The scatter points will be the seeds for the feathers and there’s a versatile node to create those points on any surface. Before you can create the points, you need an object or a character.

1. Add a Test Geometry: Rubber Toy SOP.

2. Set Uniform Scale to 0.5 to make Flippy smaller.

3. Put down a Hair Generate SOP and connect its first input with the output of the toy. This node uses the connected object’s normals to create guides. The feathers will then follow the guides.

4. On the Total Count parameter you can define the exact number of feathers. Start with a value of 5000.

5. Go the Unguided Hairs section and change Length to control the size of the feathers. In later chapter you can see how to use an attribute for randomizing the parameter.

6. Add a Guide Tangent Space SOP and connect its first input with the first output of the hair generating node. This node takes the normal direction of the guides' root points to orient the feathers correctly.

7. From the Normal Mode dropdown, choose Constant Normal Vector. This option uses the Normal Vector parameter to determine the value of the barborient attribute.

8. Turn off Normal Name and Tangent Name. They're not required and would only allocate resources.

9. Turn on Orient Name and replace the default entry with barborient.

You won’t see any changes in the viewport when you adjust orientation. The effect of your settings will kick in when you add the feathers.

Right now you have to separate network streams: the feather and the groom guides. The following node brings everything together and applies the feathers to the guides.

1. Lay down a Feather Template Interpolate SOP and connect its first input with the output of the tangent space node. The fourth input is linked to the output of the FEATHERGEO null.

2. Go to the Templates section. From the Lookup Method dropdown, choose Group. Since there’s only one feather template in this project you don’t have to specify the Template Group. The node just takes the first template it gets from its fourth input.

3. Add a Null SOP and connect its input with the first output of the interpolate node.

4. Rename the null to GROOM.

5. Turn on the null node’s blue Display/Render flag to see the feathers.

If everything is correct, you should get a result that is similar to the image below.

When you look at image you’ll notice that the feathers are placed all over the toy. You can find feathers on the eyes and nose, the bottom, the flippers, and so on. To make the feathers appear on the toy’s upside only, for example, you can use a wrangle. There you create a slope attribute together with a custom Threshold parameter (chf("threshold")) to control the distribution of the guides.

The slope attribute calculates the dot product from the vertex normals and an up vector that points into Y direction. Both vectors are normalized. The result is then fit into a range between 0 and 1 to make it more controllable. If the dot product is greater than the given Threshold, slope is set. This results in a mask.

1. Add an Attribute Wrangle SOP and place it between the toy and the hair gen nodes to connect its first input.

2. Copy ⌃ Ctrl + C and paste ⌃ Ctrl + V the complete code snippet from below to the wrangle’s VEXPression.

3. Click the Creates spare parameters… icon to add a custom Threshold parameter to the node’s UI. Now you can interactively adjust the value with the parameter’s slider.

   vector normal = normalize(v@N);
   vector up = normalize({0, 1, 0});
   float threshold = chf("threshold");
   float dot_product = fit(dot(normal, up), 0, 1, 0,1);
   if (dot_product > threshold) {
       f@slope = dot_product;
   }
   

4. On the Hair Generate SOP’s Distribution section, go to Density. From the associated dropdown, choose Skin Attribute.

5. For Density Attrib, enter slope.

6. Change Total Count if necessary.

You can also paint a mask interactively directly onto the character to define, where the feathers should appear. A convenient option lets you mirror your brush strokes to accelerate the painting process. Furthermore, it’s possible to manage several attributes through one paint node.

1. Add an Attribute Create SOP and place it between the rubber toy and hair generate nodes to connect it.

2. On the Name parameter, and enter density. density is a floating number and a point attribute.

3. Put down an Attribute Paint SOP and place it between the attribute create an hair generate nodes to connect it.

4. Open the Attributes tab and go to Attribute Name. Replace the default entry with density.

5. Click the Symmetry tab and turn on Enable Mirroring.

6. Select the paint node, hover the mouse cursor over the viewport, and press Enter to turn on the brush node.

   On the Brush tab you can customize the brush, e.g. by adjusting Soft Edge. The brush itself is displayed as a red sphere in the viewport that follows the character’s surface. You can change brush size interactively with the mouse_wheel.

   Keep the LMB pressed to paint your mask. Later, the feathers will appear on the brush strokes.

7. On the Hair Generate SOP, go to the Distribution section. Next to Density you can see a dropdown menu set to No Override. Change it to Skin Attribute. The default Density Attrib is density, so you don’t have to change anything here.

When you turn on the Feather Template Interpolate SOP’s blue Display/Render flag, you will see the feathers in those areas where you've painted the mask.

Now you have an attribute to control the Length parameter on a per-feather basis.

1. On the Hair Generate SOP’s Unguided Section, go to Length. From the associated dropdown menu, choose Skin Attribute. The Length Attrib has the correct entry already and you don’t have to change anything.

2. With Length you can change the global length of the feather: the attributes values are multiplied with the parameter value.