In this lesson, you will learn how to manipulate the Anisotropy input in your Master Material to stretch surface highlights, creating the signature look of brushed metal or fine hair.
Understanding Anisotropy
In standard rendering, metallic highlights are spherical, reflecting light equally in all directions. However, materials like brushed aluminum or stainless steel have microscopic, parallel grooves. These grooves cause the light to scatter—or "stretch"—perpendicular to the grain. In Unreal Engine, we simulate this by providing a vector that tells the engine which way these micro-grooves are aligned.
Implementing the Effect
To unlock this, set your Material's Shading Model to Default Lit and navigate to the Advanced section of your Material Details panel to enable Anisotropy.
Once enabled, the Anisotropy input slot becomes active. It accepts a scalar value between -1.0 and 1.0:
- 0: Standard, isotropic highlight.
- Positive/Negative values: Stretches the highlight along the tangent or bitangent of the surface.
To control the orientation (the direction the highlight stretches), you typically use a Tangent input. If you leave this unconnected, Unreal uses the underlying mesh's UV layout as the default flow. For precision, you can feed a Texture Sample (typically a normal map or a dedicated flow map) into the Tangent node.
Here is how you might structure the logic in your material graph:
// Example of a simple brush-direction influence
// Multiply a constant by a mask to drive the Anisotropy intensity
float AnisotropyIntensity = 0.8;
float AnisotropyMask = TextureSample(FlowMap);
Pro-Tip for Brushed Metal
When working with metallic surfaces, always ensure your Metallic input is set to 1.0. Anisotropy is most visually impactful when the material is highly reflective. If the highlight looks too "tight," increase your Roughness slightly, as real-world brushed metals rarely have perfectly smooth finishes. If the highlights appear jagged, check your mesh's UV seams, as the tangent direction relies heavily on clean, continuous UV flow to maintain a smooth, streak-like highlight.
Key Takeaway: Anisotropy allows you to break the spherical highlight of standard materials by using the Tangent input to define the direction of micro-surface grooves, essential for realistic brushed metals.