Houdini VEX

https://www.sidefx.com/docs/houdini/vex/
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VEX is a high-performance expression language used in Houdini for writing shaders, custom nodes, and...
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### Get Input Start Time in COP2 Context (VEX)

Source: https://www.sidefx.com/docs/houdini/vex/functions/istarttime

The `istarttime` function retrieves the start time of a specified input in the COP2 context. It takes one argument, `opinput`, which is the index of the input to query (0-based). It returns a float representing the start time.

```vex
float istarttime(int opinput)
{
  // Returns the start time of the specified input.
  return istarttime(opinput);
}
```

--------------------------------

### Path and Name Construction

Source: https://www.sidefx.com/docs/houdini/vex/functions/detailattribtype

Utilities for creating valid USD attribute, collection, property, and relationship paths, as well as conforming names and paths.

```APIDOC
## usd_makeattribpath

### Description
Constructs an attribute path from a primitive path and an attribute name.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **primPath** (string) - Required - The path to the USD primitive.
- **attribName** (string) - Required - The name of the attribute.

### Response
#### Success Response (200)
- **attributePath** (string) - The constructed attribute path.

## usd_makecollectionpath

### Description
Constructs a collection path from a primitive path and a collection name.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **primPath** (string) - Required - The path to the USD primitive.
- **collectionName** (string) - Required - The name of the collection.

### Response
#### Success Response (200)
- **collectionPath** (string) - The constructed collection path.

## usd_makepropertypath

### Description
Constructs a property path from a primitive path and a property name.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **primPath** (string) - Required - The path to the USD primitive.
- **propertyName** (string) - Required - The name of the property.

### Response
#### Success Response (200)
- **propertyPath** (string) - The constructed property path.

## usd_makerelationshippath

### Description
Constructs a relationship path from a primitive path and a relationship name.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **primPath** (string) - Required - The path to the USD primitive.
- **relationshipName** (string) - Required - The name of the relationship.

### Response
#### Success Response (200)
- **relationshipPath** (string) - The constructed relationship path.

## usd_makevalidprimname

### Description
Forces a string to conform to the rules for naming USD primitives.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **inputName** (string) - Required - The input string.

### Response
#### Success Response (200)
- **validName** (string) - The string conforming to USD primitive naming rules.

## usd_makevalidprimpath

### Description
Forces a string to conform to the rules for paths to USD primitives.

### Method
GET (conceptual)

### Endpoint
N/A (VEX function)

### Parameters
#### Path Parameters
- **inputPath** (string) - Required - The input string.

### Response
#### Success Response (200)
- **validPath** (string) - The string conforming to USD primitive path rules.

```

--------------------------------

### Get COP Input Start Frame (VEX)

Source: https://www.sidefx.com/docs/houdini/vex/functions/istart

The 'istart' function retrieves the starting frame number of a specified input for COP (Compositing Operators) nodes in VEX. It takes the input number as an integer argument and returns the starting frame as an integer. This function is context-specific to 'cop2'.

```vex
int istart(int opinput)
```

--------------------------------

### Path Construction and Navigation

Source: https://www.sidefx.com/docs/houdini/vex/functions/windingnumber2d

Functions for creating and navigating paths within the USD scene graph.

```APIDOC
## USD Path Construction and Navigation

### Description
This section includes utility functions for constructing valid USD paths and navigating the scene hierarchy, such as getting parent paths or creating property paths.

### Functions

*   **usd_makeattribpath(primpath, attribname)**
    *   **Description**: Constructs an attribute path from a primitive path and an attribute name.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `primpath` (string) - Required - The path to the USD primitive.
        *   `attribname` (string) - Required - The name of the attribute.

*   **usd_makecollectionpath(primpath, collectionname)**
    *   **Description**: Constructs a collection path from a primitive path and a collection name.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `primpath` (string) - Required - The path to the USD primitive.
        *   `collectionname` (string) - Required - The name of the collection.

*   **usd_makepropertypath(primpath, propertyname)**
    *   **Description**: Constructs a property path from a primitive path and a property name.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `primpath` (string) - Required - The path to the USD primitive.
        *   `propertyname` (string) - Required - The name of the property.

*   **usd_makerelationshippath(primpath, relname)**
    *   **Description**: Constructs a relationship path from a primitive path and a relationship name.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `primpath` (string) - Required - The path to the USD primitive.
        *   `relname` (string) - Required - The name of the relationship.

*   **usd_makevalidprimname(name)**
    *   **Description**: Forces a string to conform to the rules for naming USD primitives.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `name` (string) - Required - The name to validate.

*   **usd_makevalidprimpath(path)**
    *   **Description**: Forces a string to conform to the rules for paths to USD primitives.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `path` (string) - Required - The path to validate.

*   **usd_parentpath(primpath)**
    *   **Description**: Returns the path of the primitive’s parent.
    *   **Method**: N/A (VEX function)
    *   **Parameters**: 
        *   `primpath` (string) - Required - The path to the USD primitive.

```

--------------------------------

### CHOP VEX Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/chstart

Documentation for CHOP-related VEX functions, including how to get the start sample of an input.

```APIDOC
## CHOP VEX Functions

### `chstart()`

Returns the start sample of the input specified.

**Context(s):** chop

**Signature:** `int chstart()
`

**Description:** Uses `-1` as the `opinput`.

### `chstart(int opinput)`

Returns the index of the first sample in the channel data in the given CHOP input.

**Context(s):** chop

**Signature:** `int chstart(int opinput)
`

**Parameters:**
#### Path Parameters
- **opinput** (int) - Required - The input number to read from, starting from 0. If `-1`, uses the current CHOP node or input `0` if it is connected.

**Notes:**
- To get the start frame, use `chstartf`.
- To get the start time in seconds, use `chstartt`.

**See also:**
- `chstartf`
- `chstartt`
```

--------------------------------

### USD Path and Property Construction Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/erfc

Functions for creating valid USD paths and property paths.

```APIDOC
## USD Path and Property Construction Functions

### Description
Utility functions for constructing valid paths and property paths within USD.

### Functions

- **usd_makeattribpath(primitive_path, attribute_name)**
  - **Description**: Constructs an attribute path from a primitive path and an attribute name.
  - **Parameters**:
    - `primitive_path` (string): The path to the primitive.
    - `attribute_name` (string): The name of the attribute.
  - **Returns**: String representing the full attribute path.

- **usd_makecollectionpath(primitive_path, collection_name)**
  - **Description**: Constructs a collection path from a primitive path and a collection name.
  - **Parameters**:
    - `primitive_path` (string): The path to the primitive.
    - `collection_name` (string): The name of the collection.
  - **Returns**: String representing the full collection path.

- **usd_makepropertypath(primitive_path, property_name)**
  - **Description**: Constructs a property path from a primitive path and a property name.
  - **Parameters**:
    - `primitive_path` (string): The path to the primitive.
    - `property_name` (string): The name of the property.
  - **Returns**: String representing the full property path.

- **usd_makerelationshippath(primitive_path, relationship_name)**
  - **Description**: Constructs a relationship path from a primitive path and a relationship name.
  - **Parameters**:
    - `primitive_path` (string): The path to the primitive.
    - `relationship_name` (string): The name of the relationship.
  - **Returns**: String representing the full relationship path.

- **usd_makevalidprimname(name)**
  - **Description**: Forces a string to conform to the rules for naming USD primitives.
  - **Parameters**:
    - `name` (string): The string to validate.
  - **Returns**: A valid USD primitive name string.

- **usd_makevalidprimpath(path)**
  - **Description**: Forces a string to conform to the rules for paths to USD primitives.
  - **Parameters**:
    - `path` (string): The string to validate as a path.
  - **Returns**: A valid USD primitive path string.

```

--------------------------------

### Path Construction Utilities

Source: https://www.sidefx.com/docs/houdini/vex/contexts/fog

Functions for constructing valid USD paths for attributes, collections, properties, and relationships.

```APIDOC
## POST /websites/sidefx_houdini_vex/usd_makeattribpath

### Description
Constructs an attribute path from a primitive path and an attribute name.

### Method
POST

### Endpoint
/websites/sidefx_houdini_vex/usd_makeattribpath

### Parameters
#### Request Body
- **prim_path** (string) - Required - The path to the primitive.
- **attrib_name** (string) - Required - The name of the attribute.

### Response
#### Success Response (200)
- **attribute_path** (string) - The constructed attribute path.

#### Response Example
```json
{
  "attribute_path": "/World/MyPrim.myAttribute"
}
```
```

```APIDOC
## POST /websites/sidefx_houdini_vex/usd_makecollectionpath

### Description
Constructs a collection path from a primitive path and a collection name.

### Method
POST

### Endpoint
/websites/sidefx_houdini_vex/usd_makecollectionpath

### Parameters
#### Request Body
- **prim_path** (string) - Required - The path to the primitive.
- **collection_name** (string) - Required - The name of the collection.

### Response
#### Success Response (200)
- **collection_path** (string) - The constructed collection path.

#### Response Example
```json
{
  "collection_path": "/World/MyPrim/MyCollection"
}
```
```

```APIDOC
## POST /websites/sidefx_houdini_vex/usd_makepropertypath

### Description
Constructs a property path from a primitive path and a property name.

### Method
POST

### Endpoint
/websites/sidefx_houdini_vex/usd_makepropertypath

### Parameters
#### Request Body
- **prim_path** (string) - Required - The path to the primitive.
- **property_name** (string) - Required - The name of the property.

### Response
#### Success Response (200)
- **property_path** (string) - The constructed property path.

#### Response Example
```json
{
  "property_path": "/World/MyPrim.myProperty"
}
```
```

```APIDOC
## POST /websites/sidefx_houdini_vex/usd_makerelationshippath

### Description
Constructs a relationship path from a primitive path and a relationship name.

### Method
POST

### Endpoint
/websites/sidefx_houdini_vex/usd_makerelationshippath

### Parameters
#### Request Body
- **prim_path** (string) - Required - The path to the primitive.
- **relationship_name** (string) - Required - The name of the relationship.

### Response
#### Success Response (200)
- **relationship_path** (string) - The constructed relationship path.

#### Response Example
```json
{
  "relationship_path": "/World/MyPrim.myRelationship"
}
```
```

--------------------------------

### Get Channel Primitive Start Time in VEX

Source: https://www.sidefx.com/docs/houdini/vex/functions/chprim_length

The chprim_start function retrieves the start time of a channel primitive in Houdini geometry. It requires a geometry handle and the primitive number. This function is part of the channelprim group and is related to chprim_length and chprim_end.

```VEX
float chprim_start(geometry geometry, int prim)
```

--------------------------------

### Path Construction and Manipulation

Source: https://www.sidefx.com/docs/houdini/vex/functions/mdensity

Functions for creating and manipulating USD paths.

```APIDOC
## usd_makeattribpath

### Description
Constructs an attribute path from a primitive path and an attribute name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **prim_path** (string) - Required - The path to the primitive.
- **attrib_name** (string) - Required - The name of the attribute.

### Response
#### Success Response (200)
- **attribute_path** (string) - The constructed attribute path.

## usd_makecollectionpath

### Description
Constructs a collection path from a primitive path and a collection name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **prim_path** (string) - Required - The path to the primitive.
- **collection_name** (string) - Required - The name of the collection.

### Response
#### Success Response (200)
- **collection_path** (string) - The constructed collection path.

## usd_makepropertypath

### Description
Constructs an property path from a primitive path and an property name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **prim_path** (string) - Required - The path to the primitive.
- **property_name** (string) - Required - The name of the property.

### Response
#### Success Response (200)
- **property_path** (string) - The constructed property path.

## usd_makerelationshippath

### Description
Constructs an relationship path from a primitive path and a relationship name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **prim_path** (string) - Required - The path to the primitive.
- **relationship_name** (string) - Required - The name of the relationship.

### Response
#### Success Response (200)
- **relationship_path** (string) - The constructed relationship path.

## usd_makevalidprimname

### Description
Forces a string to conform to the rules for naming USD primitives.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **name** (string) - Required - The string to validate.

### Response
#### Success Response (200)
- **valid_name** (string) - The validated primitive name.

## usd_makevalidprimpath

### Description
Forces a string to conform to the rules for paths to USD primitives.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **path** (string) - Required - The path to validate.

### Response
#### Success Response (200)
- **valid_path** (string) - The validated primitive path.

## usd_parentpath

### Description
Returns the path of the primitive’s parent.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
None

### Response
#### Success Response (200)
- **parent_path** (string) - The path of the parent primitive.

```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/fuzzy_and

This section describes VEX functions for interacting with metaballs, including importing, marching, iterating, starting, and getting weights.

```APIDOC
## metaball::metaimport

### Description
Once you get a handle to a metaball using metastart and metanext, you can query attributes of the metaball with metaimport.

### Method
N/A (Function)

### Endpoint
N/A (Function)

### Parameters
N/A

### Request Example
N/A

### Response
N/A

---

## metaball::metamarch

### Description
Takes the ray defined by p0 and p1 and partitions it into zero or more sub-intervals where each interval intersects a cluster of metaballs from filename.

### Method
N/A (Function)

### Endpoint
N/A (Function)

### Parameters
N/A

### Request Example
N/A

### Response
N/A

---

## metaball::metanext

### Description
Iterate to the next metaball in the list of metaballs returned by the metastart() function.

### Method
N/A (Function)

### Endpoint
N/A (Function)

### Parameters
N/A

### Request Example
N/A

### Response
N/A

---

## metaball::metastart

### Description
Open a geometry file and return a handle for the metaballs of interest, at the position p.

### Method
N/A (Function)

### Endpoint
N/A (Function)

### Parameters
N/A

### Request Example
N/A

### Response
N/A

---

## metaball::metaweight

### Description
Returns the metaweight of the geometry at position p.

### Method
N/A (Function)

### Endpoint
N/A (Function)

### Parameters
N/A

### Request Example
N/A

### Response
N/A
```

--------------------------------

### Get Channel Primitive Start Time (VEX)

Source: https://www.sidefx.com/docs/houdini/vex/functions/chprim_start

Retrieves the start time of a channel primitive within Houdini geometry. It requires a geometry handle and the primitive number as input. This function is part of the channelprim category and is useful for time-based animation data.

```vex
float chprim_start(geometry geohandle, int prim)
{
  // Returns the start time in seconds of a channel primitive.
  return chprim_start(geohandle, prim);
}
```

--------------------------------

### Path Construction

Source: https://www.sidefx.com/docs/houdini/vex/functions/encodeattrib

Functions for constructing valid USD paths.

```APIDOC
## usd_makeattribpath

### Description
Constructs an attribute path from a primitive path and an attribute name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **primpath** (string) - Required - The path to the primitive.
- **attribname** (string) - Required - The name of the attribute.

### Request Example
```vex
attr_path = usd_makeattribpath("/path/to/prim", "myAttribute")
```

### Response
#### Success Response (200)
- **attr_path** (string) - The constructed attribute path.

#### Response Example
```json
{
  "attr_path": "/path/to/prim.myAttribute"
}
```

## usd_makecollectionpath

### Description
Constructs a collection path from a primitive path and a collection name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **primpath** (string) - Required - The path to the primitive.
- **collectionname** (string) - Required - The name of the collection.

### Request Example
```vex
coll_path = usd_makecollectionpath("/path/to/prim", "myCollection")
```

### Response
#### Success Response (200)
- **coll_path** (string) - The constructed collection path.

#### Response Example
```json
{
  "coll_path": "/path/to/prim{myCollection}"
}
```

## usd_makepropertypath

### Description
Constructs a property path from a primitive path and a property name.

### Method
N/A (VEX function)

### Endpoint
N/A

### Parameters
#### Path Parameters
- **primpath** (string) - Required - The path to the primitive.
- **propname** (string) - Required - The name of the property.

### Request Example

```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/usd_iprimvar

Functions for interacting with metaballs, including starting iteration, importing attributes, marching along rays, and getting metaweights.

```APIDOC
## Metaball Functions

### Description
Functions for querying and iterating through metaballs in a geometry.

### Functions

*   **metaimport(handle, attribute)**
    *   Description: Once you get a handle to a metaball using metastart and metanext, you can query attributes of the metaball with metaimport.
*   **metamarch(p0, p1, filename)**
    *   Description: Takes the ray defined by p0 and p1 and partitions it into zero or more sub-intervals where each interval intersects a cluster of metaballs from filename.
*   **metanext(handle)**
    *   Description: Iterate to the next metaball in the list of metaballs returned by the metastart() function.
*   **metastart(filename, p)**
    *   Description: Open a geometry file and return a handle for the metaballs of interest, at the position p.
*   **metaweight(p, filename)**
    *   Description: Returns the metaweight of the geometry at position p.
```

--------------------------------

### Connection and Input Functions

Source: https://www.sidefx.com/docs/houdini/vex/contexts/sop

Functions for checking connections and input states.

```APIDOC
## Connection and Input Functions

### Description
Functions for checking connections and input states.

### isbound
Parameters in VEX can be overridden by geometry attributes (if the attributes exist on the surface being rendered).

### isconnected
Returns 1 if input_number is connected, or 0 if the input is not connected.
```

--------------------------------

### USD Path and Property Construction

Source: https://www.sidefx.com/docs/houdini/vex/functions/usd_setactive

Functions for constructing valid USD paths and property paths.

```APIDOC
## USD Path and Property Construction

### Description
This section details functions used to create valid USD paths for attributes, collections, properties, and relationships, as well as ensuring primitive names and paths conform to USD standards.

### Functions

- **usd_makeattribpath(primitive_path, attribute_name)**
  - **Description**: Constructs an attribute path from a primitive path and an attribute name.
  - **Parameters**:
    - `primitive_path` (string) - The path to the primitive.
    - `attribute_name` (string) - The name of the attribute.
  - **Returns**: The constructed attribute path (string).

- **usd_makecollectionpath(primitive_path, collection_name)**
  - **Description**: Constructs a collection path from a primitive path and a collection name.
  - **Parameters**:
    - `primitive_path` (string) - The path to the primitive.
    - `collection_name` (string) - The name of the collection.
  - **Returns**: The constructed collection path (string).

- **usd_makepropertypath(primitive_path, property_name)**
  - **Description**: Constructs a property path from a primitive path and a property name.
  - **Parameters**:
    - `primitive_path` (string) - The path to the primitive.
    - `property_name` (string) - The name of the property.
  - **Returns**: The constructed property path (string).

- **usd_makerelationshippath(primitive_path, relationship_name)**
  - **Description**: Constructs a relationship path from a primitive path and a relationship name.
  - **Parameters**:
    - `primitive_path` (string) - The path to the primitive.
    - `relationship_name` (string) - The name of the relationship.
  - **Returns**: The constructed relationship path (string).

- **usd_makevalidprimname(name)**
  - **Description**: Forces a string to conform to the rules for naming USD primitives.
  - **Parameters**:
    - `name` (string) - The string to validate.
  - **Returns**: A string conforming to USD primitive naming rules.

- **usd_makevalidprimpath(path)**
  - **Description**: Forces a string to conform to the rules for paths to USD primitives.
  - **Parameters**:
    - `path` (string) - The path string to validate.
  - **Returns**: A string conforming to USD primitive path rules.
```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/usd_addcollectionexclude

Functions for interacting with metaballs, including starting iteration, importing attributes, marching along rays, and getting weights.

```APIDOC
## Metaball Functions

### Description
Functions for querying and iterating through metaballs in a geometry.

### Functions

*   **metaimport(handle, attribute)**: Queries attributes of a metaball using its handle.
*   **metamarch(p0, p1, filename)**: Partitions a ray into sub-intervals intersecting metaballs.
*   **metanext(handle)**: Iterates to the next metaball in the list.
*   **metastart(p, filename)**: Opens a geometry file and returns a handle for metaballs at position p.
*   **metaweight(p, filename)**: Returns the metaweight of the geometry at position p.
```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/primhedge

Functions for interacting with metaballs, including starting iteration, importing attributes, marching along rays, and getting metaweights.

```APIDOC
## Metaball Functions

### Description
Functions for querying and iterating through metaballs within a geometry.

### Functions

*   **metaimport(handle, attribute)**
    Once you get a handle to a metaball using metastart and metanext, you can query attributes of the metaball with metaimport.

*   **metamarch(p0, p1, filename)**
    Takes the ray defined by p0 and p1 and partitions it into zero or more sub-intervals where each interval intersects a cluster of metaballs from filename.

*   **metanext(handle)**
    Iterate to the next metaball in the list of metaballs returned by the metastart() function.

*   **metastart(filename, p)**
    Open a geometry file and return a handle for the metaballs of interest, at the position p.

*   **metaweight(filename, p)**
    Returns the metaweight of the geometry at position p.
```

--------------------------------

### USD Path and Name Construction

Source: https://www.sidefx.com/docs/houdini/vex/functions/re_split

Utilities for constructing valid USD attribute, property, relationship, and primitive paths, as well as ensuring valid primitive names.

```APIDOC
## USD Path and Name Construction

### Description
Functions to create valid USD paths for attributes, properties, relationships, and collections, as well as to ensure primitive names conform to USD standards.

### Functions

- **usd_makeattribpath(prim_path, attrib_name)**
  Constructs an attribute path from a primitive path and an attribute name.

- **usd_makecollectionpath(prim_path, collection_name)**
  Constructs a collection path from a primitive path and a collection name.

- **usd_makepropertypath(prim_path, property_name)**
  Constructs a property path from a primitive path and a property name.

- **usd_makerelationshippath(prim_path, relationship_name)**
  Constructs a relationship path from a primitive path and a relationship name.

- **usd_makevalidprimname(name)**
  Forces a string to conform to the rules for naming USD primitives.

- **usd_makevalidprimpath(path)**
  Forces a string to conform to the rules for paths to USD primitives.
```

--------------------------------

### Get UV Tangent at Point P (VEX Example)

Source: https://www.sidefx.com/docs/houdini/vex/functions/getuvtangents

Example of using the getuvtangents VEX function to retrieve UV tangents (Tu, Tv) at a point 'P' on '/obj/geo1', using the normal 'N' for surface searching. This variant does not explicitly retrieve the surface normal.

```vex
// Get UV tangent at 'P', searching the surface in the direction of 'N'
vector Tu, Tv;
getuvtangents("/obj/geo1", P, N, Tu, Tv);
```

--------------------------------

### USD Path and Property Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/agentsolvefbik

Functions for constructing and manipulating paths to USD primitives, properties, and relationships.

```APIDOC
## GET /websites/sidefx_houdini_vex/paths

### Description
Provides access to functions for constructing and manipulating paths related to USD primitives, attributes, properties, and relationships.

### Method
GET

### Endpoint
/websites/sidefx_houdini_vex/paths

### Parameters
None

### Request Example
None

### Response
#### Success Response (200)
- **usd_makeattribpath** (function) - Constructs an attribute path from a primitive path and an attribute name.
- **usd_makecollectionpath** (function) - Constructs a collection path from a primitive path and a collection name.
- **usd_makepropertypath** (function) - Constructs an property path from a primitive path and an property name.
- **usd_makerelationshippath** (function) - Constructs an relationship path from a primitive path and a relationship name.
- **usd_makevalidprimname** (function) - Forces a string to conform to the rules for naming USD primitives.
- **usd_makevalidprimpath** (function) - Forces a string to conform to the rules for paths to USD primitives.
- **usd_parentpath** (function) - Returns the path of the primitive’s parent.
- **usd_iscollectionpath** (function) - Checks if the path is a valid collection path.

#### Response Example
```json
{
  "functions": [
    "usd_makeattribpath",
    "usd_makecollectionpath",
    "usd_makepropertypath",
    "usd_makerelationshippath",
    "usd_makevalidprimname",
    "usd_makevalidprimpath",
    "usd_parentpath",
    "usd_iscollectionpath"
  ]
}
```
```

--------------------------------

### Get Agent Clip Start Time (VEX)

Source: https://www.sidefx.com/docs/houdini/vex/functions/agentclipstarttime

The agentclipstarttime function returns the start time in seconds of an agent's animation clip. It accepts either the clip name or its index. Returns 0 if the primitive is not an agent or if the clip is not found. Available since Houdini 18.0.

```vex
float agentclipstarttime(geometry geo, int prim, string clipname)
float agentclipstarttime(geometry geo, int prim, int clipindex)
```

--------------------------------

### USD Path and Name Construction Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/pciterate

Functions for constructing valid USD paths and attribute/property/relationship names.

```APIDOC
## USD Path and Name Construction Functions

### Description
Utility functions for creating valid USD paths and names, ensuring adherence to USD naming conventions.

### Method
N/A (VEX functions)

### Endpoint
N/A (VEX functions)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```vex
// Example usage within VEX
string full_attrib_path = usd_makeattribpath("path/to/primitive", "attribute_name");
```

### Response
#### Success Response (String)
- **Return Value** (string) - The constructed valid USD path or name.

#### Response Example
```json
{
  "example": "/path/to/primitive/attribute_name"
}
```

### Available Functions:

- **`usd_makeattribpath(string primpath, string name)`**
  Constructs an attribute path from a primitive path and an attribute name.

- **`usd_makecollectionpath(string primpath, string name)`**
  Constructs a collection path from a primitive path and a collection name.

- **`usd_makepropertypath(string primpath, string name)`**
  Constructs an property path from a primitive path and an property name.

- **`usd_makerelationshippath(string primpath, string name)`**
  Constructs an relationship path from a primitive path and a relationship name.

- **`usd_makevalidprimname(string name)`**
  Forces a string to conform to the rules for naming USD primitives.

- **`usd_makevalidprimpath(string path)`**
  Forces a string to conform to the rules for paths to USD primitives.

```

--------------------------------

### Find Surface Location with Arbitrary Ray (VEX Example)

Source: https://www.sidefx.com/docs/houdini/vex/functions/getuvtangents

Example demonstrating getuvtangents to find a surface location using an arbitrary ray. It retrieves UV tangents (Tu, Tv) and the surface normal (Tn) when the normal is not known beforehand. The evaluation starts from 'ray_orig' in the direction 'ray_dir'.

```vex
// Find a surface location using an arbitrary ray.
// In this case the surface normal isn't known beforehand and can be fetched via 'Tn'.
vector Tu, Tv, Tn;
getuvtangents("/obj/geo1", ray_orig, ray_dir, Tu, Tv, Tn);
```

--------------------------------

### USD Path and Transform Utilities

Source: https://www.sidefx.com/docs/houdini/vex/contexts/sop

Functions for constructing and manipulating USD paths, and accessing primitive transforms.

```APIDOC
## USD Path and Transform Utilities

### Description
Utility functions for creating valid USD paths, checking path types, and retrieving transform information for primitives.

### Functions

- **usd_localtransform**
  - Description: Obtains the primitive’s local transform.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makeattribpath**
  - Description: Constructs an attribute path from a primitive path and an attribute name.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makecollectionpath**
  - Description: Constructs a collection path from a primitive path and a collection name.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makepropertypath**
  - Description: Constructs an property path from a primitive path and an property name.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makerelationshippath**
  - Description: Constructs an relationship path from a primitive path and a relationship name.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makevalidprimname**
  - Description: Forces a string to conform to the rules for naming USD primitives.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_makevalidprimpath**
  - Description: Forces a string to conform to the rules for paths to USD primitives.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_parentpath**
  - Description: Returns the path of the primitive’s parent.
  - Method: N/A (Function call)
  - Endpoint: N/A

- **usd_istransformreset**
  - Description: Checks if the primitive transform is reset.
  - Method: N/A (Function call)
  - Endpoint: N/A
```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/usd_addcollectioninclude

This section details functions for interacting with metaballs, including starting iteration, importing attributes, marching along rays, and getting metaweights.

```APIDOC
## Metaball Functions

### Description
Functions for querying and iterating through metaballs within a geometry.

### Functions

*   **metaimport(handle, attribute_name)**
    *   Description: Queries attributes of a metaball using its handle.
*   **metamarch(p0, p1, filename)**
    *   Description: Partitions a ray into sub-intervals that intersect metaballs from a specified file.
*   **metanext(handle)**
    *   Description: Iterates to the next metaball in the list obtained from `metastart()`.
*   **metastart(filename, p)**
    *   Description: Opens a geometry file and returns a handle for metaballs of interest at position `p`.
*   **metaweight(p, filename)**
    *   Description: Returns the metaweight of the geometry at position `p`.
```

--------------------------------

### GET /usd_makepropertypath

Source: https://www.sidefx.com/docs/houdini/vex/functions/agentworldtransform

Constructs an property path from a primitive path and an property name. This creates a valid path for a property.

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/detailattribsize

VEX functions for interacting with metaballs, including starting iteration, importing attributes, marching along rays, and getting metaball weights.

```APIDOC
## Metaball Functions

### Description
Provides functions for querying and iterating through metaballs within a geometry file.

### Functions

*   **metaimport(handle, attribute)**: Once you get a handle to a metaball using metastart and metanext, you can query attributes of the metaball with metaimport.
*   **metamarch(p0, p1, filename)**: Takes the ray defined by p0 and p1 and partitions it into zero or more sub-intervals where each interval intersects a cluster of metaballs from filename.
*   **metanext(handle)**: Iterate to the next metaball in the list of metaballs returned by the metastart() function.
*   **metastart(filename, p)**: Open a geometry file and return a handle for the metaballs of interest, at the position p.
*   **metaweight(filename, p)**: Returns the metaweight of the geometry at position p.
```

--------------------------------

### Path and Name Construction

Source: https://www.sidefx.com/docs/houdini/vex/functions/nrandom

Functions for constructing valid USD attribute, property, relationship, and primitive paths.

```APIDOC
## USD Path and Name Construction Functions

### Description
This section details functions that assist in creating valid USD paths and names for attributes, properties, relationships, and primitives.

### Functions

- **usd_makeattribpath(primpath, attribname)**
  - **Description**: Constructs an attribute path from a primitive path and an attribute name.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `primpath` (string) - The path to the USD primitive.
    - `attribname` (string) - The name of the attribute.

- **usd_makecollectionpath(primpath, collectionname)**
  - **Description**: Constructs a collection path from a primitive path and a collection name.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `primpath` (string) - The path to the USD primitive.
    - `collectionname` (string) - The name of the collection.

- **usd_makepropertypath(primpath, propertyname)**
  - **Description**: Constructs a property path from a primitive path and a property name.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `primpath` (string) - The path to the USD primitive.
    - `propertyname` (string) - The name of the property.

- **usd_makerelationshippath(primpath, relname)**
  - **Description**: Constructs a relationship path from a primitive path and a relationship name.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `primpath` (string) - The path to the USD primitive.
    - `relname` (string) - The name of the relationship.

- **usd_makevalidprimname(name)**
  - **Description**: Forces a string to conform to the rules for naming USD primitives.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `name` (string) - The string to validate as a primitive name.

- **usd_makevalidprimpath(path)**
  - **Description**: Forces a string to conform to the rules for paths to USD primitives.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `path` (string) - The string to validate as a primitive path.

- **usd_parentpath(primpath)**
  - **Description**: Returns the path of the primitive’s parent.
  - **Method**: N/A (VEX function)
  - **Parameters**: 
    - `primpath` (string) - The path to the USD primitive.

```

--------------------------------

### Metaball Functions

Source: https://www.sidefx.com/docs/houdini/vex/functions/cbrt

Functions for interacting with metaballs in Houdini, including starting iteration, importing attributes, marching along rays, and getting metaball weights.

```APIDOC
## Metaball Functions

### Description
Functions for iterating through and querying metaballs within a geometry file.

### Functions

*   **metaimport(handle, attribute)**
    *   Description: Queries attributes of a metaball using a handle obtained from `metastart`.
*   **metamarch(p0, p1, filename)**
    *   Description: Partitions a ray defined by `p0` and `p1` into intervals intersecting metaballs from `filename`.
*   **metanext(handle)**
    *   Description: Iterates to the next metaball in the list returned by `metastart()`.
*   **metastart(filename, p)**
    *   Description: Opens a geometry file and returns a handle for metaballs of interest at position `p`.
*   **metaweight(p, filename)**
    *   Description: Returns the metaweight of the geometry at position `p`.
```
Tokens:
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