Adding blend shapes - Houdini

Let's open the man.hip file and duplicate the hairs, then edit the mesh to create multiple blend shapes target.

Then select the meshes and the original hairs and create a blend shape deformer.

Exporting meshes

You need to export the blend shapes targets. If you use the variation builder, Atoms automatically exports the blend shapes data inside the meshes.

If you want to export them manually, open the atoms mesh exporter from the atoms menu: Atoms > Export > Mesh exporter

Set the output path, then turn on the "export skin weight option". Inside the skeleton path file, pick the man.atomsskel from the AtomsMaya/data folder. Then select the man Hips joint and press the refresh button. Finally, turn on the "export blend shapes" option, select the mesh you want to export and press the "Export" button. This tool automatically writes points, normals, id and name of each target inside the mesh file.

import AtomsCore
mesh_file = "blendshape_hair.geos"
ark = AtomsCore.Archive()
if ark.readFromFile(mesh_file):
    mesh = AtomsCore.MapMetadata()
    mesh.deserialise(ark)
    for geo in mesh.keys(): #iterate over each geo
        targets_data = mesh[geo]["blendShapes"]
        for i in range(len(targets_data)):
            target = targets_data[i]
            points = target["P"].value()
            normals = target["N"].value()
            id = target["id"].value()
            name = target["name"].value()
            print id, name

Importing meshes

Create a new scene and import the man variation table. From the atoms menu execute Atoms > Variations > Import variation JSON. Select the variations.json file from the AtomsHoudini\18.5.521\data\variations folder. This will load the man variation table into the scene.

Open the variation manager from the atoms menu: Atoms > Variations > Agents Variation Manager. Select the man from the column on the left and then go inside the Geometry tab. Replace the hair01_GEO path with the mesh you just exported. Now press ctrl+s or from the widget menu execute File > Register to Atoms to save the changes.

Setting up variations

• Create an agent group node.
• Add a grid layout and set the grid size to 5,0,5
• Add a state machine module
• Add a variation module and set the variationName attribute to "casual_1"
• Change the display type to variations
• Rewind the scene

Setting targets weight

The target weights are controlled by double metadata. The metadata name should follow this convention:

AgentTypeName_VariationGeometryName_TargetIndex

In our case, the following metadata names are valid:

• man_hair01_GEO_0
• man_hair01_GEO_1

The target index is the Houdini blend shape deformer order, so the 0 index is the first blend shape, the 1 index is the second one, and so on.

We can add and control these metadata using the AddMetadata module

• Add an "AddMetadata" behaviour module
• Set the name attribute to man_hair01_GEO_0
• Set the type attribute to double
• Set the double value attribute to 1.0
• Rewind the scene

Try to add more addMetadata modules on the same agent group to control the man_hair01_GEO_1, etc.. metadata. You can also add keyframes on the doubleValue attribute to animate the blend shapes.

Blend shape manager

You can handle blend shapes more easily with the blend shape manager module.

Remove all your addMetadata modules and add a "blendShapeManager" module to your agent group. In blendShapeManager attributes, click on the "Manage Blend Shapes" button, the UI on the right will be prompted.

From there, you will select the blend shapes you want to add to the agent group. 

You can select/deselect blend shapes by double-clicking or using the button on the top of the list. 
Please be careful when clicking the "Expand" buttons, as it could take some time to populate the entire tree if you have a lot of variation geometries.

Click on the tick button on the bottom right corner. The blend shapes will now be visible under the blendShapeManager attributes tab, where you will animate them.

Adding animation

To add more complex animation or animation cycles to the blend shapes, we can use the blendShapesAnim module. Before you can use this module, you have to export some animation curves from your setup scene. Open the man scene where you created the blendshapes and add some keyframes on the blend shape deformer's target weights.

Now select the hairs and open the blend shapes anim exporter from the atoms menu: Atoms > Export > Blend shapes anim exporter.

Set the output path and the frame range, select the head mesh and press the run button.

Go back to the atoms scene and remove the blendShapeManager module.

Add a blendShapesAnim behaviour module and click on the "Manage Animations" button under the blendShapeAnim tab.

Click on the "+" button for adding a new animation, select the "hair01_GEO" in the Geo field and set the path to the animation file we just exported. Leave the property to loop (no property will play the blend shapes animation once).
You can, of course add multiple animations, but we will stick with one for this example.

Click on the tick button, and you will see this data being converted inside the "animData" parameter.

Press play, and you will see the blendshapes being animated in a loop inside the viewport.

Click on the "Manage Animations" button again and activate the "Enable Trigger Metadata" checkbox. Type "triggerAnim" as the name for your metadata.

Create an addMetadata module and place it before the blendShapesAnim module. Set the name attribute to triggerAnim, change the type to double and set the doubleValue to 1.0.

Now rewind the scene and press play. The result will be exactly as before.

Let's use an area trigger to drive the metadata.

First, let's change the agent state to 1 inside the state machine to make them walk. Inside the addMetadata module change the double value to 0 (the area trigger module will drives this value). Now create an areaTrigger module and create a plane in the scene. Connect the plane to the areaTrigger module (remember to connect the translation/rotation/scale) and set the metadata name attribute to triggerAnim, the double value to 1.0, the blend in and out to 10 and the random delay in and out to 5. Move the area trigger above the blendShapeAnim module. Rewind the scene and press play.