C++ VertLeq函数代码示例

GLdouble __gl_edgeEval( GLUvertex *u, GLUvertex *v, GLUvertex *w )
{
  /* Given three vertices u,v,w such that VertLeq(u,v) && VertLeq(v,w),
   * evaluates the t-coord of the edge uw at the s-coord of the vertex v.
   * Returns v->t - (uw)(v->s), ie. the signed distance from uw to v.
   * If uw is vertical (and thus passes thru v), the result is zero.
   *
   * The calculation is extremely accurate and stable, even when v
   * is very close to u or w.  In particular if we set v->t = 0 and
   * let r be the negated result (this evaluates (uw)(v->s)), then
   * r is guaranteed to satisfy MIN(u->t,w->t) <= r <= MAX(u->t,w->t).
   */
  GLdouble gapL, gapR;

  assert( VertLeq( u, v ) && VertLeq( v, w ));

  gapL = v->s - u->s;
  gapR = w->s - v->s;

  if( gapL + gapR > 0 ) {
    if( gapL < gapR ) {
      return (v->t - u->t) + (u->t - w->t) * (gapL / (gapL + gapR));
    } else {
      return (v->t - w->t) + (w->t - u->t) * (gapR / (gapL + gapR));
    }
  }
  /* vertical line */
  return 0;
}

/* tessMeshTessellateMonoRegion( face ) tessellates a monotone region
* (what else would it do??)  The region must consist of a single
* loop of half-edges (see mesh.h) oriented CCW.  "Monotone" in this
* case means that any vertical line intersects the interior of the
* region in a single interval.  
*
* Tessellation consists of adding interior edges (actually pairs of
* half-edges), to split the region into non-overlapping triangles.
*
* The basic idea is explained in Preparata and Shamos (which I don''t
* have handy right now), although their implementation is more
* complicated than this one.  The are two edge chains, an upper chain
* and a lower chain.  We process all vertices from both chains in order,
* from right to left.
*
* The algorithm ensures that the following invariant holds after each
* vertex is processed: the untessellated region consists of two
* chains, where one chain (say the upper) is a single edge, and
* the other chain is concave.  The left vertex of the single edge
* is always to the left of all vertices in the concave chain.
*
* Each step consists of adding the rightmost unprocessed vertex to one
* of the two chains, and forming a fan of triangles from the rightmost
* of two chain endpoints.  Determining whether we can add each triangle
* to the fan is a simple orientation test.  By making the fan as large
* as possible, we restore the invariant (check it yourself).
*/
int tessMeshTessellateMonoRegion( TESSmesh *mesh, TESSface *face )
{
	TESShalfEdge *up, *lo;

	/* All edges are oriented CCW around the boundary of the region.
	* First, find the half-edge whose origin vertex is rightmost.
	* Since the sweep goes from left to right, face->anEdge should
	* be close to the edge we want.
	*/
	up = face->anEdge;
	if(!( up->Lnext != up && up->Lnext->Lnext != up )) return 1;

	for( ; VertLeq( up->Dst, up->Org ); up = up->Lprev )
		;
	for( ; VertLeq( up->Org, up->Dst ); up = up->Lnext )
		;
	lo = up->Lprev;

	while( up->Lnext != lo ) {
		if( VertLeq( up->Dst, lo->Org )) {
			/* up->Dst is on the left.  It is safe to form triangles from lo->Org.
			* The EdgeGoesLeft test guarantees progress even when some triangles
			* are CW, given that the upper and lower chains are truly monotone.
			*/
			while( lo->Lnext != up && (EdgeGoesLeft( lo->Lnext )
				|| EdgeSign( lo->Org, lo->Dst, lo->Lnext->Dst ) <= 0 )) {
					TESShalfEdge *tempHalfEdge= tessMeshConnect( mesh, lo->Lnext, lo );
					if (tempHalfEdge == NULL) return 0;
					lo = tempHalfEdge->Sym;
			}
			lo = lo->Lprev;
		} else {
			/* lo->Org is on the left.  We can make CCW triangles from up->Dst. */
			while( lo->Lnext != up && (EdgeGoesRight( up->Lprev )
				|| EdgeSign( up->Dst, up->Org, up->Lprev->Org ) >= 0 )) {
					TESShalfEdge *tempHalfEdge= tessMeshConnect( mesh, up, up->Lprev );
					if (tempHalfEdge == NULL) return 0;
					up = tempHalfEdge->Sym;
			}
			up = up->Lnext;
		}
	}

	/* Now lo->Org == up->Dst == the leftmost vertex.  The remaining region
	* can be tessellated in a fan from this leftmost vertex.
	*/
	if( lo->Lnext == up ) return 1;
	while( lo->Lnext->Lnext != up ) {
		TESShalfEdge *tempHalfEdge= tessMeshConnect( mesh, lo->Lnext, lo );
		if (tempHalfEdge == NULL) return 0;
		lo = tempHalfEdge->Sym;
	}

	return 1;
}

static int CheckForRightSplice( GLUtesselator *tess, ActiveRegion *regUp )
/*
 * Check the upper and lower edge of "regUp", to make sure that the
 * eUp->Org is above eLo, or eLo->Org is below eUp (depending on which
 * origin is leftmost).
 *
 * The main purpose is to splice right-going edges with the same
 * dest vertex and nearly identical slopes (ie. we can't distinguish
 * the slopes numerically).  However the splicing can also help us
 * to recover from numerical errors.  For example, suppose at one
 * point we checked eUp and eLo, and decided that eUp->Org is barely
 * above eLo.  Then later, we split eLo into two edges (eg. from
 * a splice operation like this one).  This can change the result of
 * our test so that now eUp->Org is incident to eLo, or barely below it.
 * We must correct this condition to maintain the dictionary invariants.
 *
 * One possibility is to check these edges for intersection again
 * (ie. CheckForIntersect).  This is what we do if possible.  However
 * CheckForIntersect requires that tess->event lies between eUp and eLo,
 * so that it has something to fall back on when the intersection
 * calculation gives us an unusable answer.  So, for those cases where
 * we can't check for intersection, this routine fixes the problem
 * by just splicing the offending vertex into the other edge.
 * This is a guaranteed solution, no matter how degenerate things get.
 * Basically this is a combinatorial solution to a numerical problem.
 */
{
  ActiveRegion *regLo = RegionBelow(regUp);
  GLUhalfEdge *eUp = regUp->eUp;
  GLUhalfEdge *eLo = regLo->eUp;

  if( VertLeq( eUp->Org, eLo->Org )) {
    if( EdgeSign( eLo->Dst, eUp->Org, eLo->Org ) > 0 ) return FALSE;

    /* eUp->Org appears to be below eLo */
    if( ! VertEq( eUp->Org, eLo->Org )) {
      /* Splice eUp->Org into eLo */
      if ( __gl_meshSplitEdge( eLo->Sym ) == NULL) longjmp(tess->env,1);
      if ( !__gl_meshSplice( eUp, eLo->Oprev ) ) longjmp(tess->env,1);
      regUp->dirty = regLo->dirty = TRUE;

    } else if( eUp->Org != eLo->Org ) {
      /* merge the two vertices, discarding eUp->Org */
      pqDelete( tess->pq, eUp->Org->pqHandle ); /* __gl_pqSortDelete */
      SpliceMergeVertices( tess, eLo->Oprev, eUp );
    }
  } else {
    if( EdgeSign( eUp->Dst, eLo->Org, eUp->Org ) < 0 ) return FALSE;

    /* eLo->Org appears to be above eUp, so splice eLo->Org into eUp */
	regUp->dirty = TRUE;
	void* valid_ptr_check = RegionAbove(regUp);//->dirty  
	if ( valid_ptr_check ) {
		RegionAbove(regUp)->dirty = TRUE;  
	}  
    if (__gl_meshSplitEdge( eUp->Sym ) == NULL) longjmp(tess->env,1);
    if ( !__gl_meshSplice( eLo->Oprev, eUp ) ) longjmp(tess->env,1);
  }
  return TRUE;
}

GLdouble __gl_edgeSign( GLUvertex *u, GLUvertex *v, GLUvertex *w )
{
  /* Returns a number whose sign matches EdgeEval(u,v,w) but which
   * is cheaper to evaluate.  Returns > 0, == 0 , or < 0
   * as v is above, on, or below the edge uw.
   */
  GLdouble gapL, gapR;

  assert( VertLeq( u, v ) && VertLeq( v, w ));

  gapL = v->s - u->s;
  gapR = w->s - v->s;

  if( gapL + gapR > 0 ) {
    return (v->t - w->t) * gapL + (v->t - u->t) * gapR;
  }
  /* vertical line */
  return 0;
}

TESSreal tesedgeSign( TESSvertex *u, TESSvertex *v, TESSvertex *w )
{
	/* Returns a number whose sign matches EdgeEval(u,v,w) but which
	* is cheaper to evaluate.  Returns > 0, == 0 , or < 0
	* as v is above, on, or below the edge uw.
	*/
	TESSreal gapL, gapR;

//	assert( VertLeq( u, v ) && VertLeq( v, w ));
	if( ! ( VertLeq( u, v ) && VertLeq( v, w )) )
		return 0;// this is incorrect but prevents a crash with pernicious geometry

	gapL = v->s - u->s;
	gapR = w->s - v->s;

	if( gapL + gapR > 0 ) {
		return (v->t - w->t) * gapL + (v->t - u->t) * gapR;
	}
	/* vertical line */
	return 0;
}

static int CheckForLeftSplice( GLUtesselator *tess, ActiveRegion *regUp )
/*
 * Check the upper and lower edge of "regUp", to make sure that the
 * eUp->Dst is above eLo, or eLo->Dst is below eUp (depending on which
 * destination is rightmost).
 *
 * Theoretically, this should always be true.  However, splitting an edge
 * into two pieces can change the results of previous tests.  For example,
 * suppose at one point we checked eUp and eLo, and decided that eUp->Dst
 * is barely above eLo.  Then later, we split eLo into two edges (eg. from
 * a splice operation like this one).  This can change the result of
 * the test so that now eUp->Dst is incident to eLo, or barely below it.
 * We must correct this condition to maintain the dictionary invariants
 * (otherwise new edges might get inserted in the wrong place in the
 * dictionary, and bad stuff will happen).
 *
 * We fix the problem by just splicing the offending vertex into the
 * other edge.
 */
{
  ActiveRegion *regLo = RegionBelow(regUp);
  GLUhalfEdge *eUp = regUp->eUp;
  GLUhalfEdge *eLo = regLo->eUp;
  GLUhalfEdge *e;

  assert( ! VertEq( eUp->Dst, eLo->Dst ));

  if( VertLeq( eUp->Dst, eLo->Dst )) {
    if( EdgeSign( eUp->Dst, eLo->Dst, eUp->Org ) < 0 ) return FALSE;

    /* eLo->Dst is above eUp, so splice eLo->Dst into eUp */
	if ( RegionAbove(regUp) ) {
		RegionAbove(regUp)->dirty = TRUE;
	}  
	regUp->dirty = TRUE;
    e = __gl_meshSplitEdge( eUp );
    if (e == NULL) longjmp(tess->env,1);
    if ( !__gl_meshSplice( eLo->Sym, e ) ) longjmp(tess->env,1);
    e->Lface->inside = regUp->inside;
  } else {
    if( EdgeSign( eLo->Dst, eUp->Dst, eLo->Org ) > 0 ) return FALSE;

    /* eUp->Dst is below eLo, so splice eUp->Dst into eLo */
    regUp->dirty = regLo->dirty = TRUE;
    e = __gl_meshSplitEdge( eLo );
    if (e == NULL) longjmp(tess->env,1);
    if ( !__gl_meshSplice( eUp->Lnext, eLo->Sym ) ) longjmp(tess->env,1);
    e->Rface->inside = regUp->inside;
  }
  return TRUE;
}

static int EdgeLeq( GLUtesselator *tess, ActiveRegion *reg1,
		    ActiveRegion *reg2 )
/*
 * Both edges must be directed from right to left (this is the canonical
 * direction for the upper edge of each region).
 *
 * The strategy is to evaluate a "t" value for each edge at the
 * current sweep line position, given by tess->event.  The calculations
 * are designed to be very stable, but of course they are not perfect.
 *
 * Special case: if both edge destinations are at the sweep event,
 * we sort the edges by slope (they would otherwise compare equally).
 */
{
  GLUvertex *event = tess->event;
  GLUhalfEdge *e1, *e2;
  GLdouble t1, t2;

  e1 = reg1->eUp;
  e2 = reg2->eUp;

  if( e1->Dst == event ) {
    if( e2->Dst == event ) {
      /* Two edges right of the sweep line which meet at the sweep event.
       * Sort them by slope.
       */
      if( VertLeq( e1->Org, e2->Org )) {
	return EdgeSign( e2->Dst, e1->Org, e2->Org ) <= 0;
      }
      return EdgeSign( e1->Dst, e2->Org, e1->Org ) >= 0;
    }
    return EdgeSign( e2->Dst, event, e2->Org ) <= 0;
  }
  if( e2->Dst == event ) {
    return EdgeSign( e1->Dst, event, e1->Org ) >= 0;
  }

  /* General case - compute signed distance *from* e1, e2 to event */
  t1 = EdgeEval( e1->Dst, event, e1->Org );
  t2 = EdgeEval( e2->Dst, event, e2->Org );
  return (t1 >= t2);
}

int __gl_vertLeq( GLUvertex *u, GLUvertex *v )
{
  /* Returns TRUE if u is lexicographically <= v. */

  return VertLeq( u, v );
}

void __gl_edgeIntersect( GLUvertex *o1, GLUvertex *d1,
			 GLUvertex *o2, GLUvertex *d2,
			 GLUvertex *v )
/* Given edges (o1,d1) and (o2,d2), compute their point of intersection.
 * The computed point is guaranteed to lie in the intersection of the
 * bounding rectangles defined by each edge.
 */
{
  GLdouble z1, z2;

  /* This is certainly not the most efficient way to find the intersection
   * of two line segments, but it is very numerically stable.
   *
   * Strategy: find the two middle vertices in the VertLeq ordering,
   * and interpolate the intersection s-value from these.  Then repeat
   * using the TransLeq ordering to find the intersection t-value.
   */

  if( ! VertLeq( o1, d1 )) { Swap( o1, d1 ); }
  if( ! VertLeq( o2, d2 )) { Swap( o2, d2 ); }
  if( ! VertLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }

  if( ! VertLeq( o2, d1 )) {
    /* Technically, no intersection -- do our best */
    v->s = (o2->s + d1->s) / 2;
  } else if( VertLeq( d1, d2 )) {
    /* Interpolate between o2 and d1 */
    z1 = EdgeEval( o1, o2, d1 );
    z2 = EdgeEval( o2, d1, d2 );
    if( z1+z2 < 0 ) { z1 = -z1; z2 = -z2; }
    v->s = Interpolate( z1, o2->s, z2, d1->s );
  } else {
    /* Interpolate between o2 and d2 */
    z1 = EdgeSign( o1, o2, d1 );
    z2 = -EdgeSign( o1, d2, d1 );
    if( z1+z2 < 0 ) { z1 = -z1; z2 = -z2; }
    v->s = Interpolate( z1, o2->s, z2, d2->s );
  }

  /* Now repeat the process for t */

  if( ! TransLeq( o1, d1 )) { Swap( o1, d1 ); }
  if( ! TransLeq( o2, d2 )) { Swap( o2, d2 ); }
  if( ! TransLeq( o1, o2 )) { Swap( o1, o2 ); Swap( d1, d2 ); }

  if( ! TransLeq( o2, d1 )) {
    /* Technically, no intersection -- do our best */
    v->t = (o2->t + d1->t) / 2;
  } else if( TransLeq( d1, d2 )) {
    /* Interpolate between o2 and d1 */
    z1 = TransEval( o1, o2, d1 );
    z2 = TransEval( o2, d1, d2 );
    if( z1+z2 < 0 ) { z1 = -z1; z2 = -z2; }
    v->t = Interpolate( z1, o2->t, z2, d1->t );
  } else {
    /* Interpolate between o2 and d2 */
    z1 = TransSign( o1, o2, d1 );
    z2 = -TransSign( o1, d2, d1 );
    if( z1+z2 < 0 ) { z1 = -z1; z2 = -z2; }
    v->t = Interpolate( z1, o2->t, z2, d2->t );
  }
}

static void ConnectLeftVertex( TESStesselator *tess, TESSvertex *vEvent )
/*
* Purpose: connect a "left" vertex (one where both edges go right)
* to the processed portion of the mesh.  Let R be the active region
* containing vEvent, and let U and L be the upper and lower edge
* chains of R.  There are two possibilities:
*
* - the normal case: split R into two regions, by connecting vEvent to
*   the rightmost vertex of U or L lying to the left of the sweep line
*
* - the degenerate case: if vEvent is close enough to U or L, we
*   merge vEvent into that edge chain.  The subcases are:
*	- merging with the rightmost vertex of U or L
*	- merging with the active edge of U or L
*	- merging with an already-processed portion of U or L
*/
{
	ActiveRegion *regUp, *regLo, *reg;
	TESShalfEdge *eUp, *eLo, *eNew;
	ActiveRegion tmp;

	/* assert( vEvent->anEdge->Onext->Onext == vEvent->anEdge ); */

	/* Get a pointer to the active region containing vEvent */
	tmp.eUp = vEvent->anEdge->Sym;
	/* __GL_DICTLISTKEY */ /* tessDictListSearch */
	regUp = (ActiveRegion *)dictKey( dictSearch( tess->dict, &tmp ));
	regLo = RegionBelow( regUp );
	if( !regLo ) {
		// This may happen if the input polygon is coplanar.
		return;
	}
	eUp = regUp->eUp;
	eLo = regLo->eUp;

	/* Try merging with U or L first */
	if( EdgeSign( eUp->Dst, vEvent, eUp->Org ) == 0 ) {
		ConnectLeftDegenerate( tess, regUp, vEvent );
		return;
	}

	/* Connect vEvent to rightmost processed vertex of either chain.
	* e->Dst is the vertex that we will connect to vEvent.
	*/
	reg = VertLeq( eLo->Dst, eUp->Dst ) ? regUp : regLo;

	if( regUp->inside || reg->fixUpperEdge) {
		if( reg == regUp ) {
			eNew = tessMeshConnect( tess->mesh, vEvent->anEdge->Sym, eUp->Lnext );
			if (eNew == NULL) longjmp(tess->env,1);
		} else {
			TESShalfEdge *tempHalfEdge= tessMeshConnect( tess->mesh, eLo->Dnext, vEvent->anEdge);
			if (tempHalfEdge == NULL) longjmp(tess->env,1);

			eNew = tempHalfEdge->Sym;
		}
		if( reg->fixUpperEdge ) {
			if ( !FixUpperEdge( tess, reg, eNew ) ) longjmp(tess->env,1);
		} else {
			ComputeWinding( tess, AddRegionBelow( tess, regUp, eNew ));
		}
		SweepEvent( tess, vEvent );
	} else {
		/* The new vertex is in a region which does not belong to the polygon.
		* We don''t need to connect this vertex to the rest of the mesh.
		*/
		AddRightEdges( tess, regUp, vEvent->anEdge, vEvent->anEdge, NULL, TRUE );
	}
}

static void ConnectRightVertex( TESStesselator *tess, ActiveRegion *regUp,
							   TESShalfEdge *eBottomLeft )
/*
* Purpose: connect a "right" vertex vEvent (one where all edges go left)
* to the unprocessed portion of the mesh.  Since there are no right-going
* edges, two regions (one above vEvent and one below) are being merged
* into one.  "regUp" is the upper of these two regions.
*
* There are two reasons for doing this (adding a right-going edge):
*  - if the two regions being merged are "inside", we must add an edge
*    to keep them separated (the combined region would not be monotone).
*  - in any case, we must leave some record of vEvent in the dictionary,
*    so that we can merge vEvent with features that we have not seen yet.
*    For example, maybe there is a vertical edge which passes just to
*    the right of vEvent; we would like to splice vEvent into this edge.
*
* However, we don't want to connect vEvent to just any vertex.  We don''t
* want the new edge to cross any other edges; otherwise we will create
* intersection vertices even when the input data had no self-intersections.
* (This is a bad thing; if the user's input data has no intersections,
* we don't want to generate any false intersections ourselves.)
*
* Our eventual goal is to connect vEvent to the leftmost unprocessed
* vertex of the combined region (the union of regUp and regLo).
* But because of unseen vertices with all right-going edges, and also
* new vertices which may be created by edge intersections, we don''t
* know where that leftmost unprocessed vertex is.  In the meantime, we
* connect vEvent to the closest vertex of either chain, and mark the region
* as "fixUpperEdge".  This flag says to delete and reconnect this edge
* to the next processed vertex on the boundary of the combined region.
* Quite possibly the vertex we connected to will turn out to be the
* closest one, in which case we won''t need to make any changes.
*/
{
	TESShalfEdge *eNew;
	TESShalfEdge *eTopLeft = eBottomLeft->Onext;
	ActiveRegion *regLo = RegionBelow(regUp);
	TESShalfEdge *eUp = regUp->eUp;
	TESShalfEdge *eLo = regLo->eUp;
	int degenerate = FALSE;

	if( eUp->Dst != eLo->Dst ) {
		(void) CheckForIntersect( tess, regUp );
	}

	/* Possible new degeneracies: upper or lower edge of regUp may pass
	* through vEvent, or may coincide with new intersection vertex
	*/
	if( VertEq( eUp->Org, tess->event )) {
		if ( !tessMeshSplice( tess->mesh, eTopLeft->Oprev, eUp ) ) longjmp(tess->env,1);
		regUp = TopLeftRegion( tess, regUp );
		if (regUp == NULL) longjmp(tess->env,1);
		eTopLeft = RegionBelow( regUp )->eUp;
		FinishLeftRegions( tess, RegionBelow(regUp), regLo );
		degenerate = TRUE;
	}
	if( VertEq( eLo->Org, tess->event )) {
		if ( !tessMeshSplice( tess->mesh, eBottomLeft, eLo->Oprev ) ) longjmp(tess->env,1);
		eBottomLeft = FinishLeftRegions( tess, regLo, NULL );
		degenerate = TRUE;
	}
	if( degenerate ) {
		AddRightEdges( tess, regUp, eBottomLeft->Onext, eTopLeft, eTopLeft, TRUE );
		return;
	}

	/* Non-degenerate situation -- need to add a temporary, fixable edge.
	* Connect to the closer of eLo->Org, eUp->Org.
	*/
	if( VertLeq( eLo->Org, eUp->Org )) {
		eNew = eLo->Oprev;
	} else {
		eNew = eUp;
	}
	eNew = tessMeshConnect( tess->mesh, eBottomLeft->Lprev, eNew );
	if (eNew == NULL) longjmp(tess->env,1);

	/* Prevent cleanup, otherwise eNew might disappear before we've even
	* had a chance to mark it as a temporary edge.
	*/
	AddRightEdges( tess, regUp, eNew, eNew->Onext, eNew->Onext, FALSE );
	eNew->Sym->activeRegion->fixUpperEdge = TRUE;
	WalkDirtyRegions( tess, regUp );
}

static int CheckForIntersect( TESStesselator *tess, ActiveRegion *regUp )
/*
* Check the upper and lower edges of the given region to see if
* they intersect.  If so, create the intersection and add it
* to the data structures.
*
* Returns TRUE if adding the new intersection resulted in a recursive
* call to AddRightEdges(); in this case all "dirty" regions have been
* checked for intersections, and possibly regUp has been deleted.
*/
{
	ActiveRegion *regLo = RegionBelow(regUp);
	TESShalfEdge *eUp = regUp->eUp;
	TESShalfEdge *eLo = regLo->eUp;
	TESSvertex *orgUp = eUp->Org;
	TESSvertex *orgLo = eLo->Org;
	TESSvertex *dstUp = eUp->Dst;
	TESSvertex *dstLo = eLo->Dst;
	TESSreal tMinUp, tMaxLo;
	TESSvertex isect, *orgMin;
	TESShalfEdge *e;

	assert( ! VertEq( dstLo, dstUp ));
	assert( EdgeSign( dstUp, tess->event, orgUp ) <= 0 );
	assert( EdgeSign( dstLo, tess->event, orgLo ) >= 0 );
	assert( orgUp != tess->event && orgLo != tess->event );
	assert( ! regUp->fixUpperEdge && ! regLo->fixUpperEdge );

	if( orgUp == orgLo ) return FALSE;	/* right endpoints are the same */

	tMinUp = MIN( orgUp->t, dstUp->t );
	tMaxLo = MAX( orgLo->t, dstLo->t );
	if( tMinUp > tMaxLo ) return FALSE;	/* t ranges do not overlap */

	if( VertLeq( orgUp, orgLo )) {
		if( EdgeSign( dstLo, orgUp, orgLo ) > 0 ) return FALSE;
	} else {
		if( EdgeSign( dstUp, orgLo, orgUp ) < 0 ) return FALSE;
	}

	/* At this point the edges intersect, at least marginally */
	DebugEvent( tess );

	tesedgeIntersect( dstUp, orgUp, dstLo, orgLo, &isect );
	/* The following properties are guaranteed: */
	assert( MIN( orgUp->t, dstUp->t ) <= isect.t );
	assert( isect.t <= MAX( orgLo->t, dstLo->t ));
	assert( MIN( dstLo->s, dstUp->s ) <= isect.s );
	assert( isect.s <= MAX( orgLo->s, orgUp->s ));

	if( VertLeq( &isect, tess->event )) {
		/* The intersection point lies slightly to the left of the sweep line,
		* so move it until it''s slightly to the right of the sweep line.
		* (If we had perfect numerical precision, this would never happen
		* in the first place).  The easiest and safest thing to do is
		* replace the intersection by tess->event.
		*/
		isect.s = tess->event->s;
		isect.t = tess->event->t;
	}
	/* Similarly, if the computed intersection lies to the right of the
	* rightmost origin (which should rarely happen), it can cause
	* unbelievable inefficiency on sufficiently degenerate inputs.
	* (If you have the test program, try running test54.d with the
	* "X zoom" option turned on).
	*/
	orgMin = VertLeq( orgUp, orgLo ) ? orgUp : orgLo;
	if( VertLeq( orgMin, &isect )) {
		isect.s = orgMin->s;
		isect.t = orgMin->t;
	}

	if( VertEq( &isect, orgUp ) || VertEq( &isect, orgLo )) {
		/* Easy case -- intersection at one of the right endpoints */
		(void) CheckForRightSplice( tess, regUp );
		return FALSE;
	}

	if(    (! VertEq( dstUp, tess->event )
		&& EdgeSign( dstUp, tess->event, &isect ) >= 0)
		|| (! VertEq( dstLo, tess->event )
		&& EdgeSign( dstLo, tess->event, &isect ) <= 0 ))
	{
		/* Very unusual -- the new upper or lower edge would pass on the
		* wrong side of the sweep event, or through it.  This can happen
		* due to very small numerical errors in the intersection calculation.
		*/
		if( dstLo == tess->event ) {
			/* Splice dstLo into eUp, and process the new region(s) */
			if (tessMeshSplitEdge( tess->mesh, eUp->Sym ) == NULL) longjmp(tess->env,1);
			if ( !tessMeshSplice( tess->mesh, eLo->Sym, eUp ) ) longjmp(tess->env,1);
			regUp = TopLeftRegion( tess, regUp );
			if (regUp == NULL) longjmp(tess->env,1);
			eUp = RegionBelow(regUp)->eUp;
			FinishLeftRegions( tess, RegionBelow(regUp), regLo );
			AddRightEdges( tess, regUp, eUp->Oprev, eUp, eUp, TRUE );
			return TRUE;
		}
		if( dstUp == tess->event ) {
			/* Splice dstUp into eLo, and process the new region(s) */
//.........这里部分代码省略.........

static void AddRightEdges( TESStesselator *tess, ActiveRegion *regUp,
						  TESShalfEdge *eFirst, TESShalfEdge *eLast, TESShalfEdge *eTopLeft,
						  int cleanUp )
/*
* Purpose: insert right-going edges into the edge dictionary, and update
* winding numbers and mesh connectivity appropriately.  All right-going
* edges share a common origin vOrg.  Edges are inserted CCW starting at
* eFirst; the last edge inserted is eLast->Oprev.  If vOrg has any
* left-going edges already processed, then eTopLeft must be the edge
* such that an imaginary upward vertical segment from vOrg would be
* contained between eTopLeft->Oprev and eTopLeft; otherwise eTopLeft
* should be NULL.
*/
{
	ActiveRegion *reg, *regPrev;
	TESShalfEdge *e, *ePrev;
	int firstTime = TRUE;

	/* Insert the new right-going edges in the dictionary */
	e = eFirst;
	do {
		assert( VertLeq( e->Org, e->Dst ));
		AddRegionBelow( tess, regUp, e->Sym );
		e = e->Onext;
	} while ( e != eLast );

	/* Walk *all* right-going edges from e->Org, in the dictionary order,
	* updating the winding numbers of each region, and re-linking the mesh
	* edges to match the dictionary ordering (if necessary).
	*/
	if( eTopLeft == NULL ) {
		eTopLeft = RegionBelow( regUp )->eUp->Rprev;
	}
	regPrev = regUp;
	ePrev = eTopLeft;
	for( ;; ) {
		reg = RegionBelow( regPrev );
		e = reg->eUp->Sym;
		if( e->Org != ePrev->Org ) break;

		if( e->Onext != ePrev ) {
			/* Unlink e from its current position, and relink below ePrev */
			if ( !tessMeshSplice( tess->mesh, e->Oprev, e ) ) longjmp(tess->env,1);
			if ( !tessMeshSplice( tess->mesh, ePrev->Oprev, e ) ) longjmp(tess->env,1);
		}
		/* Compute the winding number and "inside" flag for the new regions */
		reg->windingNumber = regPrev->windingNumber - e->winding;
		reg->inside = IsWindingInside( tess, reg->windingNumber );

		/* Check for two outgoing edges with same slope -- process these
		* before any intersection tests (see example in tessComputeInterior).
		*/
		regPrev->dirty = TRUE;
		if( ! firstTime && CheckForRightSplice( tess, regPrev )) {
			AddWinding( e, ePrev );
			DeleteRegion( tess, regPrev );
			if ( !tessMeshDelete( tess->mesh, ePrev ) ) longjmp(tess->env,1);
		}
		firstTime = FALSE;
		regPrev = reg;
		ePrev = e;
	}
	regPrev->dirty = TRUE;
	assert( regPrev->windingNumber - e->winding == reg->windingNumber );

	if( cleanUp ) {
		/* Check for intersections between newly adjacent edges. */
		WalkDirtyRegions( tess, regPrev );
	}
}

int tesvertLeq( TESSvertex *u, TESSvertex *v )
{
	/* Returns TRUE if u is lexicographically <= v. */

	return VertLeq( u, v );
}