; //!< a list of angle values which is cycled through to determine the roofing angle of each layer
    std::vector<AngleDegrees> skin_angles; //!< a list of angle values which is cycled through to determine the skin angle of each layer
    std::vector<Polygons> overhang_areas; //!< For each layer the areas that are classified as overhang on this mesh.
    std::vector<Polygons> full_overhang_areas; //!< For each layer the full overhang without the tangent of the overhang angle removed, such that the overhang area adjoins the areas of the next layers.
    std::vector<std::vector<Polygons>> overhang_points; //!< For each layer a list of points where point-overhang is detected. This is overhang that hasn't got any surface area, such as a corner pointing downwards.
    AABB3D bounding_box; //!< the mesh's bounding box

    SubDivCube* base_subdiv_cube;
    SierpinskiFillProvider* cross_fill_provider; //!< the fractal pattern for the cross (3d) filling pattern

    /*!
     * \brief Creates a storage space for slice results of a mesh.
     * \param mesh The mesh that the storage space belongs to.
     * \param slice_layer_count How many layers are needed to store the slice
     * results of the mesh. This needs to be at least as high as the highest
     * layer that contains a part of the mesh.
     */
    SliceMeshStorage(Mesh* mesh, const size_t slice_layer_count);

    virtual ~SliceMeshStorage();