C++ RegionBelow函数代码示例

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;
}

static void ConnectLeftDegenerate( TESStesselator *tess,
								  ActiveRegion *regUp, TESSvertex *vEvent )
/*
* The event vertex lies exacty on an already-processed edge or vertex.
* Adding the new vertex involves splicing it into the already-processed
* part of the mesh.
*/
{
	TESShalfEdge *e, *eTopLeft, *eTopRight, *eLast;
	ActiveRegion *reg;

	e = regUp->eUp;
	if( VertEq( e->Org, vEvent )) {
		/* e->Org is an unprocessed vertex - just combine them, and wait
		* for e->Org to be pulled from the queue
		*/
		assert( TOLERANCE_NONZERO );
		SpliceMergeVertices( tess, e, vEvent->anEdge );
		return;
	}

	if( ! VertEq( e->Dst, vEvent )) {
		/* General case -- splice vEvent into edge e which passes through it */
		if (tessMeshSplitEdge( tess->mesh, e->Sym ) == NULL) longjmp(tess->env,1);
		if( regUp->fixUpperEdge ) {
			/* This edge was fixable -- delete unused portion of original edge */
			if ( !tessMeshDelete( tess->mesh, e->Onext ) ) longjmp(tess->env,1);
			regUp->fixUpperEdge = FALSE;
		}
		if ( !tessMeshSplice( tess->mesh, vEvent->anEdge, e ) ) longjmp(tess->env,1);
		SweepEvent( tess, vEvent );	/* recurse */
		return;
	}

	/* vEvent coincides with e->Dst, which has already been processed.
	* Splice in the additional right-going edges.
	*/
	assert( TOLERANCE_NONZERO );
	regUp = TopRightRegion( regUp );
	reg = RegionBelow( regUp );
	eTopRight = reg->eUp->Sym;
	eTopLeft = eLast = eTopRight->Onext;
	if( reg->fixUpperEdge ) {
		/* Here e->Dst has only a single fixable edge going right.
		* We can delete it since now we have some real right-going edges.
		*/
		assert( eTopLeft != eTopRight );   /* there are some left edges too */
		DeleteRegion( tess, reg );
		if ( !tessMeshDelete( tess->mesh, eTopRight ) ) longjmp(tess->env,1);
		eTopRight = eTopLeft->Oprev;
	}
	if ( !tessMeshSplice( tess->mesh, vEvent->anEdge, eTopRight ) ) longjmp(tess->env,1);
	if( ! EdgeGoesLeft( eTopLeft )) {
		/* e->Dst had no left-going edges -- indicate this to AddRightEdges() */
		eTopLeft = NULL;
	}
	AddRightEdges( tess, regUp, eTopRight->Onext, eLast, eTopLeft, TRUE );
}

static TESShalfEdge *FinishLeftRegions( TESStesselator *tess,
									  ActiveRegion *regFirst, ActiveRegion *regLast )
/*
* We are given a vertex with one or more left-going edges.  All affected
* edges should be in the edge dictionary.  Starting at regFirst->eUp,
* we walk down deleting all regions where both edges have the same
* origin vOrg.  At the same time we copy the "inside" flag from the
* active region to the face, since at this point each face will belong
* to at most one region (this was not necessarily true until this point
* in the sweep).  The walk stops at the region above regLast; if regLast
* is NULL we walk as far as possible.  At the same time we relink the
* mesh if necessary, so that the ordering of edges around vOrg is the
* same as in the dictionary.
*/
{
	ActiveRegion *reg, *regPrev;
	TESShalfEdge *e, *ePrev;

	regPrev = regFirst;
	ePrev = regFirst->eUp;
	while( regPrev != regLast ) {
		regPrev->fixUpperEdge = FALSE;	/* placement was OK */
		reg = RegionBelow( regPrev );
		e = reg->eUp;
		if( e->Org != ePrev->Org ) {
			if( ! reg->fixUpperEdge ) {
				/* Remove the last left-going edge.  Even though there are no further
				* edges in the dictionary with this origin, there may be further
				* such edges in the mesh (if we are adding left edges to a vertex
				* that has already been processed).  Thus it is important to call
				* FinishRegion rather than just DeleteRegion.
				*/
				FinishRegion( tess, regPrev );
				break;
			}
			/* If the edge below was a temporary edge introduced by
			* ConnectRightVertex, now is the time to fix it.
			*/
			e = tessMeshConnect( tess->mesh, ePrev->Lprev, e->Sym );
			if (e == NULL) longjmp(tess->env,1);
			if ( !FixUpperEdge( tess, reg, e ) ) longjmp(tess->env,1);
		}

		/* Relink edges so that ePrev->Onext == e */
		if( ePrev->Onext != e ) {
			if ( !tessMeshSplice( tess->mesh, e->Oprev, e ) ) longjmp(tess->env,1);
			if ( !tessMeshSplice( tess->mesh, ePrev, e ) ) longjmp(tess->env,1);
		}
		FinishRegion( tess, regPrev );	/* may change reg->eUp */
		ePrev = reg->eUp;
		regPrev = reg;
	}
	return ePrev;
}

static void SweepEvent( TESStesselator *tess, TESSvertex *vEvent )
/*
* Does everything necessary when the sweep line crosses a vertex.
* Updates the mesh and the edge dictionary.
*/
{
	ActiveRegion *regUp, *reg;
	TESShalfEdge *e, *eTopLeft, *eBottomLeft;

	tess->event = vEvent;		/* for access in EdgeLeq() */
	DebugEvent( tess );

	/* Check if this vertex is the right endpoint of an edge that is
	* already in the dictionary.  In this case we don't need to waste
	* time searching for the location to insert new edges.
	*/
	e = vEvent->anEdge;
	while( e->activeRegion == NULL ) {
		e = e->Onext;
		if( e == vEvent->anEdge ) {
			/* All edges go right -- not incident to any processed edges */
			ConnectLeftVertex( tess, vEvent );
			return;
		}
	}

	/* Processing consists of two phases: first we "finish" all the
	* active regions where both the upper and lower edges terminate
	* at vEvent (ie. vEvent is closing off these regions).
	* We mark these faces "inside" or "outside" the polygon according
	* to their winding number, and delete the edges from the dictionary.
	* This takes care of all the left-going edges from vEvent.
	*/
	regUp = TopLeftRegion( tess, e->activeRegion );
	if (regUp == NULL) longjmp(tess->env,1);
	reg = RegionBelow( regUp );
	eTopLeft = reg->eUp;
	eBottomLeft = FinishLeftRegions( tess, reg, NULL );

	/* Next we process all the right-going edges from vEvent.  This
	* involves adding the edges to the dictionary, and creating the
	* associated "active regions" which record information about the
	* regions between adjacent dictionary edges.
	*/
	if( eBottomLeft->Onext == eTopLeft ) {
		/* No right-going edges -- add a temporary "fixable" edge */
		ConnectRightVertex( tess, regUp, eBottomLeft );
	} else {
		AddRightEdges( tess, regUp, eBottomLeft->Onext, eTopLeft, eTopLeft, TRUE );
	}
}

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 ActiveRegion *TopLeftRegion( TESStesselator *tess, ActiveRegion *reg )
{
	TESSvertex *org = reg->eUp->Org;
	TESShalfEdge *e;

	/* Find the region above the uppermost edge with the same origin */
	do {
		reg = RegionAbove( reg );
	} while( reg->eUp->Org == org );

	/* If the edge above was a temporary edge introduced by ConnectRightVertex,
	* now is the time to fix it.
	*/
	if( reg->fixUpperEdge ) {
		e = tessMeshConnect( tess->mesh, RegionBelow(reg)->eUp->Sym, reg->eUp->Lnext );
		if (e == NULL) return NULL;
		if ( !FixUpperEdge( tess, reg, e ) ) return NULL;
		reg = RegionAbove( reg );
	}
	return reg;
}

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 void WalkDirtyRegions( TESStesselator *tess, ActiveRegion *regUp )
/*
* When the upper or lower edge of any region changes, the region is
* marked "dirty".  This routine walks through all the dirty regions
* and makes sure that the dictionary invariants are satisfied
* (see the comments at the beginning of this file).  Of course
* new dirty regions can be created as we make changes to restore
* the invariants.
*/
{
	ActiveRegion *regLo = RegionBelow(regUp);
	TESShalfEdge *eUp, *eLo;

	for( ;; ) {
		/* Find the lowest dirty region (we walk from the bottom up). */
		while( regLo->dirty ) {
			regUp = regLo;
			regLo = RegionBelow(regLo);
		}
		if( ! regUp->dirty ) {
			regLo = regUp;
			regUp = RegionAbove( regUp );
			if( regUp == NULL || ! regUp->dirty ) {
				/* We've walked all the dirty regions */
				return;
			}
		}
		regUp->dirty = FALSE;
		eUp = regUp->eUp;
		eLo = regLo->eUp;

		if( eUp->Dst != eLo->Dst ) {
			/* Check that the edge ordering is obeyed at the Dst vertices. */
			if( CheckForLeftSplice( tess, regUp )) {

				/* If the upper or lower edge was marked fixUpperEdge, then
				* we no longer need it (since these edges are needed only for
				* vertices which otherwise have no right-going edges).
				*/
				if( regLo->fixUpperEdge ) {
					DeleteRegion( tess, regLo );
					if ( !tessMeshDelete( tess->mesh, eLo ) ) longjmp(tess->env,1);
					regLo = RegionBelow( regUp );
					eLo = regLo->eUp;
				} else if( regUp->fixUpperEdge ) {
					DeleteRegion( tess, regUp );
					if ( !tessMeshDelete( tess->mesh, eUp ) ) longjmp(tess->env,1);
					regUp = RegionAbove( regLo );
					eUp = regUp->eUp;
				}
			}
		}
		if( eUp->Org != eLo->Org ) {
			if(    eUp->Dst != eLo->Dst
				&& ! regUp->fixUpperEdge && ! regLo->fixUpperEdge
				&& (eUp->Dst == tess->event || eLo->Dst == tess->event) )
			{
				/* When all else fails in CheckForIntersect(), it uses tess->event
				* as the intersection location.  To make this possible, it requires
				* that tess->event lie between the upper and lower edges, and also
				* that neither of these is marked fixUpperEdge (since in the worst
				* case it might splice one of these edges into tess->event, and
				* violate the invariant that fixable edges are the only right-going
				* edge from their associated vertex).
				*/
				if( CheckForIntersect( tess, regUp )) {
					/* WalkDirtyRegions() was called recursively; we're done */
					return;
				}
			} else {
				/* Even though we can't use CheckForIntersect(), the Org vertices
				* may violate the dictionary edge ordering.  Check and correct this.
				*/
				(void) CheckForRightSplice( tess, regUp );
			}
		}
		if( eUp->Org == eLo->Org && eUp->Dst == eLo->Dst ) {
			/* A degenerate loop consisting of only two edges -- delete it. */
			AddWinding( eLo, eUp );
			DeleteRegion( tess, regUp );
			if ( !tessMeshDelete( tess->mesh, eUp ) ) longjmp(tess->env,1);
			regUp = RegionAbove( regLo );
		}
	}
}

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 );
	}
}