ModelBuilder, MeshBuilder and MeshPartBuilder

Kirill Nesmeyanov edited this page Jun 22, 2015 · 4 revisions

ModelBuilder

ModelBuilder (code) is a utility class to create one or more models on code. It allows you to include one or more nodes, each node consisting of one or more parts. It does, however, not support building a node hierarchy (child nodes). Be aware that building a model on code can be a costly operation and might trigger the garbage collector.

Building one or more models

To start building a model use the begin() method, after which you must call the end() when you're done building the model. The end() method will return the newly created model. You can build multiple models using the same ModelBuilder, but not at the same time. For example:

ModelBuilder modelBuilder = new ModelBuilder();

modelBuilder.begin();
... //build one or more nodes
Model model1 = modelBuilder.end();

modelBuilder.begin();
... //build one or more nodes
Model model2 = modelBuilder.end();

Managing resources

Keep in mind that models contain one or more meshes and therefore needs to be disposed. A model built via ModelBuilder will always be responsible for disposing all meshes it contains, even if you provide the Mesh yourself. Do not share a Mesh along multiple Models.

A Model built via ModelBuilder will not be made responsible for disposing any textures or any other resources contained in the materials. You can, however, use the manage(disposable) method to make the model responsible for disposing those resources. For example:

ModelBuilder modelBuilder = new ModelBuilder();
modelBuilder.begin();
Texture texture = new Texture(...);
modelBuilder.manage(texture);
... //build one or more nodes
Model model = modelBuilder.end();
... //use the model and when done:
model.dispose(); // this will dispose the texture as well

Creating nodes

A Model consists of one or more nodes. To start building a new node inside the model you can use the node() method. This will add a new node and make it active for building. It will also return the Node so you can reference it for later use or for example set its id.

ModelBuilder modelBuilder = new ModelBuilder();
modelBuilder.begin();
Node node1 = modelBuilder.node();
node1.id = "node1";
node1.translation.set(1, 2, 3);
...//build node1
Node node2 = modelBuilder.node();
node2.id = "node2";
...//build node2
Model model = modelBuilder.end();

Note that node id's should unique within the model. A typical use-case would be:

ModelBuilder modelBuilder = new ModelBuilder();
modelBuilder.begin();
modelBuilder.node().id = "node1";
...//build node1
modelBuilder.node().id = "node2";
...//build node2
Model model = modelBuilder.end();

Using the node() method for the first node is optional. For example, for models consisting of only a single node, you can immediately start creating the node parts without having to call the node() method.

There can only be one Node active for building at a time. Calling the node() method will stop building the previous node (if any) and start building the newly created node. The nodes will only be valid (complete), however, after the Model is completely built (the call to end() is made).

Creating node parts

A Node can contain one or more parts. Each part of a node will be rendered at the same location (the node transformation), but can be made up of a different material (e.g. shader uniforms) and/or mesh (e.g. shader (vertex) attributes).

A NodePart is the smallest renderable part of a Model. Every visible NodePart implies a render call (or "draw call" if you prefer). Reducing the number of render calls can help to decrease the time it takes to render the model. Therefore it is advised to try to combine multiple parts to a single part where possible.

To add a NodePart to the current node you can use one of the part(...) methods. A NodePart is basically the combination of a MeshPart and Material. You must always supply the material when calling one of the part(...) methods. For the MeshPart, however, ModelBuilder allows you to either specify the (part of the) mesh yourself, or to start building the MeshPart using a MeshPartBuilder.

Keep in mind that the Model will always be made responsible for disposing the Mesh, regardless the method used to create part.

A MeshPartBuilder is an interface (implemented by MeshBuilder, see below) which contains various helper methods to create a mesh. If you use the part(...) method to construct the MeshPart using a MeshPartBuilder, then ModelBuilder will try to combine multiple parts into the same Mesh. This will in most cases reduce the number of Mesh binds. This is only possible if the parts are made up using the same vertex attributes. For example:

ModelBuilder modelBuilder = new ModelBuilder();
modelBuilder.begin();
MeshPartBuilder meshBuilder;
meshBuilder = modelBuilder.part("part1", GL20.GL_TRIANGLES, Usage.Position | Usage.Normal, new Material());
meshBuilder.cone(5, 5, 5, 10);
Node node = modelBuilder.node();
node.translation.set(10,0,0);
meshBuilder = modelBuilder.part("part2", GL20.GL_TRIANGLES, Usage.Position | Usage.Normal, new Material());
meshBuilder.sphere(5, 5, 5, 10, 10);
Model model = modelBuilder.end();

This will create a model consisting of two nodes. Each node consisting of one part. The Mesh of both parts is shared, so there's only a single Mesh created for this Model. Note that in this example the vertex attributes are specified using a bit mask, which will cause ModelBuilder to create default (3D) VertexAttributes. You could also specify the VertexAttributes yourself.

Because ModelBuilder reuses the MeshPartBuilder instances for multiple parts, you cannot build multiple parts at the same time. Per ModelBuilder you can only build one Model, Node and MeshPart at any given time. Calling the part(...) method will make the previous MeshPartBuilder invalid.

See the MeshPartBuilder section below for more information on how to use the MeshPartBuilder to create the shape of the part.

MeshBuilder

MeshBuilder (code) is a utility class to create one or more meshes, optionally consisting of one or more MeshParts. While a MeshBuilder is typically constructed and maintained by the ModelBuilder using the ModelBuilder#part(...) method, it is possible to use MeshBuilder without using a ModelBuilder. For this, you can use the begin(...) method to start building a mesh, after which you must call the end() method when you're done building the mesh. The begin methods accepts various arguments to specify the vertex attributes and optionally primitive type (required when not creating mesh part(s)). The end() method will return the newly created Mesh. You can build multiple meshes using the same MeshBuilder instance, but not at the same time:

MeshBuilder meshBuilder = new MeshBuilder();
meshBuilder.begin(Usage.Position | Usage.Normal, GL20.GL_TRIANGLES);
...//build the first mesh
Mesh mesh1 = meshBuilder.end();

meshBuilder.begin(Usage.Position | Usage.Normal | Usage.ColorPacked, GL20.GL_TRIANGLES);
...//build the second mesh
Mesh mesh2 = meshBuilder.end();

Keep in mind that the Mesh must be disposed when you no longer need it.

Use the part(...) method to create a Mesh consisting of multiple parts. This will create a new MeshPart and set it active for building.

MeshBuilder meshBuilder = new MeshBuilder();
meshBuilder.begin(Usage.Position | Usage.Normal);
MeshPart part1 = meshBuilder.part("part1", GL20.GL_TRIANGLES);
... // build the first part
MeshPart part2 = meshBuilder.part("part2", GL20.GL_TRIANGLES);
... // build the second part
Mesh mesh = meshBuilder.end();

While the part(...) method returns the MeshPart so you can reference it for later use, it will not be valid until the end() method is called. You can only create one MeshPart at a time, calling the part(...) method will stop building the previous part and start building the new part.

All parts of the same Mesh share the same VertexAttributes. The primitive type can vary among parts though. For example, the following snippet creates two parts each with a different primitive type, but sharing the same mesh:

meshBuilder.begin(Usage.Position | Usage.Normal);
MeshPart part1 = meshBuilder.part("part1", GL20.GL_TRIANGLES);
... // build the first part
MeshPart part2 = meshBuilder.part("part2", GL20.GL_TRIANGLE_STRIP);
... // build the second part
Mesh mesh = meshBuilder.end();

MeshBuilder implements MeshPartBuilder. Creating the actual shape of the (part of the) mesh, is described in the MeshPartBuilder section.

MeshPartBuilder

MeshPartBuilder (code) is a utility interface which supplies various methods for creating a (part of a) mesh. You can either use ModelBuilder.part(...) or construct a MeshBuilder to obtain a MeshPartBuilder. All methods of the MeshPartBuilder interface can only be called as long as the MeshPart is being build (most commonly between the call to the part(...) method and the call to the next part(...) or end() method of either ModelBuilder or MeshBuilder).

Use the getMeshPart() method to obtain the MeshPart currently being build. Use the getAttributes() method to obtain the VertexAttributes of the Mesh being build.

A VertexAttribute of Usage.Position (either 2D or 3D) is required. There are no further restriction on the specified vertex attributes. However, most (especially higher level) methods are only implemented for position, normal, color (either packed or unpacked) and texture coordinates attributes. If you use other attributes as well, then a default (commonly zero) value will be used.

Most methods allow multiple signatures to specify the values for the vertex attributes. A little helper class VertexInfo is used to specify these on a per vertex basis. For example the rect(...) method accepts a VertexInfo for each corner, instead of using a method with all possible combinations or arguments for the vertex values of each corner. Be aware that the VertexInfo keeps track of whether a specific value has been set, therefor you should always use the setXXX methods. Use null in case you want to unset a value.

Use the setColor(...) method to specify the default color that will be used when the VertexAttributes contain a color VertexAttribute, but no color is set in e.g. the VertexInfo. For example:

meshPartBuilder.setColor(Color.RED);
VertexInfo v1 = new VertexInfo().setPos(0, 0, 0).setNor(0, 0, 1).setCol(null).setUV(0.5f, 0.0f);
VertexInfo v2 = new VertexInfo().setPos(3, 0, 0).setNor(0, 0, 1).setCol(null).setUV(0.0f, 0.0f);
VertexInfo v3 = new VertexInfo().setPos(3, 3, 0).setNor(0, 0, 1).setCol(null).setUV(0.0f, 0.5f);
VertexInfo v4 = new VertexInfo().setPos(0, 3, 0).setNor(0, 0, 1).setCol(null).setUV(0.5f, 0.5f);
meshPartBuilder.rect(v1, v2, v3, v4);

In this example, because the VertexInfo has no color set (setCol(null)), the default will be used which is set to a red color.

Use the setUVRange to specify the default texture coordinates range that will be used when no texture coordinates are specified. Along with the default color, this is especially useful for simple shapes where only positions are needed and other vertex information can be derived from the shape. For example:

meshPartBuilder.setColor(Color.RED);
meshPartBuilder.setUVRange(0.5f, 0f, 0f, 0.5f);
meshPartBuilder.rect(0,0,0, 3,0,0, 3,3,0, 0,3,0, 0,0,1); // the last three arguments specify the normal

Use the setVertexTransform(...) method to supply a transformation matrix that should be applied to all vertices following after that call.

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