Rasagar/Library/PackageCache/com.unity.visualeffectgraph/Documentation~/CustomHLSL-Common.md

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 block for vertical flow (in contexts). To be valid and correctly interpreted by the VFX Graph some conventions must be adopted.

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. In both cases you are allowed to include any other valid HLSL file (using #include ""). You can also 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.

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 have the in, out or inout access modifier
• Each function parameter must be of a Supported types
• If you declare multiple functions, they must have unique names.
• Function can take a maximum of 4 parameters

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 some helper function that you don't want to be exposed in the node's choice list. In that case, simply put this special comment:

/// Hidden

Supported 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.
VFXSampler2D	Texture2D	A two-dimensional texture.
VFXSampler3D	Texture3D	A three-dimensional texture.
VFXGradient	Gradient	A structure that describes a gradient that can be sampled.
VFXCurve	AnimationCurve	A structure that describes a curve that can be sampled.
StructuredBuffer	GraphicsBuffer	A read-only buffer for storing an array of structures or basic HLSL data types.
ByteAddressBuffer	GraphicsBuffer	A read-only raw buffer.

Sampling

Textures

To sample a texture you must use the VFX Graph structure called VFXSampler2D (or VFXSample3D) which is defined as shown below:

struct VFXSampler2D
{
    Texture2D t;
    SamplerState s;
};

The easiest way to sample a texture is to use a function provided by the VFX Graph common HLSL code: 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);