gluNurbsCallback
GLUNURBSCALLBACK(3G) 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 tessella-
tor (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 call-
back 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 GL_LINES, GL_LINE_STRIP, GL_TRIANGLE_FAN,
GL_TRIANGLE_STRIP, GL_TRIANGLES, or GL_QUAD_STRIP. The
default begin callback function is NULL. The function proto-
type 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 ‘‘ver-
tex’’. 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 gen-
erated. 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 (GL_MAP1_NORMAL). In the case of a NURBS sur-
face, if a normal map (GL_MAP2_NORMAL) is provided, then the
generated normal is computed from the normal map. If a nor-
mal map is not provided then a surface normal is computed in
a manner similar to that described for evaluators when
GL_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 (GL_MAP1_COLOR_4 or
GL_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 coordi-
nates can be 1, 2, 3, or 4 depending on which type of tex-
ture map is specified (GL_MAP1_TEXTURE_COORD_1,
GL_MAP1_TEXTURE_COORD_2, GL_MAP1_TEXTURE_COORD_3,
GL_MAP1_TEXTURE_COORD_4, GL_MAP2_TEXTURE_COORD_1,
GL_MAP2_TEXTURE_COORD_2, GL_MAP2_TEXTURE_COORD_3,
GL_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 proto-
type 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(3G), gluNewNurbsRenderer(3G), gluNurbsCallbackData(3G),
gluNurbsProperty(3G)
GLUNURBSCALLBACK(3G)
