11.12.2023 - Session 02

UE Basic Materials Intro

Materials in Unreal Engine define the surface properties of the objects in your scene. In the broadest sense, you can think of a Material as the "paint" that is applied to a mesh to control its visual appearance. In more technical terms, Materials tell the render engine exactly how a surface should interact with the light in your scene. Materials define every aspect of the surface including color, reflectivity, bumpiness, transparency, and so on. These calculations are done using data that is input to the Material from a variety of images (textures) and node-based Material expressions, as well as from various property settings inherent to the Material itself.

Base Color

Base Color defines the overall color of the Material. In principle, Base Color should represent the diffuse light reflected off a surface, minus any specular reflections/highlights. If taken from the real world, base color textures should be photographed using a polarizing filter. Polarization removes the specular of nonmetals when aligned.

Metallic

The Metallic input controls how 'metal-like' your surface will be. Metallic accepts any value between 0 and 1, but in a majority of cases Metallic is considered an either/or property. Nonmetals have a Metallic value of 0. Metals have a Metallic value of 1. For pure surfaces, such as pure metal, pure stone, or pure plastic this value will be 0 or 1, not anything in between. When creating hybrid surfaces like corroded, dusty, or rusty metals, you may find that you need some value between 0 and 1.

Specular

Specularity is a measure of how much light a surface reflects. The Specular input takes a value between 0 and 1, and defines the extent to which a surface is reflective: Value of 0 - Fully non-reflective Value of 1 - Fully reflective The default value is 0.5, which represents approximately 4% reflectivity.

Roughness

The Roughness input controls how rough or smooth a Material's surface is. Rough Materials scatter reflected light in more directions than smooth Materials. This value controls how blurry or sharp a reflection is (or how broad or tight a specular highlight is). A Roughness of 0 (smooth) results in a mirror-like reflection. A Roughness of 1 (rough) results in a diffuse or matte surface.

Emissive Color

The Emissive Color input controls which parts of your Material will glow or emit light, and the brightness of the emission. Ideally this input will receive a masked texture (mostly black except the areas that need to glow). Values greater than 1 are allowed as HDR lighting is supported. <be>
Opacity

The Opacity input is enabled when the Translucent Blend Mode is selected, typically for Translucent, Additive, and Modulated Materials. 0.0 represents a completely transparent Material. 1.0 represents a fully opaque Material. Fractional values between 0 and 1 produce semi-transparent or translucent Materials. Opaque and masked blend modes also use Opacity when using one of the subsurface shading models.

Normal

The Normal input takes in a normal map, which is used to add significant physical detail to the surface by modifying the "normal," or facing direction, of each individual pixel.

Instanced Materials

Material instancing in Unreal Engine is used to change the appearance of a Material without incurring an expensive recompilation of the Material. Whereas a typical Material cannot be changed without recompiling (something that must happen prior to gameplay), a parameterized Material can be edited in a Material instance without such recompilation. This has numerous workflow advantages, and can improve Material performance.

Material Parameterization

It is important to know that you cannot edit every single characteristic of a Material instance by default. To make Material attributes editable within an instance, you must designate them as parameters in the parent Material. This is called parameterizing your Material. A parameter is created like any other data node in the Material Editor, and contains the same information as its non-parameterized counterpart. For example, a Constant expression contains a single floating-point value, and is frequently used to control Material inputs like Roughness and Metallic. The parameterized version of this node is called a Scalar Parameter.

Expression Index

This is a reference list of many, but not all, Material Expressions. All links shown here can also be accessed through the Expression Types pages listed above. Additionally, you can use Ctrl+F to find the expression node you need and follow the link to its description.
More info under:
https://docs.unrealengine.com/5.0/en-US/unreal-engine-material-expressions-reference/

More info about PBR Textures:
https://www.cgbookcase.com/learn/how-to-use-pbr-textures-in-unreal-engine/#importing-textures
For free PBR Texures outside quixel megascan:
https://www.textures.com/browse/pbr-materials/114558