glGetActiveAttrib
3G

# glGetActiveAttrib

return information about an active attribute variable

## C Specification

    		void glGetActiveAttrib
    		GLuint program
    		GLuint index
    		GLsizei bufSize
    		GLsizei *length
    		GLint *size
    		GLenum *type
    		GLchar *name

## Parameters

`program`

  Specifies the program object to be queried.

`index`

  Specifies the index of the attribute variable to be queried.

`bufSize`

  Specifies the maximum number of characters OpenGL is allowed to write in the character buffer indicated by `name`.

`length`

  Returns the number of characters actually written by OpenGL in the string indicated by `name` (excluding the null terminator) if a value other than `NULL` is passed.

`size`

  Returns the size of the attribute variable.

`type`

  Returns the data type of the attribute variable.

`name`

  Returns a null terminated string containing the name of the attribute variable.

## Description

`glGetActiveAttrib` returns information about an active attribute variable in the program object specified by `program`. The number of active attributes can be obtained by calling glGetProgramiv with the value `GL_ACTIVE_ATTRIBUTES`. A value of 0 for `index` selects the first active attribute variable. Permissible values for `index` range from 0 to the number of active attribute variables minus 1.

Attribute variables have arbitrary names and obtain their values through numbered generic vertex attributes. An attribute variable is considered active if it is determined during the link operation that it may be accessed during program execution. Therefore, `program` should have previously been the target of a call to glLinkProgram, but it is not necessary for it to have been linked successfully.

The size of the character buffer required to store the longest attribute variable name in `program` can be obtained by calling glGetProgramiv with the value `GL_ACTIVE_ATTRIBUTE_MAX_LENGTH`. This value should be used to allocate a buffer of sufficient size to store the returned attribute name. The size of this character buffer is passed in `bufSize`, and a pointer to this character buffer is passed in `name`.

`glGetActiveAttrib` returns the name of the attribute variable indicated by `index`, storing it in the character buffer specified by `name`. The string returned will be null terminated. The actual number of characters written into this buffer is returned in `length`, and this count does not include the null termination character. If the length of the returned string is not required, a value of `NULL` can be passed in the `length` argument.

The `type` argument will return a pointer to the attribute variable's data type. The symbolic constants `GL_FLOAT`, `GL_FLOAT_VEC2`, `GL_FLOAT_VEC3`, `GL_FLOAT_VEC4`, `GL_FLOAT_MAT2`, `GL_FLOAT_MAT3`, or `GL_FLOAT_MAT4` may be returned. The `size` argument will return the size of the attribute, in units of the type returned in `type`.

This function will return as much information as it can about the specified active attribute variable. If no information is available, `length` will be 0, and `name` will be an empty string. This situation could occur if this function is called after a link operation that failed. If an error occurs, the return values `length`, `size`, `type`, and `name` will be unmodified.

## Errors

`GL_INVALID_VALUE` is generated if `program` is not a value generated by OpenGL.

`GL_INVALID_OPERATION` is generated if `program` is not a program object.

`GL_INVALID_VALUE` is generated if `index` is greater than or equal to the number of active attribute variables in `program`.

`GL_INVALID_VALUE` is generated if `bufSize` is less than 0.

## Associated Gets

glGet with argument `GL_MAX_VERTEX_ATTRIBS`.

glGetProgramiv with argument `GL_ACTIVE_ATTRIBUTES` or `GL_ACTIVE_ATTRIBUTE_MAX_LENGTH`.

glIsProgram

## See Also

glBindAttribLocation, glGetActiveUniform, glLinkProgram, glVertexAttrib, glVertexAttribPointer

## Copyright

Copyright 2003-2005 3Dlabs Inc. Ltd. This material may be distributed subject to the terms and conditions set forth in the Open Publication License, v 1.0, 8 June 1999. http://opencontent.org/openpub/.