Question

我发现我的应用程序在GLU源代码的sweep.c中崩溃时出现空引用异常：

static void ConnectLeftVertex( GLUtesselator *tess, GLUvertex *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;
  GLUhalfEdge *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 */ /* __gl_dictListSearch */
  regUp = (ActiveRegion *)dictKey( dictSearch( tess->dict, &tmp ));
  regLo = RegionBelow( regUp );
  eUp = regUp->eUp;
  eLo = regLo->eUp; //CRASHES RIGHT HERE SINCE RegLo is = 0x000000 FOR SOME REASON

  /* 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 = __gl_meshConnect( vEvent->anEdge->Sym, eUp->Lnext );
      if (eNew == NULL) longjmp(tess->env,1);
    } else {
      GLUhalfEdge *tempHalfEdge= __gl_meshConnect( eLo->Dnext, vEvent->anEdge);
      if (tempHalfEdge == NULL) longjmp(tess->env,1);

      eNew = tempHalfEdge->Sym;
    }
    if( reg->fixUpperEdge ) {
      if ( !FixUpperEdge( 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 );
  }
}

似乎eRegLo有时会导致我的应用程序崩溃。我怎样才能修改源代码以防止它崩溃我的应用程序？

由于

Answer 1

您必须查看RegionBelow的来源，并查看它是否以及何时可以返回NULL指针。在致电RegionBelow和取消regLo之前，请执行regLo == NULL检查。您可以使用assert或抛出异常（在C ++中）执行此操作。最有可能的是，如果RegionBelow在出错时可以返回NULL，则可以使用其他方法来确定错误是什么以及如何处理错误。您必须查阅RegionBelow的源代码或文档才能找到该信息。

为什么GLU会在这个地方崩溃？

1 个答案: