Houdini 20.5 Feathers

Working with brushes and tools

On this page

Brushes are used to modify the feathers, for example to create or emphasize certain structures or to change their orientation. The Guide Groom SOP provides a wide range of tools for brushing and shaping your feathers. When you select a Guide Groom SOP you can see a Tool dropdown menu that’s set to Brush by default. Open the menu to see the other options.

To activate and use the brush, choose a Tool and hover the mouse cursor over the viewport. When you press Enter, a HUD appears in the viewport’s upper left corner. The shortcuts and settings are different for each tool. You will also see a red circle or - when the default radius is very small - just a dot. This gizmo indicates the brush and its size is directly related to the node’s radius parameters. You can also use the to change brush size interactively.

Click the image to zoom.

When you browse through the tools, you will see that sometimes the brush is a flat circle and sometimes it follows the contours of the character. These two modes are called screen and surface. You can use most tools in screen and surface mode, while others like Plant only support the surface mode. To change brush size directly, open the Brush Options section.

Also on the Brush Options section, turn on or off Surface Brush to switch between the modes. If the checkbox isn’t accessible, you can only work in the tool’s fixed mode. Another important parameter is Softness. When you set Softness to 0, you will get a hard brush with no falloff. Here’s how the surface brush looks.

Multiple Guide Grooms

The Guide Groom SOP was designed to let you switch between its tools and work on your feathers with just a single node. However, it might be easier to manage your setting through multiple guides, esp. when you want to groom certain areas independently.

The most important thing to consider is that Guide Groom SOPs should not be chained, but used in parallel instead. With chained nodes, you’ll lose the input from the upstream guides. With parallel nodes there’s also one limitation to bear in mind: when you merge your guides together, the feathers' id has to be overwritten manually with the primnum attribute through a Primitive Wrangle SOP. Currently, there’s no tool available to perform this conversion automatically.

Tip

It can be efficient to draw feathers on the wings, and use the interpolation and guide processes for the body.

Feathers section

The Feathers section connects the feather template with the character. Turn on Create & Output Feathers to apply the feathers to the guides. Its usage is explained in detail on the Applying feathers page.

  • Feather Draw Mode let you decide how to display the feathers in the viewport. In networks with multiple Guide Grooms, the first node determines the mode for downstream following nodes.

  • Template Geometry SOP points to the node with the feather geometry, typically a Null SOP.

  • Template Group lets you choose certain feathers from a template by name.

  • You must press the Set Feather Settings button to turn on the Orientation Setting section’s Create and Maintain orient Attribute (see directly below for more information). This option creates a barborient attribute and uses the normal (N) attribute as up vector for the feathers.

The barborient attribute is required for aligning the feathers with the character’s surface normals. Orientation and the groom’s overall look also depend on two other toggles when you're in Draw mode. If you encounter problems or deformed feathers, then go to the Brush Options section and

  • turn off Interpolate Orient.

  • turn on Limit to Template Length.

Mirroring

Mirroring is not only a convenient way to accelerate your groom, but also to plant feathers and draw guides. You can find all relevant parameters in the Mirroring section of the Guide Groom SOP. A typical workflow is to draw guides on one side of the character and mirror them. Then you turn off mirroring and groom/brush each side separately to avoid an artificial look.

Mirroring will mirror existing feathers as well as any operations as they're applied. You can turn this on and off by pressing ⇧ Shift + M in the viewport. You can also create, move, remove, sculpt, brush, and edit feathers on either side of the character and the changes will be reflected on both sides. Once you turn off mirroring, your changes will all be preserved on one side of the character, so you won’t lose any drawn feathers or edits regardless of which side was changed.

Note

Unlike hair, some feathers have a “direction”, where the shaft is bent to the left or the right. Or the barbs have a certain shape that influences the bird’s flying characteristics. In grooms with left- and right-handed feathers you must consider the feather’s side option on the Feather Template from Shape SOP’s to get correct mirroring.

Segment count

When you draw guides, you will notice that the curves are not straight, but follow the motion of your mouse streaks. This often leads to curves with lots of irregularities. The guide’s shape will then be transferred to feather and this is not always wanted.

The reason, why the Guide Groom SOP produces curves, lies in the node’s Brush Options section. There you can find a Segment Count parameter. The default value of 8 is suited for hair, where a certain amount of curvature is required to get a realistic look. However, for feathers, this value might be too high and you can decrease the parameter to values between 2 and 4.

Radial menu

The groom tools also provide a radial menu. If you want to use this helper, go to the main menu bar’s second dropdown menu and choose Hair ▸ Grooming. When you're on the viewport, press C to show or hide the radial menu.

Selecting feathers

You can select individual feathers to manipulate them. When you do this, you create a group and your tool will be applied to this feathers/guides in that group. Once you're done, you can delete the group and your changes will be maintained. There are several ways to select feathers:

  • On the Guide Groom SOP. Next to Group, click the Select geometry from any available viewport. Hover the mouse cursor over the feather you want to select. When the shaft turn blue, click it to add it to the Group input field. Use ⇧ Shift + to multi-select feathers. Press Enter to add confirm your selection.s

  • In the viewport, press S to turn on the selection mode. (()LMB)-click or ⇧ Shift + -click the feather you want to select.

  • If you know the ids of the feathers, meant to be grouped, enter them to the Group input field, e.g. 1 5-7 9.

Brush options and tools

The Guide Groom node and the radial menu provide many tools to shape feather feathers exactly to your needs. Some tools and functions, however, are not really suited for feathers. The following list describes tools that make sense in conjunction with feathers and how to use them.

Drawing feathers

The Draw option lets you interactively draw guides from your perspective. By default, the guides are aligned to your view (projected into screen space) and will all be the same orientation. Each guide also has a default Segment Count of 8. This is typically sufficient for hair or fur. Note that too many points per strand could affect performance and create wavy feathers. You can also straighten a feather through the radial menu: see the Brushing and editing feathers below and look for Straighten feathers.

The tools and functions, listed below, are accessible through the node and the Grooming radial menu. If you can find the described options, make sure that the correct radial menu is turned on.

To...Do this

Draw guides in screen space

  1. Press C in the viewport to open the radial menu.

  2. Hover your mouse over Create & Move and choose Draw.

  3. Click the surface of your character to create the root, and drag with your mouse to draw the curve in the viewport.

Draw feathers on the skin of a character

  1. Make sure you're in Draw mode and press C in the viewport to open the radial menu.

  2. Hover your mouse over Tool Options to access the different draw options.

  3. Choose Draw on Skin.

  4. Click the surface of your character to create the root, and drag with your mouse to draw the curve along the the skin.

Change the default number of segments on a guide

  1. Select the guide in the viewport.

  2. Right-click the guide and choose Resample.

  3. Change the Segment Count and click OK.

    You can increase the points per guide for long and wavy feathers to smooth out any jagged looking pieces, or decrease the points for very short and straight feathers to speed up performance.

Change the default number of segments on all guides

Update the Segment Count parameter in the Brush Options section of the Guide Groom SOP.

This will save your preference for all future guides you draw.

Automatically create more segments as you draw longer curves

  1. Make sure you're in Draw mode and press C in the viewport to open the radial menu.

  2. Hover your mouse over Tool Options to access the different draw options.

  3. Choose Adaptive Segment Mode.

  4. Click the surface of your character to create the root, and drag to draw the guide. This option will automatically create points based on the length of your curve.

Spread out points evenly along a curve

  1. Select the curve(s) in the viewport.

  2. Right-click the curve and choose Redistribute Curve Points. This will keep the number of points, but evenly spreads them along the guide.

Draw a parting line to separate groups of hairs

Note

This tool is mainly suited for hair and fur, but it also works for feathers.

  1. Make sure you're in Draw mode and press C in the viewport to open the radial menu.

  2. Hover your mouse over Tool Options to access the different draw options and choose Parting Line Curve Type.

  3. Drag along the surface of your character to draw the parting line.

    This will create an invisible barrier so that when you interpolate hairs, they will only be influenced by the guides on one side of the parting line. This also applies to any sculpting, brushing, or editing operations you perform on the hairs. Please note that the Surface Brush has to be active. You can find this option in the node’s Brush Options section.

Planting feathers

The Plant option lets you interactively place feathers based on the closest existing curves. It will create these new guide feathers in the same orientation and interpolate the length based on the surrounding feathers.

To...Do this

Plant single guide feather

  1. Draw some guide feathers on your character. The tool will use the guides as reference point to interpolate length and orientation.

    It is also possible to restrict the tool to a selection of guides.

  2. Make sure you're in Plant mode and press C in the viewport to open the radial menu.

  3. Hover your mouse over Tool Options to access the different draw options.

  4. Choose Single Mode.

  5. Click to place single guide feathers that are interpolated based on the surrounding guides.

Plant multiple guide feathers

  1. Draw some guide feathers on your character. The tool will use the guides as reference point to interpolate length and orientation.

    It is also possible to restrict the tool to a selection of guides.

  2. Make sure you're in Plant mode and press C in the viewport to open the radial menu.

  3. Hover your mouse over Tool Options to access the different draw options.

  4. Choose Scatter Mode. This will give you a brush that lets you to paint clusters of guide feathers that are interpolated based on the surrounding guides.

Moving feathers

The Move option allows you to slide the roots of selected feathers along the surface without changing the orientation. This is very useful when creating feather lines or facial feathers on a character. Sometimes after sculpting feathers, you may need to clean up areas like this to push feathers back into place.

To...Do this

Move feathers at the root

  1. Select the feather(s) you want to move.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Create & Move and choose Move.

  4. Drag the feathers to slide them along the surface.

Relaxing feathers

The Relax option lets you push the roots of feathers apart if they're drawn too close together. It will try to spread the roots out evenly along the surface, so they're not too clumped together.

To...Do this

Spread out feathers at the root

  1. Select the feathers you want to spread out.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Create & Move and choose Relax.

  4. Drag the feathers you want to move in the viewport. This will smooth out the distribution of the feathers.

Removing feathers

To...Do this

Delete guide feathers

  1. Make sure the feathers you want to delete are selected.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Remove and choose Delete.

  4. Drag your brush over the feathers you want to remove.

    This will delete any feathers that you touch with your brush while holding in the viewport.

Thin out patches of feathers

  1. Select the patch of feathers you want to thin out.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Remove and choose Cull.

  4. Drag your brush over a patch of feathers to remove feathers.

    This will remove feathers and also redistribute them to reach a specific density. You can set the density using Density parameter in the Brush Options section.

Orienting feathers

Orientation plays an important role with feathers and this property is controlled through the barborient attribute. Here you can adjust and change orientation for singles feather or groups. To work with the Orient tools, it’s mandatory to turn on Create and Maintain orient Attribute. The most convenient way to do this, is to click the Set Feather Settings button in the Feathers section. This action creates the necessary barborient and N attributes.

To...Do this

Twist feathers around their shafts

  1. Select the feathers you want to orient.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Orient and choose Twist.

    When you brush over the feathers, their feathers are rotated around their shafts. When you drag the mouse to the left/up, the twist is counter clockwise, to the right/down it’s a clockwise rotation.

Orient feathers towards the camera

  1. Select the feathers you want to orient.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Orient and choose Face Camera.

    When you brush over the feathers, the feathers are rotated towards the camera or current point view.

Align feathers with their shafts

  1. Select the feathers you want to orient.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Orient and choose Align to Shaft.

    When you brush over the feathers, they're oriented along their shaft normals. In many cases you won’t see any difference.

Align feathers with the character surface

  1. Select the feathers you want to orient.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Orient and choose Align to Skin.

    When you brush over the feathers, they're oriented along the character’s surface normals.

Sculpting feathers

The options in the Sculpt menu allow you to Smooth, Clump, Blur, Sculpt, and Sculpt with Physics.

To...Do this

Brush feathers while maintaining the length

  1. Select the feathers you want to brush.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Sculpt and choose Sculpt.

    This will let you brush selected feathers while maintaining their length.

Tip

You can also select a single hair if you only want to brush one hair into place.

Brush feathers while keeping their offset from each other

  1. Select the feathers you want to brush.

  2. Make sure you're in Sculpt mode and press C in the viewport to open the radial menu.

  3. Hover your mouse over Tool Options to access the different draw options.

  4. Choose Edit Selection as Clump.

    This will treat the group of selected feathers as if they are one hair, instead of individual feathers. When you drag your brush over the feathers, they will maintain their offset from each other and not become pushed together. This is useful to move shaped feathers around as one piece without disturbing the overall shape, such as a tail of an animal or a braid of hair.

Remove the kinks from jagged looking guide feathers

  1. Select the feathers you want to smooth.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Sculpt and choose Smooth.

  4. Click the section of the hair you want to smooth in the viewport to smooth out any kinks.

    This option looks at the other points along the hair averages the point positions. You only need to click the sections with the kinks and then move the mouse to see them update. You don’t need to click and drag to brush the feathers.

Pull feathers together

  1. Select the feathers you want to clump.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Sculpt and choose Clump.

  4. Drag your brush over feathers to pull them together.

    This lets you to pull any feathers under the brush together into a clump. Holding and brushing will push the feathers apart.

Tip

This option is often used in combination with the the Smooth option, to create more natural looking clumps of feathers. You can use the Smooth option to remove harsh bends in feathers as they're pulled into the clump.

Average the direction and length of feathers

  1. Select the feathers you want to blend the transition between.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Sculpt and choose Blur.

  4. Click the group of hair you want to blur. This will only affect the feathers that are under your brush.

    This option is similar to Smooth, but instead of removing kinks, it allows you to align the orientation of feathers that are pointing in two different directions. It also changes the length of the feathers and tries to pull them all to be the same length. This is useful for blending the transition between sections of hair, so the separation isn’t so harsh.

Run a simulation on existing feathers

  1. Select the feathers you want to affect.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Sculpt and choose Sculpt with Physics.

    The default Tool Option is Settle Simulation Mode, which will take the selected feathers and run a simulation with gravity on them. Changing this to Damped Simulation Mode will let you brush the feathers in the viewport without them becoming too close together since they are colliding against each other with physics. This is useful to get a preview of how hair will act once it’s simulated.

Brushing and editing feathers

The options in the Brush & Edit menu are mostly designed to fine-tune your sculpted feathers or fix errors.

To...Do this

Stretch and rotate feathers

  1. Select the feathers you want to stretch and rotate.

  2. Right-click the selected feathers and choose Select Tip(s).

  3. Press C in the viewport to open the radial menu.

  4. Hover your mouse over Brush & Edit and choose Transform Handle.

  5. Use the transform handle to pull or rotate the selected feathers.

    Note

    You can use this Transform Handle on any point in the curve (not just on the tips) to pull or rotate any portion of the feathers.

Push feathers outside the collision object that have gotten stuck

  1. Select the feathers you want to free from the collision object.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Brush & Edit and choose Deintersect.

  4. Drag your brush over the selected feathers that have gotten stuck inside the collision object.

    Tip

    Once the feather is free from inside the collision object, you can use the Transform Handle to move and reposition it.

Rotate feathers from the root without changing the shape

  1. Select the feathers you want to rotate.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Brush & Edit and choose Brush.

  4. Drag your brush over the selected feathers to rotate them at the root.

    This will push feathers over and treat them as if they are rigid objects.

Push feathers away from the surface

  1. Select the feathers you want to lift.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Brush & Edit and choose Lift.

  4. Drag your brush over the selected feathers to lift them away from the surface.

  5. You can set a target Angle for the lift in the Guide Groom SOP’s parameter section.

Straighten feathers

  1. Select the feathers you want to straighten.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Brush & Edit and choose Straighten.

  4. Drag your brush over the selected feathers to straighten them.

    This option will keep the same orientation at the root.

Change the length of feathers

  1. Select the feathers you want to lengthen or shorten.

  2. Press C in the viewport to open the radial menu.

  3. Hover your mouse over Brush & Edit and choose Adjust Length.

  4. Hold and drag the selected feathers to increase the length or hold and drag to reduce the length of feathers.

  5. If you want to fine-tune the length of the feathers, go to the Guide Groom node’s parameter section and set Value to a small value, e.g. 0.02. Then, apply the again in the viewport.

Grouping and masking

Groups are used to separate different parts of feathers, for example feathers around the eye or tail. You can use the Geometry Spreadsheet pane’s Primitives switch to control if the feathers have been added to a group.

The Name Attribute on the Names section doesn’t have to be changed in most cases. It can be used to further subdivide groups, e.g. if you want to split wing_feathers into flight and coverts

Masks let you define areas where feathers will appear.

Note

A single feather or a selection of feathers can belong to more than one group.

To...Do this

Adding feathers to a group through brushing

  1. Go to the Guide Groom SOP node’s Group parameter section.

  2. Under Active Group enter a name for the group, e.g. wing_feathers

  3. The feathers, meant to be grouped, will get the entry from Active Name. Change this name if necessary.

  4. Press C in the viewport to open the radial menu, and go to Group & Mask.

  5. Drag the brush over the feathers you want to add the wing_feathers group.

Adding feathers to an existing group through selection

  1. Press S in the viewport and drag the mouse over the feathers you want to select.

  2. Open the Guide Groom SOP node’s Group parameter section.

  3. Under Active Group enter a name, for example wing_feathers.

  4. The feathers, meant to be grouped, will get the entry from Active Name. Change this name if necessary.

  5. Click Add Selection to Group.

Adding new feathers to an existing group

  1. Open the Guide Groom SOP node’s Group section.

  2. Turn on Add New Curves to Group

  3. Under Active Group enter the name of the group you want to add the new feathers, e.g. wing_feathers

  4. The new feathers will get the entry from Active Name. Change this name if necessary.

  5. Press C in the viewport to open the radial menu.

  6. Hover your mouse over Create & Move and choose Draw.

Change the name of a feather selection

  1. Press S in the viewport and drag the mouse over the feathers you want to select.

  2. Open the Guide Groom SOP node’s Group parameter section.

  3. Enter a new group name under Active Name, e.g. wing_feathers.

    The name can be different from the Active Group entry.

  4. Click Set Name on Selected Primitives.

Transform handle

This tool lets you stretch and rotate feathers.

  1. Select the feathers you want to stretch and rotate.

  2. Right-click the selected feather and choose Select Tip(s).

  3. Press C in the viewport to open the radial menu.

  4. Hover your mouse over Brush & Edit and choose Transform Handle.

  5. Use the transform handle to pull or rotate the selected feathers.

    Note

    You can use this Transform Handle on any point in the curve (not just on the tips) to pull or rotate any portion of the feathers.

Utilities

Utilities are a convenient way to ease resampling, twisting, and mirroring. You will find specific parameters for each tool in the Guide Groom SOP node’s Utility options. Utilities can be applied to one or more groups of feathers: If a group exists, add its name to the node’s Group field, and execute the utility.

Resample Utility

This tool lets you change the number of intermediate points interactively. Choose the utility from the Guide Groom node’s Tool menu, and go to Utility options. There, choose a Segment Mode and make sure that Preview is turned on to get a life preview in the viewport.

Drag the appropriate segment slider to increase or decrease the number of points. You can also consider using group names to differentiate between long ans short feathers, for example.

Click Apply to confirm your changes.

Twist Utility

This tool lets you curl the entire set of feathers or a group. In the Guide Groom SOP node’s parameter section go to Utility Options. There, turn on Preview to monitor your actions in the viewport. Drag the Angle slider or enter a fixed value. Click Apply to confirm your changes.

Mirror Utility

This utility lets you preview the mirroring process. Go the parameter section of the Guide Groom SOP node, and open Utility options. There, turn Preview on and off. This is useful if you want to evaluate the result of the mirroring process. In the Mirroring section you can find all associated parameters to adjust the result, as well as the Mirror Group field for restricting the process to selected groups.

In Utility options, click Apply to confirm your changes.

Feathers

Basic setup

Drawing and shaping

Brushing and grooming

APEX Add Groom

Simulation

Textures and rendering

Tools

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