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GLUNURBSCALLBACK(3G)			  OpenGL Manual 		     GLUNURBSCALLBACK(3G)

NAME
       gluNurbsCallback - define a callback for a NURBS object

C SPECIFICATION
       void gluNurbsCallback(GLUnurbs* nurb, GLenum which, _GLUfuncptr CallBackFunc);

PARAMETERS
       nurb
	   Specifies the NURBS object (created with gluNewNurbsRenderer()).

       which
	   Specifies the callback being defined. Valid values are GLU_NURBS_BEGIN,
	   GLU_NURBS_VERTEX, GLU_NURBS_NORMAL, GLU_NURBS_COLOR, GLU_NURBS_TEXTURE_COORD,
	   GLU_NURBS_END, GLU_NURBS_BEGIN_DATA, GLU_NURBS_VERTEX_DATA, GLU_NURBS_NORMAL_DATA,
	   GLU_NURBS_COLOR_DATA, GLU_NURBS_TEXTURE_COORD_DATA, GLU_NURBS_END_DATA, and
	   GLU_NURBS_ERROR.

       CallBackFunc
	   Specifies the function that the callback calls.

DESCRIPTION
       gluNurbsCallback 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 CallBackFunc 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
       GLU_NURBS_MODE is set to be GLU_NURBS_TESSELLATOR) to return back the OpenGL polygon
       primitives resulting 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
       gluNurbsCallbackData.

       The error callback function is effective no matter which value that GLU_NURBS_MODE is set
       to. All other callback functions are effective only when GLU_NURBS_MODE is set to
       GLU_NURBS_TESSELLATOR.

       The legal callbacks are as follows:

       GLU_NURBS_BEGIN

	   The begin callback indicates the start of a primitive. The function takes a single
	   argument of type GLenum, which can be one of GLU_LINES, GLU_LINE_STRIP,
	   GLU_TRIANGLE_FAN, GLU_TRIANGLE_STRIP, GLU_TRIANGLES, or GLU_QUAD_STRIP. The default
	   begin callback function is NULL. The function prototype for this callback looks like:

	       void begin( GLenum type );

       GLU_NURBS_BEGIN_DATA

	   The same as the GLU_NURBS_BEGIN 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
	   gluNurbsCallbackData. The default callback function is NULL. The function prototype
	   for this callback function looks like:

	       void beginData(GLenum type, void *userData);

       GLU_NURBS_VERTEX

	   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 );

       GLU_NURBS_VERTEX_DATA

	   This is the same as the GLU_NURBS_VERTEX 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 gluNurbsCallbackData. The default callback function is NULL. The function
	   prototype for this callback function looks like:

	       void vertexData( GLfloat *vertex, void *userData );

       GLU_NURBS_NORMAL

	   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
	   (GLU_MAP1_NORMAL). In the case of a NURBS surface, if a normal map (GLU_MAP2_NORMAL)
	   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 GLU_AUTO_NORMAL is enabled. The default normal callback
	   function is NULL. The function prototype for this callback function looks like:

	       void normal( GLfloat *normal );

       GLU_NURBS_NORMAL_DATA

	   The same as the GLU_NURBS_NORMAL 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
	   gluNurbsCallbackData. The default callback function is NULL. The function prototype
	   for this callback function looks like:

	       void normalData( GLfloat *normal, void *userData );

       GLU_NURBS_COLOR

	   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 (GLU_MAP1_COLOR_4 or GLU_MAP2_COLOR_4). ``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 );

       GLU_NURBS_COLOR_DATA

	   The same as the GLU_NURBS_COLOR 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
	   gluNurbsCallbackData. The default callback function is NULL. The function prototype
	   for this callback function looks like:

	       void colorData( GLfloat *color, void *userData );

       GLU_NURBS_TEXTURE_COORD

	   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
	   (GLU_MAP1_TEXTURE_COORD_1, GLU_MAP1_TEXTURE_COORD_2, GLU_MAP1_TEXTURE_COORD_3,
	   GLU_MAP1_TEXTURE_COORD_4, GLU_MAP2_TEXTURE_COORD_1, GLU_MAP2_TEXTURE_COORD_2,
	   GLU_MAP2_TEXTURE_COORD_3, GLU_MAP2_TEXTURE_COORD_4). 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 );

       GLU_NURBS_TEXTURE_COORD_DATA

	   This is the same as the GLU_NURBS_TEXTURE_COORD 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 gluNurbsCallbackData. The default callback function is NULL. The
	   function prototype for this callback function looks like:

	       void texCoordData( GLfloat *texCoord, void *userData );

       GLU_NURBS_END

	   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 );

       GLU_NURBS_END_DATA

	   This is the same as the GLU_NURBS_END 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 gluNurbsCallbackData. The default callback function is NULL. The function
	   prototype for this callback function looks like:

	       void endData( void  *userData );

       GLU_NURBS_ERROR

	   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 GLU_NURBS_ERROR1 through GLU_NURBS_ERROR37. Character strings
	   describing these errors can be retrieved with gluErrorString().

NOTES
       gluNurbsCallback is available only if the GLU version is 1.2 or greater.

       GLU version 1.2 supports only the GLU_ERROR parameter for which. The GLU_ERROR value is
       deprecated in GLU version 1.3 in favor of GLU_NURBS_ERROR. All other accepted values for
       CallBackFunc are available only if the GLU version is 1.3 or greater.

SEE ALSO
       gluErrorString(), gluNewNurbsRenderer(), gluNurbsCallbackData, gluNurbsProperty()

COPYRIGHT
       Copyright (C) 1991-2006 Silicon Graphics, Inc. This document is licensed under the SGI
       Free Software B License. For details, see http://oss.sgi.com/projects/FreeB/.

AUTHORS
       opengl.org

opengl.org				    06/10/2014			     GLUNURBSCALLBACK(3G)
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