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gluTessCallback

Chapter 18

415

GLU_TESS_ERROR

The error callback is called when an error is encountered. The one argument is of type

GLenum; it indicates the speciﬁc error that occurred and will be set to one of

GLU_TESS_MISSING_BEGIN_POLYGON, GLU_TESS_MISSING_END_POLYGON,

GLU_TESS_MISSING_BEGIN_CONTOUR, GLU_TESS_MISSING_END_CONTOUR,

GLU_TESS_COORD_TOO_LARGE, GLU_TESS_NEED_COMBINE_CALLBACK.

Character strings describing these errors can be retrieved with the gluErrorString call.

The function prototype for this callback is:

void error(GLenum errno);

The GLU library will recover from the ﬁrst four errors by inserting the missing call(s).

GLU_TESS_COORD_TOO_LARGE indicates that some vertex coordinate exceeded the

predeﬁned constant GLU_TESS_MAX_COORD in absolute value, and that the value

has been clamped. (Coordinate values must be small enough so that two can be

multiplied together without overﬂow.)

GLU_TESS_NEED_COMBINE_CALLBACK indicates that the tessellation detected an

intersection between two edges in the input data, and the GLU_TESS_COMBINE or

GLU_TESS_COMBINE_DATA callback was not provided. No output is generated.

GLU_TESS_ERROR_DATA

The same as the GLU_TESS_ERROR callback except that it takes an additional pointer

argument. This pointer is identical to the opaque pointer provided when

gluTessBeginPolygon was called. The function prototype for this callback is:

void errorData(GLenum errno, void *polygon_data);

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