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GLGETACTIVEATTRIB(3G)                            OpenGL 3.3                            GLGETACTIVEATTRIB(3G)



NAME
       glGetActiveAttrib - Returns information about an active attribute variable for the specified program
       object

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 glGetProgram() 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.

       A vertex shader may use either built-in attribute variables, user-defined attribute variables, or
       both. Built-in attribute variables have a prefix of "gl_" and reference conventional OpenGL vertex
       attribtes (e.g., gl_Vertex, gl_Normal, etc., see the OpenGL Shading Language specification for a
       complete list.) User-defined attribute variables have arbitrary names and obtain their values through
       numbered generic vertex attributes. An attribute variable (either built-in or user-defined) 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 glGetProgram() 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, GL_FLOAT_MAT4,
       GL_FLOAT_MAT2x3, GL_FLOAT_MAT2x4, GL_FLOAT_MAT3x2, GL_FLOAT_MAT3x4, GL_FLOAT_MAT4x2, GL_FLOAT_MAT4x3,
       GL_INT, GL_INT_VEC2, GL_INT_VEC3, GL_INT_VEC4, GL_UNSIGNED_INT_VEC, GL_UNSIGNED_INT_VEC2,
       GL_UNSIGNED_INT_VEC3, or GL_UNSIGNED_INT_VEC4 may be returned. The size argument will return the size
       of the attribute, in units of the type returned in type.

       The list of active attribute variables may include both built-in attribute variables (which begin
       with the prefix "gl_") as well as user-defined attribute variable names.

       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.

       glGetProgram() with argument GL_ACTIVE_ATTRIBUTES or GL_ACTIVE_ATTRIBUTE_MAX_LENGTH.

       glIsProgram()

SEE ALSO
       glBindAttribLocation(), glLinkProgram(), glVertexAttrib(), glVertexAttribPointer()


COPYRIGHT
       Copyright (C) 2003-2005 3Dlabs Inc. Ltd. Copyright (C) 2010 Khronos Group. 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/.



OpenGL 3.3                                       03/08/2011                            GLGETACTIVEATTRIB(3G)