Shading Models

Shading Models control how your Material will reflect incoming light. Or, put another way, it controls how the input data that makes up the Material will be used to create the final look.

LightingModelProperties.png

There are six Shading Models in Unreal Engine 4: Default Lit, Unlit, Subsurface, Preintegrated Skin, Clear Coat, and Subsurface Profile. The first, Default Lit, is the one you will likely use for most of your surfaces, while the remaining five are special case shading models, intended to aid in producing more realistic results on certain types of objects and surfaces.

The following examples are all using Materials with their Blend Modes set to Opaque.

Default Lit

Default Lit is, as the name suggests, the default shading model and will likely be the one that you will use most often. This shading model makes use of direct and indirect lighting, as well as specularity for reflections.

DefaultLitObjects.png

When using the Default Lit Shading Model, you are given access to the following inputs:

  • Base Color

  • Metallic

  • Specular

  • Roughness

  • Emissive Color

  • Normal

  • World Position Offset

  • Ambient Occlusion

Unlit

The Unlit Shading Model only outputs Emissive for color, making this perfect for special effects such as fire or illuminating objects. Note that in this example, the Material is not casting light into the scene. Instead, its high Emissive value results in a glow effect, which is also picked up by the Dirt Mask applied to the camera. It seems to illuminate, but no lighting or shadows will be cast by this object.

UnlitExample.png

When using the Unlit Shading Model, you are given access to the following inputs:

  • Emissive Color

  • World Position Offset

Subsurface

The Subsurface Shading Model simulates the effect of Subsurface Scattering. This is a real-world phenomenon in which light penetrates a surface and then diffuses throughout it. It can be most readily seen on such objects as ice, wax candles, and skin. The Subsurface model (as well as the Preintegrated Skin model described below) relies on the Subsurface Color input. You can think of this as the color of the matter just beneath the surface of the object, such that when light scatters through the surface, this color will be seen. For human skin, you can often get good results from using a dark red color. In the Ice Elemental below, a dark blue-green color (with a variety of calculations based on lighting) is used to give a sense of translucent depth to the surface.

For more information on the Subsurface Shading model, please see the Subsurface Shading Model documentation .

IceElemental.png

When using the Subsurface Shading Model, you are given access to the following inputs:

  • Base Color

  • Metallic

  • Specular

  • Roughness

  • Emissive Color

  • Opacity

  • Normal

  • World Position Offset

  • Subsurface Color

  • Ambient Occlusion

Preintegrated Skin

The Preintegrated Skin Shading Model is very similar in nature to the Subsurface model, but geared toward low performance cost skin rendering on human characters. While not physically perfect, this Shading Model will often give nice results on your characters while being a bit cheaper to render than the Subsurface method. In the image below, the character's flesh has been set to use the Preintegrated Skin Shading Model.

InfiltratorPreintegrated.png

When using the Preintegrated Skin Shading Model, you are given access to the following inputs:

  • Base Color

  • Metallic

  • Specular

  • Roughness

  • Emissive Color

  • Opacity

  • Normal

  • World Position Offset

  • Subsurface Color

  • Ambient Occlusion

Clear Coat

The Clear Coat Shading Model can be used to better simulate multilayer materials that have a thin translucent layer of film over the surface of a standard material. In addition to this, the Clear Coat Shading Model can also be used with either a metal or nonmetal surfaces. In fact, it was specifically designed to model this second class of smooth colored films over a non-colored metal. Some examples include acrylic or lacquer clear coats, and colored films over metals such as soda cans and car paint.

Monte Carlo Reference

UE4

(Note that the flecks were done in the material editor and are not part of the shading model)

Dual-Normal Clear Coat

The Clear Coat Shading Model also has the option to add a 2nd Normal Map for the surface that is below the clear coat layer. This allows us to more accurately model complex materials such as carbon fiber which have a different geometric surface than the clear coat layer.

Dual_Clear_Coat_Old Dual_Clear_Coat_New (Dual_Clear_Coat_Photo
Old UE4 Clear Coat New UE4 Clear Coat with Bottom Normal Actual Photograph

When using the Clear Coat Shading Model or the Clear Coat with Dual Normals Shading Model, you are given access to the following inputs:

  • Base Color

  • Metallic

  • Specular

  • Roughness

  • Emissive Color

  • Opacity

  • Normal

  • World Position Offset

  • Ambient Occlusion

  • Clear Coat

  • Clear Coat Roughness

Subsurface Profile

The Subsurface Profile Shading Model is very similar in nature to both the Subsurface model and the Preintegrated Skin Shading Model, but geared towards higher end skin rendering. If you are trying to simulate skin, epically human skin, this is the best Shading Model to use in order to do so.

Standard Shading

Subsurface Profile Shading

When using the Subsurface Profile Shading Model, you are given access to the following inputs:

  • Base Color

  • Specular

  • Roughness

  • Emissive Color

  • Opacity

  • Normal

  • World Position Offset

  • Ambient Occlusion

Two Sided Foliage

The Two Sided Foliage shading model was introduced to help give foliage a more natural and uniform look when being lit. When using the Default Lit shading model for foliage parts of the foliage can look almost black. The Default Lit shading model also does not simulate any kind of light transmission which is key to having believable looking foliage. The Two Sided Foliage shading model helps to eliminate these issues by using a variation of the Subsurface scattering lighting model that accounts for objects that are very thin helping to give the illusion that light is being transferred through the foliage. This also helps to eliminate the dark parts of the foliage and give the foliage a more uniform look to it's lighting.

Two Sided Foliage Enabled

Two Sided Foliage Disabled

When using the Two Sided Foliage Model, you are given access to the following inputs.

  • Base Color

  • Specular

  • Roughness

  • Emissive Color

  • Opacity

  • Normal

  • World Position Offset

  • Subsurface Color

  • Ambient Occlusion

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