glGetActiveAttrib man page on Oracle
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GLGETACTIVEATTRIB(3G) OpenGL Manual 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 specifies a pointer to a variable into which the
attribute variable's data type will be written. 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, GL_UNSIGNED_INT_VEC4,
DOUBLE, DOUBLE_VEC2, DOUBLE_VEC3, DOUBLE_VEC4, DOUBLE_MAT2,
DOUBLE_MAT3, DOUBLE_MAT4, DOUBLE_MAT2x3, DOUBLE_MAT2x4, DOUBLE_MAT3x2,
DOUBLE_MAT3x4, DOUBLE_MAT4x2, or DOUBLE_MAT4x3 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 © 2003-2005 3Dlabs Inc. Ltd. Copyright © 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/.
AUTHORS
opengl.org
opengl.org 04/29/2014 GLGETACTIVEATTRIB(3G)
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