Custom Material Reference

Sceneform provides default material defintions (.sfm) to make it easy for developers to get great looking results. Developers who want to deeply customize the way their assets look can create their own material definitions (*.mat files) and apply them to their assets by specifying the source attribute in the asset definition.

This page describes the structure and format of (*.mat) material definition files.

Material definitions

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

  • Name
  • User parameters
  • Material model
  • Required attributes
  • Interpolants (called variables)
  • Raster state (blending mode, etc.)
  • Shader code (fragment shader, optionally vertex shader)

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 block 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, 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, cloth, unlit. Defaults to lit.
Description
Selects the material model as described in the Material models section.
material {
    shadingModel : unlit
}

material {
    shadingModel : "lit"
}

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 the table below.

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
sampler2d 2D texture
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.

Description

Lists the parameters required by your material. These parameters can be set at runtime using Sceneform'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, tangents.
Description
Lists the vertex attributes required by the material. The position attribute is automatically included 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 : sampler2d,
           name : skybox
        }
    ],
    variables : [
         eyeDirection
    ],
    vertexDomain : device,
    depthWrite : false,
    shadingModel : unlit
}

fragment {
    void material(inout MaterialInputs material) {
        prepareMaterial(material);
        float theta = acos(variable_eyeDirection.y);
        float phi = atan(variable_eyeDirection.z / variable_eyeDirection.x) +
            (variable_eyeDirection.x > 0.0 ? 0.0 : PI);
        material.baseColor = texture(materialParams_skybox,
            vec2((phi + PI / 2.0) / (2.0 * PI), theta / PI));
    }
}

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, 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.
  • 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
}

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. Transparent materials (see blending section) never write to the depth buffer even if this property is set to true.
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 or disables two-sided rendering. When set to true, culling is automatically set to none; if the triangle is back-facing, the triangle's normal is automatically flipped to become front-facing.
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:

  • default: the transparent object is rendered normally, honoring the culling mode, etc.

  • twoPassesOneSide: the transparent object is first rendered in the depth buffer, then again in the color buffer, honoring the cullling mode. This effectively renders only half of the transparent object as shown below.

  • twoPassesTwoSides: the transparent object is rendered twice in the color buffer: first with its back faces, then with its front faces. This mode lets you render both set of faces while reducing or eliminating sorting issues, as shown below. twoPassesTwoSides can be combined with doubleSided for better effect.

material {
    transparency : twoPassesOneSide
}

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);
    }
}

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(frameUniforms.time);
    }
}

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
};

Fragment block

The fragment block must be used to control the fragment shading stage of the material. The fragment 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 model. 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)

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

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



    // only available when the shading model is cloth
    float3 sheenColor;         // default: sqrt(baseColor)
    float3 subsurfaceColor;    // default: float3(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
float4x4 mat4 A 4x4 float matrix
float3x3 mat3 A 3x3 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
mulMat4x4Float3(float4x4 m, float3 v) float4 Returns \(m * v\)
mulMat3x3Float3(float4x4 m, float3 v) float4 Returns \(m * v\)

Matrices

Name Type Description
getViewFromWorldMatrix() float4x4 Matrix that converts from world space to view/eye space
getWorldFromViewMatrix() float4x4 Matrix that converts from view/eye space to world space
getClipFromViewMatrix() float4x4 Matrix that converts from view/eye space to clip (NDC) space
getViewFromClipMatrix() float4x4 Matrix that converts from clip (NDC) space to view/eye space
getClipFromWorldMatrix() float4x4 Matrix that converts from world to clip (NDC) space
getWorldFromClipMatrix() float4x4 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 Tim since the sceneform engine was initialized, may be reset regularly to avoid precision loss
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() float4x4 Matrix that converts from model (object) space to world space
getWorldFromModelNormalMatrix() float3x3 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() float3x3 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. This operation may be an approximation
inverseTonemapSRGB(float3) float3 Applies the inverse tone mapping operator to the specified non-linear sRGB color. This operation may be an approximation
luminance(float3) float Computes the luminance of the specified linear sRGB color

Material models

Sceneform materials can use one of the following material models:

  • Lit (or standard)
  • Cloth
  • Unlit

Lit model

The lit model is Scenform'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 the table below.

Properties of the standard model

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)
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

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

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
emissive float4 rgb=[0..1], a=[-n..n] Alpha is the exposure compensation

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 the table below.

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
 
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 the table below.

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
 

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 below (click on the image to see a larger version).

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 below (click on the image to see a larger version).

Metals

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

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 below (click on the image to see a larger version).

The graph below shows common values and how they relate to the mapping function.

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

Material Reflectance Property value
Glass 3.5% 0.46
Water 2% 0.35
Common liquids 2% to 4% 0.35 to 0.5
Common gemstones 8% to 16% 0.70 to 1.0
Other dielectric materials 2% to 5% 0.35 to 0.56
Default value 4% 0.50

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. The following image compares 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 below (click on the image to see a larger version).

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 below (click on the image to see a larger version).

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. The following image compares an isotropic material (left) and an anistropic material (right).

The effect of varying anisotropy from 0.0 (left) to 1.0 (right) on a rough metal is shown below (click on the image to see a larger version).

The image below shows how the direction of the anisotropic highlights can be controlled by using either positive or negative values: positive values (left) define anisotropy in the tangent direction and negative values (right) in the bitangent direction.

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 rendering anisotropyDirection on a metal with a direction map is shown below (click on the image to see a larger version).

The direction map used to render the image above is shown below.

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. The following image compares materials without diffuse ambient occlusion (left) and with it (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. Then you can apply the base map to a simplified mesh. The following image compares a simple mesh without normal mapping (left) and with it (right).

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

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.

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).

The following image compares denim fabric rendered using the standard model (left) and the cloth model (right). Notice how the standard material model fails to capture the appearance of a sample of denim fabric (left). The surface appears rigid (almost plastic-like), more similar to a tarp than a piece of clothing. This also shows how important the softer specular lobe caused by absorption and scattering is to the faithful recreation of the fabric.

Velvet is an interesting use case for a cloth material model. As shown in the image below, 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 from the same direction as the view direction, the fibers will scatter the light backward.

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 the table below 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

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

Property Type Range Note
sheenColor float3 [0..1] Linear RGB
subsurfaceColor float3 [0..1] Linear RGB

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.

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 following image compares blue fabric with and without (left) and with (right) sheen (click on the image to see a larger version).

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 following image demonstrates the effect of subsurfaceColor. It shows white cloth (left column) vs white cloth with brown subsurface scatting (right column). Click on the image to see a larger version.

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 the table below.

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

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

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

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 following image shows an example of the unlit material model used to render debug information (click on the image to see a larger version).

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.

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