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Filament Materials Guide

Filament Materials Guide

Contents

About
  1.1  Authors
Overview
  2.1  Core concepts
Material models
  3.1  Lit model
    3.1.1  Base color
    3.1.2  Metallic
    3.1.3  Roughness
    3.1.4  Non-metals
    3.1.5  Metals
    3.1.6  Reflectance
    3.1.7  Clear coat
    3.1.8  Clear coat roughness
    3.1.9  Anisotropy
    3.1.10  Anisotropy direction
    3.1.11  Ambient occlusion
    3.1.12  Normal
    3.1.13  Clear coat normal
    3.1.14  Emissive
    3.1.15  Post-lighting color
  3.2  Subsurface model
    3.2.1  Thickness
    3.2.2  Subsurface color
    3.2.3  Subsurface power
  3.3  Cloth model
    3.3.1  Sheen color
    3.3.2  Subsurface color
  3.4  Unlit model
  3.5  Specular glossiness
Material definitions
  4.1  Format
    4.1.1  Differences with JSON
    4.1.2  Example
  4.2  Material block
    4.2.1  name
    4.2.2  shadingModel
    4.2.3  parameters
    4.2.4  requires
    4.2.5  variables
    4.2.6  blending
    4.2.7  postLightingBlending
    4.2.8  vertexDomain
    4.2.9  interpolation
    4.2.10  culling
    4.2.11  colorWrite
    4.2.12  depthWrite
    4.2.13  depthCulling
    4.2.14  doubleSided
    4.2.15  transparency
    4.2.16  maskThreshold
    4.2.17  shadowMultiplier
    4.2.18  curvatureToRoughness
    4.2.19  limitOverInterpolation
    4.2.20  clearCoatIorChange
    4.2.21  variantFilter
    4.2.22  flipUV
  4.3  Vertex block
    4.3.1  Material vertex inputs
  4.4  Fragment block
    4.4.1  prepareMaterial function
    4.4.2  Material fragment inputs
  4.5  Shader public APIs
    4.5.1  Types
    4.5.2  Math
    4.5.3  Matrices
    4.5.4  Frame constants
    4.5.5  Vertex only
    4.5.6  Fragment only
Compiling materials
  5.1  Shader validation
  5.2  Flags
    5.2.1  —platform
    5.2.2  —api
    5.2.3  —optimize-size
    5.2.4  —reflect
    5.2.5  —variant-filter
Handling colors
  6.1  Linear colors
  6.2  Pre-multiplied alpha

   

About

This document is part of the Filament project. To report errors in this document please use the project's issue tracker.

   

Authors

   

Overview

Filament is a physically based rendering (PBR) engine for Android. Filament offers a customizable material system that you can use to create both simple and complex materials. This document describes all the features available to materials and how to create your own material.

   

Core concepts

Material

A material defines the visual appearance of a surface. To completely describe and render a surface, a material provides the following information:

  • Material model
  • Set of use-controllable named parameters
  • Raster state (blending mode, backface culling, etc.)
  • Vertex shader code
  • Fragment shader code

Material model

Also called shading model or lighting model, the material model defines the intrinsic properties of a surface. These properties have a direct influence on the way lighting is computed and therefore on the appearance of a surface.

Material definition

A text file that describes all the information required by a material. This is the file that you will directly author to create new materials.

Material package

At runtime, materials are loaded from material packages compiled from material definitions using the matc tool. A material package contains all the information required to describe a material, and shaders generated for the target runtime platforms. This is necessary because different platforms (Android, macOS, Linux, etc.) use different graphics APIs or different variants of similar graphics APIs (OpenGL vs OpenGL ES for instance).

Material instance

A material instance is a reference to a material and a set of values for the different values of that material. Material instances are not covered in this document as they are created and manipulated directly from code using Filament's APIs.

   

Material models

Filament materials can use one of the following material models:

   

Lit model

The lit model is Filament's standard material model. This physically-based shading model was designed after to offer good interoperability with other common tools and engines such as Unity 5, Unreal Engine 4, Substance Designer or Marmoset Toolbag.

This material model can be used to describe a large number of non-metallic surfaces (dielectrics) or metallic surfaces (conductors).

The appearance of a material using the standard model is controlled using the properties described in table 1.

Property Definition
baseColor Diffuse albedo for non-metallic surfaces, and specular color for metallic surfaces
metallic Whether a surface appears to be dielectric (0.0) or conductor (1.0). Often used as a binary value (0 or 1)
roughness Perceived smoothness (1.0) or roughness (0.0) of a surface. Smooth surfaces exhibit sharp reflections
reflectance Fresnel reflectance at normal incidence for dielectric surfaces. This directly controls the strength of the reflections
clearCoat Strength of the clear coat layer
clearCoatRoughness Perceived smoothness or roughness of the clear coat layer
anisotropy Amount of anisotropy in either the tangent or bitangent direction
anisotropyDirection Local surface direction
ambientOcclusion Defines how much of the ambient light is accessible to a surface point. It is a per-pixel shadowing factor between 0.0 and 1.0
normal A detail normal used to perturb the surface using bump mapping (normal mapping)
clearCoatNormal A detail normal used to perturb the clear coat layer using bump mapping (normal mapping)
emissive Additional diffuse albedo to simulate emissive surfaces (such as neons, etc.) This property is mostly useful in an HDR pipeline with a bloom pass
postLightingColor Additional color that can be blended with the result of the lighting computations. See postLightingBlending
 Table 1: Properties of the standard model

The type and range of each property is described in table 2.

Property Type Range Note
baseColor float4 [0..1] Pre-multiplied linear RGB
metallic float [0..1] Should be 0 or 1
roughness float [0..1]  
reflectance float [0..1] Prefer values > 0.35
clearCoat float [0..1] Should be 0 or 1
clearCoatRoughness float [0..1] Remaps to [0..0.6]
anisotropy float [−1..1] Anisotropy is in the tangent direction when this value is positive
anisotropyDirection float3 [0..1] Linear RGB, encodes a direction vector in tangent space
ambientOcclusion float [0..1]  
normal float3 [0..1] Linear RGB, encodes a direction vector in tangent space
clearCoatNormal float3 [0..1] Linear RGB, encodes a direction vector in tangent space
emissive float4 rgb=[0..1], a=[-n..n] Alpha is the exposure compensation
postLightingColor float4 [0..1] Pre-multiplied linear RGB
 Table 2: Range and type of the standard model's properties

About linear RGB

Several material model properties expect RGB colors. Filament materials use RGB colors in linear space and you must take proper care of supplying colors in that space. See the Linear colors section for more information.

About pre-multiplied RGB

Filament materials expect colors to use pre-multiplied alpha. See the Pre-multiplied alpha section for more information.

   

Base color

The baseColor property defines the perceived color of an object (sometimes called albedo). The effect of baseColor depends on the nature of the surface, controlled by the metallic property explained in the Metallic section.

Non-metals (dielectrics)

Defines the diffuse color of the surface. Real-world values are typically found in the range \([10..240]\) if the value is encoded between 0 and 255, or in the range \([0.04..0.94]\) between 0 and 1. Several examples of base colors for non-metallic surfaces can be found in table 3.

Metal sRGB Hexadecimal Color
Coal 0.19, 0.19, 0.19 #323232
 
Rubber 0.21, 0.21, 0.21 #353535
 
Mud 0.33, 0.24, 0.19 #553d31
 
Wood 0.53, 0.36, 0.24 #875c3c
 
Vegetation 0.48, 0.51, 0.31 #7b824e
 
Brick 0.58, 0.49, 0.46 #947d75
 
Sand 0.69, 0.66, 0.52 #b1a884
 
Concrete 0.75, 0.75, 0.73 #c0bfbb
 
 Table 3: baseColor for common non-metals

Metals (conductors)

Defines the specular color of the surface. Real-world values are typically found in the range \([170..255]\) if the value is encoded between 0 and 255, or in the range \([0.66..1.0]\) between 0 and 1. Several examples of base colors for metallic surfaces can be found in table 4.

Metal sRGB Hexadecimal Color
Silver 0.97, 0.96, 0.91 #f7f4e8
 
Aluminum 0.91, 0.92, 0.92 #e8eaea
 
Titanium 0.76, 0.73, 0.69 #c1baaf
 
Iron 0.77, 0.78, 0.78 #c4c6c6
 
Platinum 0.83, 0.81, 0.78 #d3cec6
 
Gold 1.00, 0.85, 0.57 #ffd891
 
Brass 0.98, 0.90, 0.59 #f9e596
 
Copper 0.97, 0.74, 0.62 #f7bc9e
 
 Table 4: baseColor for common metals

   

Metallic

The metallic property defines whether the surface is a metallic (conductor) or a non-metallic (dielectric) surface. This property should be used as a binary value, set to either 0 or 1. Intermediate values are only truly useful to create transitions between different types of surfaces when using textures.

This property can dramatically change the appearance of a surface. Non-metallic surfaces have chromatic diffuse reflection and achromatic specular reflection (reflected light does not change color). Metallic surfaces do not have any diffuse reflection and chromatic specular reflection (reflected light takes on the color of the surfaced as defined by baseColor).

The effect of metallic is shown in figure 1 (click on the image to see a larger version).

 Figure 1: metallic varying from 0.0 (left) to 1.0 (right)

   

Roughness

The roughness property controls the perceived smoothness of the surface. When roughness is set to 0, the surface is perfectly smooth and highly glossy. The rougher a surface is, the “blurrier” the reflections are. This property is often called glossiness in other engines and tools, and is simply the opposite of the roughness (roughness = 1 - glossiness).

   

Non-metals

The effect of roughness on non-metallic surfaces is shown in figure 2 (click on the image to see a larger version).

 Figure 2: Dielectric roughness varying from 0.0 (left) to 1.0 (right)

   

Metals

The effect of roughness on metallic surfaces is shown in figure 3 (click on the image to see a larger version).

 Figure 3: Conductor roughness varying from 0.0 (left) to 1.0 (right)

   

Reflectance

The reflectance property only affects non-metallic surfaces. This property can be used to control the specular intensity. This value is defined between 0 and 1 and represents a remapping of a percentage of reflectance. For instance, the default value of 0.5 corresponds to a reflectance of 4%. Values below 0.35 (2% reflectance) should be avoided as no real-world materials have such low reflectance.

The effect of reflectance on non-metallic surfaces is shown in figure 4 (click on the image to see a larger version).

 Figure 4: reflectance varying from 0.0 (left) to 1.0 (right)

Figure 5 shows common values and how they relate to the mapping function.

 Figure 5: Common reflectance values

Table 5 describes acceptable reflectance values for various types of materials (no real world material has a value under 2%).

Material Reflectance Property value
Water 2% 0.35
Fabric 4% to 5.6% 0.5 to 0.59
Common liquids 2% to 4% 0.35 to 0.5
Common gemstones 5% to 16% 0.56 to 1.0
Plastics, glass 4% to 5% 0.5 to 0.56
Other dielectric materials 2% to 5% 0.35 to 0.56
Eyes 2.5% 0.39
Skin 2.8% 0.42
Hair 4.6% 0.54
Teeth 5.8% 0.6
Default value 4% 0.5
 Table 5: Reflectance of common materials

   

Clear coat

Multi-layer materials are fairly common, particularly materials with a thin translucent layer over a base layer. Real world examples of such materials include car paints, soda cans, lacquered wood and acrylic.

The clearCoat property can be used to describe materials with two layers. The clear coat layer will always be isotropic and dielectric.

 Figure 6: Comparison of a carbon-fiber material under the standard material model (left) and the clear coat model (right)

The clearCoat property controls the strength of the clear coat layer. This should be treated as a binary value, set to either 0 or 1. Intermediate values are useful to control transitions between parts of the surface that have a clear coat layers and parts that don't.

The effect of clearCoat on a rough metal is shown in figure 7 (click on the image to see a larger version).

 Figure 7: clearCoat varying from 0.0 (left) to 1.0 (right)

The clear coat layer effectively doubles the cost of specular computations. Do not assign a value, even 0.0, to the clear coat property if you don't need this second layer.

   

Clear coat roughness

The clearCoatRoughness property is similar to the roughness property but applies only to the clear coat layer. In addition, since clear coat layers are never completely rough, the value between 0 and 1 is remapped internally to an actual roughness of 0 to 0.6.

The effect of clearCoatRoughness on a rough metal is shown in figure 8 (click on the image to see a larger version).

 Figure 8: clearCoatRoughness varying from 0.0 (left) to 1.0 (right)

   

Anisotropy

Many real-world materials, such as brushed metal, can only be replicated using an anisotropic reflectance model. A material can be changed from the default isotropic model to an anisotropic model by using the anisotropy property.

 Figure 9: Comparison of isotropic material (left) and anistropic material (right)

The effect of anisotropy on a rough metal is shown in figure 10 (click on the image to see a larger version).

 Figure 10: anisotropy varying from 0.0 (left) to 1.0 (right)

The figure 11 below shows how the direction of the anisotropic highlights can be controlled by using either positive or negative values: positive values define anisotropy in the tangent direction and negative values in the bitangent direction.

 Figure 11: Positive (left) vs negative (right) anisotropy values

The anisotropic material model is slightly more expensive than the standard material model. Do not assign a value (even 0.0) to the anisotropy property if you don't need anisotropy.

   

Anisotropy direction

The anisotropyDirection property defines the direction of the surface at a given point and thus control the shape of the specular highlights. It is specified as vector of 3 values that usually come from a texture, encoding the directions local to the surface.

The effect of anisotropyDirection on a metal is shown in figure 13 (click on the image to see a larger version).

 Figure 12: Anisotropic metal rendered with a direction map

The result shown in figure 13 was obtained using the direction map shown in figure 13.

 Figure 13: Example of a direction map

   

Ambient occlusion

The ambientOcclusion property defines how much of the ambient light is accessible to a surface point. It is a per-pixel shadowing factor between 0.0 (fully shadowed) and 1.0 (fully lit). This property only affects diffuse indirect lighting (image-based lighting), not direct lights such as directional, point and spot lights, nor specular lighting.

 Figure 14: Comparison of materials without diffuse ambient occlusion (left) and with (right)

   

Normal

The normal property defines the normal of the surface at a given point. It usually comes from a normal map texture, which allows to vary the property per-pixel. The normal is supplied in tangent space, which means that +Z points outside of the surface.

For example, let's imagine that we want to render a piece of furniture covered in tufted leather. Modeling the geometry to accurately represent the tufted pattern would require too many triangles so we instead bake a high-poly mesh into a normal map. Once the base map is applied to a simplified mesh, we get the result in figure 15.

Note that the normal property affects the base layer and not the clear coat layer.

 Figure 15: Low-poly mesh without normal mapping (left) and with (right)

Using a normal map increases the runtime cost of the material model.

   

Clear coat normal

The clearCoatNormal property defines the normal of the clear coat layer at a given point. It behaves otherwise like the normal property.

 Figure 16: A material with a clear coat normal map and a surface normal map

Using a clear coat normal map increases the runtime cost of the material model.

   

Emissive

The emissive property can be used to simulate additional light emitted by the surface. It is defined as a float4 value that contains an RGB color (in linear space) as well as an exposure compensation value (in the alpha channel).

Even though an exposure value actually indicates combinations of camera settings, it is often used by photographers to describe light intensity. This is why cameras let photographers apply an exposure compensation to over or under-expose an image. This setting can be used for artistic control but also to achieve proper exposure (snow for instance will be exposed for as 18% middle-grey).

The exposure compensation value of the emissive property can be used to force the emissive color to be brighter (positive values) or darker (negative values) than the current exposure. If the bloom effect is enabled, using a positive exposure compensation can force the surface to bloom.

   

Post-lighting color

The postLightingColor can be used to modify the surface color after lighting computations. This property has no physical meaning and only exists to implement specific effects or to help with debugging. This property is defined as a float4 value containing a pre-multiplied RGB color in linear space.

The post-lighting color is blended with the result of lighting according to the blending mode specified by the postLightingBlending material option. Please refer to the documentation of this option for more information.

postLightingColor can be used as a simpler emissive property by setting postLightingBlending to add and by providing an RGB color with alpha set to 0.0.

   

Subsurface model

   

Thickness

   

Subsurface color

   

Subsurface power

   

Cloth model

All the material models described previously are designed to simulate dense surfaces, both at a macro and at a micro level. Clothes and fabrics are however often made of loosely connected threads that absorb and scatter incident light. When compared to hard surfaces, cloth is characterized by a softer specular lob with a large falloff and the presence of fuzz lighting, caused by forward/backward scattering. Some fabrics also exhibit two-tone specular colors (velvets for instance).

Figure 17 shows how the standard material model fails to capture the appearance of a sample of denim fabric. The surface appears rigid (almost plastic-like), more similar to a tarp than a piece of clothing. This figure also shows how important the softer specular lobe caused by absorption and scattering is to the faithful recreation of the fabric.

 Figure 17: Comparison of denim fabric rendered using the standard model (left) and the cloth model (right)

Velvet is an interesting use case for a cloth material model. As shown in figure 18 this type of fabric exhibits strong rim lighting due to forward and backward scattering. These scattering events are caused by fibers standing straight at the surface of the fabric. When the incident light comes from the direction opposite to the view direction, the fibers will forward scatter the light. Similarly, when the incident light from the same direction as the view direction, the fibers will scatter the light backward.

 Figure 18: Velvet fabric showcasing forward and backward scattering

It is important to note that there are types of fabrics that are still best modeled by hard surface material models. For instance, leather, silk and satin can be recreated using the standard or anisotropic material models.

The cloth material model encompasses all the parameters previously defined for the standard material mode except for metallic and reflectance. Two extra parameters described in table 6 are also available.

Parameter Definition
sheenColor Specular tint to create two-tone specular fabrics (defaults to \(\sqrt{baseColor}\))
subsurfaceColor Tint for the diffuse color after scattering and absorption through the material
 Table 6: Cloth model parameters

The type and range of each property is described in table 7.

Property Type Range Note
sheenColor float3 [0..1] Linear RGB
subsurfaceColor float3 [0..1] Linear RGB
 Table 7: Range and type of the cloth model's properties

To create a velvet-like material, the base color can be set to black (or a dark color). Chromaticity information should instead be set on the sheen color. To create more common fabrics such as denim, cotton, etc. use the base color for chromaticity and use the default sheen color or set the sheen color to the luminance of the base color.

To see the effect of the roughness parameter make sure the sheenColor is brighter than baseColor. This can be used to create a fuzz effect. Taking the luminance of baseColor as the sheenColor will produce a fairly natural effect that works for common cloth. A dark baseColor combined with a bright/saturated sheenColor can be used to create velvet.

The subsurfaceColor parameter should be used with care. High values can interfere with shadows in some areas. It is best suited for subtle transmission effects through the material.

   

Sheen color

The sheenColor property can be used to directly modify the specular reflectance. It offers better control over the appearance of cloth and gives give the ability to create two-tone specular materials.

The effect of sheenColor is shown in figure 19 (click on the image to see a larger version).

 Figure 19: Blue fabric without (left) and with (right) sheen

   

Subsurface color

The subsurfaceColor property is not physically-based and can be used to simulate the scattering, partial absorption and re-emission of light in certain types of fabrics. This is particularly useful to create softer fabrics.

The cloth material model is more expensive to compute when the subsurfaceColor property is used.

The effect of subsurfaceColor is shown in figure 20 (click on the image to see a larger version).

 Figure 20: White cloth (left column) vs white cloth with brown subsurface scatting (right)

   

Unlit model

The unlit material model can be used to turn off all lighting computations. Its primary purpose is to render pre-lit elements such as a cubemap, external content (such as a video or camera stream), user interfaces, visualization/debugging etc. The unlit model exposes only two properties described in table 8.

Property Definition
baseColor Surface diffuse color
emissive Additional diffuse color to simulate emissive surfaces. This property is mostly useful in an HDR pipeline with a bloom pass
postLightingColor Additional color to blend with base color and emissive
 Table 8: Properties of the standard model

The type and range of each property is described in table 9.

Property Type Range Note
baseColor float4 [0..1] Pre-multiplied linear RGB
emissive float4 rgb=[0..1], a=N/A Pre-multiplied linear RGB, alpha is ignored
postLightingColor float4 [0..1] Pre-multiplied linear RGB
 Table 9: Range and type of the unlit model's properties

The value of emissive is simply added to baseColor when present. The main use of emissive is to force an unlit surface to bloom if the HDR pipeline is configured with a bloom pass. The value of postLightingColor is blended with the sum of emissive and baseColor according to the blending mode specified by the postLightingBlending material option.

Figure 21 shows an example of the unlit material model (click on the image to see a larger version).

 Figure 21: The unlit model is used to render debug information

   

Specular glossiness

This alternative lighting model exists to comply with legacy standards. Since it is not a physically-based formulation, we do not recommend using it except when loading legacy assets.

This model encompasses the parameters previously defined for the standard lit mode except for metallic, reflectance, and roughness. It adds parameters for specularColor and glossiness.

Parameter Definition
baseColor Surface diffuse color
specularColor Specular tint (defaults to black)
glossiness Glossiness (defaults to 0.0)
 Table 10: Properties of the specular-glossiness shading model

The type and range of each property is described in table 11.

Property Type Range Note
baseColor float4 [0..1] Pre-multiplied linear RGB
specularColor float3 [0..1] Linear RGB
glossiness float [0..1] Inverse of roughness
 Table 11: Range and type of the specular-glossiness model's properties

   

Material definitions

A material definition is a text file that describes all the information required by a material:

   

Format

The material definition format is a format loosely based on JSON that we call JSONish. At the top level a material definition is composed of 3 different blocks that use the JSON object notation:

material {
    // material properties
}

vertex {
    // vertex shader, optional
}

fragment {
    // fragment shader
}

A minimum viable material definition must contain a material section and a fragment block. The vertex block is optional.

   

Differences with JSON

In JSON, an object is made of key/value pairs. A JSON pair has the following syntax:

"key" : value

Where value can be a string, number, object, array or a literal (true, false or null). While this syntax is perfectly valid in a material definition, a variant without quotes around strings is also accepted in JSONish:

key : value

Quotes remain mandatory when the string contains spaces.

The vertex and fragment blocks contain unescaped, unquoted GLSL code, which is not valid in JSON.

Single-line C++-style comments are allowed.

The key of a pair is case-sensitive.

The value of a pair is not case-sensitive.

   

Example

The following code listing shows an example of a valid material definition. This definition uses the lit material model (see Lit model section), uses the default opaque blending mode, requires that a set of UV coordinates be presented in the rendered mesh and defines 3 user parameters. The following sections of this document describe the material and fragment blocks in detail.

material {
    name : "Textured material",
    parameters : [
        {
           type : sampler2d,
           name : texture
        },
        {
           type : float,
           name : metallic
        },
        {
            type : float,
            name : roughness
        }
    ],
    requires : [
        uv0
    ],
    shadingModel : lit,
    blending : opaque
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        material.baseColor = texture(materialParams_texture, getUV0());
        material.metallic = materialParams.metallic;
        material.roughness = materialParams.roughness;
    }
}
   

Material block

The material block is mandatory block that contains a list of property pairs to describe all non-shader data.

   

name

Type

string

Value

Any string. Double quotes are required if the name contains spaces.

Description

Sets the name of the material. The name is retained at runtime for debugging purpose.

material {
    name : stone
}

material {
    name : "Wet pavement"
}
   

shadingModel

Type

string

Value

Any of lit, subsurface, cloth, unlit, specularGlossiness. Defaults to lit.

Description

Selects the material model as described in the Material models section.

material {
    shadingModel : unlit
}

material {
    shadingModel : "subsurface"
}
   

parameters

Type

array of parameter objects

Value

Each entry is an object with the properties name and type, both of string type. The name must be a valid GLSL identifier. The type must be one of the types described in table 12.

Type Description
bool Single boolean
bool2 Vector of 2 booleans
bool3 Vector of 3 booleans
bool4 Vector of 4 booleans
float Single float
float2 Vector of 2 floats
float3 Vector of 3 floats
float4 Vector of 4 floats
int Single integer
int2 Vector of 2 integers
int3 Vector of 3 integers
int4 Vector of 4 integers
uint Single unsigned integer
uint2 Vector of 2 unsigned integers
uint3 Vector of 3 unsigned integers
uint4 Vector of 4 unsigned integers
float3×3 Matrix of 3×3 floats
float4×4 Matrix of 4×4 floats
sampler2d 2D texture
samplerExternal External texture (platform-specific)
samplerCubemap Cubemap texture
 Table 12: Material parameter types

Samplers

Sampler types can also specify a format (defaults to float) and a precision (defaults to default). The format can be one of int, float. The precision can be one of default (best precision for the platform, typically high on desktop, medium on mobile), low, medium, high.

Arrays

A parameter can define an array of values by appending [size] after the type name, where size is a positive integer. For instance: float[9] declares an array of nine float values. Arrays of samplers are not supported at the moment.

Description

Lists the parameters required by your material. These parameters can be set at runtime using Filament's material API. Accessing parameters from the shaders varies depending on the type of parameter:

  • Samplers types: use the parameter name prefixed with materialParams_. For instance, materialParams_myTexture.
  • Other types: use the parameter name as the field of a structure called materialParams. For instance, materialParams.myColor.

material {
    parameters : [
        {
           type : float4,
           name : albedo
        },
        {
           type      : sampler2d,
           format    : float,
           precision : high,
           name      : roughness
        },
        {
            type : float2,
            name : metallicReflectance
        }
    ],
    requires : [
        uv0
    ],
    shadingModel : lit,
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        material.baseColor = materialParams.albedo;
        material.roughness = texture(materialParams_roughness, getUV0());
        material.metallic = materialParams.metallicReflectance.x;
        material.reflectance = materialParams.metallicReflectance.y;
    }
}
   

requires

Type

array of string

Value

Each entry must be any of uv0, uv1, color, position, tangents.

Description

Lists the vertex attributes required by the material. The position attribute is always required and does not need to be specified. The tangents attribute is automatically required when selecting any shading model that is not unlit. See the shader sections of this document for more information on how to access these attributes from the shaders.

material {
    parameters : [
        {
           type : sampler2d,
           name : texture
        },
    ],
    requires : [
        uv0
    ],
    shadingModel : lit,
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        material.baseColor = texture(materialParams_texture, getUV0());
    }
}
   

variables

Type

array of string

Value

Up to 4 strings, each must be a valid GLSL identifier.

Description

Defines custom interpolants (or variables) that are output by the material's vertex shader. Each entry of the array defines the name of an interpolant. The full name in the fragment shader is the name of the interpolant with the variable_ prefix. For instance, if you declare a variable called eyeDirection you can access it in the fragment shader using variable_eyeDirection. In the vertex shader, the interpolant name is simply a member of the MaterialVertexInputs structure (material.eyeDirection in your example). Each interpolant is of type float4 (vec4) in the shaders.

material {
    name : Skybox,
    parameters : [
        {
           type : samplerCubemap,
           name : skybox
        }
    ],
    variables : [
         eyeDirection
    ],
    vertexDomain : device,
    depthWrite : false,
    shadingModel : unlit
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        float3 sky = texture(materialParams_skybox, variable_eyeDirection.xyz).rgb;
        material.baseColor = vec4(sky, 1.0);
    }
}

vertex {
    void materialVertex(inout MaterialVertexInputs material) {
        float3 p = getPosition().xyz;
        float3 u = mulMat4x4Float3(getViewFromClipMatrix(), p).xyz;
        material.eyeDirection.xyz = mulMat3x3Float3(getWorldFromViewMatrix(), u);
    }
}
   

blending

Type

string

Value

Any of opaque, transparent, fade, add, masked. Defaults to opaque.

Description

Defines how/if the rendered object is blended with the content of the render target. The possible blending modes are:

  • Opaque: blending is disabled, the alpha channel of the material's output is ignored.
  • Transparent: blending is enabled. The material's output is alpha composited with the render target, using Porter-Duff's source over rule. This blending mode assumes pre-multiplied alpha.
  • Fade: acts as transparent but transparency is also applied to specular lighting. In transparent mode, the material's alpha values only applies to diffuse lighting. This blending mode is useful to fade lit objects in and out.
  • Add: blending is enabled. The material's output is added to the content of the render target.
  • Masked: blending is disabled. This blending mode enables alpha masking. The alpha channel of the material's output defines whether a fragment is discarded or not. See the maskThreshold section for more information.

material {
    blending : transparent
}
   

postLightingBlending

Type

string

Value

Any of opaque, transparent, add. Defaults to transparent.

Description

Defines how the postLightingColor material property is blended with the result of the lighting computations. The possible blending modes are:

  • Opaque: blending is disabled, the material will output postLightingColor directly.
  • Transparent: blending is enabled. The material's computed color is alpha composited with the postLightingColor, using Porter-Duff's source over rule. This blending mode assumes pre-multiplied alpha.
  • Add: blending is enabled. The material's computed color is added to postLightingColor.

material {
    postLightingBlending : add
}
   

vertexDomain

Type

string

Value

Any of object, world, view, device. Defaults to object.

Description

Defines the domain (or coordinate space) of the rendered mesh. The domain influences how the vertices are transformed in the vertex shader. The possible domains are:

  • Object: the vertices are defined in the object (or model) coordinate space. The vertices are transformed using the rendered object's transform matrix
  • World: the vertices are defined in world coordinate space. The vertices are not transformed using the rendered object's transform.
  • View: the vertices are defined in view (or eye or camera) coordinate space. The vertices are not transformed using the rendered object's transform.
  • Device: the vertices are defined in normalized device (or clip) coordinate space. The vertices are not transformed using the rendered object's transform.

material {
    vertexDomain : device
}
   

interpolation

Type

string

Value

Any of smooth, flat. Defaults to smooth.

Description

Defines how interpolants (or variables) are interpolated between vertices. When this property is set to smooth, a perspective correct interpolation is performed on each interpolant. When set to flat, no interpolation is performed and all the fragments within a given triangle will be shaded the same.

material {
    interpolation : flat
}
   

culling

Type

string

Value

Any of none, front, back, frontAndBack. Defaults to back.

Description

Defines which triangles should be culled: none, front-facing triangles, back-facing triangles or all.

material {
    culling : none
}
   

colorWrite

Type

boolean

Value

true or false. Defaults to true.

Description

Enables or disables writes to the color buffer.

material {
    colorWrite : false
}
   

depthWrite

Type

boolean

Value

true or false. Defaults to true.

Description

Enables or disables writes to the depth buffer.

material {
    depthWrite : false
}
   

depthCulling

Type

boolean

Value

true or false. Defaults to true.

Description

Enables or disables depth testing. When depth testing is disabled, an object rendered with this material will always appear on top of other opaque objects.

material {
    depthCulling : false
}
   

doubleSided

Type

boolean

Value

true or false. Defaults to false.

Description

Enables two-sided rendering and its capability to be toggled at run time. When set to true, culling is automatically set to none; if the triangle is back-facing, the triangle's normal is flipped to become front-facing. When explicitly set to false, this allows the doubleSided property to be toggled at run time.

material {
    doubleSided : true
}
   

transparency

Type

string

Value

Any of default, twoPassesOneSide or twoPassesTwoSides. Defaults to default.

Description

Controls how transparent objects are rendered. It is only valid when the blending mode is not opaque. None of these methods can accurately render concave geometry, but in practice they are often good enough.

The three possible transparency modes are:

material {
    transparency : twoPassesOneSide
}

 Figure 22: This double sided model shows the type of sorting issues transparent objects can be subject to in default mode

 Figure 23: In twoPassesOneSide mode, only one set of faces is visible and correctly sorted

 Figure 24: In twoPassesTwoSides mode, both set of faces are visible and sorting issues are minimized or eliminated

   

maskThreshold

Type

number

Value

A value between 0.0 and 1.0. Defaults to 0.4.

Description

Sets the minimum alpha value a fragment must have to not be discarded when the blending mode is set to masked. When the blending mode is not masked, this value is ignored. This value can be used to controlled the appearance of alpha-masked objects.

material {
    blending : masked,
    maskThreshold : 0.5
}
   

shadowMultiplier

Type

boolean

Value

true or false. Defaults to false.

Description

Only available in the unlit shading model. If this property is enabled, the final color computed by the material is multiplied by the shadowing factor (or visibility). This allows to create transparent shadow-receiving objects (for instance an invisible ground plane in AR).

material {
    name : "Invisible shadow plane",
    shadingModel : unlit,
    shadowMultiplier : true,
    blending : transparent
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        // baseColor defines the color and opacity of the final shadow
        material.baseColor = vec4(0.0, 0.0, 0.0, 0.7);
    }
}
   

curvatureToRoughness

Type

boolean

Value

true or false. Defaults to false.

Description

Reduces specular aliasing by increasing roughness based on the local geometric curvature. This property is particularly effective if you only use MSAA as your anti-aliasing method.

material {
    curvatureToRoughness : true
}

 Figure 25: Close up of a glossy metallic surface rendered normally (left) and with curvatureToRoughness (right).

   

limitOverInterpolation

Type

boolean

Value

true or false. Defaults to false.

Description

Reduces specular aliasing by attempting to eliminate normal over-interpolation. When this property is turned on, the material switches to centroid normal interpolation when the interpolated normals are too long. This property should only be used if your anti-aliasing method is MSAA. The effects are a lot more subtle than curvatureToRoughness, which should be used first to eliminate specular aliasing.

material {
    limitOverInterpolation : true
}
   

clearCoatIorChange

Type

boolean

Value

true or false. Defaults to true.

Description

When adding a clear coat layer, the change in index of refraction (IoR) is taken into account to modify the specular color of the base layer. This appears to darken baseColor. When this effect is disabled, baseColor is left unmodified. See figure 26 for an example of how this property can affect a red metallic base layer.

material {
    clearCoatIorChange : false
}

 Figure 26: The same rough metallic ball with a clear coat layer rendered with clearCoatIorChange enabled (left) and disabled (right).

   

variantFilter

Type

array of string

Value

Each entry must be any of dynamicLighting, directionalLighting, shadowReceiver or skinning.

Description

Used to specify a list of shader variants that the application guarantees will never be needed. These shader variants are skipped during the code generation phase, thus reducing the overall size of the material. Note that some variants may automatically be filtered out. For instance, all lighting related variants (directionalLighting, etc.) are filtered out when compiling an unlit material. Use the variant filter with caution, filtering out a variant required at runtime may lead to crashes.

Description of the variants:

material {
    name : "Invisible shadow plane",
    shadingModel : unlit,
    shadowMultiplier : true,
    blending : transparent,
    variantFilter : [ skinning ]
}
   

flipUV

Type

boolean

Value

true or false. Defaults to true.

Description

When set to true (default value), the Y coordinate of UV attributes will be flipped when read by this material's vertex shader. Flipping is equivalent to y = 1.0 - y. When set to false, flipping is disabled and the UV attributes are read as is.

material {
    flipUV : false
}
   

Vertex block

The vertex block is optional and can be used to control the vertex shading stage of the material. The vertex block must contain valid ESSL 3.0 code (the version of GLSL supported in OpenGL ES 3.0). You are free to create multiple functions inside the vertex block but you must declare the materialVertex function:

vertex {
    void materialVertex(inout MaterialVertexInputs material) {
        // vertex shading code
    }
}

This function will be invoked automatically at runtime by the shading system and gives you the ability to read and modify material properties using the MaterialVertexInputs structure. This full definition of the structure can be found in the Material vertex inputs section.

You can use this structure to compute your custom variables/interpolants or to modify the value of the attributes. For instance, the following vertex blocks modifies both the color and the UV coordinates of the vertex over time:

material {
    requires : [uv0, color]
}
vertex {
    void materialVertex(inout MaterialVertexInputs material) {
        material.color *= sin(getTime());
        material.uv0 *= sin(getTime());
    }
}

In addition to the MaterialVertexInputs structure, your vertex shading code can use all the public APIs listed in the Shader public APIs section.

   

Material vertex inputs

struct MaterialVertexInputs {
    float4 color;         // if the color attribute is required
    float2 uv0;           // if the uv0 attribute is required
    float2 uv1;           // if the uv1 attribute is required
    float3 worldNormal;   // only if the shading model is not unlit
    float4 worldPosition; // always available
    // variable* names are replaced with actual names
    float4 variable0;     // if 1 or more variables is defined
    float4 variable1;     // if 2 or more variables is defined
    float4 variable2;     // if 3 or more variables is defined
    float4 variable3;     // if 4 or more variables is defined
};

UV attributes

By default the vertex shader of a material will flip the Y coordinate of the UV attributes of the current mesh: material.uv0 = vec2(mesh_uv0.x, 1.0 - mesh_uv0.y). You can control this behavior using the flipUV property and setting it to false.

   

Fragment block

The fragment block must be used to control the fragment shading stage of the material. The vertex block must contain valid ESSL 3.0 code (the version of GLSL supported in OpenGL ES 3.0). You are free to create multiple functions inside the vertex block but you must declare the material function:

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        // fragment shading code
    }
}

This function will be invoked automatically at runtime by the shading system and gives you the ability to read and modify material properties using the MaterialInputs structure. This full definition of the structure can be found in the Material fragment inputs section. The full definition of the various members of the structure can be found in the Material models section of this document.

The goal of the material() function is to compute the material properties specific to the selected shading model. For instance, here is a fragment block that creates a glossy red metal using the standard lit shading model:

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        material.baseColor.rgb = vec3(1.0, 0.0, 0.0);
        material.metallic = 1.0;
        material.roughness = 0.0;
    }
}
   

prepareMaterial function

Note that you must call prepareMaterial(material) before exiting the material() function. This prepareMaterial function sets up the internal state of the material mdoel. Some of the APIs described in the Fragment APIs section - like shading_normal for instance - can only be accessed after invoking prepareMaterial().

It is also important to remember that the normal property - as described in the Material fragment inputs section - only has an effect when modified before calling prepareMaterial(). Here is an example of a fragment shader that properly modifies the normal property to implement a glossy red plastic with bump mapping:

fragment {
    void material(inout MaterialInputs material) {
        // fetch the normal in tangent space
        vec3 normal = texture(materialParams_normalMap, getUV0()).xyz;
        material.normal = normal * 2.0 - 1.0;

        // prepare the material
        prepareMaterial(material);

        // from now on, shading_normal, etc. can be accessed
        material.baseColor.rgb = vec3(1.0, 0.0, 0.0);
        material.metallic = 0.0;
        material.roughness = 1.0;
    }
}
   

Material fragment inputs

struct MaterialInputs {
    float4 baseColor;           // default: float4(1.0)
    float4 emissive;            // default: float4(0.0)
    float4 postLightingColor;   // default: float4(0.0)

    // no other field is available with the unlit shading model
    float  roughness;           // default: 1.0
    float  metallic;            // default: 0.0, not available with cloth or specularGlossiness
    float  reflectance;         // default: 0.5, not available with cloth or specularGlossiness
    float  ambientOcclusion;    // default: 0.0

    // not available when the shading model is subsurface or cloth
    float  clearCoat;           // default: 1.0
    float  clearCoatRoughness;  // default: 0.0
    float3 clearCoatNormal;     // default: float3(0.0, 0.0, 1.0)
    float  anisotropy;          // default: 0.0
    float3 anisotropyDirection; // default: float3(1.0, 0.0, 0.0)

    // only available when the shading model is subsurface
    float  thickness;           // default: 0.5
    float  subsurfacePower;     // default: 12.234
    float3 subsurfaceColor;     // default: float3(1.0)

    // only available when the shading model is cloth
    float3 sheenColor;          // default: sqrt(baseColor)
    float3 subsurfaceColor;     // default: float3(0.0)

    // only available when the shading model is specularGlossiness
    float3 specularColor;       // default: float3(0.0)
    float  glossiness;          // default: 0.0

    // not available when the shading model is unlit
    // must be set before calling prepareMaterial()
    float3 normal;              // default: float3(0.0, 0.0, 1.0)
}
   

Shader public APIs

   

Types

While GLSL types can be used directly (vec4 or mat4) we recommend the use of the following type aliases:

Name GLSL type Description
bool2 bvec2 A vector of 2 booleans
bool3 bvec3 A vector of 3 booleans
bool4 bvec4 A vector of 4 booleans
int2 ivec2 A vector of 2 integers
int3 ivec3 A vector of 3 integers
int4 ivec4 A vector of 4 integers
uint2 uvec2 A vector of 2 unsigned integers
uint3 uvec3 A vector of 3 unsigned integers
uint4 uvec4 A vector of 4 unsigned integers
float2 float2 A vector of 2 floats
float3 float3 A vector of 3 floats
float4 float4 A vector of 4 floats
float4×4 mat4 A 4×4 float matrix
float3×3 mat3 A 3×3 float matrix

   

Math

Name Type Description
PI float A constant that represent \(\pi\)
HALF_PI float A constant that represent \(\frac{\pi}{2}\)
saturate(float x) float Clamps the specified value between 0.0 and 1.0
pow5(float x) float Computes \(x^5\)
sq(float x) float Computes \(x^2\)
max3(float3 v) float Returns the maximum value of the specified float3
mulMat4×4Float3(float4×4 m, float3 v) float4 Returns \(m * v\)
mulMat3×3Float3(float4×4 m, float3 v) float4 Returns \(m * v\)

   

Matrices

Name Type Description
getViewFromWorldMatrix() float4×4 Matrix that converts from world space to view/eye space
getWorldFromViewMatrix() float4×4 Matrix that converts from view/eye space to world space
getClipFromViewMatrix() float4×4 Matrix that converts from view/eye space to clip (NDC) space
getViewFromClipMatrix() float4×4 Matrix that converts from clip (NDC) space to view/eye space
getClipFromWorldMatrix() float4×4 Matrix that converts from world to clip (NDC) space
getWorldFromClipMatrix() float4×4 Matrix that converts from clip (NDC) space to world space

   

Frame constants

Name Type Description
getResolution() float4 Resolution of the view in pixels: width, height, 1 / width, 1 / height
getWorldCameraPosition() float3 Position of the camera/eye in world space
getTime() float Current time in seconds, may be reset regularly to avoid precision loss
getUserTime() float4 Current time in seconds: time, (double)time - time, 0, 0
getUserTimeMode(float m) float Current time modulo m in seconds
getExposure() float Photometric exposure of the camera
getEV100() float Exposure value at ISO 100 of the camera

   

Vertex only

The following APIs are only available from the vertex block:

Name Type Description
getPosition() float4 Vertex position in the domain defined by the material (default: object/model space)
getWorldFromModelMatrix() float4×4 Matrix that converts from model (object) space to world space
getWorldFromModelNormalMatrix() float3×3 Matrix that converts normals from model (object) space to world space

   

Fragment only

The following APIs are only available from the fragment block:

Name Type Description
getWorldTangentFrame() float3×3 Matrix containing in each column the tangent (frame[0]), bi-tangent (frame[1]) and normal (frame[2]) of the vertex in world space. If the material does not compute a tangent space normal for bump mapping or if the shading is not anisotropic, only the normal is valid in this matrix.
getWorldPosition() float3 Position of the fragment in world space
getWorldViewVector() float3 Normalized vector in world space from the fragment position to the eye
getWorldNormalVector() float3 Normalized normal in world space, after bump mapping (must be used after prepareMaterial())
getWorldReflectedVector() float3 Reflection of the view vector about the normal (must be used after prepareMaterial())
getNdotV() float The result of dot(normal, view), always strictly greater than 0 (must be used after prepareMaterial())
getColor() float4 Interpolated color of the fragment, if the color attribute is required
getUV0() float2 First interpolated set of UV coordinates, if the uv0 attribute is required
getUV1() float2 First interpolated set of UV coordinates, if the uv1 attribute is required
inverseTonemap(float3) float3 Applies the inverse tone mapping operator to the specified linear sRGB color and returns a linear sRGB color. This operation may be an approximation
inverseTonemapSRGB(float3) float3 Applies the inverse tone mapping operator to the specified non-linear sRGB color and returns a linear sRGB color. This operation may be an approximation
luminance(float3) float Computes the luminance of the specified linear sRGB color

   

Compiling materials

Material packages can be compiled from material definitions using the command line tool called matc. The simplest way to use matc is to specify an input material definition (car_paint.mat in the example below) and an output material package (car_paint.filamat in the example below):

$ matc -o ./materials/bin/car_paint.filamat ./materials/src/car_paint.mat
   

Shader validation

matc attempts to validate shaders when compiling a material package. The example below shows an example of an error message generated when compiling a material definition containing a typo in the fragment shader (metalic instead of metallic). The reported line numbers are line numbers in the source material definition file.

ERROR: 0:13: 'metalic' : no such field in structure
ERROR: 0:13: '' : compilation terminated
ERROR: 2 compilation errors.  No code generated.

Could not compile material metal.mat
   

Flags

The command line flags relevant to application development are described in table 13.

Flag Value Usage
-o, —output [path] Specify the output file path
-p, —platform desktop/mobile/all Select the target platform(s)
-a, —api opengl/vulkan/all Specify the target graphics API
-S, —optimize-size N/A Optimize compiled material for size instead of just performance
-r, —reflect parameters Outputs the specified metadata as JSON
-v, —variant-filter [variant] Filters out the specified, comma-separated variants
 Table 13: List of matc flags

matc offers a few other flags that are irrelevant to application developers and for internal use only.

   

—platform

By default, matc generates material packages containing shaders for all supported platforms. If you wish to reduce the size of your material packages, it is recommended to select only the appropriate target platform. For instance, to compile a material package for Android only, run the following command:

$ matc -p mobile -o ./materials/bin/car_paint.filamat ./materials/src/car_paint.mat
   

—api

By default, matc generates material packages containing shaders for the OpenGL API. You can choose to generate shaders for the Vulkan API in addition to the OpenGL shaders. If you intend on targeting only Vulkan capable devices, you can reduce the size of the material packages by generating only the set of Vulkan shaders:

$ matc -a vulkan -o ./materials/bin/car_paint.filamat ./materials/src/car_paint.mat
   

—optimize-size

This flag applies fewer optimization techniques to try and keep the final material as small as possible. If the compiled material is deemed too large by default, using this flag might be a good compromise between runtime performance and size.

   

—reflect

This flag was designed to help build tools around matc. It allows you to print out specific metadata in JSON format. The example below prints out the list of parameters defined in Filament's standard skybox material. It produces a list of 2 parameters, named showSun and skybox, respectively a boolean and a cubemap texture.

$ matc --reflect parameters filament/src/materials/skybox.mat 
{
  "parameters": [
    {
      "name": "showSun",
      "type": "bool",
      "size": "1"
    },
    {
      "name": "skybox",
      "type": "samplerCubemap",
      "format": "float",
      "precision": "default"
    }
  ]
}
   

—variant-filter

This flag can be used to further reduce the size of a compiled material. It is used to specify a list of shader variants that the application guarantees will never be needed. These shader variants are skipped during the code generation phase of matc, thus reducing the overall size of the material.

The variants must be specified as a comma-separated list, using one of the following available variants:

Example:

--variant-filter=skinning,shadowReceiver

Note that some variants may automatically be filtered out. For instance, all lighting related variants (directionalLighting, etc.) are filtered out when compiling an unlit material.

When this flag is used, the specified variant filters are merged with the variant filters specified in the material itself.

Use this flag with caution, filtering out a variant required at runtime may lead to crashes.

   

Handling colors

   

Linear colors

If the color data comes from a texture, simply make sure you use an sRGB texture to benefit from automatic hardware conversion from sRGB to linear. If the color data is passed as a parameter to the material you can convert from sRGB to linear by running the following algorithm on each color channel:

float sRGB_to_linear(float color) {
	return color <= 0.04045 ? color / 12.92 : pow((color + 0.055) / 1.055, 2.4);
}

Alternatively you can use one of the two cheaper but less accurate versions shown below:

// Cheaper
linearColor = pow(color, 2.2);
// Cheapest
linearColor = color * color;
   

Pre-multiplied alpha

A color uses pre-multiplied alpha if its RGB components are multiplied by the alpha channel:

// Compute pre-multiplied color
color.rgb *= color.a;

If the color is sampled from a texture, you can simply ensure that the texture data is pre-multiplied ahead of time. On Android, any texture uploaded from a Bitmap will be pre-multiplied by default.

formatted by Markdeep 1.03