Group
The Group node picks out some of the points or fibres, by where they are or with an expression, and gives them a group name. Later nodes can then work on just that group: enter the group's name in another node's Group parameter to limit that node to the grouped points or fibres. For example, you could group the fibres on a character's tail and curl only those.
When the Yeti node's Draw Feedback is on and the Group node is the Root, Yeti highlights the grouped points in the viewport.
Inputs
| Input | Accepts | Description |
|---|---|---|
| 0 | Fibres or Particles | The objects whose elements to group. Elements are grouped by their ID, so objects without IDs, such as meshes, have nothing grouped. |
| 1 | Mesh | Optional. The mesh to use in Bounding Object mode. |
Parameters
| Parameter | Description |
|---|---|
| Group Name | The name of the new group. If it's empty, the node does nothing. |
| Mode | Bounding Volume (the default) groups elements inside a sphere set by Origin and Radius. Bounding Object uses the mesh connected to the second input. Expression uses the Expression to decide whether each element is in the group. |
| Origin | In Bounding Volume mode, the centre of the sphere. |
| Radius | In Bounding Volume mode, the radius of the sphere. |
| Expression | In Expression mode, the expression to evaluate for each element. An element is grouped when the result is 1 or more. For example, $P[1] > 0.5 groups all of the elements whose Y position is greater than 0.5. |
| Sidedness | In Bounding Object mode, whether elements Inside/Below or Outside/Above the mesh are grouped. Close To Surface groups elements near the mesh's surface. |
| Distance From Surface | With Close To Surface, how close to the surface an element must be to be grouped. |
| Attribute | The vector attribute to test. This is usually P, but you could use N, for example, to group by the direction of the normal. |
Each element is grouped as a whole: a particle by its position, and a fibre by its root.
Example
This example groups the points of a sphere that are below an animated plane, then grows fur only from those points.
First, create a sphere and a plane, and scale the plane to 5 units.
Next, add a Wave deformer to animate the plane. You can animate the plane any way you like, but a wave shows off the Group node well.
Set the Wave's Amplitude to 0.15 and its Wavelength to 0.5, and add the expression wave1.offset = frame * 0.05; to its Offset. The wave now animates and intersects the sphere. You may also want to template the plane, so it's easier to see.
Now create the Yeti node. Select the sphere and click CRM (Create Yeti Node On Selected Mesh) on the Yeti shelf. This creates a Yeti node with the sphere as its input.
Open the Yeti node's Attribute Editor and, in Graph > Input Objects, add the plane to the list of input objects. Make sure you select the plane's shape, not its original (intermediate) shape.
Now build the graph. Open the Graph Editor and create an Import node. In its Inspector, set Selection to the sphere's shape (for example, pSphereShape1), so the node imports only the sphere. If you leave it at the default, *, it imports all of the input objects, so it's a good idea to be explicit. Make the Import node the Root, and Yeti draws the sphere in your scene.
Connect a Scatter node to the Import node, and set its Density Multiplier to 20. Create another Import node, with its Selection set to the plane's shape. Then connect a Group node to the Scatter node, making sure the Scatter node is connected to the Group node's first input, and connect the plane's Import node to the Group node's second input.
Make the Group node the Root and, in its Inspector, set Group Name to wave. All of the scattered points are highlighted in red, showing that the wave group now contains them all. By default, the Group node uses a bounding volume set by its parameters, so change Mode to Bounding Object. Now only the points below the deforming plane are grouped.
With the Yeti node selected, scrub the timeline, and the group updates with the animation.
Finally, connect a Grow node to the Group node. Leave its settings at their defaults, but enter wave in its Group parameter. The fur now grows only from the grouped points.
This is only a basic introduction, but it shows how powerful groups can be. You can create any number of groups, and with expressions the possibilities grow even further.