[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 > )
             {
                 //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), (int));

                 //Add the interior polygons (holes)

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

                 // 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 = ; 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 <= ) /* nothing to clip */
                 return vertices;

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

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

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

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

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

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

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

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

                                 if ( > 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 > )
                 line.Add(new PointF(line[].X, line[].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 > )
                     gp.AddPolygon(clippedPolygon);
             }
         }