Custom HLSL Nodes (block and operator)

These Custom HLSL nodes let you execute custom HLSL code during particle simulation. You can use an operator for horizontal flow or a block for vertical flow (in contexts).

Node settings

Setting name	UI	Location	Action
Name	Text field	Inspector	Choose the name of the block
HLSL Code	Button	Graph node	Opens a code editor window
Available Function	Drop down	Graph node	Pick which function to execute

HLSL Code

The HLSL code can be either embedded in the node or an HLSL file can be used. You can provide multiple functions in the same HLSL source (embedded or file), in this case, you'll have to pick the desired one in a choice list in the node.
To be valid and correctly interpreted by the VFX Graph, some conventions must be adopted.

Function declaration

To be properly recognized by VFX Graph the function must fulfill the following requirements:

• Return a supported type Supported types
• Each function parameter must be of a Supported types
• If you declare multiple functions, they must have unique names.

Inline documentation

You can specify a tooltip for each function parameter using the three slash comment notation as shown below:

/// <parameter-name>: the tooltip's text

These comments must be right above the function declaration.

/// a: the tooltip for parameter a
/// b: the tooltip for parameter b
float Distance(in float3 a, in float3 b)
{
  return distance(a, b);
}

You may want to write a helper function that you don't want to be exposed in the node's choice list.
In that case, simply put this special comment above the function declaration:

/// Hidden
float SomeFunction(in float a)
{
  ...
}

Important

When you need to implement helper functions, you must use a HLSL file, not the embedded HLSL code.

Supported types

Basic types

HLSL Type	Port Type	Description
bool	bool	A scalar value represented as a boolean.
uint	uint	A scalar value represented as an unsigned integer.
int	int	A scalar value represented as a integer.
float	float	A scalar value represented as a float.
float2	Vector2	A structure containing two float.
float3	Vector3	A structure containing three float.
float4	Vector4	A structure containing four float.
float4x4	Matrix4x4	A structure representing a matrix.
VFXGradient	Gradient	A structure that describes a gradient that can be sampled.
VFXCurve	AnimationCurve	A structure that describes a curve that can be sampled.

Texture types

HLSL Type	Port Type	Description
VFXSampler2D	Texture2D	A structure containing a sampler state and a two-dimensional texture.
VFXSampler3D	Texture3D	A structure containing a sampler state and a three-dimensional texture.
VFXSampler2DArray	Texture2DArray	A structure containing a sampler state and an array of two-dimensional textures.
VFXSamplerCube	TextureCube	A structure containing a sampler state and a cube texture.

Buffers

HLSL Type	Port Type	Description
StructuredBuffer	GraphicsBuffer	A read-only buffer for storing an array of structures or basic HLSL data types.
ByteAddressBuffer	GraphicsBuffer	A read-only raw buffer.
Buffer	GraphicsBuffer	A read-only raw buffer for basic HLSL types.
AppendStructuredBuffer	GraphicsBuffer	A read-only buffer where you can append new entries.
ConsumeStructuredBuffer	GraphicsBuffer	A read-only buffer where you can remove entries.
RWBuffer	GraphicsBuffer	A read-write raw buffer for basic HLSL types.
RWStructuredBuffer	GraphicsBuffer	A read-write buffer for storing an array of structures or basic HLSL data types.
RWByteAddressBuffer	GraphicsBuffer	A read-write raw buffer.

Sampling

Textures

The simplest way to sample a texture is to use the VFX Graph structure called VFXSampler2D (or VFXSample3D) which is defined as shown below:

struct VFXSampler2D
{
    Texture2D t;
    SamplerState s;
};

VFX Graph provides this function: float4 SampleTexture(VFXSampler2D texure, float2 coordinates).
But you can also use HLSL built-in functions to sample a texture using the VFXSampler2D fields.
In that case, since this is used in a compute shader you must specify which mipmap level to sample (use SampleLevel for instance).

Buffers

You can use two types of buffers: ByteAddressBuffer and StructuredBuffer<>. In both cases the usage is the same as in any HLSL code:

• ByteAddressBuffer: use the Load function

uint char = buffer.Load(attributes.particleId % count);

• StructuredBuffer<>: use classic index accessor

float angle = phase + freq * buffer[attributes.particleId % bufferSize];

Gradient

Gradients are handled specifically in VFX Graph (they are packed in a single texture) so you must use a dedicated function to sample them.
Here is the function definition: SampleGradient(VFXGradient gradient, float t)

float3 color = SampleGradient(grad, t);

Curve

Sampling a curve is really similar to sampling a gradient.
Here is the function definition: SampleCurve(VFXCurve curve, float t)

float r = SampleCurve(curve, t);

HLSL Code Editor

You can edit your HLSL code directly inside Unity Editor by clicking the Edit button on the node in the graph (see screenshot above).
The HLSL Code Editor supports the following shortcuts:

• Ctrl + Z and Ctrl + Y for Undo/Redo (independent from the Unity Editor undo stack)
• Ctrl + S to save the current HLSL code
• Ctrl + Mouse Wheel to change the font size

If you need to write down the name of a particle attribute, you can drag&drop drop the attribute from the blackboard to the code editor. This way you avoid any risk of typo.