Custom Material Nodes

Overview

This custom material node reconstructs a tangent-space normal vector from a LinearColor texture's Red and Green channels, assuming the normal is encoded in the RG channels (X = R, Y = G). It is designed to work with BC7 texture compression, which retains all four channels (RGBA), unlike BC5 (which only uses RG but discards BA).

Technical Details

Class: UMaterialExpressionNormalFromLinearRG

Input: InputLinearNormal (FExpressionInput)

Takes either a Texture Sample (LinearColor) or float2 input
Reads only R and G; ignores B/A

Output: Tangent-space normal float3

Features:

bFlipGreen toggle (checkbox in UI)
Tooltip and clean caption for artist clarity
Appears under "Utility" in the Material Graph

Why It's useful

BC7 lets you pack normals + masks into a single texture

With this node, Red & Green carry X/Y normal data, while Blue & Alpha remain untouched for packing roughness, metal, masks, etc.

Per-node Flip Green support

The node has a checkbox that allows Y (Green) inversion, which is helpful when working across DirectX vs OpenGL workflows or custom tangent spaces.

More efficient asset pipelines

Artists can work with a single packed texture instead of multiple maps, reducing draw calls and texture reads.

Instead of a BC5 Normal map, the user can use a BC7 Linear Color map. This enables packing for the blue and alpha channel. In this example I'm simply packing an opacity map in the alpha

The node lets the user flip the green channel of the normal map

Breakdown

1. Custom Class: Inheriting from `UMaterialExpression`

At its core, the node is a subclass of Unreal’s shader expression base:

class UMaterialExpressionNormalFromLinearRG : public UMaterialExpression

This makes it fully compatible with the Material Graph. By inheriting from UMaterialExpression, you can override key functions like:

Compile() → defines HLSL generation logic
GetCaption() → customizes the label visible in the material graph
UPROPERTY() → expose inputs and settings in the graph UI

2. Inputs: `FExpressionInput`

UPROPERTY()
FExpressionInput InputLinearNormal;

This is the primary input socket shown on the node. It accepts a float2, float3, or float4 — typically a Texture Sample (LinearColor).

Internally, it uses only the Red and Green channels, ignoring Blue and Alpha (which remain free for other data like roughness/masks).

3. Checkbox Parameter: `UPROPERTY` Toggle

UPROPERTY(EditAnywhere)
bool bFlipGreen = false;

This is an exposed checkbox in the Details Panel for the node. It lets artists or tech artists invert the Green/Y channel of the input (common when flipping between DirectX/OpenGL normal conventions).

It's marked with:

EditAnywhere to expose in the editor
Category and ToolTip for clean UI

4. `Compile()`: Shader Code Generation

This is the heart of the node. Unreal Engine uses a virtual compiler interface (FMaterialCompiler) to convert the node into HLSL at material compile time.

All logic is safe, fast, and efficient — no branching in the shader!

5. Material Graph Integration

The node automatically appears in the Material Editor after compiling the plugin because it’s:

Declared as a UCLASS
Inherits from UMaterialExpression
Registered via your plugin module’s StartupModule()

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