Surface¶

The Surface material aims to be a general purpose material that can render a broad range of surfaces with a realistic look and offers consistent responses under different lighting conditions. The Surface material is built on top of the Standard shader node and features a physically based shading model while remaining artist friendly.

In this section we will study all the Standard shader parameters.

The Standard shader uses a simple coated model suited for coated or layered materials. The model is made of two specular layers, Spec2 and Spec1 on top of a base layer that can range between a Metal, Glass, SSS or Diffuse. Finally a Dirt layer re-uses the diffuse component to simulate wear or tear.

Surface layers: Dirt Spec2 Metal Spec1 Glass SSS Diffuse

By default, if the Standard shader is left untouched, it will react as a matte diffuse material. The first seven sliders control how much the shader interpolates from the default matte diffuse surface to the other kind of surfaces. In our case, the interpolation is controlled by shading nodes (that can be texture nodes) and drive the seven sliders. Using this, we can render a same surface with different looking materials that blend in an intuitive and realistic way.

Spec 1

The blend factor of the first specular layer. A value of 0.0 disables the layer. As the value increases towards 1.0, the specular layer is totally enabled.

Metal 1

The blend factor of the metal layer. A value of 0.0 is comparable to a Lambert diffusion. As the value increases towards 1.0, the metal layer fully prevails.

Spec 2

The blend factor of the second specular layer. A value of 0.0 disables the layer. As the value increases towards 1.0, the specular layer is totally enabled. This layer is used to make coated materials like car paints, varnished woods or plastics.

Dirt

The blend factor of the dirt layer. A value of 0.0 disables the layer. As the value increases towards 1.0, the dirt layer fully prevails. Here the effect is shown on a polished metal.

SSS

The blend factor of the SSS layer. A value of 0.0 is comparable to a Lambert diffusion. As the value increases towards 1.0, the SSS layer fully prevails.

Glass

The blend factor of the glass layer. A value of 0.0 is comparable to a Lambert diffusion. As the value increases towards 1.0, the glass layer fully prevails.

To render a closed object using refraction, make sure the object is double sided and the the RenderPass > Render Settings > Raytracing > Refraction Bounces is at least 2. To render a glass, Refraction Bounces should be at least 4.

Additional parameters

Incandescence

The color used to simulate emitted light. A color of black is comparable to no light emission. It's not recommanded to use an incandescent material to light a scene since it produces noisy results compared to the counterpart mesh light method.

Aniso Rotation

The orientation of the anisotropic reflectance in texture space. A value of 0.0 is comparable to no rotation. A value of 0.5 is comparable to a 90 degrees rotation and a value of 1.0 to a 180 degrees rotation. This value affects the reflectance orientation of all the standard shader's specular layers : Spec 1, Spec 2 and Metal.

Using anisotropy usually requires enabling tangent in Attributes > Geometry > Tangent Mode, as the default tangent space may not be continuous across polygons.

Diffuse parameters

The Diffuse tab gathers all the parameters related to the base diffuse layer.

Color

The color used to multiply the diffuse component.

Translucence Color

The color used to multiply the diffuse component. This is used to simulate shading of backlighted thin objects that are modeled as two sided surface.

The User Guide/Shading/Translucence section.

Spec 1 parameters

The Spec1 tab gathers all the parameters related to the first specular layer. This specular layer is used for materials exhibiting mirror-like reflection of light. Our specular model is based on "An Anisotropic Phong BRDF Model" by Michael Ashikhmin and Peter Shirley, August 13, 2000. This model is intuitive, physically plausible and well suited for brushed metals.

Roughness

The amount of roughness in the specular reflections. Decreasing this value makes reflections more and more sharp (or less and less shiny). A value approaching 0.0 matches mirror like surfaces.

Color

The color of the specular reflections.

Anisotropy

The degree of anisotropy in the specular reflections. A value of 0.5 is comparable to isotropic reflections. As the value decreases towards 0.0 the material is more rougher in the X direction of texture space. As the value increases towards 1.0 the material is more rougher in the Y direction.

Iridescence

The amount of iridescence in the specular reflections. A value of 0.0 is comparable to no iridescence. As the value increases towards 1.0 the iridescence effect is more pronounced. Iridescence is used to render materials like beetle exoskeletons, oil spills or soap bubbles.

Iridescence Wave

The offset in the wavelength for iridescence.

Metal parameters

The Metal tab gathers all the parameters related to the metal layer if enabled. Its parameters roughness, anisotropy, iridescence and iridescence wave are all akin to the first specular layer.

Metal Color

The metal color.

Spec 2 parameters

The Spec 2 tab gathers all the parameters related to the second specular layer plus specific ones to coating. Its parameters roughness, color, anisotropy, iridescence and iridescence wave are all akin to the first specular layer.

Spec 2 Thickness

The thickness of the coated layer. The more the thickness is, the more the material will seem coated. The Absorption color is used to tint the coat.

Spec 2 IOR

The index of refraction of the coated layer. The default value is 1.3 which somewhat corresponds to a plastic coat. A value of 1.0, is comparable to a coat made or air, the rays won't be refracted and no coat will be visible.

Dirt parameters

The dirt layer is used to simulate wear and tear and simply reuses the diffuse color of the base layer and put it on top of all layers.

Dirt Color

The dirt color.

SSS parameters

The subsurface scattering simulates the transport of light through the surface of objects like marble, skin or milk. The computed SSS factor multiplies the diffuse color. An easy way to create a human skin material is to put in the diffuse color a texture of flesh and set the three gaussians to the appropriate color/depth values.

SSS Width

The width of the SSS layer. The more the value is, the deeper the light will seem to enter into the matter. As the width decreases towards 0.0, the SSS layer is comparable to a Lambert diffusion.

SSS Layer Color

The color of the first SSS gaussian.

SSS Layer Width

The width of the first SSS gaussian.

SSS Layer Weight

The weight of the first SSS gaussian.

The User Guide/Shading/Sub Surface Scattering section.

Glass parameters

Guerilla provides in its library a preset for glass objects. This preset uses the Surface shader and overrides specific attributes. To load the Glass into the RenderGraph, press Ctrl+Space, and choose Presets/Glass in the picker list, or drag'n drop the Library > Rendergraph > Presets > Glass node from the Library. You can still override the Glass aspect using the following values. Glass Color

The color of the glass. This color is used to render lacquered glass (or transparent plastic) without the need to add a special coat for it.

Glass Absorption Color

The absorption color of the glass. The absorption color is used to render tinted glass, as it will colored the refracted rays according to the Beer's law.

Glass Absorbtion Scale

The absorption scale of the glass. This parameter is used to scale the absorption, for example to fake a variation in glass thickness.

Glass IOR

The index of refraction of the glass. A value of 1.0 corresponds to the air IOR. Glasses have an IOR ranging from 1.2 to 2.0. Typical values for a crown and flint glass are 1.52 and 1.62. Diamonds have an IOR of 2.42.