gluTessCallback

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.

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 .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 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);

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• 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 .gluTessBeginPolygon was called. The method prototype for this callback is:

  void beginData(int type, Object polygonData);

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• GLU_TESS_EDGE_FLAG
  
  The edge flag callback is similar to 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);

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• 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 .gluTessBeginPolygon was called. The method prototype for this callback is:

  void edgeFlagData(boolean boundaryEdge, Object polygonData);

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• GLU_TESS_VERTEX
  
  The vertex callback is invoked between the begin and end callbacks. It is similar to 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);

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• 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 .gluTessBeginPolygon was called. The method prototype for this callback is:

  void vertexData(Object vertexData, Object polygonData);

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• GLU_TESS_END
  
  The end callback serves the same purpose as glEnd. It indicates the end of a primitive and it takes no arguments. The method prototype for this callback is:

  void end();

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• 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 .gluTessBeginPolygon was called. The method prototype for this callback is:

  void endData(Object polygonData);

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• 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 = coords0; newVertex.y = coords1; newVertex.z = coords2; newVertex.r = weight0*data0.r + weight1*data1.r + weight2*data2.r + weight3*data3.r; newVertex.g = weight0*data0.g + weight1*data1.g + weight2*data2.g + weight3*data3.g; newVertex.b = weight0*data0.b + weight1*data1.b + weight2*data2.b + weight3*data3.b; newVertex.a = weight0*data0.a + weight1*data1.a + weight2*data2.a + weight3*data3.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.
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• 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 .gluTessBeginPolygon was called. The method prototype for this callback is:

   void combineData(double[] coords, Object[] data, float[] weight, Object[] outData, Object polygonData);

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• **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][.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.
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• **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 [gluTessBeginPolygon][.gluTessBeginPolygon] was called. The method prototype for this callback is:

  void errorData(int errnum, Object polygonData);

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Parameters

See also