Utility Expressions

Utility Expressions nodes are nodes that can affect Materials in a number of different ways than one might be used to. For example the GIReplace node will Replace an objects indirect bounce color with a given value you input while the Linear Interpolate node will help blend between two Textures based on an Alpha input. On the following page you will find detailed descriptions for all of the Utility Expressions nodes that are available in the UE4 Material Editor.

AntialiasedTextureMask

The AntialiasedTextureMask expression allows you to create a material using a soft (anti-aliased) transition mask. The mask can be used to blend between two complex material properties or to fade out an alpha blended material (works well with SoftMasked). Simply specify a texture with the mask specified in one channel (red, green, blue, or alpha), set the used channel in the expression and specify the comparison value. Assuming the channel stores a grayscale value in the range 0 = black to 1 = white the comparison function defines if the resulting mask should be 0 or 1. This expression is a parameter, allowing the Texture property to be overridden by child MaterialInstances.

Item	Description
Properties
Threshold	Specifies the value used as the cutoff point in pixel coverage. Pixel coverage values less than this become black; values greater become white.
Channel	Specifies the channel of the Texture to use as the mask.
Texture	Specifies the mask texture to use.
Inputs
UVs	Takes in texture coordinates to apply to the texture mask.

Pseudo code:

	Result = 1
	if TextureLookup < Threshold then Result = 0
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Result = 1 if TextureLookup < Threshold then Result = 0

The actual implementation is quite a bit more complicated as it tries to return values between 0 and 1 depending on the actual pixel coverage to avoid aliasing.

Example (this tiny 128x128 texture, uncompressed for best quality):

Was used as a normal texture (left top) and used with the described material expression (bottom right):

The technique works best in magnification and with blurred input content. Compression hurts the quality a lot so try to use uncompressed low resolution textures.

BlackBody

The BlackBody expression simulates the effects of black body radiation within your Material. The user inputs a temperature (in Kelvin) and the resulting color and intensity can be used to drive Base Color and Emissive values to get a physically accurate result.

BumpOffset

BumpOffset is the Unreal Engine 4 term for what is commonly known as 'Parallax Mapping'. The Bump Offset expression allows a material to give the illusion of depth without the need for additional geometry. BumpOffset materials use a grayscale heightmap to give depth information. The brighter the value in the heightmap, the more 'popped out' the material will be; these areas will parallax (shift) as a camera moves across the surface. Darker areas in the heightmap are 'further away' and will shift the least.

ConstantBiasScale

The ConstantBiasScale expression takes an input value, adds a bias value to it, and then multiplies it by a scaling factor outputting the result. So for example, to convert input data from [-1,1] to [0,1] you would use a bias of 1.0 and a scale of 0.5.

DDX

The DDX expression exposes DDX derivative calculation, a GPU hardware feature used in pixel shader calculation.

DDY

The DDY expression exposes DDX derivative calculation, a GPU hardware feature used in pixel shader calculation.

DepthFade

The DepthFade expression is used to hide unsightly seams that take place when translucent objects intersect with opaque ones.

Click image for full size view.

DepthOfFieldFunction

The Depth of Field Function expression is designed to give artists control over what happens to a Material when it is being blurred by Depth of Field. It outputs a value between 0-1 such that 0 represents "in focus" and 1 represents "completely blurred." This is useful for interpolating between sharp and blurry versions of a texture, for instance. The Depth input allows for the existing results from the scene's Depth of Field calculations to be overridden by other calculations.

Click image for full size view.

Desaturation

The Desaturation expression desaturates its input, or converts the colors of its input into shades of gray, based a certain percentage.

Item	Description
Properties
Luminance Factors	Specifies the amount that each channel contributes to the desaturated color. This is what controls that green is brighter than red which is brighter than blue when desaturated.
Inputs
Fraction	Specifies the amount of desaturation to apply to the input. Percent can range from 0.0 (full original color, no desaturation) to 1.0 (fully desaturated).

Programmers: Define desaturated color D, input color I and luminance factor L. The output will be O = (1 - Percent)*( D.dot( I )) + Percent * I

Distance

The Distance expression computes the (Euclidian) distance between two points/colors/positions/vectors and outputs the resulting value. This works on one, two, three and four component vectors, but both inputs to the expression must have the same number of channels.

Item	Description
Inputs
A	Takes in a value or vector of any length.
B	Takes in a value or vector of any length.

Pseudo code:

	Result = length (A - B)
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Result = length (A - B)

Low level HLSL code:

	float Result = sqrt (dot (A-B, A-B))
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float Result = sqrt (dot (A-B, A-B))

DistanceFieldGradient

The DistanceFieldGradient Material Expression node, when normalized, outputs the X,Y,Z direction an object would move with in the distance field. This makes the Distance Field Gradient Material Expression node well-suited for Materials that need to simulate the flow of liquids.

Generate Mesh Distance Fields must be enabled in Project Settings under Rendering for this expression to work correctly.

Here is an example of how to use the DistanceFieldGradient Material Expression in your Materials. In this example below make sure to note that the DistanceFieldGradient was first normalized and then input into a Mask Channel node. The reason for this is because without normalizing the DistanceFieldGradient first you can not get directional data. The Mask Channel Parameter was added to allow for easier RGB channel switching with in the Material Instance.

Click image for full size view.

Here is an example of the DistanceFieldGradient in action. The image below shows what data the DistanceFieldGradient will use when the various RGB are enabled.

Click image for full size view.

DistanceToNearestSurface

The Distance To Nearest Surface Material Expression node allows Materials to sample any point in the levels Global Distance Field. This Material Expression works by outputting the signed distance in world space units from the distance field to the nearest occluders in the scene.

Generate Mesh Distance Fields must be enabled in Project Settings under Rendering for this expression to work correctly.

Here is an example of the Distance To Nearest Surface Material Expression in action.

Click image for full size view.

In this example the Distance To Nearest Surface was fed into the Opacity input on a Material and that Material was applied to a Static Mesh plane that was placed just above the levels floor. What the Distance To Nearest Surface is doing is telling the Material to only color areas red were the Static Meshes plane will start to intersect other Static Meshes placed in the scene.

FeatureLevelSwitch

The Feature Level Switch node allows you to make simplified materials for lower powered devices.

Example Usage: You might have a material with 10 textures overlapping and complex math, but just a single static texture for mobile (feature level ES2).

Item	Description
Inputs
Default	The default Feature Level.
ES2	Feature Level defined by the core capabilities of OpenGL ES2.
ES3.1	Feature Level defined by the capabilities of Metal-level devices.
SM4	Feature Level defined by the core capabilities of DX10 Shader Model 4.
SM5	Feature Level defined by the core capabilities of DX11 Shader Model 5.

Fresnel

The Fresnel expression calculates a falloff based on the dot product of the surface normal and the direction to the camera. When the surface normal points directly at the camera, a value of 0 is output. When the surface normal is perpendicular to the camera, a value of 1 is output. The result is clamped to [0,1] so you do not have any negative color in the center.

GIReplace

GIReplace allows artists to specify a different, usually simpler, expression chain when the material is being used for GI.

Example Usage: Lightmass static GI and LPV dynamic GI use it.

Item	Description
Inputs
Default	The default GI.
StaticIndirect	Used for baked indirect lighting.
DynamicIndirect	Used for dynamic indirect lighting.

Notice the two red boxes - one is bouncing off green instead of red.

This was achieved by using a new material expression.

Normally you do not want to have a completely different color but some darkening, brightening, or a minor color adjustment can be useful.

LightmassReplace

The LightmassReplace expression simply passes through the Realtime input when compiling the material for normal rendering purposes, and passes through the Lightmass input when exporting the material to Lightmass for global illumination. This is useful to work around material expressions that the exported version cannot handle correctly, for example WorldPosition.

LinearInterpolate

The LinearInterpolate expression blends between two input value(s) based on a third input value used as a mask. This can be thought of as a mask to define transitions between two textures, like a layer mask in Photoshop. The intensity of the mask Alpha determines the ratio of color to take from the two input values. If Alpha is 0.0, the first input is used. If Alpha is 1.0, the second input is used. If Alpha is between 0.0 and 1.0, the output is a blend between the two inputs. Keep in mind that the blend happens per channel. So, if Alpha is an RGB color, Alpha's red channel value defines the blend between A and B's red channels independently of Alpha's green channel, which defines the blend between A and B's green channels.

Item	Description
Properties
Const A	The value mapped to 0.0. Only used if the A input is unconnected.
Const B	The value mapped to 1.0. Only used if the B input is unconnected.
Const Alpha	Takes in the value to use as the mask alpha. Only used if the Alpha input is unconnected.
Inputs
A	Takes in the value(s) mapped to 0.0.
B	Takes in the value(s) mapped to 1.0.
Alpha	Takes in the value to use as the mask alpha.

Programmers: LinearInterpolate does a per-channel lerp between A and B based on the parametric value Alpha.

Noise

The Noise expression creates a procedural noise field, giving you control over how it is generated.

Previous Frame Switch

The Previous Frame Switch Material Expression enables you to support complex vertex animations implemented in your materials to generate correct motion vectors so that they can work correctly with Temporal AA and Motion Blur.

Materials that are only a function of time already work without modification, however, they cannot account for other variables, such as Material Parameters, that can affect the animation. The Previous Frame Switch Material Expression enables Artists to solve these types of problem manually by tracking how these parameters change, for instance, in Blueprints, where they can manually provide expressions for motion vector generation that is caused by changes in World Position Offset between frames.

Velocities from vertex deformation must be enabled in Project Settings under Rendering for this expression to work:

• 4.24 and later versions use Accurate velocities from Vertex Deformation
• 4.25 and future versions use Output velocities from vertex deformation

Here is an example using Previous Frame Switch Material Expression in a Material.

In this example, the Previous Frame Switch is using a constant value to control the directional blur through a Multiply node.

In this example, you can see how this is being used in Epic's own games, like Fortnite, to control the motion blur with a Vertex Animation that assembles on screen. The animation on the right is using Previous Frame Switch to add some motion blur, while the animation on the left is not.

QualitySwitch

The QualitySwitch expression allows for the use of different expression networks based on the engine is switched between quality levels, such as using lower quality on lower-end devices.

RotateAboutAxis

The RotateAboutAxis expression rotates a three-channel vector input given the rotation axis, a point on the axis, and the angle to rotate. It is useful for animations using WorldPositionOffset that have better quality than simple shears.

Item	Description
Inputs
NormalizedRotationAxis	Takes in a normalized (0-1) vector which represents the axis about which the object will rotate.
RotationAngle	The angle of rotation. A value of 1 equals a full 360-degree rotation.
PivotPoint	Takes in the three-channel vector representing the pivot point about which the object will rotate.
Position	Takes in the three-channel vector representing the position of the object. When the RotateAboutAxis expression is created, a WorldPosition expression is automatically created and connected to this input.

In the above example, the preview plane would appear to spin on its vertical axis.

SphereMask

The SphereMask expression outputs a mask value based on a distance calculation. If one input is the position of a point and the other input is the center of a sphere with some radius, the mask value is 0 outside and 1 inside with some transition area. This works on one, two, three, and four component vectors

In this example, the preview object will smoothly fade to black as the camera exceeds 256 units away from it.

Thin Translucent

The Thin Translucent Material Output expression accurately represents physically based transparent materials in a single pass. This enables you to create true tinted or colored transparent materials that accurately respond to lighting and shading.

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When creating a tinted glass material, a white specular highlight and tinted background are needed. These are rendered in a single pass with a physically based shader that accounts for light bounces from the air into the glass and the glass into the air.

Enable Thin Translucent material output by setting the following in the Material Details panel:

• Blend Mode: Translucent
• Shading Model: Thin Translucent
• Lighting Mode: Surface ForwardShading

Vector Noise