Generate a 3MF package

Important APIs

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This guide describes the structure of the 3D Manufacturing Format document and how it can be created and manipulated with the Windows.Graphics.Printing3D API.

What is 3MF?

The 3D Manufacturing Format is a set of conventions for using XML to describe the appearance and structure of 3D models for the purpose of manufacturing (3D printing). It defines a set of parts (some required and some optional) and their relationships, with the goal of providing all necessary information to a 3D manufacturing device. A data set that adheres to the 3D Manufacturing Format can be saved as a file with the .3mf extension.

In Windows 10, the Printing3D3MFPackage class in the Windows.Graphics.Printing3D namespace is analogous to a single .3mf file, and other classes map to the particular XML elements in the file. This guide describes how each of the main parts of a 3MF document can be created and set programmatically, how the 3MF Materials Extension can be utilized, and how a Printing3D3MFPackage object can be converted and saved as a .3mf file. For more information on the standards of 3MF or the 3MF Materials Extension, see the 3MF Specification.

Core classes in the 3MF structure

The Printing3D3MFPackage class represents a complete 3MF document, and at the core of a 3MF document is its model part, represented by the Printing3DModel class. Most of the information we wish to specify about a 3D model will be stored by setting the properties of the Printing3DModel class and the properties of their underlying classes.

var localPackage = new Printing3D3MFPackage();
var model = new Printing3DModel();
// specify scaling units for model data
model.Unit = Printing3DModelUnit.Millimeter;

Metadata

The model part of a 3MF document can hold metadata in the form of key/value pairs of strings stored in the Metadata property. There are a number of predefined names of metadata, but other pairs can be added as part of an extension (described in more detail in the 3MF specification). It is up to the receiver of the package (a 3D manufacturing device) to determine whether and how to handle metadata, but it is good practice to include as much basic info as possible in the 3MF package:

model.Metadata.Add("Title", "Cube");
model.Metadata.Add("Designer", "John Smith");
model.Metadata.Add("CreationDate", "1/1/2016");

Mesh data

In the context of this guide, a mesh is a body of 3-dimensional geometry constructed from a single set of vertices (though it does not have to appear as a single solid). A mesh part is represented by the Printing3DMesh class. A valid mesh object must contain information about the location of all of its vertices as well as all the triangle faces that exist between certain sets of vertices.

The following method adds vertices to a mesh and then gives them locations in 3D space:

private async Task GetVerticesAsync(Printing3DMesh mesh) {
    Printing3DBufferDescription description;

    description.Format = Printing3DBufferFormat.Printing3DDouble;

    // have 3 xyz values
    description.Stride = 3;

    // have 8 vertices in all in this mesh
    mesh.CreateVertexPositions(sizeof(double) * 3 * 8);
    mesh.VertexPositionsDescription = description;

    // set the locations (in 3D coordinate space) of each vertex
    using (var stream = mesh.GetVertexPositions().AsStream()) {
        double[] vertices =
        {
            0, 0, 0,
            10, 0, 0,
            0, 10, 0,
            10, 10, 0,
            0, 0, 10,
            10, 0, 10,
            0, 10, 10,
            10, 10, 10,
        };

        // convert vertex data to a byte array
        byte[] vertexData = vertices.SelectMany(v => BitConverter.GetBytes(v)).ToArray();

        // write the locations to each vertex
        await stream.WriteAsync(vertexData, 0, vertexData.Length);
    }
    // update vertex count: 8 vertices in the cube
    mesh.VertexCount = 8;
}

The next method defines all of the triangles to be drawn across these vertices:

private static async Task SetTriangleIndicesAsync(Printing3DMesh mesh) {

    Printing3DBufferDescription description;

    description.Format = Printing3DBufferFormat.Printing3DUInt;
    // 3 vertex indices
    description.Stride = 3;
    // 12 triangles in all in the cube
    mesh.IndexCount = 12;

    mesh.TriangleIndicesDescription = description;

    // allocate space for 12 triangles
    mesh.CreateTriangleIndices(sizeof(UInt32) * 3 * 12);

    // get a datastream of the triangle indices (should be blank at this point)
    var stream2 = mesh.GetTriangleIndices().AsStream();
    {
        // define a set of triangle indices: each row is one triangle. The values in each row
        // correspond to the index of the vertex. 
        UInt32[] indices =
        {
            1, 0, 2,
            1, 2, 3,
            0, 1, 5,
            0, 5, 4,
            1, 3, 7,
            1, 7, 5,
            2, 7, 3,
            2, 6, 7,
            0, 6, 2,
            0, 4, 6,
            6, 5, 7,
            4, 5, 6,
        };
        // convert index data to byte array
        var vertexData = indices.SelectMany(v => BitConverter.GetBytes(v)).ToArray();
        var len = vertexData.Length;
        // write index data to the triangle indices stream
        await stream2.WriteAsync(vertexData, 0, vertexData.Length);
    }

}

Note

All triangles must have their indices defined in counter-clockwise order (when viewing the triangle from outside of the mesh object), so that their face-normal vectors point outward.

When a Printing3DMesh object contains valid sets of vertices and triangles, it should then be added to the model's Meshes property. All Printing3DMesh objects in a package must be stored under the Meshes property of the Printing3DModel class.

// add the mesh to the model
model.Meshes.Add(mesh);

Create materials

A 3D model can hold data for multiple materials. This convention is intended to take advantage of 3D manufacturing devices that can use multiple materials on a single print job. There are also multiple types of material gropus, each one capable of supporting a number of different individual materals. Each material group must have a unique reference id number, and each material within that group must also have a unique id.

The different mesh objects within a model can then reference these materials. Furthermore, individual triangles on each mesh can specify different materials. Further still, different materials can even be represented within a single triangle, with each triangle vertex having a different material assigned to it and the face material calculated as the gradient between them.

This guide will first show how to create different kinds of materials within their respective material groups and store them as resources on the model object. Then, we will go about assigning different materials to individual meshes and individual triangles.

Base materials

The default material type is Base Material, which has both a Color Material value (described below) and a name attribute that is intended to specify the type of material to use.

// add material group
// all material indices need to start from 1: 0 is a reserved id
// create new base materialgroup with id = 1
var baseMaterialGroup = new Printing3DBaseMaterialGroup(1);

// create color objects
// 'A' should be 255 if alpha = 100%
var darkBlue = Windows.UI.Color.FromArgb(255, 20, 20, 90);
var orange = Windows.UI.Color.FromArgb(255, 250, 120, 45);
var teal = Windows.UI.Color.FromArgb(255, 1, 250, 200);

// create new ColorMaterials, assigning color objects
var colrMat = new Printing3DColorMaterial();
colrMat.Color = darkBlue;

var colrMat2 = new Printing3DColorMaterial();
colrMat2.Color = orange;

var colrMat3 = new Printing3DColorMaterial();
colrMat3.Color = teal;

// setup new materials using the ColorMaterial objects
// set desired material type in the Name property
var baseMaterial = new Printing3DBaseMaterial {
    Name = Printing3DBaseMaterial.Pla,
    Color = colrMat
};

var baseMaterial2 = new Printing3DBaseMaterial {
    Name = Printing3DBaseMaterial.Abs,
    Color = colrMat2
};

// add base materials to the basematerialgroup

// material group index 0
baseMaterialGroup.Bases.Add(baseMaterial);
// material group index 1
baseMaterialGroup.Bases.Add(baseMaterial2);

// add material group to the basegroups property of the model
model.Material.BaseGroups.Add(baseMaterialGroup);

Note

 The 3D manufacturing device will determine which available physical materials map to which virtual material elements stored in the 3MF. Material mapping doesn't have to be 1:1: if a 3D printer only uses one material, it will print the whole model in that material, regardless of which objects or faces were assigned different materials.

Color materials

Color Materials are similar to Base Materials, but they do not contain a name. Thus, they give no instructions as to what type of material should be used by the machine. They hold only color data, and let the machine choose the material type (and the machine may then prompt the user to choose). In the code below, the colrMat objects from the previous method are used on their own.

// add ColorMaterials to the Color Material Group (with id 2)
var colorGroup = new Printing3DColorMaterialGroup(2);

// add the previous ColorMaterial objects to this ColorMaterialGroup
colorGroup.Colors.Add(colrMat);
colorGroup.Colors.Add(colrMat2);
colorGroup.Colors.Add(colrMat3);

// add colorGroup to the ColorGroups property on the model
model.Material.ColorGroups.Add(colorGroup);

Composite materials

Composite Materials simply instruct the manufacturing device to use a uniform mixture of different Base Materials. Each Composite Material Group must reference exactly one Base Material Group from which to draw ingredients. Additonally, the Base Materials within this group that are to be made available must be listed out in a Material Indices list, which each Composite Material will then reference when specifying the ratios (every Composite Material is simply a ratio of Base Materials).

// CompositeGroups
// create new composite material group with id = 3
var compositeGroup = new Printing3DCompositeMaterialGroup(3);

// indices point to base materials in BaseMaterialGroup with id =1
compositeGroup.MaterialIndices.Add(0);
compositeGroup.MaterialIndices.Add(1);

// create new composite materials
var compMat = new Printing3DCompositeMaterial();
// fraction adds to 1.0
compMat.Values.Add(0.2); // .2 of first base material in BaseMaterialGroup 1
compMat.Values.Add(0.8); // .8 of second base material in BaseMaterialGroup 1

var compMat2 = new Printing3DCompositeMaterial();
// fraction adds to 1.0
compMat2.Values.Add(0.5);
compMat2.Values.Add(0.5);

var compMat3 = new Printing3DCompositeMaterial();
// fraction adds to 1.0
compMat3.Values.Add(0.8);
compMat3.Values.Add(0.2);

var compMat4 = new Printing3DCompositeMaterial();
// fraction adds to 1.0
compMat4.Values.Add(0.4);
compMat4.Values.Add(0.6);

// add composites to group
compositeGroup.Composites.Add(compMat);
compositeGroup.Composites.Add(compMat2);
compositeGroup.Composites.Add(compMat3);
compositeGroup.Composites.Add(compMat4);

// add group to model
model.Material.CompositeGroups.Add(compositeGroup);

Texture coordinate materials

3MF supports the use of 2D images to color the surfaces of 3D models. This way, the model can convey much more color data per triangle face (as opposed to having just one color value per triangle vertex). Like Color Materials, texture coordinate materials only convery color data. To use a 2D texture, a texture resource must first be declared:

// texture resource setup
Printing3DTextureResource texResource = new Printing3DTextureResource();
// name conveys the path within the 3MF document
texResource.Name = "/3D/Texture/msLogo.png";

// in this case, we reference texture data in the sample appx, convert it to 
// an IRandomAccessStream, and assign it as the TextureData
Uri texUri = new Uri("ms-appx:///Assets/msLogo.png");
StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(texUri);
IRandomAccessStreamWithContentType iRandomAccessStreamWithContentType = await file.OpenReadAsync();
texResource.TextureData = iRandomAccessStreamWithContentType;
// add this testure resource to the 3MF Package
localPackage.Textures.Add(texResource);

// assign this texture resource to a Printing3DModelTexture
var modelTexture = new Printing3DModelTexture();
modelTexture.TextureResource = texResource;

Note

Texture data belongs to the 3MF Package itself, not to the model part within the package.

Next, we must fill out Texture3Coord Materials. Each of these references a texture resource and specifies a particular point on the image (in UV coordinates).

// texture2Coord Group
// create new Texture2CoordMaterialGroup with id = 4
var tex2CoordGroup = new Printing3DTexture2CoordMaterialGroup(4);

// create texture materials:
// set up four tex2coordmaterial objects with four (u,v) pairs, 
// mapping to each corner of the image:

var tex2CoordMaterial = new Printing3DTexture2CoordMaterial();
tex2CoordMaterial.U = 0.0;
tex2CoordMaterial.V = 1.0;
tex2CoordGroup.Texture2Coords.Add(tex2CoordMaterial);

var tex2CoordMaterial2 = new Printing3DTexture2CoordMaterial();
tex2CoordMaterial2.U = 1.0;
tex2CoordMaterial2.V = 1.0;
tex2CoordGroup.Texture2Coords.Add(tex2CoordMaterial2);

var tex2CoordMaterial3 = new Printing3DTexture2CoordMaterial();
tex2CoordMaterial3.U = 0.0;
tex2CoordMaterial3.V = 0.0;
tex2CoordGroup.Texture2Coords.Add(tex2CoordMaterial3);

var tex2CoordMaterial4 = new Printing3DTexture2CoordMaterial();
tex2CoordMaterial4.U = 1.0;
tex2CoordMaterial4.V = 0.0;
tex2CoordGroup.Texture2Coords.Add(tex2CoordMaterial4);

// add our Printing3DModelTexture to the Texture property of the group
tex2CoordGroup.Texture = modelTexture;

// add metadata about the texture so that u,v values can be used
model.Metadata.Add("tex4", "/3D/Texture/msLogo.png");
// add group to groups on the model's material
model.Material.Texture2CoordGroups.Add(tex2CoordGroup);

Map materials to faces

In order to dictate which materials are mapped to which vertices on each triangle, we must do some more work on the mesh object of our model (if a model contains multiple meshes, they must each have their materials assigned separately). As mentioned above, materials are assigned per-vertex, per-triangle. Refer to the code below to see how this information is entered and interpreted.

private static async Task SetMaterialIndicesAsync(Printing3DMesh mesh) {
    // declare a description of the material indices
    Printing3DBufferDescription description;
    description.Format = Printing3DBufferFormat.Printing3DUInt;
    // 4 indices for material description per triangle
    description.Stride = 4;
    // 12 triangles total
    mesh.IndexCount = 12;
    mesh.TriangleMaterialIndicesDescription = description;

    // create space for storing this data
    mesh.CreateTriangleMaterialIndices(sizeof(UInt32) * 4 * 12);

    {
        // each row is a triangle face (in the order they were created)
        // first column is the id of the material group, last 3 columns show which material id (within that group)
        // maps to each triangle vertex (in the order they were listed when creating triangles)
        UInt32[] indices =
        {
            // base materials:
            // in  the BaseMaterialGroup (id=1), the BaseMaterial with id=0 will be applied to these triangle vertices
            1, 0, 0, 0, 
            1, 0, 0, 0,
            // color materials:
            // in the ColorMaterialGroup (id=2), the ColorMaterials with these ids will be applied to these triangle vertices
            2, 1, 1, 1,
            2, 1, 1, 1,
            2, 0, 0, 0,
            2, 0, 0, 0,
            2, 0, 1, 2,
            2, 1, 0, 2,
            // composite materials:
            // in the CompositeMaterialGroup (id=3), the CompositeMaterial with id=0 will be applied to these triangles
            3,0,0,0,
            3,0,0,0,
            // texture materials:
            // in the Texture2CoordMaterialGroup (id=4), each texture coordinate is mapped to the appropriate vertex on these
            // two adjacent triangle faces, so that the square face they create displays the original rectangular image
            4, 0, 3, 1,
            4, 2, 3, 0,
        };

        // get the current (unassigned) vertex data as a stream and write our new 'indices' data to it.
        var stream = mesh.GetTriangleMaterialIndices().AsStream();
        var vertexData = indices.SelectMany(v => BitConverter.GetBytes(v)).ToArray();
        var len = vertexData.Length;
        await stream.WriteAsync(vertexData, 0, vertexData.Length);
    }
}

Components and build

The component structure allows the user to place more than one mesh object in a printable 3D model. A Printing3DComponent object contains a single mesh and a list of references to other components. This is actually a list of Printing3DComponentWithMatrix objects. Printing3DComponentWithMatrix objects each contain a Printing3DComponent and, importantly, a transform matrix that applies to the mesh and contained components of said Printing3DComponent.

For example, a model of a car might consist of a "Body" Printing3DComponent that holds the mesh for the car's body. The "Body" component may then contain references to four different Printing3DComponentWithMatrix objects, which all reference the same Printing3DComponent with the "Wheel" mesh and contain four different transform matrices (mapping the wheels to four different positions on the car's body). In this scenario, the "Body" mesh and "Wheel" mesh would each only need to be stored once, even though the final product would feature five meshes in total.

All Printing3DComponent objects must be directly referenced in the model's Components property. The one particular component that is to be used in the printing job is stored in the Build Property.

// create new component
Printing3DComponent component = new Printing3DComponent();

// assign mesh to the component's mesh
component.Mesh = mesh;

// add component to the model's list of all used components
// a model can have references to multiple components
model.Components.Add(component);

// create the transform matrix
var componentWithMatrix = new Printing3DComponentWithMatrix();
// assign component to this componentwithmatrix
componentWithMatrix.Component = component;

// create an identity matrix
var identityMatrix = Matrix4x4.Identity;

// use the identity matrix as the transform matrix (no transformation)
componentWithMatrix.Matrix = identityMatrix;

// add component to the build property.
model.Build.Components.Add(componentWithMatrix);

Save package

Now that we have a model, with defined materials and components, we can save it to the package.

// save the model to the package:
await localPackage.SaveModelToPackageAsync(model);
// get the model stream
var modelStream = localPackage.ModelPart;

// fix any textures in the model file
localPackage.ModelPart = await FixTextureContentType(modelStream);

From here, we can either initiate a print job within the app (see 3D printing from your app), or save this Printing3D3MFPackage as a .3mf file.

The following method takes a finished Printing3D3MFPackage and saves its data to a .3mf file.

private async void SaveTo3mf(Printing3D3MFPackage localPackage) {

    // prompt the user to choose a location to save the file to
    FileSavePicker savePicker = new FileSavePicker();
    savePicker.DefaultFileExtension = ".3mf";
    savePicker.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
    savePicker.FileTypeChoices.Add("3MF File", new[] { ".3mf" });
    var storageFile = await savePicker.PickSaveFileAsync();
    if (storageFile == null) {
        return;
    }

    // save the 3MF Package to an IRandomAccessStream
    using (var stream = await localPackage.SaveAsync()) {
        // go to the beginning of the stream
        stream.Seek(0);

        // read from the file stream and write to a buffer
        using (var dataReader = new DataReader(stream)) {
            await dataReader.LoadAsync((uint)stream.Size);
            var buffer = dataReader.ReadBuffer((uint)stream.Size);

            // write from the buffer to the storagefile specified
            await FileIO.WriteBufferAsync(storageFile, buffer);
        }
    }
}

3D printing from your app
3D printing UWP sample