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
aCallback is null, then the existing callback
becomes undefined.
Optional, throws GLException if not available in profile
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
polygonData parameter used by some of the methods is a copy of the
reference that was specified when
#gluTessBeginPolygonwas called. The legal callbacks are as follows:
GLU_TESS_BEGIN
The begin callback is invoked like
javax.media.opengl.GL#glBegin to indicate the start of a (triangle) primitive. The method
takes a single argument of type int. 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 method prototype for
this callback is:
void begin(int type);
GLU_TESS_BEGIN_DATA
The same as the GLU_TESS_BEGIN callback except
that it takes an additional reference argument. This reference is
identical to the opaque reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void beginData(int type, Object polygonData);
GLU_TESS_EDGE_FLAG
The edge flag callback is similar to
javax.media.opengl.GL#glEdgeFlag. The method takes
a single boolean boundaryEdge that indicates which edges lie on the
polygon boundary. If the boundaryEdge is GL_TRUE, then each vertex
that follows begins an edge that lies on the polygon boundary, that is,
an edge that separates an interior region from an exterior one. If the
boundaryEdge is GL_FALSE, then each vertex that follows begins an
edge that lies in the polygon interior. The edge flag callback (if
defined) is invoked before the first vertex callback.
Since triangle fans and triangle strips do not support edge flags, the
begin callback is not called with GL_TRIANGLE_FAN or
GL_TRIANGLE_STRIP if a non-null edge flag callback is provided.
(If the callback is initialized to null, there is no impact on
performance). Instead, the fans and strips are converted to independent
triangles. The method prototype for this callback is:
void edgeFlag(boolean boundaryEdge);
GLU_TESS_EDGE_FLAG_DATA
The same as the GLU_TESS_EDGE_FLAG callback except that it takes
an additional reference argument. This reference is identical to the
opaque reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void edgeFlagData(boolean boundaryEdge, Object polygonData);
GLU_TESS_VERTEX
The vertex callback is invoked between the begin and end callbacks. It is
similar to
javax.media.opengl.GL#glVertex3f, and it
defines the vertices of the triangles created by the tessellation
process. The method takes a reference as its only argument. This
reference is identical to the opaque reference provided by the user when
the vertex was described (see
#gluTessVertex). The method
prototype for this callback is:
void vertex(Object vertexData);
GLU_TESS_VERTEX_DATA
The same as the GLU_TESS_VERTEX callback except that it takes an
additional reference argument. This reference is identical to the opaque
reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void vertexData(Object vertexData, Object polygonData);
GLU_TESS_END
The end callback serves the same purpose as
javax.media.opengl.GL#glEnd. It indicates the end of a
primitive and it takes no arguments. The method prototype for this
callback is:
void end();
GLU_TESS_END_DATA
The same as the GLU_TESS_END callback except that it takes an
additional reference argument. This reference is identical to the opaque
reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void endData(Object polygonData);
GLU_TESS_COMBINE
The combine callback is called to create a new vertex when the
tessellation detects an intersection, or wishes to merge features. The
method takes four arguments: an array of three elements each of type
double, an array of four references, an array of four elements each of
type float, and a reference to a reference. The prototype is:
void combine(double[] coords, Object[] data,
float[] weight, Object[] outData);
The vertex is defined as a linear combination of up to four existing
vertices, stored in data. The coefficients of the linear
combination are given by weight; these weights always add up to 1.
All vertex pointers are valid even when some of the weights are 0.
coords gives the location of the new vertex.
The user must allocate another vertex, interpolate parameters using
data and weight, and return the new vertex pointer
in outData. This handle is supplied during rendering callbacks.
The user is responsible for freeing the memory some time after
#gluTessEndPolygon is
called.
For example, if the polygon lies in an arbitrary plane in 3-space, and a
color is associated with each vertex, the GLU_TESS_COMBINE
callback might look like this:
void myCombine(double[] coords, Object[] data,
float[] weight, Object[] outData)
{
MyVertex newVertex = new MyVertex();
newVertex.x = coords[0];
newVertex.y = coords[1];
newVertex.z = coords[2];
newVertex.r = weight[0]*data[0].r +
weight[1]*data[1].r +
weight[2]*data[2].r +
weight[3]*data[3].r;
newVertex.g = weight[0]*data[0].g +
weight[1]*data[1].g +
weight[2]*data[2].g +
weight[3]*data[3].g;
newVertex.b = weight[0]*data[0].b +
weight[1]*data[1].b +
weight[2]*data[2].b +
weight[3]*data[3].b;
newVertex.a = weight[0]*data[0].a +
weight[1]*data[1].a +
weight[2]*data[2].a +
weight[3]*data[3].a;
outData = newVertex;
}
If the tessellation detects an intersection, then the
GLU_TESS_COMBINE or GLU_TESS_COMBINE_DATA callback (see
below) must be defined, and it must write a non-null reference into
outData. Otherwise the GLU_TESS_NEED_COMBINE_CALLBACK error
occurs, and no output is generated.
GLU_TESS_COMBINE_DATA
The same as the GLU_TESS_COMBINE callback except that it takes an
additional reference argument. This reference is identical to the opaque
reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void combineData(double[] coords, Object[] data,
float[] weight, Object[] outData,
Object polygonData);
GLU_TESS_ERROR
The error callback is called when an error is encountered. The one
argument is of type int; 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 or GLU_OUT_OF_MEMORY.
Character strings describing these errors can be retrieved with the
#gluErrorString call. The
method prototype for this callback is:
void error(int errnum);
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_OUT_OF_MEMORY indicates that
there is not enough memory so no output is generated.
GLU_TESS_ERROR_DATA
The same as the GLU_TESS_ERROR callback except that it takes an
additional reference argument. This reference is identical to the opaque
reference provided when
#gluTessBeginPolygonwas called. The method prototype for this callback is:
void errorData(int errnum, Object polygonData);