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gluTessCallback

Chapter 18

412

gluTessCallback

gluTessCallback: deﬁne a callback for a tessellation object.

C Speciﬁcation

void gluTessCallback(

GLUtesselator* tess,

GLenum which,

GLvoid (*CallBackFunc)()

Parameters

tess Speciﬁes the tessellation object (created with gluNewTess).

which Speciﬁes the callback being deﬁned. The following values are valid:

GLU_TESS_BEGIN, GLU_TESS_BEGIN_DATA,

GLU_TESS_EDGE_FLAG, GLU_TESS_EDGE_FLAG_DATA,

GLU_TESS_VERTEX, GLU_TESS_VERTEX_DATA,

GLU_TESS_END, GLU_TESS_END_DATA, GLU_TESS_COMBINE,

GLU_TESS_COMBINE_DATA, GLU_TESS_ERROR, and

GLU_TESS_ERROR_DATA.

CallBackFunc Speciﬁes the function to be called.

Description

gluTessCallback is used to indicate a callback to be used by a tessellation object. If the

speciﬁed callback is already deﬁned, then it is replaced. If CallBackFunc is NULL, then

the existing callback becomes undeﬁned.

These callbacks are used by the tessellation object to describe how a polygon speciﬁed by

the user is broken into triangles. Note that there are two versions of each callback: one

with user-speciﬁed polygon data and one without. If both versions of a particular

callback are speciﬁed, then the callback with user-speciﬁed polygon data will be used.

Note that the polygon_data parameter used by some of the functions is a copy of the

pointer that was speciﬁed when gluTessBeginPolygon was called. The legal callbacks are

as follows:

GLU_TESS_BEGIN

The begin callback is invoked like glBegin to indicate the start of a (triangle) primitive.

The function takes a single argument of type GLenum. If the

GLU_TESS_BOUNDARY_ONLY property is set to GL_FALSE, then the argument is set

to either GL_TRIANGLE_FAN, GL_TRIANGLE_STRIP, or GL_TRIANGLES. If the

GLU_TESS_BOUNDARY_ONLY property is set to GL_TRUE, then the argument will

be set to GL_LINE_LOOP. The function prototype for this callback is:

void begin(GLenum type);

GLU_TESS_BEGIN_DATA

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