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 par-
ticular 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
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 gen-
erated vertices have dimension 3, that is, homo-
geneous 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 call-
back, 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 *user-
Data );
GLU_NURBS_NORMAL
The normal callback is invoked as the vertex
normal is generated. The components of the nor-
mal are stored in the parameter ``normal''. In
the case of a NURBS curve, the callback function
is effective only when the user provides a nor-
mal map (GL_MAP1_NORMAL). In the case of a
NURBS surface, if a normal map (GL_MAP2_NORMAL)
is provided, then the generated normal is com-
puted 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 evalu-
ators when GL_AUTO_NORMAL is enabled.
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 *user-
Data );
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 compo-
nents: R,G,B,A. The default color callback func-
tion 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 ``texCo-
ord''. The number of texture coordinates can be
1, 2, 3, or 4 depending on which type of texture
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.
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 argu-
ment. 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.
1.3 in favor of GLU_NURBS_ERROR. All other accepted val-
ues for CallBackFunc are available only if the GLU version
is 1.3 or greater.
SEE ALSO
gluErrorString, gluNewNurbsRenderer, gluNurbsCallbackData,
gluNurbsProperty
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