XML3D Standard Surface Shader Documentation

Matte Shader

Uniform Resource Name (URN):
```
urn:xml3d:shader:flat
```

This shader colors the surface of an object using a single color L_e, which can be defined using the emissiveColor parameter:

L_c = L_e = emissiveColor

Example:

                <shader id="flat" script="urn:xml3d:shader:matte">
                  <float3 name="emissiveColor">1.0 0.0 0.0</float3>
                </shader>

Parameters

Name	Type	Default Value	Description
emissiveColor	<float3>	`1 1 1`	Defines the emissive color of the surface.

Diffuse Shader

Uniform Resource Name (URN):
```
urn:xml3d:shader:diffuse
```

The Diffuse Shader extends the Flat Shader by Lambertian reflectance:

L_c(p) = L_e + L_d(p)

The shading depends on the incident radiance and the angle between the light source and the surface normal. The diffuse term L_d(p) models the perfect diffuse response of a Lambertian surface:

L_d(p) =

∫
Ω(p)

k_d(p) L_i(p; ω_i) cosθ_idω_i

where

θ_i is the angle between the surface normal and the direction of the incoming light

k_d(p) is diffuseColor *

{

useVertexColor == false: the value sampled from diffuseTexture or 1.0 if diffuseTexture is not specified.

useVertexColor == true: the vertex attribute color interpolated for (p).

kd(p) = diffuseColor *  ( useVertexColor ? va("color") :  diffuseTexture ? sample(diffuseTexture, va("texcoord")) : 1.0 )

A possible alpha value in the diffuseTexture sample is ignored.

Example:

                <shader id="flat" script="urn:xml3d:shader:diffuse">
                  <float3 name="diffuseColor">1.0 0.0 0.0</float3>
                  <texture name="diffuseTexture"><img src="logo.png"/></texture>
                </shader>

Parameters

Name	Type	Default Value	Description
emissiveColor	<float3>	`0 0 0`	Defines the emissive color of the surface.
diffuseColor	<float3>	`1 1 1`	Defines the base color of the surface.
diffuseTexture	<texture>	-	Defines the texture to sample the diffuse color from.
useVertexColor	<bool>	`false`	Turns on/off usage of the vertex attribute "color" as diffuseColor.

Phong Shader

Uniform Resource Name (URN):
```
urn:xml3d:shader:phong
```

The Phong Shader extends the Diffuse Shader by a glossy term for specular highlights, perfect reflection and simple transparency.

Glossy term

The glossy term L_g, simulates the specular highlights due to microfacets on the surface. The result depends on the surface location p and view direction w:

L_p(p,w) = L_e + L_d(p) + L_g(p,w)

L_gis calculated using the specular highlight term of the Phong reflection model:

L_g(p,ω_i) =

∫
Ω(p)

k_s (cosθ_v)ⁿ L_i(p; ω_i) cosθ_idω_i

where

θ_v is the angle between the viewing direction and the perfect reflection direction
θ_i is the angle between the surface normal and the direction of the incoming light
k_s is the specularColor parameter
n is the shininess parameter linearly mapped to 0-512.

Perfect reflection

The term L_r(p,w) describes the irradiance coming from the direction of the perfect reflection:

L_r(p,ω_i) = k_r L(p',ω_i')

where

k_r is the reflectionColor parameter

This is typically done shooting secondary rays in direction of the perfect reflection or by rendering a dynamic reflection map.

Transparency

The transparency is a simple blending operation and thus differs from real refraction calculation. The result is a weighted mix of L_p(p,w) with the underlying fragment color L_c(p',w) (typically in the frame buffer for z-sorted rasterization and the result of a refractive ray in the same direction as the incoming ray for ray tracing):

L_c(p,w) =  (1-t(p)) * L_p(p,w)  + t(p) * L_c(p',w)

where t is the transparency of the surface at point p. If diffuseTexture is defined and has an alpha channel, t is 1 - alpha value at the sample defined by vertex attribute "texcoord". Otherwise the transparency parameter is used.

Example:

                <shader id="myPhong" script="urn:xml3d:shader:phong">
                </shader>

Parameters

Name	Type	Default Value	Description
emissionColor	<float3>	`0 0 0`	Defines the self-emission of the surface.
ambientColor	<float3>	`0 0 0`	Defines the ambient color of the surface.
diffuseColor	<float3>	`1 1 1`	Defines the diffuse color of the surface.
diffuseTexture	<texture>	-	Defines the texture to sample the diffuse color from.
specularColor	<float3>	`0 0 0`	Defines the specular value of the surface
shininess	<float>	`0.2`	Shininess of the surface (values in [0,1])
reflectionColor	<float3>	`0 0 0`	Factor to scale the contribution from the perfect reflection.
transparency	<float>	`0 0 0`	Factor to scale the contribution from the perfect reflection.
castShadow	<int>	`≥1`	Turns on/off shadow cast. Specify `0` to activate shadow cast and a value `≥1` otherwise.