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The following tutorial focuses on a real-world production challenge that can occur while using the Maya software. The premise for this situation can and often does occur due to the nonlinear nature of production.

Exercise 13.4 Transferring UVs onto a Bound, Smooth-Skinned Character

Here is the basic premise for this exercise:

The character model has traveled through the modeling phase of the production and has passed into the character-rigging phase. But then a huge problem arises in the geometry of the character.

At the last minute, you realize that somewhere along the line, a miscommunication was made and the wrong geometry was used to bind the character and paint the smooth-skin weights. In fact, the geometry that was used doesn't have UVs for texturing.

For this scenario example, you go through a full workflow, to make geometry modifications (transferring UVs) to a bound smooth-skinned character, without adding any extra undesirable node history to the geometry.

The bound character model does not have UVs, so you will use a tricky technique of transferring UVs to the intermediate shape node of the bound geometry to achieve the desired result.

1.
Open the file nonLinearWorkflow_start.mb, found on the accompanying CD.

Notice that the character's geometry is already bound to the joints with a smooth bind. If you open the UV Texture view, however, you will see that there are no UVs on the geometry (see Figure 13.34).

Figure 13.34. This model is smooth-skinned and weighted, but it is the wrong model! Here you go through the steps involved to transfer UVs to the geometry without adding any unwanted history nodes to the geometry.

2.
Make sure that your Hypergraph menu's view options have shape nodes, underworld nodes, and hidden nodes turned on (see Figure 13.35).

Figure 13.35. Be sure that you have Options, Display, Shape Nodes, and Options, Display, Hidden Nodes checked to On in your Hypergraph window.

First, you'll import the geometry that has the UVs on it that you want to transfer. It is important to note that the geometry with the UVs on it is an exact duplicate of the current mesh, but it has had an automatic mapping procedure applied to it.

3.
Import the file nonLinearWorkflow_importUVs.mb from the accompanying CD for this chapter.

4.
Next, select the imported model. Notice that it has UVs.

The next step is to transfer the UVs from the imported character onto the bound character, without leaving any trace of node history behind (see Figure 13.36).

Figure 13.36. Notice that the imported model has UVs. These are the UVs that you will transfer onto the bound mesh, without leaving any unwanted node history behind.

Normally, if you transferred the UVs onto the geometry of the skinned dog, Maya would insert a node called polyTransferUv after the skin cluster's deformations. The trick to transferring the UVs without leaving any history behind lies deep within the secrets of the Hypergraph and the way Maya connects your nodes to create its dependency connections.

Notice the hidden node in Figure 13.36, just below the dogLowResShape, called dogLowResShapeOrig. This is the node that you will be examining for the moment.

At the base of the node connections that form the node network to deform your geometry lies a polygon-shape intermediate node. This is the node that starts the entire flow of data that creates your character's geometry and sends the skin cluster the vertices from which to deform. This is also the node on which you will perform your history operations. Then you will delete history on this node.

5.
Select the dogLowResShapeOrig node, open the Attribute Editor by hitting Ctrl+a, and, in the Hypergraph window, perform the menu command Graph, Input and Output Connections (see Figure 13.37).

Figure 13.37. The dogLowResShapeOrig node is a polygon mesh node with its intermediate object attribute flagged on. This node actually begins the data flow that creates your character's deformations.

6.
In the Attribute Editor for the dogLowResShapeOrig node, expand the Object Display portion and uncheck the Intermediate Object check box.

7.
Next, select the imported mesh that has the UVs and Shift-select (to add to the current selection) the dogLowResShapeOrig node. Now perform Polygons, Transfer, Options, and make sure only the UVs option is checked. When this is completed, select only the dogLowResShapeOrig node, and perform the menu command Edit, Delete by Type, History (see Figure 13.38).

Figure 13.38. The trick is to transfer the UVs from the imported mesh onto the dogLowResShapeOrig and then just delete the history from the dogLowResShapeOrig.

8.
Finally, set the Intermediate Object check box back on for the dogLowResShapeOrig node.

You have now transferred the polygon UVs, without adding any polygon UV transfer history nodes to your geometry.

You can now delete the imported model from which the UVs were transferred. A completed file, nonLinearWorkflow_finished.mb, is found on the CD.

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