[RGEOS]绘制多边形Polygon

 绘制OGIS定义的Polygon

   public void DrawPolygon(Polygon pol, Brush brush, Pen pen, bool clip)
        {
            gc = Graphics.FromHwnd(Handle);
            if (pol.ExteriorRing == null)
                return;
            if (pol.ExteriorRing.Vertices.Count > 2)
            {
                //Use a graphics path instead of DrawPolygon. DrawPolygon has a problem with several interior holes
                GraphicsPath gp = new GraphicsPath();

                //Add the exterior polygon
                PointF[] pts = TransformLineString(pol.ExteriorRing);
                if (!clip)
                    gp.AddPolygon(LimitValues(pts, extremeValueLimit));
                else
                    DrawPolygonClipped(gp, pts, (int)100, (int)100);

                //Add the interior polygons (holes)

                for (int i = 0; i < pol.InteriorRings.Count; i++)
                {
                    PointF[] pts1 = TransformLineString(pol.InteriorRings[i]);
                    if (!clip)
                        gp.AddPolygon(LimitValues(pts1, extremeValueLimit));
                    else
                        DrawPolygonClipped(gp, pts1, (int)100, (int)100);
                }

                // Only render inside of polygon if the brush isn't null or isn't transparent
                if (brush != null && brush != Brushes.Transparent)
                    gc.FillPath(brush, gp);
                // Create an outline if a pen style is available
                if (pen != null)
                    gc.DrawPath(pen, gp);
                gc.Dispose();
            }
        }

 

  public static PointF[] TransformLineString(LineString line)
        {
            PointF[] v = new PointF[line.Vertices.Count];
            for (int i = 0; i < line.Vertices.Count; i++)
                v[i] = new PointF((float)line.Vertices[i].X, (float)line.Vertices[i].Y);
            return v;
        }

 

        internal static PointF[] clipPolygon(PointF[] vertices, int width, int height)
        {
            float deltax, deltay, xin, xout, yin, yout;
            float tinx, tiny, toutx, touty, tin1, tin2, tout;
            float x1, y1, x2, y2;

            List<PointF> line = new List<PointF>();
            if (vertices.Length <= 1) /* nothing to clip */
                return vertices;

            for (int i = 0; i < vertices.Length - 1; i++)
            {
                x1 = vertices[i].X;
                y1 = vertices[i].Y;
                x2 = vertices[i + 1].X;
                y2 = vertices[i + 1].Y;

                deltax = x2 - x1;
                if (deltax == 0)
                {
                    // bump off of the vertical
                    deltax = (x1 > 0) ? -nearZero : nearZero;
                }
                deltay = y2 - y1;
                if (deltay == 0)
                {
                    // bump off of the horizontal
                    deltay = (y1 > 0) ? -nearZero : nearZero;
                }

                if (deltax > 0)
                {
                    //  points to right
                    xin = 0;
                    xout = width;
                }
                else
                {
                    xin = width;
                    xout = 0;
                }

                if (deltay > 0)
                {
                    //  points up
                    yin = 0;
                    yout = height;
                }
                else
                {
                    yin = height;
                    yout = 0;
                }

                tinx = (xin - x1) / deltax;
                tiny = (yin - y1) / deltay;

                if (tinx < tiny)
                {
                    // hits x first
                    tin1 = tinx;
                    tin2 = tiny;
                }
                else
                {
                    // hits y first
                    tin1 = tiny;
                    tin2 = tinx;
                }

                if (1 >= tin1)
                {
                    if (0 < tin1)
                        line.Add(new PointF(xin, yin));

                    if (1 >= tin2)
                    {
                        toutx = (xout - x1) / deltax;
                        touty = (yout - y1) / deltay;

                        tout = (toutx < touty) ? toutx : touty;

                        if (0 < tin2 || 0 < tout)
                        {
                            if (tin2 <= tout)
                            {
                                if (0 < tin2)
                                {
                                    if (tinx > tiny)
                                        line.Add(new PointF(xin, y1 + tinx * deltay));
                                    else
                                        line.Add(new PointF(x1 + tiny * deltax, yin));
                                }

                                if (1 > tout)
                                {
                                    if (toutx < touty)
                                        line.Add(new PointF(xout, y1 + toutx * deltay));
                                    else
                                        line.Add(new PointF(x1 + touty * deltax, yout));
                                }
                                else
                                    line.Add(new PointF(x2, y2));
                            }
                            else
                            {
                                if (tinx > tiny)
                                    line.Add(new PointF(xin, yout));
                                else
                                    line.Add(new PointF(xout, yin));
                            }
                        }
                    }
                }
            }
            if (line.Count > 0)
                line.Add(new PointF(line[0].X, line[0].Y));

            return line.ToArray();
        }

        private void DrawPolygonClipped(GraphicsPath gp, PointF[] polygon, int width, int height)
        {
            ClipState clipState = DetermineClipState(polygon, width, height);
            if (clipState == ClipState.Within)
            {
                gp.AddPolygon(polygon);
            }
            else if (clipState == ClipState.Intersecting)
            {
                PointF[] clippedPolygon = clipPolygon(polygon, width, height);
                if (clippedPolygon.Length > 2)
                    gp.AddPolygon(clippedPolygon);
            }
        }