glGetActiveAttrib — return information about an active attribute variable
void glGetActiveAttrib( | GLuint program, |
| GLuint index, | |
| GLsizei bufSize, | |
| GLsizei *length, | |
| GLint *size, | |
| GLenum *type, | |
GLchar *name); |
programSpecifies the program object to be queried.
indexSpecifies the index of the attribute variable to be queried.
bufSizeSpecifies the maximum number of characters
OpenGL is allowed to write in the character buffer
indicated by name.
lengthReturns 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.
sizeReturns the size of the attribute variable.
typeReturns the data type of the attribute variable.
nameReturns a null terminated string containing the name of the attribute variable.
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.
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.
glGet
with argument GL_MAX_VERTEX_ATTRIBS.
glGetProgramiv
with argument GL_ACTIVE_ATTRIBUTES or
GL_ACTIVE_ATTRIBUTE_MAX_LENGTH.
glBindAttribLocation, glGetActiveUniform, glLinkProgram, glVertexAttrib, glVertexAttribPointer
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/.