glGetActiveAttrib man page on Darwin

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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 © 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/.

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