Adding prefetch menu :

- select zoom min, zoom max
- show how many tiles will be downloaded by zoom
- show the total estimated size
Fix TilePrefetcher progress at 0 at start

Author: Godeffroy

ExtLibs/GMap.NET.Core/GMap.NET/PureProjection.cs

@@ -232,6 +232,16 @@ public List<GPoint> GetAreaTileList(RectLatLng rect, int zoom, int padding)
          return ret;
       }
 
+      /// <summary>
+      /// get number of tiles in rect at specific zoom
+      /// </summary>
+      public long GetAreaTileNumber(RectLatLng rect, int zoom, int padding)
+      {
+         GPoint topLeft = FromPixelToTileXY(FromLatLngToPixel(rect.LocationTopLeft, zoom));
+         GPoint rightBottom = FromPixelToTileXY(FromLatLngToPixel(rect.LocationRightBottom, zoom));
+         return (rightBottom.X - topLeft.X + 1) * (rightBottom.Y - topLeft.Y + 1);
+      }
+
       /// <summary>
       /// The ground resolution indicates the distance (in meters) on the ground that’s represented by a single pixel in the map.
       /// For example, at a ground resolution of 10 meters/pixel, each pixel represents a ground distance of 10 meters.

ExtLibs/GMap.NET.WindowsForms/GMap.NET.WindowsForms/TilePrefetcher.cs

@@ -228,6 +228,7 @@ void worker_DoWork(object sender, DoWorkEventArgs e)
             list.Clear();
             list = null;
          }
+         worker.ReportProgress(0, 0);
          list = provider.Projection.GetAreaTileList(area, zoom, 0);
          maxOfTiles = provider.Projection.GetTileMatrixMaxXY(zoom);
          all = list.Count;