Hair Shader

Overview

The hair shader is a dedicated rendering technique for rendering hair and fur. Hair rendering is a relatively hard task to achieve in real-time with high quality results due to the very fine geometry and specific lighting behavior.

The most recent implementation of hair shading strongly implies the use of alpha test in conjunction with soft alpha test enabled so the use of opacity is strongly discouraged since its visual result is prone to issues especially when sorting multiple polygons using opacity.

For Ryse, we relied heavily on the 3dsMax plugin Ornatrix to do our Hair and Fur work. Ornatrix was being used to generate both Highpoly source art as well as Lowpoly meshes that went into the game – specifically its powerful features in regards to lowpoly hair planes make it stand apart from other applications. You are not limited to using this tool but when it comes to the general process of developing your own asset workflows may be similar.

DCC Tool Setup

Types of Hair/Hair Geometry

This will be the base/foundation of most hairstyles. Depending on the hairstyle, it will either be a simple scalp plane, or a more complex shape that defines the volume of the hairstyle. In some cases it can also be sensible to break a hairstyle up into multiple large patches. This section will use the workflow as an example which you can hopefully adapt to your own process regardless of which tool you are using. The general idea is to first create a full hair setup, which is then baked down to simple chunks of geometry - resulting in a number of texture maps.

Diffuse

Color information from your hair system can easily be baked down to a flat texture, if you set the hair to mesh display mode (Ox Mesh from and Ox Render Settings). What usually works best is to bake down multiple maps and then comp everything together in Photoshop.

Color map

Ornatrix will color individual hairs based on the color of the growth objects at the hair’s root. A simple, hand painted color map with nice value shifts over the scalp (e.g. brighter colors in the temple area, etc.etc.) can create great results.

This method is especially useful for fur like pictured here:

Make sure to turn ‘Per-Strand UV Coords’ OFF (Ox Mesh from Strands)

Randomly scattered Colors/Materials

Ornatrix can randomly assign different material IDs to individual hairs - this allows for a generic ‘salt and pepper’ look. Useful both on its own and in combination with a color map (i.e. to get some ‘mutant’ hairs to break up the look). Assign a Multi/Sub material to the hair; set up 3-4 submaterials; in Ox Mesh from Strands, turn on Random Scattering and set the number of Material IDs.

Falloff

Its quite useful to bake down a falloff map, i.e. setting the hair tips to white, the roots to black. Note: for this to work ‘Per-Strand UV Coords’ must be ON.

Height/AO Maps

Other than the above, height/AO maps can also be very helpful for making diffuse maps. It can be useful to bake down AO/heightmaps from a hair system with fewer hairs and increased hair thickness (as well as increased number of sides for the Hair cylinder > Ox Mesh from Strands) – basically something that has a somewhat lumpy/clustery look.

When changing hair count, distribution+hair will be reset – meaning even if you revert back to the initial number of hairs, distribution and clustering will be different. Therefore it is not a good idea to change the number of hairs on the main copy of your hair system (if you have already started baking down other diffuse maps)

Normal Map

As above, its best to bake normal maps from a hair system with reduced hair count and increased hair thickness. Also, make sure not to use smoothing groups, and to set the hair cylinders to use more than 3 sides (in Ox Mesh from Strands)

Directionality map

Similar to normal maps, but instead the mesh must have per strand UVs (the UVs filling the entire 0-1 range in both, U and V coordinates, but not exceeding that range) and the mesh must be exported with the Directionality Normals 3dsMax plugin. Make sure to check whether the resulting map works in the engine – you might have to swap the red and green channels.

Braids

In addition to the above, you will probably want to bake down separate normalmap/AO maps for braids based on pretty much solid geometry, so as to really capture the big shapes.

Parts that are hard to bake: baking down complex hair can be somewhat tricky – you are dealing with rather messy and heavy models, and baking issues are not uncommon. What usually works best is to reduce baking problems to an acceptable level and then fix remaining problems manually. You can use backdrop objects in your bake to stop the lowpoly hair from capturing unwanted areas.

Another option that works very well (esp. on secondary elements) is to morph your model to UV space and set up a flattened hair system.

Hair Planes

Having more resources allows for a larger number, which in turn changes what kind of hairstyle can be solved with planes rather than solid geometry/large patches of hair. However, keep in mind that LODs are required for many characters, making a hairstyle that uses hundreds of individual planes for a random NPC - not a good idea. Generally, this approach (as well as View aligned Cards, see below) will create the best looking results. Also, creating these planes (based on an existing hair system) can be very fast, depending on which tool you use. In Ryse we used Ornatrix. Ox (Ornatrix) Mesh from Strands (for UVs/orientation of hair planes), Ox Render Settings (for plane size and tapering) as well as Ox Hair from guides (for distribution settings and hair count) all play together in making good lowpoly hair (or at least, a decent starting point).

Variation

By default, all hair planes generated by Ornatrix will share the same UV layout – which is bad for variation/tweaking specific areas of a hairstyle. While it is possible to achieve strand variation with Ornatrix (e.g. randomly scattered hair instance meshes with varying UV layouts), doing it manually works better: Add a EditPoly modifier to the top of your stack >> Graphite Modeling Tool’s randomized face selection >> convert selection to Element Sub-Object >> change UVs as needed. Additionally, tweak UVs of key areas that needs special attention (e.g. border regions, hair/beard connection, etc.)

Vertex Colors

If the original hair system had colors, those can be baked down to vertex colors to recreate the look of your high-res hair system(since your UVs will be shared, you cant do this with textures)

If you are using a texture to color your hair, there will be a problem with UVs (mesh needs unique UVs to get color info from growth object/growth object's color map - but the mesh also needs 'per strand'/shared UVs to work with the actual hair textures)

Initially set up the Ox Mesh from Strands to use Per-Strand UV Coords >> add a Unwrap UVW modifier to the top of the stack (turn this modifier OFF) >> in Ox Mesh from Strand, turn off Per-Strand UV Coords., apply whatever texture/material you want to use for the hair >> bake down Vertex Colors (Utilities Tab > Assign Vertex Colors) – this modifier will be put at the top of your stack. Finally, turn the Unwrap UVW modifier back on.

Vertex Color display in CRYENGINE can be somewhat different from what you see in your DCC tool. Some tweaking of Hue/Contrast in the Assign Vertex Colors modifier might be necessary to achieve the desired results.

Custom Normals

Using vertex custom normals for hairplanes can make a huge difference. Generally, the default normals will lead to uneven shading which breaks the look and makes the individual planes stand out.

A good tool for copying normals from a simple reference object over to your hair planes is SlideNormalThief.

Transfer Maps can be a useful tool for transferring normals or projecting them to a target mesh.

Shader Overview

Opacity Settings

Opacity

At 100, the shader uses Alpha Test (or rather, a variation thereof, results will generally be softer than real Alpha Test).

99 and below will use Alpha Blend (‘Thin Hair’). When using alpha blend, Thin Hair (in ‘Shader Generation Params’) MUST be turned ON.

Alpha Test

When using Alpha Test (Opacity 100) this value will control transparency (it determines how grayscale values are being interpreted).

When Using Alpha Blend (Opacity <=99), this value will control transparency of the hair shadow, rather than transparency of the actual hair (use Alpha Blend Multiplier for that, see below.

Thin Hair/Alpha Blend is prone to sorting issues. To counteract this, split your hair strands to use two shaders, one alpha test (to counteract sorting issues), and one using Thin Hair for smoothness.

Texture Settings

Diffuse/Specular Color/Glossiness

Work as with most other shaders. The hair shader does not use gloss maps, so the glossiness value has to be set globally – make sure not to use super low values, as those might cause shading issues. Similarly, even very dry/coarse hair should have some specularity.

As with most other shaders. Again, the hair shader does not support gloss maps, thus use ddn format for normal maps. The directionality maps should also be saved out as a standard normalmap.

In order to get accurate environment lighting, make sure to set Environment Map to use the nearest cube-map (‘Nearest Cube-Map probe for alpha blended’), and specify an appropriate name in the Environment slot.

Textures for traditional Hair Planes can be created either by manually painting them, or by creating a number of quick Ox Hairsystems and baking them down (see 3.1 - Solid Geometry).

By default, anisotropic highlights will be aligned to the V coordinate in UV space - this means that in many cases a Directionality Map is not needed for hair planes, if the UV are set up properly.

Advanced Settings

In some cases turning off shadows can be beneficial (e.g. shadow artifacts with a multi-layered hair mesh).

An extra shadow mesh can then be used to still get decent shadows from the hair (e.g. Marius’ helmet plume uses a separate mesh to cast shadows, the actual hair bits that are visible in the game have shadows turned off).

Similar to traditional Hair Planes, the difference lies in functionality within CRYENGINE: view aligned cards will always face the camera – this can be extremely useful for faking volume/covering up the typical ‘hair plane’ look. For view aligned cards to work, the hair strands in question must be assigned a unique material ID – then in the material in CRYENGINE, turn on ‘View Aligned Cards’. When generating the mesh for VACs, its best to make them very thin - thickness/width can be adjusted in the Editor/Material; Meshes that are too thick tend to break during the scaling process.

If both, front and back faces of a hair strand are visible, the aligned will create a weird looking ‘twist’ at the peak point. This limits the use of view aligned cards to short hair, or hair that is relatively straight.

Shader Params

Shader Params	Description	Shader Gen Option
Alpha Blend Multiplier	This functions as a multiplier for your alpha map – grayscale values get boosted. Esp. useful for Thin Hair (see below).	Default
Diffuse Wrap	This allows for light to pass through the hair, thus illuminating a wider area. A tightly woven braid would have a lower Diffuse Wrap value (the hair being very dense), whereas sparse, loose hair would have a high Diffuse Wrap value.	Default
Indirect bounce color	Best left at default value.	Default
Secondary Color	Color and intensity of the secondary specular highlight. Primary highlight color depends on the hairs diffuse color, whereas the secondary highlight will usually have a more neutral color.	Default
Secondary Shift	This allows the secondary highlight to be shifted over the surface of your hair mesh. Make sure it works with the primary highlight, the position of which can not be shifted.	Default
Secondary Width	Width of the secondary specular highlight.	Default
Shift Variation	Adds variation to the shift of the secondary highlight.	Default
Soft Intersection	This controls the alpha blending of the hair against a close, solid backdrop (i.e. the scalp). Powerful feature that can help a lot with achieving a nice, smooth transition from hair to skin.	Default
Strand Width	This controls the width of the view aligned strands. The mesh you exported utilizing this feature from DCC tools should be rather thin. The value functions as a multiplier relative to the meshes V coordinate (width) in UV space, this can be used to control strand thickness (e.g. thinner strands around the border areas). This parameter only applies if View aligned strands is turned on in "Shader Generation Params".	View aligned strands
Thin Hair Threshold	Determines how alpha blending works for screen space effects (DOF, motion blur, etc.). Lower values will make the blending harder, but can cause artifacts. Higher values will soften the blending, but in some cases the hair will turn into a blurry mess. For most gameplay situations, the (rather low) default value will work fine, but in cinematics manual tweaking may be needed. The Thin Hair Threshold value must then be animated throughout the scene. This parameter only applies if Thin Hair is turned on in "Shader Generation Params".	Thin Hair
Wind Settings	Allows tweaking of the force field controlling wind animation.	Default

Shader Generation Params

Param	Description
Vertex Colors	See Illum Shader for more information.
View Aligned Strands	Checks if you want the hair strands to self align to the camera. Since this is a global setting for the material, using view aligned strands will require an extra material/draw call.
Thin Hair	See Above
Ambient Cubemap	Should always be on.
Enforce Tiled Shading	This works as an override for the global tiled shading settings. With tiled shading off, improper lighting of a scene can cause shading artifacts on hair (e.g. hair turning very dark). Use this VERY carefully, as tiled shading for hair is generally quite expensive.
Wind bending	Simulate wind effects. If turned on options will appear under Shader Params where you can control frequency, phase and amplitude.

Hair Shader Pre-CRYENGINE 3.6

Shader Params

Shader Params	Description	Shader Gen Option
Alpha test softening	Sets amount of alpha test softening to apply.	Soft alpha test
Ambient spec multiplier	Controls over specular intensity.	Default
Bump scale	Sets hair bumpiness.	Default
Detail tilling	Sets detail tilling scale.	Default
Diffuse wrap	Sets diffuse wrapping.	Default
Hair color	Sets hair color.	Default
Indirect bounce color	See Illum Shader for more information.	Default
Primary spec color	Sets primary spec color.	Default
Primary spec glossiness	Sets primary specular glossiness.	Default
Primary spec shift	Sets primary specular shift.	Default
Rim multiplier	Sets rim strength.	Default
Secondary spec color	Sets hair secondary spec color.	Default
Secondary spec glossiness	Sets secondary specular glossiness.	Default
Secondary spec shift	Sets secondary specular specular shift.	Default
Self-shadow softening	Sets geometry self-shadowing multiplier.	Default
Wind frequency	Sets the speed at which the verts are deformed.	Wind bending
Wind phase	Sets hair animation phase and randomizes the deformation.	Wind bending
Wind wave0 amp	Sets the amount or amplitude at which the verts are deformed.	Wind bending
Wind wave2 amp	Sets the amount or amplitude at which the verts are deformed on a different curve.	Wind bending

Shader Generation Params

Param	Description
Vertex Colors	See Illum Shader for more information.
Soft alpha test	Enable for alpha test to have soft edges and for more stable rendering.
Wind bending	Simulate wind effects.

Guidelines for Modeling Hair

Due to limitations in hardware regarding alpha blending sorting, we cannot at this point have per-pixel sorting which would save a lot of work, so we need to use a very cheap sorting approximation which works something like this:

Render hair opaque areas (this is where your alpha channel is 1 (white)). Then render hair backfaces, and finally render hair frontfaces.

This works for many cases but it has a lot of limitations, regarding modeling for it to work:

Start by making an initial hair cap (imagine a hair helmet), this will give missing shading (anisotropic, etc.) details from base head while making sure each hair patch should be modeled as single sided.
Use vertical UV patches so that they follow the hair strands vertically. This adheres to the anisotropic shape.
Then add all of the little details by adding hair patches.

When "Soft alpha test" is enabled, the hair will be rendered using the usual opaque rendering pipeline. In a post process we apply alpha test smoothing. You can also enable double sided option at will.

Hair Texturing Guidelines

Regarding hair texture, the trick for having very thin hair is to make texture as pixel perfect and with as little distortions/rotations (else filtering will kick in more and look blurrier). One way of achieving this is in Photoshop making a uniform noise, then using strong Motion Blur.
Then add little details to hair texture, colored noisy, alpha blended areas, etc.
Important note regarding alpha blended areas, we are trying to avoid them as much as possible, so try to make alpha blended areas only at the bottom tip of the hair.
For better "thinner" results enable Anisotropic texture filtering in diffuse texture filter options.