GLUNURBSCALLBACK() MachTen Programmer’s Manual GLUNURBSCALLBACK()

NAME
gluNurbsCallback - define a callback for a NURBS object

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

delim $$

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

which Specifies the callback being defined. Valid
values are GLU_NURBS_BEGIN_EXT,
GLU_NURBS_VERTEX_EXT, GLU_NORMAL_EXT,
GLU_NURBS_COLOR_EXT,
GLU_NURBS_TEXTURE_COORD_EXT, GLU_END_EXT,
GLU_NURBS_BEGIN_DATA_EXT,
GLU_NURBS_VERTEX_DATA_EXT,
GLU_NORMAL_DATA_EXT,
GLU_NURBS_COLOR_DATA_EXT,
GLU_NURBS_TEXTURE_COORD_DATA_EXT,
GLU_END_DATA_EXT, and GLU_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_EXT is set to be
GLU_NURBS_TESSELLATOR_EXT) to return back the openGL poly-
gon 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 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
gluNurbsCallbackDataEXT.

The error callback function is effective no matter which
value that GLU_NURBS_MODE_EXT is set to. All other call-
back functions are effective only when GLU_NURBS_MODE_EXT
is set to GLU_NURBS_TESSELLATOR_EXT.

The legal callbacks are as follows:

GLU_NURBS_BEGIN_EXT
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_STRIPS, GL_TRIANGLE_FAN,
GL_TRIANGLE_STRIP, GL_TRIANGLES, or
GL_QUAD_STRIP. The default begin callback func-
tion is NULL. The function prototype for this
callback looks like:
void begin ( GLenum type );

GLU_NURBS_BEGIN_DATA_EXT
The same as the GLU_NURBS_BEGIN_EXT 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 gluNurbsCall-
backDataEXT. The default callback function is
NULL. The function prototype for this callback
function looks like:
void beginData (GLenum type, void *userData);

GLU_NURBS_VERTEX_EXT
The vertex callback indicates a vertex of the
primitive. The coordinates of the vertex are
stored in the parameter "vertex". All the gener-
ated vertices have dimension 3, that is, homoge-
neous 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_EXT
The same as the GLU_NURBS_VERTEX_EXT 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 gluNurbsCall-
backDataEXT. The default callback function is
NULL. The function prototype for this callback
function looks like:
void vertexData ( GLfloat *vertex, void *user-
Data );

GLU_NORMAL_EXT
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. The
default normal callback function is NULL. The
function prototype for this callback function
looks like:
void normal ( GLfloat *normal );

GLU_NORMAL_DATA_EXT
The same as the GLU_NURBS_NORMAL_EXT 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 gluNurbsCall-
backDataEXT. 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_EXT
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 pro-
vides 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_EXT
The same as the GLU_NURBS_COLOR_EXT 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 gluNurbsCall-
backDataEXT. 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_EXT
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_MAP*_TEXTURE_COORD_1,
GL_MAP*_TEXTURE_COORD_2,
GL_MAP*_TEXTURE_COORD_3, GL_MAP*_TEXTURE_COORD_4
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 );

GLU_NURBS_TEXTURE_COORD_DATA_EXT
The same as the GLU_NURBS_TEXTURE_COORD_EXT
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
gluNurbsCallbackDataEXT. The default callback
function is NULL. The function prototype for
this callback function looks like:
void texCoordData (GLfloat *texCoord, void
*userData);

GLU_END_EXT
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_END_DATA_EXT
The same as the GLU_NURBS_TEXTURE_COORD_EXT
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
gluNurbsCallbackDataEXT. The default callback
function is NULL. The function prototype for
this callback function looks like:
void endData ( void *userData );

GLU_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 gluEr-
rorString.

SEE ALSO
gluErrorString, gluNewNurbsRenderer

MachTen 4