C# Otri.Lprev方法代码示例

        /// <summary>
        /// Transform two triangles to two different triangles by flipping an edge 
        /// counterclockwise within a quadrilateral.
        /// </summary>
        /// <param name="flipedge">Handle to the edge that will be flipped.</param>
        /// <remarks>Imagine the original triangles, abc and bad, oriented so that the
        /// shared edge ab lies in a horizontal plane, with the vertex b on the left
        /// and the vertex a on the right. The vertex c lies below the edge, and
        /// the vertex d lies above the edge. The 'flipedge' handle holds the edge
        /// ab of triangle abc, and is directed left, from vertex a to vertex b.
        ///
        /// The triangles abc and bad are deleted and replaced by the triangles cdb
        /// and dca.  The triangles that represent abc and bad are NOT deallocated;
        /// they are reused for dca and cdb, respectively.  Hence, any handles that
        /// may have held the original triangles are still valid, although not
        /// directed as they were before.
        ///
        /// Upon completion of this routine, the 'flipedge' handle holds the edge
        /// dc of triangle dca, and is directed down, from vertex d to vertex c.
        /// (Hence, the two triangles have rotated counterclockwise.)
        ///
        /// WARNING:  This transformation is geometrically valid only if the
        /// quadrilateral adbc is convex.  Furthermore, this transformation is
        /// valid only if there is not a subsegment between the triangles abc and
        /// bad.  This routine does not check either of these preconditions, and
        /// it is the responsibility of the calling routine to ensure that they are
        /// met.  If they are not, the streets shall be filled with wailing and
        /// gnashing of teeth.
        /// 
        /// Terminology
        ///
        /// A "local transformation" replaces a small set of triangles with another
        /// set of triangles.  This may or may not involve inserting or deleting a
        /// vertex.
        ///
        /// The term "casing" is used to describe the set of triangles that are
        /// attached to the triangles being transformed, but are not transformed
        /// themselves.  Think of the casing as a fixed hollow structure inside
        /// which all the action happens.  A "casing" is only defined relative to
        /// a single transformation; each occurrence of a transformation will
        /// involve a different casing.
        /// </remarks>
        internal void Flip(ref Otri flipedge)
        {
            Otri botleft = default(Otri), botright = default(Otri);
            Otri topleft = default(Otri), topright = default(Otri);
            Otri top = default(Otri);
            Otri botlcasing = default(Otri), botrcasing = default(Otri);
            Otri toplcasing = default(Otri), toprcasing = default(Otri);
            Osub botlsubseg = default(Osub), botrsubseg = default(Osub);
            Osub toplsubseg = default(Osub), toprsubseg = default(Osub);
            Vertex leftvertex, rightvertex, botvertex;
            Vertex farvertex;

            // Identify the vertices of the quadrilateral.
            rightvertex = flipedge.Org();
            leftvertex = flipedge.Dest();
            botvertex = flipedge.Apex();
            flipedge.Sym(ref top);

            // SELF CHECK

            //if (top.triangle == dummytri)
            //{
            //    logger.Error("Attempt to flip on boundary.", "Mesh.Flip()");
            //    flipedge.LnextSelf();
            //    return;
            //}

            //if (checksegments)
            //{
            //    flipedge.SegPivot(ref toplsubseg);
            //    if (toplsubseg.ss != dummysub)
            //    {
            //        logger.Error("Attempt to flip a segment.", "Mesh.Flip()");
            //        flipedge.LnextSelf();
            //        return;
            //    }
            //}

            farvertex = top.Apex();

            // Identify the casing of the quadrilateral.
            top.Lprev(ref topleft);
            topleft.Sym(ref toplcasing);
            top.Lnext(ref topright);
            topright.Sym(ref toprcasing);
            flipedge.Lnext(ref botleft);
            botleft.Sym(ref botlcasing);
            flipedge.Lprev(ref botright);
            botright.Sym(ref botrcasing);
            // Rotate the quadrilateral one-quarter turn counterclockwise.
            topleft.Bond(ref botlcasing);
            botleft.Bond(ref botrcasing);
            botright.Bond(ref toprcasing);
            topright.Bond(ref toplcasing);

            if (checksegments)
            {
                // Check for subsegments and rebond them to the quadrilateral.
//.........这里部分代码省略.........

        /// <summary>
        /// Removes ghost triangles.
        /// </summary>
        /// <param name="startghost"></param>
        /// <returns>Number of vertices on the hull.</returns>
        int RemoveGhosts(ref Otri startghost)
        {
            Otri searchedge = default(Otri);
            Otri dissolveedge = default(Otri);
            Otri deadtriangle = default(Otri);
            Vertex markorg;
            int hullsize;

            bool noPoly = !mesh.behavior.Poly;

            // Find an edge on the convex hull to start point location from.
            startghost.Lprev(ref searchedge);
            searchedge.SymSelf();
            Mesh.dummytri.neighbors[0] = searchedge;
            // Remove the bounding box and count the convex hull edges.
            startghost.Copy(ref dissolveedge);
            hullsize = 0;
            do
            {
                hullsize++;
                dissolveedge.Lnext(ref deadtriangle);
                dissolveedge.LprevSelf();
                dissolveedge.SymSelf();

                // If no PSLG is involved, set the boundary markers of all the vertices
                // on the convex hull.  If a PSLG is used, this step is done later.
                if (noPoly)
                {
                    // Watch out for the case where all the input vertices are collinear.
                    if (dissolveedge.triangle != Mesh.dummytri)
                    {
                        markorg = dissolveedge.Org();
                        if (markorg.mark == 0)
                        {
                            markorg.mark = 1;
                        }
                    }
                }
                // Remove a bounding triangle from a convex hull triangle.
                dissolveedge.Dissolve();
                // Find the next bounding triangle.
                deadtriangle.Sym(ref dissolveedge);

                // Delete the bounding triangle.
                mesh.TriangleDealloc(deadtriangle.triangle);
            } while (!dissolveedge.Equal(startghost));

            return hullsize;
        }

        /// <summary>
        /// Delete a vertex from a Delaunay triangulation, ensuring that the 
        /// triangulation remains Delaunay.
        /// </summary>
        /// <param name="deltri"></param>
        /// <remarks>The origin of 'deltri' is deleted. The union of the triangles 
        /// adjacent to this vertex is a polygon, for which the Delaunay triangulation 
        /// is found. Two triangles are removed from the mesh.
        ///
        /// Only interior vertices that do not lie on segments or boundaries 
        /// may be deleted.
        /// </remarks>
        internal void DeleteVertex(ref Otri deltri)
        {
            Otri countingtri = default(Otri);
            Otri firstedge = default(Otri), lastedge = default(Otri);
            Otri deltriright = default(Otri);
            Otri lefttri = default(Otri), righttri = default(Otri);
            Otri leftcasing = default(Otri), rightcasing = default(Otri);
            Osub leftsubseg = default(Osub), rightsubseg = default(Osub);
            Vertex delvertex;
            Vertex neworg;
            int edgecount;

            delvertex = deltri.Org();

            VertexDealloc(delvertex);

            // Count the degree of the vertex being deleted.
            deltri.Onext(ref countingtri);
            edgecount = 1;
            while (!deltri.Equal(countingtri))
            {
                edgecount++;
                countingtri.OnextSelf();
            }

            if (edgecount > 3)
            {
                // Triangulate the polygon defined by the union of all triangles
                // adjacent to the vertex being deleted.  Check the quality of
                // the resulting triangles.
                deltri.Onext(ref firstedge);
                deltri.Oprev(ref lastedge);
                TriangulatePolygon(firstedge, lastedge, edgecount, false, behavior.NoBisect == 0);
            }
            // Splice out two triangles.
            deltri.Lprev(ref deltriright);
            deltri.Dnext(ref lefttri);
            lefttri.Sym(ref leftcasing);
            deltriright.Oprev(ref righttri);
            righttri.Sym(ref rightcasing);
            deltri.Bond(ref leftcasing);
            deltriright.Bond(ref rightcasing);
            lefttri.SegPivot(ref leftsubseg);
            if (leftsubseg.seg != Mesh.dummysub)
            {
                deltri.SegBond(ref leftsubseg);
            }
            righttri.SegPivot(ref rightsubseg);
            if (rightsubseg.seg != Mesh.dummysub)
            {
                deltriright.SegBond(ref rightsubseg);
            }

            // Set the new origin of 'deltri' and check its quality.
            neworg = lefttri.Org();
            deltri.SetOrg(neworg);
            if (behavior.NoBisect == 0)
            {
                quality.TestTriangle(ref deltri);
            }

            // Delete the two spliced-out triangles.
            TriangleDealloc(lefttri.triangle);
            TriangleDealloc(righttri.triangle);
        }

        /// <summary>
        /// Transform two triangles to two different triangles by flipping an edge 
        /// clockwise within a quadrilateral. Reverses the flip() operation so that 
        /// the data structures representing the triangles are back where they were 
        /// before the flip().
        /// </summary>
        /// <param name="flipedge"></param>
        /// <remarks>
        /// See above Flip() remarks for more information.
        ///
        /// Upon completion of this routine, the 'flipedge' handle holds the edge
        /// cd of triangle cdb, and is directed up, from vertex c to vertex d.
        /// (Hence, the two triangles have rotated clockwise.)
        /// </remarks>
        internal void Unflip(ref Otri flipedge)
        {
            Otri botleft = default(Otri), botright = default(Otri);
            Otri topleft = default(Otri), topright = default(Otri);
            Otri top = default(Otri);
            Otri botlcasing = default(Otri), botrcasing = default(Otri);
            Otri toplcasing = default(Otri), toprcasing = default(Otri);
            Osub botlsubseg = default(Osub), botrsubseg = default(Osub);
            Osub toplsubseg = default(Osub), toprsubseg = default(Osub);
            Vertex leftvertex, rightvertex, botvertex;
            Vertex farvertex;

            // Identify the vertices of the quadrilateral.
            rightvertex = flipedge.Org();
            leftvertex = flipedge.Dest();
            botvertex = flipedge.Apex();
            flipedge.Sym(ref top);

            farvertex = top.Apex();

            // Identify the casing of the quadrilateral.
            top.Lprev(ref topleft);
            topleft.Sym(ref toplcasing);
            top.Lnext(ref topright);
            topright.Sym(ref toprcasing);
            flipedge.Lnext(ref botleft);
            botleft.Sym(ref botlcasing);
            flipedge.Lprev(ref botright);
            botright.Sym(ref botrcasing);
            // Rotate the quadrilateral one-quarter turn clockwise.
            topleft.Bond(ref toprcasing);
            botleft.Bond(ref toplcasing);
            botright.Bond(ref botlcasing);
            topright.Bond(ref botrcasing);

            if (checksegments)
            {
                // Check for subsegments and rebond them to the quadrilateral.
                topleft.SegPivot(ref toplsubseg);
                botleft.SegPivot(ref botlsubseg);
                botright.SegPivot(ref botrsubseg);
                topright.SegPivot(ref toprsubseg);
                if (toplsubseg.seg == Mesh.dummysub)
                {
                    botleft.SegDissolve();
                }
                else
                {
                    botleft.SegBond(ref toplsubseg);
                }
                if (botlsubseg.seg == Mesh.dummysub)
                {
                    botright.SegDissolve();
                }
                else
                {
                    botright.SegBond(ref botlsubseg);
                }
                if (botrsubseg.seg == Mesh.dummysub)
                {
                    topright.SegDissolve();
                }
                else
                {
                    topright.SegBond(ref botrsubseg);
                }
                if (toprsubseg.seg == Mesh.dummysub)
                {
                    topleft.SegDissolve();
                }
                else
                {
                    topleft.SegBond(ref toprsubseg);
                }
            }

            // New vertex assignments for the rotated quadrilateral.
            flipedge.SetOrg(botvertex);
            flipedge.SetDest(farvertex);
            flipedge.SetApex(leftvertex);
            top.SetOrg(farvertex);
            top.SetDest(botvertex);
            top.SetApex(rightvertex);
        }

        /// <summary>
        /// Find a triangle or edge containing a given point.
        /// </summary>
        /// <param name="searchpoint">The point to locate.</param>
        /// <param name="searchtri">The triangle to start the search at.</param>
        /// <param name="stopatsubsegment"> If 'stopatsubsegment' is set, the search 
        /// will stop if it tries to walk through a subsegment, and will return OUTSIDE.</param>
        /// <returns>Location information.</returns>
        /// <remarks>
        /// Begins its search from 'searchtri'. It is important that 'searchtri'
        /// be a handle with the property that 'searchpoint' is strictly to the left
        /// of the edge denoted by 'searchtri', or is collinear with that edge and
        /// does not intersect that edge. (In particular, 'searchpoint' should not
        /// be the origin or destination of that edge.)
        ///
        /// These conditions are imposed because preciselocate() is normally used in
        /// one of two situations:
        ///
        /// (1)  To try to find the location to insert a new point.  Normally, we
        ///      know an edge that the point is strictly to the left of. In the
        ///      incremental Delaunay algorithm, that edge is a bounding box edge.
        ///      In Ruppert's Delaunay refinement algorithm for quality meshing,
        ///      that edge is the shortest edge of the triangle whose circumcenter
        ///      is being inserted.
        ///
        /// (2)  To try to find an existing point.  In this case, any edge on the
        ///      convex hull is a good starting edge. You must screen out the
        ///      possibility that the vertex sought is an endpoint of the starting
        ///      edge before you call preciselocate().
        ///
        /// On completion, 'searchtri' is a triangle that contains 'searchpoint'.
        ///
        /// This implementation differs from that given by Guibas and Stolfi.  It
        /// walks from triangle to triangle, crossing an edge only if 'searchpoint'
        /// is on the other side of the line containing that edge. After entering
        /// a triangle, there are two edges by which one can leave that triangle.
        /// If both edges are valid ('searchpoint' is on the other side of both
        /// edges), one of the two is chosen by drawing a line perpendicular to
        /// the entry edge (whose endpoints are 'forg' and 'fdest') passing through
        /// 'fapex'. Depending on which side of this perpendicular 'searchpoint'
        /// falls on, an exit edge is chosen.
        ///
        /// This implementation is empirically faster than the Guibas and Stolfi
        /// point location routine (which I originally used), which tends to spiral
        /// in toward its target.
        ///
        /// Returns ONVERTEX if the point lies on an existing vertex. 'searchtri'
        /// is a handle whose origin is the existing vertex.
        ///
        /// Returns ONEDGE if the point lies on a mesh edge. 'searchtri' is a
        /// handle whose primary edge is the edge on which the point lies.
        ///
        /// Returns INTRIANGLE if the point lies strictly within a triangle.
        /// 'searchtri' is a handle on the triangle that contains the point.
        ///
        /// Returns OUTSIDE if the point lies outside the mesh. 'searchtri' is a
        /// handle whose primary edge the point is to the right of.  This might
        /// occur when the circumcenter of a triangle falls just slightly outside
        /// the mesh due to floating-point roundoff error. It also occurs when
        /// seeking a hole or region point that a foolish user has placed outside
        /// the mesh.
        ///
        /// WARNING:  This routine is designed for convex triangulations, and will
        /// not generally work after the holes and concavities have been carved.
        /// However, it can still be used to find the circumcenter of a triangle, as
        /// long as the search is begun from the triangle in question.</remarks>
        public LocateResult PreciseLocate(Point searchpoint, ref Otri searchtri,
                                        bool stopatsubsegment)
        {
            Otri backtracktri = default(Otri);
            Osub checkedge = default(Osub);
            Vertex forg, fdest, fapex;
            float orgorient, destorient;
            bool moveleft;

            // Where are we?
            forg = searchtri.Org();
            fdest = searchtri.Dest();
            fapex = searchtri.Apex();
            while (true)
            {
                // Check whether the apex is the point we seek.
                if ((fapex.x == searchpoint.X) && (fapex.y == searchpoint.Y))
                {
                    searchtri.LprevSelf();
                    return LocateResult.OnVertex;
                }
                // Does the point lie on the other side of the line defined by the
                // triangle edge opposite the triangle's destination?
                destorient = Primitives.CounterClockwise(forg, fapex, searchpoint);
                // Does the point lie on the other side of the line defined by the
                // triangle edge opposite the triangle's origin?
                orgorient = Primitives.CounterClockwise(fapex, fdest, searchpoint);
                if (destorient > 0.0)
                {
                    if (orgorient > 0.0)
                    {
                        // Move left if the inner product of (fapex - searchpoint) and
                        // (fdest - forg) is positive.  This is equivalent to drawing
                        // a line perpendicular to the line (forg, fdest) and passing
//.........这里部分代码省略.........

        /// <summary>
        /// Recursively form a Delaunay triangulation by the divide-and-conquer method.
        /// </summary>
        /// <param name="left"></param>
        /// <param name="right"></param>
        /// <param name="axis"></param>
        /// <param name="farleft"></param>
        /// <param name="farright"></param>
        /// <remarks>
        /// Recursively breaks down the problem into smaller pieces, which are
        /// knitted together by mergehulls(). The base cases (problems of two or
        /// three vertices) are handled specially here.
        ///
        /// On completion, 'farleft' and 'farright' are bounding triangles such that
        /// the origin of 'farleft' is the leftmost vertex (breaking ties by
        /// choosing the highest leftmost vertex), and the destination of
        /// 'farright' is the rightmost vertex (breaking ties by choosing the
        /// lowest rightmost vertex).
        /// </remarks>
        void DivconqRecurse(int left, int right, int axis,
                            ref Otri farleft, ref Otri farright)
        {
            Otri midtri = default(Otri);
            Otri tri1 = default(Otri);
            Otri tri2 = default(Otri);
            Otri tri3 = default(Otri);
            Otri innerleft = default(Otri), innerright = default(Otri);
            double area;
            int vertices = right - left + 1;
            int divider;

            if (vertices == 2)
            {
                // The triangulation of two vertices is an edge.  An edge is
                // represented by two bounding triangles.
                mesh.MakeTriangle(ref farleft);
                farleft.SetOrg(sortarray[left]);
                farleft.SetDest(sortarray[left + 1]);
                // The apex is intentionally left NULL.
                mesh.MakeTriangle(ref farright);
                farright.SetOrg(sortarray[left + 1]);
                farright.SetDest(sortarray[left]);
                // The apex is intentionally left NULL.
                farleft.Bond(ref farright);
                farleft.LprevSelf();
                farright.LnextSelf();
                farleft.Bond(ref farright);
                farleft.LprevSelf();
                farright.LnextSelf();
                farleft.Bond(ref farright);

                // Ensure that the origin of 'farleft' is sortarray[0].
                farright.Lprev(ref farleft);
                return;
            }
            else if (vertices == 3)
            {
                // The triangulation of three vertices is either a triangle (with
                // three bounding triangles) or two edges (with four bounding
                // triangles).  In either case, four triangles are created.
                mesh.MakeTriangle(ref midtri);
                mesh.MakeTriangle(ref tri1);
                mesh.MakeTriangle(ref tri2);
                mesh.MakeTriangle(ref tri3);
                area = Primitives.CounterClockwise(sortarray[left], sortarray[left + 1], sortarray[left + 2]);
                if (area == 0.0)
                {
                    // Three collinear vertices; the triangulation is two edges.
                    midtri.SetOrg(sortarray[left]);
                    midtri.SetDest(sortarray[left + 1]);
                    tri1.SetOrg(sortarray[left + 1]);
                    tri1.SetDest(sortarray[left]);
                    tri2.SetOrg(sortarray[left + 2]);
                    tri2.SetDest(sortarray[left + 1]);
                    tri3.SetOrg(sortarray[left + 1]);
                    tri3.SetDest(sortarray[left + 2]);
                    // All apices are intentionally left NULL.
                    midtri.Bond(ref tri1);
                    tri2.Bond(ref tri3);
                    midtri.LnextSelf();
                    tri1.LprevSelf();
                    tri2.LnextSelf();
                    tri3.LprevSelf();
                    midtri.Bond(ref tri3);
                    tri1.Bond(ref tri2);
                    midtri.LnextSelf();
                    tri1.LprevSelf();
                    tri2.LnextSelf();
                    tri3.LprevSelf();
                    midtri.Bond(ref tri1);
                    tri2.Bond(ref tri3);
                    // Ensure that the origin of 'farleft' is sortarray[0].
                    tri1.Copy(ref farleft);
                    // Ensure that the destination of 'farright' is sortarray[2].
                    tri2.Copy(ref farright);
                }
                else
                {
                    // The three vertices are not collinear; the triangulation is one
                    // triangle, namely 'midtri'.
//.........这里部分代码省略.........

        /// <summary>
        /// Test a triangle for quality and size.
        /// </summary>
        /// <param name="testtri">Triangle to check.</param>
        /// <remarks>
        /// Tests a triangle to see if it satisfies the minimum angle condition and
        /// the maximum area condition.  Triangles that aren't up to spec are added
        /// to the bad triangle queue.
        /// </remarks>
        public void TestTriangle(ref Otri testtri)
        {
            Otri tri1 = default(Otri), tri2 = default(Otri);
            Osub testsub = default(Osub);
            Vertex torg, tdest, tapex;
            Vertex base1, base2;
            Vertex org1, dest1, org2, dest2;
            Vertex joinvertex;
            double dxod, dyod, dxda, dyda, dxao, dyao;
            double dxod2, dyod2, dxda2, dyda2, dxao2, dyao2;
            double apexlen, orglen, destlen, minedge;
            double angle;
            double area;
            double dist1, dist2;

            double maxangle;

            torg = testtri.Org();
            tdest = testtri.Dest();
            tapex = testtri.Apex();
            dxod = torg.x - tdest.x;
            dyod = torg.y - tdest.y;
            dxda = tdest.x - tapex.x;
            dyda = tdest.y - tapex.y;
            dxao = tapex.x - torg.x;
            dyao = tapex.y - torg.y;
            dxod2 = dxod * dxod;
            dyod2 = dyod * dyod;
            dxda2 = dxda * dxda;
            dyda2 = dyda * dyda;
            dxao2 = dxao * dxao;
            dyao2 = dyao * dyao;
            // Find the lengths of the triangle's three edges.
            apexlen = dxod2 + dyod2;
            orglen = dxda2 + dyda2;
            destlen = dxao2 + dyao2;

            if ((apexlen < orglen) && (apexlen < destlen))
            {
                // The edge opposite the apex is shortest.
                minedge = apexlen;
                // Find the square of the cosine of the angle at the apex.
                angle = dxda * dxao + dyda * dyao;
                angle = angle * angle / (orglen * destlen);
                base1 = torg;
                base2 = tdest;
                testtri.Copy(ref tri1);
            }
            else if (orglen < destlen)
            {
                // The edge opposite the origin is shortest.
                minedge = orglen;
                // Find the square of the cosine of the angle at the origin.
                angle = dxod * dxao + dyod * dyao;
                angle = angle * angle / (apexlen * destlen);
                base1 = tdest;
                base2 = tapex;
                testtri.Lnext(ref tri1);
            }
            else
            {
                // The edge opposite the destination is shortest.
                minedge = destlen;
                // Find the square of the cosine of the angle at the destination.
                angle = dxod * dxda + dyod * dyda;
                angle = angle * angle / (apexlen * orglen);
                base1 = tapex;
                base2 = torg;
                testtri.Lprev(ref tri1);
            }

            if (behavior.VarArea || behavior.fixedArea || behavior.Usertest)
            {
                // Check whether the area is larger than permitted.
                area = 0.5 * (dxod * dyda - dyod * dxda);
                if (behavior.fixedArea && (area > behavior.MaxArea))
                {
                    // Add this triangle to the list of bad triangles.
                    queue.Enqueue(ref testtri, minedge, tapex, torg, tdest);
                    return;
                }

                // Nonpositive area constraints are treated as unconstrained.
                if ((behavior.VarArea) && (area > testtri.triangle.area) && (testtri.triangle.area > 0.0))
                {
                    // Add this triangle to the list of bad triangles.
                    queue.Enqueue(ref testtri, minedge, tapex, torg, tdest);
                    return;
                }

                // Check whether the user thinks this triangle is too large.
//.........这里部分代码省略.........