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<HTML><BODY><PRE>     <STRONG>NAME</STRONG>	  <STRONG>gluNurbsCallback</STRONG> - define a callback for a NURBS object     <STRONG>C</STRONG> <STRONG>SPECIFICATION</STRONG>	  void <STRONG>gluNurbsCallback</STRONG>( GLUnurbs* <EM>nurb</EM>,				 GLenum	<EM>which</EM>,				 GLvoid	(*<EM>CallBackFunc</EM>)( )     <STRONG>PARAMETERS</STRONG>	  <EM>nurb</EM>		Specifies the NURBS object (created with			<STRONG>gluNewNurbsRenderer</STRONG>).	  <EM>which</EM>		Specifies the callback being defined. Valid			values are <STRONG>GLU_NURBS_BEGIN_EXT</STRONG>,			<STRONG>GLU_NURBS_VERTEX_EXT</STRONG>, <STRONG>GLU_NORMAL_EXT</STRONG>,			<STRONG>GLU_NURBS_COLOR_EXT</STRONG>,			<STRONG>GLU_NURBS_TEXTURE_COORD_EXT</STRONG>, <STRONG>GLU_END_EXT</STRONG>,			<STRONG>GLU_NURBS_BEGIN_DATA_EXT</STRONG>,			<STRONG>GLU_NURBS_VERTEX_DATA_EXT</STRONG>,			<STRONG>GLU_NORMAL_DATA_EXT</STRONG>, <STRONG>GLU_NURBS_COLOR_DATA_EXT</STRONG>,			<STRONG>GLU_NURBS_TEXTURE_COORD_DATA_EXT</STRONG>,			<STRONG>GLU_END_DATA_EXT</STRONG>, and <STRONG>GLU_ERROR</STRONG>.	  <EM>CallBackFunc</EM>	Specifies the function that the	callback			calls.     <STRONG>DESCRIPTION</STRONG>	  <STRONG>gluNurbsCallback</STRONG> is used to define a callback	to be used by	  a NURBS object.  If the specified callback is	already	  defined, then	it is replaced.	 If <EM>CallBackFunc</EM> is NULL, then	  this callback	will not get invoked and the related data, if	  any, will be lost.	  Except the error callback, these callbacks are used by NURBS	  tessellator (when <STRONG>GLU_NURBS_MODE_EXT</STRONG> is set to be	  <STRONG>GLU_NURBS_TESSELLATOR_EXT</STRONG>) to	return back the	openGL polygon	  primitives resulted from the tessellation. Note that there	  are two versions of each callback: one with a	user data	  pointer and one without. If both versions for	a particular	  callback are specified then the callback with	the user data	  pointer will be used.	Note that "userData" is	a copy of the	  pointer that was specified at	the last call to	  <STRONG>gluNurbsCallbackDataEXT</STRONG>.	  The error callback function is effective no matter which	  value	that <STRONG>GLU_NURBS_MODE_EXT</STRONG>	is set to.  All	other callback	  functions are	effective only when <STRONG>GLU_NURBS_MODE_EXT</STRONG> is set	  to <STRONG>GLU_NURBS_TESSELLATOR_EXT</STRONG>.	  The legal callbacks are as follows:	  <STRONG>GLU_NURBS_BEGIN_EXT</STRONG>		    The	begin callback indicates the start of a		    primitive. The function takes a single argument of		    type GLenum	which can be one of <STRONG>GL_LINES</STRONG>,		    <STRONG>GL_LINE_STRIPS</STRONG>, <STRONG>GL_TRIANGLE_FAN</STRONG>,		    <STRONG>GL_TRIANGLE_STRIP</STRONG>, <STRONG>GL_TRIANGLES</STRONG>, or	<STRONG>GL_QUAD_STRIP</STRONG>.		    The	default	begin callback function	is NULL. The		    function prototype for this	callback looks like:		    void begin ( GLenum	type );	  <STRONG>GLU_NURBS_BEGIN_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_BEGIN_EXT</STRONG>	callback		    except that	it takes an additional pointer		    argument. This pointer is a	copy of	the pointer		    that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void beginData (GLenum type, void *userData);	  <STRONG>GLU_NURBS_VERTEX_EXT</STRONG>		    The	vertex callback	indicates a vertex of the		    primitive. The coordinates of the vertex are		    stored in the parameter "vertex". All the		    generated vertices have dimension 3, that is,		    homogeneous	coordinates have been transformed into		    affine coordinates.	The default vertex callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void vertex	( GLfloat *vertex );	  <STRONG>GLU_NURBS_VERTEX_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_VERTEX_EXT</STRONG> callback		    except that	it takes an additional pointer		    argument. This pointer is a	copy of	the pointer		    that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void vertexData ( GLfloat *vertex, void *userData		    );	  <STRONG>GLU_NORMAL_EXT</STRONG>		    The	normal callback	is invoked as the vertex		    normal is generated.  The components of the	normal		    are	stored in the parameter	"normal".  In the case		    of a NURBS curve, the callback function is		    effective only when	the user provides a normal map		    (<STRONG>GL_MAP1_NORMAL</STRONG>).  In the case of a	NURBS surface,		    if a normal	map (<STRONG>GL_MAP2_NORMAL</STRONG>) is	provided, then		    the	generated normal is computed from the normal		    map.  If a normal map is not provided then a		    surface normal is computed in a manner similar to		    that described for evaluators when <STRONG>GL_AUTO_NORMAL</STRONG>		    is enabled.	The  default normal callback function		    is NULL. The function prototype for	this callback		    function looks like:		    void normal	( GLfloat *normal );	  <STRONG>GLU_NORMAL_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_NORMAL_EXT</STRONG> callback		    except that	it takes an additional pointer		    argument. This pointer is a	copy of	the pointer		    that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void normalData ( GLfloat *normal, void *userData		    );	  <STRONG>GLU_NURBS_COLOR_EXT</STRONG>		    The	color callback is invoked as the color of a		    vertex is generated.  The components of the	color		    are	stored in the parameter	"color".  This		    callback is	effective only when the	user provides		    a color map	(<STRONG>GL_MAP1_COLOR_4</STRONG> or <STRONG>GL_MAP2_COLOR_4</STRONG>).		    "color" contains four components: R,G,B,A. The		    default color callback function is NULL. The		    prototype for this callback	function looks like:		    void color ( GLfloat *color	);	  <STRONG>GLU_NURBS_COLOR_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_COLOR_EXT</STRONG>	callback		    except that	it takes an additional pointer		    argument. This pointer is a	copy of	the pointer		    that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void colorData ( GLfloat *color, void *userData );	  <STRONG>GLU_NURBS_TEXTURE_COORD_EXT</STRONG>		    The	texture	callback is invoked as the texture		    coordinates	of a vertex are	generated. These		    coordinates	are stored in the parameter		    "texCoord".	The number of texture coordinates can		    be 1, 2, 3,	or 4 depending on which	type of		    texture map	is specified (<STRONG>GL_MAP*_TEXTURE_COORD_1</STRONG>,		    <STRONG>GL_MAP*_TEXTURE_COORD_2</STRONG>, <STRONG>GL_MAP*_TEXTURE_COORD_3</STRONG>,		    <STRONG>GL_MAP*_TEXTURE_COORD_4</STRONG> where * can	be either 1 or		    2).	 If no texture map is specified, this callback		    function will not be called.  The default texture		    callback function is NULL. The function prototype		    for	this callback function looks like:		    void texCoord ( GLfloat *texCoord );	   <STRONG>GLU_NURBS_TEXTURE_COORD_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_TEXTURE_COORD_EXT</STRONG>		    callback except that it takes an additional		    pointer argument. This pointer is a	copy of	the		    pointer that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void texCoordData (GLfloat *texCoord, void		    *userData);	  <STRONG>GLU_END_EXT</STRONG>		    The	end callback is	invoked	at the end of a		    primitive. The default end callback	function is		    NULL. The function prototype for this callback		    function looks like:		    void end ( void );	  <STRONG>GLU_END_DATA_EXT</STRONG>		    The	same as	the <STRONG>GLU_NURBS_TEXTURE_COORD_EXT</STRONG>		    callback except that it takes an additional		    pointer argument. This pointer is a	copy of	the		    pointer that was specified at the last call	to		    <STRONG>gluNurbsCallbackDataEXT</STRONG>.  The default callback		    function is	NULL. The function prototype for this		    callback function looks like:		    void endData ( void	 *userData );	  <STRONG>GLU_ERROR</STRONG> The	error function is called when an error is		    encountered.  Its single argument is of type		    GLenum, and	it indicates the specific error	that		    occurred.  There are 37 errors unique to NURBS		    named <STRONG>GLU_NURBS_ERROR1</STRONG> through <STRONG>GLU_NURBS_ERROR37</STRONG>.		    Character strings describing these errors can be		    retrieved with <STRONG>gluErrorString</STRONG>.     <STRONG>SEE</STRONG> <STRONG>ALSO</STRONG>	  <STRONG>gluErrorString</STRONG>, <STRONG>gluNewNurbsRenderer</STRONG></PRE></BODY></HTML>
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