NAME

C SPECIFICATION

	GLenum which,
	GLvoid (*CallBackFunc)( )

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

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 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 gluNurbsCallbackDataEXT.

The error callback function is effective no matter which value that GLU_NURBS_MODE_EXT is set to. All other callback 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 function is NULL. The function prototype for this callback looks like:

GLU_NURBS_BEGIN_DATA_EXT

The same as the GLU_NURBS_BEGIN_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:

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 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:

GLU_NURBS_VERTEX_DATA_EXT

The same as the GLU_NURBS_VERTEX_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:

GLU_NORMAL_EXT

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 (GL_MAP1_NORMAL). In the case of a NURBS surface, if a normal map (GL_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 GL_AUTO_NORMAL is enabled. The default normal callback function is NULL. The function prototype for this callback function looks like:

GLU_NORMAL_DATA_EXT

The same as the GLU_NURBS_NORMAL_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:

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 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:

GLU_NURBS_COLOR_DATA_EXT

The same as the GLU_NURBS_COLOR_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:

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 "texCoord". 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:

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:

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:

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:

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 gluErrorString.

SEE ALSO