Hair System

Hair System¶

Overview¶

Hair System Diagram

Hair System assists you in creating procedural hair strands in a non-destructive way, utilizing Blender's Geometry Nodes technology.
Hair System is made from:

A setup section to assign a guide curve and source mesh
Hair sub-systems with generators and Deformers to create and modify strands
A hair profile to add geometry, UVs, and materials to strands

Hair Sub-Systems in stack can communicate together with usage of Tags - this help to describe which Hair System is affecting which strands.

Hair System is located in Right Sidebar → Hair Tool Tab → Hair System Panel. Click [+] to add Hair System to selected mesh or curve object.

Hair System UI On image above we have Two Hair Systems named: Parent, Child. You can see Child system is made from: Strand Generator, Noise, Clump, Set Radius etc. deformers. Whole system is guided by: HairCurve guide - second input at very top

Strands generated with Hair Systems are then passed to hair profile generation system, which convert these strands to hair-cards.

One Minute Hair Setup¶

Below I show you demo of how to setup game ready hair in 1 minute:

Full setup (with audio) starting from scalp mesh, drawing few guide strands and generation of denser interpolated child strands

Text description of steps:

Select scalp mesh, and go to Draw Hair Panel > Enable Draw Hair
Hold D key, and draw guide curves with LMB (default Hair Material and UVs will be automatically assigned to them)
You may need to adjust flat profile width
Add Hair System > Strand Generator type,
In Hair System > Deformers sub-panel > Strand Generator > increase strands density (value depends on size of your object)
Adding Deformers:
- Noise - it will break the even look of hair
- Align Tilt - it will force hair cards to face scalp surface
- Optional Radius Set - it will taper the haircards
Ctrl+Shift+H > Convert Hair to Mesh (or you can use Finalize, to create mesh copy of HSystem)

That is it, you can now export generated mesh to Game. If you want, you can restore curve hair object with Ctrl+Shift+H > 'Restore Hair Object' - and continue working on it.

Two Minute Hair Setup¶

In video below we make hairstyle with split.

Full setup - starting from scalp mesh, and ending with mesh haircards ready for export

Above we used option of selecting strands by mesh island > see Strand Selection section.

Transfer Hair System¶

Hair System can be assigned to Mesh or Curve Hair object, depending on which object is selected when you add Hair System. If you want to change Hair System 'owner' you can use Transfer Hair System operator. System Owner

Hair System that generates hair-cards (in center above) can be assigned to:

Source/Base Mesh mesh from which strands are spawned from (often scalp mesh)
Empty Mesh helper, without geometry, usually linked with Source Mesh and Guide Curve
Guide Curve curve object that guides strands
Empty Curve helper, without geometry, (usually linked with Source Mesh and Guide Curve)

Hair system transfer possibilities:

Current Owner	Transfer To	Result
Guide Curve	Base Mesh	Hair System will be moved to Base Mesh Surface (usually scalp)
Guide Curve	Empty Mesh	Hair System will be moved to new, empty mesh object
Empty Curve	Base Mesh	Hair System will be moved to Base Mesh Surface (usually scalp)
Base Mesh	Guide Curve	Hair System will be moved to Guide Curve
Base Mesh	Empty Curve	Hair System will be moved to Empty Curve Hair object
Base Mesh	Empty Mesh	Hair System will be moved to Empty Mesh object
Empty Mesh	Guide Curve	Hair System will be moved to Guide Curve
Empty Mesh	Base Mesh	Hair System will be moved to Base Mesh

Visually, there should not be any noticeable difference. However, the owner of the Hair System will change
User cases when you want to use Transfer Hair System:

if you want to 'Bake' curves generated by Hair System to curve, but it is assigned to Mesh (meshes cannot receive curves geometry). In that case you can transfer Hair System to Empty Curve, and then bake it to it
if hair interpolation is broken (e.g. stops working after you select and try to sculpt Guide Curve. See note in Hair Interpolation section

General Operations¶

General Operations

Remove whole Hair System - removes all Hair Systems, Setup and Profile modifiers from object
Update Whole Hair System - updates Setup, Profile, Hair SubSystems (without deformers) nodes. All nodes are recreated from scratch, it is destructive operation and may break your Hair setup!
Bake All SubSystems - bake curves generated by All Hair sub-Systems into 'real' curves geometry. This works only on hair curve type of objects (try: Ctr+Shift+H > Transfer Hair System: to Empty Curve, or to Guide Curve)
Transfer Hair System - explained here

Sub-Systems Types¶

After adding a Hair Sub-System, you'll see the first slot in the deformer stack is added automatically. This is determined by the selected hair sub-system type.

Strands Generator¶

It will grow strands, from Base Mesh surface. You can control parameters like: resolution, density, length, interpolation (Parent Child relation must be set) etc. These strands are affected by all subsequent deformers in current system stack

Set parent Tags and enable interplation option, so that generated strands will follow these Tagged strands. See Child Parent Setup

Align to Surface Normal¶

Align to Surface Normal - option changes how the interplation works. Do not confuse with Align Tilt To Source Surface

Strands Distribution¶

Poisson distribution is a better way to spread things out evenly than just randomly placing them.

Here's why:

Imagine you're trying to place hair strands on a surface.

Random placement: You might end up with clumps of hair in some areas and gaps in others.
Poisson distribution: This method makes sure the hair is spread out more evenly. It does this by removing any hair strands that are too close together.

Random vs Poisson Left: notice the clumping of hair roots; Center: Poisson distribution helps to remove these clumped dots (colored in black), by removing roots that are closer than Min Distance parameter. Right: Increase Density parameter to fill up the empty spots

Strands Filter¶

This hair (sub)System type lets you affect existing hair strands - whether these strands are:

'real' (for example generated with Hair Drawing),
or generated procedurally by another Hair subSystem > Strands Generator.

This way you can e.g. add Noise effect to all existing strands (or make them curl, taper etc).
There is option to affect only selected strands, by filtering them with TAGs.

Imagine you want to modify two Hair Systems, by adding Set Radius or Align Tilt. Instead of applying these deformers to each individual Hair subSystem, you can utilize the Filter System to affect all strands simultaneously.

Demo of applying 'Scale' deformer to strands generated with Right Tag

Note: If no filter tag is specified, then all strands will be affected

Strands From Grid Surface¶

This type of Strand Generator, will guide strands using guide mesh (grid mesh, made of quads only). Root of strands will be placed:

on edge loop marked as Sharp (Ctrl+E -> Mark Sharp)
or on crease edge (Shift+E -> Crease Edge).

These strands can be affected by all subsequent deformers in current system stack

In video above - top, boundary edge loop was marked as sharp

Note: Notice how guide grid, in video above, has uneven topology - getting dense to the right. This is important when adjusting 'Uniform Spacing' option

Note: To mask-out placement of roots, just plugin in vertex group mask into 'Placement Mask' input

Examples of proper grid guide topology: Bad Grid Mesh Check out the FAQ to see examples of wrong mesh topology

Interpolated Strands¶

This Strand Generator, will use existing curves add extra strands in between them. In that case order of strand matter!

In video above I used drawn strands to guide the 'Interpolated Strands' generator (video is narrated)

Note: If order of your strands is wrong, and Automatic Spline Sorting option fails, you can use Sort Strands by Stroke operator to manually fix the order (see video above)

Child - Parent setup¶

Linking two Hair SubSystems, with Child-Parent relation, enables capabilities such as: interpolation, clumping, curls, braids, twist and others.
Use Tags to link two Hair SubSystems, establishing a parent-child relationship.

In the video above, I show how to make the red strands (called "ParentSys") the parent (guide) for the yellow strands (named "Child"). You can use any tag name you want. In this example, I used "RED".

Note: Parent Hair System has to be placed above Child System in the stack, or else Child strands won't 'see' the Parent strands

Hair Interpolation¶

To enable hair interpolation, current Hair System has to have parent - see above.

After that Toggle Interpolation button will be accessible (enabled by default) in first deformer - Strands Generator properties

Note: In some cases interpolation may behave erratically (e.g interpolation breaks when you select Guide Curve). The most likely cause is - cyclic dependency:
- Guide curve depends on your base mesh (usually scalp),
- Base Mesh (with Hair System attached) depends on guide curve (through enabled interpolation to Parent - Guide Curve).
To fix it and break the cyclic dependency use Transfer Hair System and move Hair System to either Empty Mesh or Guide Curve.

Since Hair Tool 3.0 and later versions, strands interpolation operates within areas surrounded by mesh islands - meaning, if you want to make hairstyle with split:

split scalp mesh in two, without separating to new object, (e.g. select edge loop, that divides the scalp in half - and press 'V' to rip it). Now child strands will not cross this edge.

In video above I have cut mesh in 4 parts (visualised with 4 colors). Strands won't cross islands boundaries

Note: If you want to make hairstyle with split, you can use Select By Island to select guide strands from specific island

Note: instead of splitting the edges physically, you can use the Edges split modifier

Sub-Systems Menu

You can copy settings from any hair system, and paste to target using entries above.

Bake¶

Procedurally generated strands cannot be groomed. First convert them into 'real' geometry with 'Bake' operator. This will bake: active (and preceding) Hair sub-Systems or All Hair sub-systems into 'real' curve geometry, that can then be groomed using Blender 'Curve Sculpt' mode.

Note: Baking works only if Hair System is attached to hair curve type of objects! If not the use: Ctr+Shift+H > Transfer Hair System > to Empty Curve or to Guide Curve)

Curves in video cannot be groomed, since they are generated procedurally. After baking, you can groom them without issues

Update Node Pack¶

Update selected Hair Components (geometry node setup) to its latest version, for example after updating add-on

Copy/Paste Hair System¶

Copy Hair System settings from: Active Hair sub-System or All sub-Systems

Paste Hair System settings to: Active Hair sub-System or to All sub-Systems

Copying All SubSystems (and profile settings) from one object to another. Receiving object has to have at least one Hair subSystem attached. Also make sure both objects share same vertex groups, similar sharp (or crease) edges - if you copy Curves From Grid type of setup

Switch Hair System Type¶

Switch Hair System Type - for example from Strands Generator to Strands Filter.

Hair System UI Pasting Hair System settings (or instancing object that uses Hair System), will create linked copy. This means that change performed on new copy, will affect original Hair subSystem too. Number of Hair System users is displayed next to Hair Tag (green box in image above)

Note: You can unlink Hair System, by clicking on 'users number' (see green box above)

Tags¶

Think of Tags as labels we apply to the strands in a Hair System. They enable us to establish child-parent relations or manipulate specific strands with strands filter. Why won't we use system name for that functionality? The reason is, that you can assign multiple tags to same strand e.g.:

Hair System A strands Tags: LONG and CURLY.
Hair System B strands Tags: LONG

Now you can modify strands tagged with LONG label - using Strands Filter, without having to create same deformers on Hair System A then B twice.

Tags can be also assigned to subset of strands from within Hair System with Assign Tag deformer.

Hair System Tags In image above we tagged 'First' Hair System A with label. 'Second' and 'Third' system are linked to it - which allows us to use e.g. interpolation on them. Note: Guide curves received GUIDE tag automatically

Tag can be assigned in few ways:

by typing it in next to system name see A tag in image above. If system has no tag assigned then [TAG] label is shown
by using Assign Tag deformer
you can also assign tags to Hair System guide object (new Curve Hair) using Tags Panel. See Below

Tags Panel¶

In video above we create Tag A, then assign selected curves to tag A using Assign button

Note: Assigning Tags only works on new Hair Curves. To be able to select individual curves, like in video above, you have to use Hair Modeling mode. For now only selection works from all the available Modeling Tools

Hair Deformers¶

Deformers gives you ability change chair look - add noise to hair, make them curl, snap to surface etc. They are stacked one on top of each other in similar way than Blender modifiers. They can be reordered. Some deformers (e.g. clump, twist, braids) will only work, if Hair System, to which deformers belong to is Set as Child

Animation¶

Attach Curves UV¶

Attach strands roots to source mesh UVs, without it animation of hair with 'Surface Deform' modifier will not work.

Bake/Cache Hair¶

Save hair strands into cached memory. They will no longer be editable, but will be faster to animate, since they will not be re-generated on every frame change.

Surface Deform¶

Same as blender built-in modifier. Allows hair to follow source mesh deformation (by rig or shape keys).

Note: You may want to use Bake deformer first, so that strands will not be regenerated on every frame

Physics¶

You can add collision objects, control: wind, gravity, damping etc. Not perfect yet, but can give some nice results. For more advanced physics simulation we may need to wait for native blender geo-nodes physics integration.

Note: You may want to use Bake deformer first, so that strands will not be regenerated on every frame

Note: If you notice some jittering, try reducing gravity and increasing damping.

For now self collisions are disabled, since you would have to subdivide strands a lot, to get good results. Long hair simulation may not look the best. But at least new HTool 4.x physics does not exploade like it used to in HT 3.x

Assign Group ID¶

Assign Group ID attribute to strands. After baking hair system you can use this to select strands by group ID.

Braids (Child)¶

Clump child strands to Guide/Parent strands (FIRST tag) in shape of Braids. Set Hair System as child first

Color Set (System)¶

It will alow your to colorize haircards generated inside current hair system (added mostly for debugging hair sub-systems setups)

Clumps (Child)¶

Clumps child strands toward parent strands. Set Hair System as child first

Curls¶

Clump child strands to Guide/Parent strands (FIRST tag) in shape of Curls. Can be used with Hair System as child first

Generators¶

Duplicate Strands¶

Simple duplication of exisitng strands

Braid Generator¶

Each strand will be duplicated 2 times (3 strands with original one), and braided together. Works best with 'Circular' Profile

The Idea in above video is:

Take single strand, and convert it to 3 braided ones with 'Braid Generator'
Duplicate each sub-strand few times with Duplicate Strands deformer
Add some randomization with Noise deformer and UV Region Distribute deformer

This should make it more volumetric looking, since braid will be made from multiple textured haircards, rather than single one.

Instance on Strand¶

Instance any mesh on hair Strands (can be used to eg. add tie and tail on the end of braid) - since HTool 2.44

Mirror¶

Mirror hair, with optional option of bisect (remove one half of hair first, then mirror the remaining part)

Move in/out of Surface¶

Embed Roots¶

Helps to push hair roots into surface. Best to used before Align Tilt deformer, since it can lead to haircard twisting

Push Out¶

Push hair outside surface. Useful when wanting to push out layer of hair or to prevent hair clipping through character geometry

Attach To Surface¶

Attach hair to surface. Useful when wanting to 'glue' hair to character geometry (scalp)

Move to Border¶

In the video above, a source mesh is created using two half-sphere meshes. We use the "Move to Border" deformer to move the strands to the edge of this mesh. Then, we apply the 'Track To Mesh' deformer, to clump tips of strands together

Snap¶

Snap hair to source surface (could be used for wet hair effect)

Lengthen¶

Lenghtens hair strands. Unlike simple scale - it will make hair extend from the tips

Noise¶

Add noise distortion to strands

Radius Set¶

Set Radius - for hair tapering, strand width randomization, etc. Can also guide Curls amplitude or Braid size - for child Hair Systems

Roll Strands¶

Basically the same as blender build-in Roll

Scale¶

Scale hair up or down. With trim deformer we can reduce length of hair, but Scale deformer helps to make them longer.

Simplify Strands¶

Resamples strands - assigning lower points count to shorter strands

Slide Points¶

Give more resolution to hair root or tips (depending on 'Influence Range'), by 'sliding' points along the curves

Smooth Strands¶

Smooth out the strands

Tag¶

Assign Tag¶

Here we assign R tag to right side of head (masking it with vertex group). Then in 'Scale' Hair System that is set to Strands Filter we resize these tagged strands with Scale deformer

Note: Assigning any tag e.g. X will create negative tag 'X, for example if we create tag RIGHT with some strands, then tag 'RIGHT will contain opposite set of strands.

Delete Strands¶

Simple delete strands operation based on their Tag. In video above I removed strands tagged as R then GUIDE strands (bit hard too see, since they are covered by other strands)

Tilt¶

Add Tilt¶

Add tilt to hair strands. If 'Flip Probability' is 0.5 - then half strands will be rotated clockwise and half counter clockwise

Align Tilt¶

Aligns tilt to hair source surface (hair normal will point outside of surface)

Align Tilt to Parent¶

Aligns tilt to Parent (Guide) strands. Hair card backfaces are shown in blue. Great for Dragon Ball hairstyle :)

Align Tilt to Target¶

Aligns tilt to target surface (hair normal will point outside of target surface)

Align Tilt to Mesh Border¶

Align strands tilt to border of source surface (usually scalp). Backfaces are shown in blue

Force Align if checked, it will align curve and force curve normal to point outside border edge. If unchecked, tilt will be aligned to border, but curve normal will point with the 'flow' - see video above.

Track To:¶

Track to Mesh¶

Track to Mesh - Strands from closes mesh island will follow tracked mesh object. Use Bind button to prevets hair tips from 'sliding' on mesh surface

Note: Closest affected island is determined by Tracked object origin. Move it to change which island will be affected. After finding desired island, you can move tracked object in edit mode, so that affected strands won't change.

Note: If you want to 'Freeze' tracked points, use 'Bind Tracked Mesh' button. Now strands will follow point at which they were bound, rather than sliding around mesh surface.

Track to Curve¶

Track to Curve - Strands from closes mesh island will follow tracked curve object. Use Bind button to prevets hair tips from 'sliding' on tracked surface surface

Note: Closest affected island is determined by Tracked object origin. Move it to change which island will be affected. After finding desired island, you can move tracked object in edit mode, so that affected strands won't change.

Note: If you want to 'Freeze' tracked points, use 'Bind Tracked Curve' button (this will convert 'old' curve to 'new' type). Now strands will follow point at which they were bound, rather than sliding around curve surface.

Note: Curve Shape Keys are great addition to Track To Curve deformer.

Trim¶

It will shorten strands roots and/or tips. Best to use with randomization mask

Twist¶

Twist effect requires to set Hair System to be set as child. For best effect is is good idea to place it after Clump deformer

Profile Distribute¶

Mesh Profile or Multi Curve Profile holds profile objects list for instancing on strands, but it does not tell which strand will receive which profile object. This is where 'Profile Distribute' deformer comes in.

It will tell which strand will receive which profile object, based 'Profile_ID' attribute, assigned to each strand.

You can use multiple 'Profile Distribute' Deformers, and stack them on top of each other (think of them as layers). In video above, I used RED and GREEN profile objects as base layer, then added PURPLE on top - masked by vertex group

UV Region Distribute¶

Hair Profile holds UV Boxes/Regions amount and dimensions, but it does not tell which strand will receive which UV Region. This is where 'UV Region Distribute' deformer comes in - it will assign random (or masked) UV Region to each strand.

Note: use multiple 'UV Region Distribute' deformers + Input Masks, to achieve layered UVs effect (see video below),

Example use of multiple 'UV Regions Distribute' Deformers, to stack them on top of each other (as layers). Region ID_2 as base layer + Region ID_0 on top - masked by vertex group

Note: UV Region Distribute is often created automatically when hair system is added

Input Masks¶

You can mask most of the hair deformers inputs with various kind of effects. Multiple masks can be added.

Note: The order matters: first top mask is evaluated then next to the bottom

To add mask click drop down menu icon on right and pick mask type

Border Edge Distance¶

Border Edge Distance: mask an effect based on strands distance to border of source mesh. Above we used Align Tilt to Mesh Border deformer, to align tilt only on strands that are closest to mesh border. It has invert option too.

Curve Attribute¶

Curve Attribute: Use Curve attribute to mask hair effect. This is intended to be used with Edit Curve Attribute feature in HTool

Vertex Group/Texture¶

Vertex Group/Texture: Use vertex group or texture for input masking

Object Vertex Group/Texture¶

Same as above, but samples vertex group/texture from custom object

Radius Mask¶

Radius Mask: Mask an effect based on strand radius. In video above I reduced noise on braids, at thinner places.

Offset/Gain¶

Mask Offset Gain: Not useful by itself, but placed after another mask, it can increase the mask contrast (gain) or brightness (offset)

Invert¶

Invert: Not useful by itself, but placed after another mask, it will invert the previous mask effect

Randomize¶

Randomize: Outputs random value for each strand.

Random value will be picked from within [x-RandRange; x+RandRange] bounds, where x - is any input value - e.g. from vertex group mask
You can disable lower/upper bound using </> buttons, thus limiting Random value range.

Rand Range - 0 - no randomization; 1 - maximum randomization
Variance < 0.5 outputs mostly smaller values, from within given range,
Variance == 0.5 all random values are drawn uniformly, from within given range,
Variance < 0.5 outputs mostly bigger values, from within given range,
Use Parent IDs - if enabled each child strand will inherit random value from its closest parent.

Length Mask¶

Assigns Min value to the shortest strands,
Assigns Max value to the longest strands.
Swapping Min and Max values will invert the effect

Procedural Mask¶

Procedural Mask: Use procedural noise texture to randomize hair look. No need for UVs

Min, Max - bring these values closer together to get sharper noise transition,
Scale - the bigger scale the more detailed the texture will be,
Distort - distorts the noise,
Offset - offset the noise sampling position

Influence Range¶

Special mask that allows to modulate influence of deformer over strand length (e.g. taper only tip of strand). 0 - no effect, 1 - maximum effect

Types of Influence range masks:

Constant - the effect is uniform along the whole strand length
Simple - gradually changes the influence from 0 to 100%. Influence can be flipped using invert button
Quadratic - gives more detailed control: modulate effect independently at strand beginning, center and end
Profile Curve - most detailed control using profile curve

Updating¶

After updating Hair Tool add-on, you may need to update your Hair Setup:

There is option to update Individual Hair System elements (Deformers, Masks, Profiles etc.) - located in Deformers dropdown menu
Setup and Profile node (green and blue box on image below)
Update Whole Hair System located in General Menu - this will update all nodes, in all Hair Systems for all objects on scene. Be warned though: add-on will try to recreate whole node tree structure from scratch, so this may now always work.

Updating Hair System Nodes You may update deformer, profile, mask etc. nodes using menu above

Note:: Using individual node packs update (only Deformers, or only Masks etc.) method is usually safer.

Limitations¶

~~Only One UV box can be assigned to profile - you can use Mesh Profile with multiple meshes as a workaround for randomizing UVs~~ (No longer the case Since HT 2.44)
Hair Modeling Tools do not work (except selection)
Hair interpolation is using booleans under the hood. Because of this, interpolation may fail if boolean fails. And Interpolation may be slow on heavy base meshes (I recommend using lowpoly hair surface meshes). Hopefully I will find better way in the future, to create interpolations. (No longer the case since Blender 3.5 and Hair Tool 2.44)

FAQ¶

I get Errors in console¶

If you open old blend file with old Hair Tool setup, after you updated Hair Tool, you may get some errors, and UI wont be drawn correctly. Use Update Whole Hair System located in General Menu - this will update all nodes, in all Hair Systems for all objects on scene

Warning this is potentially destructive operation, since whole node tree will be recreated from scratch. Updated nodes behavior may change, resulting in slightly different hair look

Hair Interpolation won't work¶

In some cases interpolation may behave erratically (e.g interpolation breaks when you select Guide Curve). The most likely cause is - cyclic dependency between Base Mesh with attached Hair System and Guide Curve. See note in Hair Iterpolation section.
To fix the cyclic dependency use Transfer Hair System and move Hair System to either: Empty Mesh or Guide Curve.