public void RenderGeometry(MultiPolygon multiPolygon, IStyle style, IFeature feature, IViewport viewport)
        {
            if (_bgWorker == null)
                _bgWorker = new BackgroundWorker();
            /*
            while (_bgWorker.IsBusy) {
                Thread.Sleep (00001);
            }
            */
            _bgWorker.RunWorkerCompleted += (sender, e) =>
                {
                    var layer = e.Result as CALayer;

                    if (layer != null)
                    {
                        var styleKey = style.GetHashCode().ToString();
                        feature[styleKey] = layer;
                    }
                };

            _bgWorker.DoWork += delegate(object sender, DoWorkEventArgs e)
                {
                    var layer = RenderImage(multiPolygon, style, viewport);
                    e.Result = layer;
                };

            _bgWorker.RunWorkerAsync();
        }

 public static bool AreStylesEqual(IStyle lhs, IStyle rhs)
 {
     Assert.AreEqual(lhs.MinVisible, rhs.MinVisible, "MinVisible differs");
     Assert.AreEqual(lhs.MaxVisible, rhs.MaxVisible, "MaxVisible differs");
     Assert.AreEqual(lhs.Enabled, rhs.Enabled, "Enabled differs");
     return true;
 }

 private static void GetGeneralProperties(ICssStyleDeclaration csd, IStyle style)
 {
     if (csd.GetPropertyValue("zoom-min-visible") != string.Empty)
         style.MinVisible = double.Parse(csd.GetPropertyValue("zoom-min-visible"));
     if (csd.GetPropertyValue("zoom-max-visible") != string.Empty)
         style.MaxVisible = double.Parse(csd.GetPropertyValue("zoom-max-visible"));
 }

        public static void Draw(SKCanvas canvas, IViewport viewport, IStyle style, IFeature feature,
            IDictionary<object, SKBitmapInfo> skBitmapCache, long currentIteration)
        {
            try
            {
                var raster = (IRaster)feature.Geometry;

                SKBitmapInfo textureInfo;

                if (!skBitmapCache.Keys.Contains(raster))
                {
                    textureInfo = BitmapHelper.LoadTexture(raster.Data);
                    skBitmapCache[raster] = textureInfo;
                }
                else
                {
                    textureInfo = skBitmapCache[raster];
                }

                textureInfo.IterationUsed = currentIteration;
                skBitmapCache[raster] = textureInfo;
                var destination = WorldToScreen(viewport, feature.Geometry.GetBoundingBox());
                BitmapHelper.RenderRaster(canvas, textureInfo.Bitmap, RoundToPixel(destination).ToSkia());
            }
            catch (Exception ex)
            {
                Logger.Log(LogLevel.Error, ex.Message, ex);
            }
        }

        // todo:
        // try to remove the feature argument. LabelStyle should already contain the feature specific text
        // The visible feature iterator should create this LabelStyle
        public static void Draw(SKCanvas canvas, IViewport viewport, IStyle style, IFeature feature, 
            IGeometry geometry, IDictionary<int, SKBitmapInfo> symbolBitmapCache)
        {
            var point = geometry as Point;
            var destination = viewport.WorldToScreen(point);

            if (style is LabelStyle)              // case 1) LabelStyle
            {
                LabelRenderer.Draw(canvas, (LabelStyle) style, feature, (float) destination.X, (float) destination.Y);
            }
            else if (style is SymbolStyle)
            {
                var symbolStyle = (SymbolStyle)style;

                if ( symbolStyle.BitmapId >= 0)   // case 2) Bitmap Style
                {
                    DrawPointWithBitmapStyle(canvas, symbolStyle, destination, symbolBitmapCache);
                }
                else                              // case 3) SymbolStyle without bitmap
                {
                    DrawPointWithSymbolStyle(canvas, symbolStyle, destination, symbolStyle.SymbolType);
                }
            }
            else if (style is VectorStyle)        // case 4) VectorStyle
            {
                DrawPointWithVectorStyle(canvas, (VectorStyle) style, destination);
            }
            else
            {
                throw new Exception($"Style of type '{style.GetType()}' is not supported for points");
            }
        }

        public static void Render(Graphics graphics, IGeometry feature, IStyle style, IViewport viewport)
        {
            var stream = ((IRaster)feature).Data;
            stream.Position = 0;
            var bitmap = new Bitmap(stream);

            Geometries.Point min = viewport.WorldToScreen(new Geometries.Point(feature.GetBoundingBox().MinX, feature.GetBoundingBox().MinY));
            Geometries.Point max = viewport.WorldToScreen(new Geometries.Point(feature.GetBoundingBox().MaxX, feature.GetBoundingBox().MaxY));

            Rectangle destination = RoundToPixel(new RectangleF((float)min.X, (float)max.Y, (float)(max.X - min.X), (float)(min.Y - max.Y)));
            graphics.DrawImage(bitmap,
                destination,
                0, 0, bitmap.Width, bitmap.Height,
                GraphicsUnit.Pixel,
                new ImageAttributes());

            if (DeveloperTools.DeveloperMode)
            {
                var font = new System.Drawing.Font("Arial", 12);
                var message = (GC.GetTotalMemory(true) / 1000).ToString(CultureInfo.InvariantCulture) + " KB";
                graphics.DrawString(message, font, new SolidBrush(Color.Black), 10f, 10f);
            }

            bitmap.Dispose();
        }

        public static UIElement RenderPoint(Point point, IStyle style, IViewport viewport)
        {
            UIElement symbol;
            var matrix = XamlMedia.Matrix.Identity;

            if (style is SymbolStyle)
            {
                var symbolStyle = style as SymbolStyle;

                if (symbolStyle.Symbol == null || symbolStyle.Symbol.Data == null)
                    symbol = CreateSymbolFromVectorStyle(symbolStyle, symbolStyle.Opacity, symbolStyle.SymbolType);
                else
                    symbol = CreateSymbolFromBitmap(symbolStyle.Symbol.Data, symbolStyle.Opacity);
                matrix = CreatePointSymbolMatrix(viewport.Resolution, symbolStyle);
            }
            else
            {
                symbol = CreateSymbolFromVectorStyle((style as VectorStyle) ?? new VectorStyle());
                MatrixHelper.ScaleAt(ref matrix, viewport.Resolution, viewport.Resolution);
            }

            MatrixHelper.Append(ref matrix, CreateTransformMatrix(point, viewport));

            symbol.RenderTransform = new XamlMedia.MatrixTransform { Matrix = matrix };

            symbol.IsHitTestVisible = false;

            return symbol;
        }

        public static XamlShapes.Shape RenderPoint(Point point, IStyle style, IViewport viewport)
        {
            XamlShapes.Shape symbol;
            var matrix = XamlMedia.Matrix.Identity;

            if (style is SymbolStyle)
            {
                var symbolStyle = style as SymbolStyle;

                if (symbolStyle.BitmapId < 0)
                    symbol = CreateSymbolFromVectorStyle(symbolStyle, symbolStyle.Opacity, symbolStyle.SymbolType, symbolStyle.Width, symbolStyle.Height);
                else
                    symbol = CreateSymbolFromBitmap(BitmapRegistry.Instance.Get(symbolStyle.BitmapId), symbolStyle.Opacity);
                matrix = CreatePointSymbolMatrix(viewport.Resolution, symbolStyle);
            }
            else
            {
                symbol = CreateSymbolFromVectorStyle((style as VectorStyle) ?? new VectorStyle());
                MatrixHelper.ScaleAt(ref matrix, viewport.Resolution, viewport.Resolution);
            }

            MatrixHelper.Append(ref matrix, CreateTransformMatrix(point, viewport));

            symbol.RenderTransform = new XamlMedia.MatrixTransform { Matrix = matrix };
            symbol.IsHitTestVisible = false;

            return symbol;
        }

 public void Load(IStyle[] styles)
 {
     this._attributeValue = null;
     this._dirty = false;
     string attribute = styles[0].GetAttribute(this._omName);
     if (attribute != null)
     {
         attribute = attribute.Trim();
         for (int i = 1; i < styles.Length; i++)
         {
             string str2 = styles[i].GetAttribute(this._omName);
             if (str2 == null)
             {
                 str2 = null;
                 break;
             }
             str2 = str2.Trim();
             if ((this._caseSignificant && !attribute.Equals(str2)) || (string.Compare(attribute, str2, true, CultureInfo.InvariantCulture) != 0))
             {
                 attribute = null;
                 break;
             }
         }
         if (attribute != null)
         {
             this._attributeValue = this._caseSignificant ? attribute : attribute.ToLower(CultureInfo.InvariantCulture);
         }
     }
 }

 /// <summary>
 /// Creates an instance of this class
 /// </summary>
 /// <param name="minValue">The minimum value</param>
 /// <param name="maxValue">The maximum value</param>
 /// <param name="minStyle">The <see cref="IStyle">style</see> to apply for values equal to <paramref name="minValue"/></param>
 /// <param name="maxStyle">The <see cref="IStyle">style</see> to apply for values equal to <paramref name="maxValue"/></param>
 protected GradientThemeBase(double minValue, double maxValue, IStyle minStyle, IStyle maxStyle)
 {
     _min = minValue;
     _max = maxValue;
     _maxStyle = maxStyle;
     _minStyle = minStyle;
 }

        public static void Draw(SKCanvas canvas, IViewport viewport, IStyle style, IGeometry geometry)
        {
            var polygon = (Polygon)geometry;

            float lineWidth = 1;
            var lineColor = Color.Black; // default
            var fillColor = Color.Gray; // default

            var vectorStyle = style as VectorStyle;

            if (vectorStyle != null)
            {
                lineWidth = (float) vectorStyle.Outline.Width;
                lineColor = vectorStyle.Outline.Color;
                fillColor = vectorStyle.Fill?.Color;
            }

            using (var path = ToSkia(viewport, polygon))
            {
                using (var paint = new SKPaint())
                {
                    paint.IsAntialias = true;
                    paint.StrokeWidth = lineWidth;

                    paint.Style = SKPaintStyle.Fill;
                    paint.Color = fillColor.ToSkia();
                    canvas.DrawPath(path, paint);
                    paint.Style = SKPaintStyle.Stroke;
                    paint.Color = lineColor.ToSkia();
                    canvas.DrawPath(path, paint);
                }
            }
        }

        public static void Draw(Canvas canvas, IViewport viewport, IStyle style, IFeature feature)
        {
            try
            {
                if (!feature.RenderedGeometry.ContainsKey(style)) feature.RenderedGeometry[style] = ToAndroidBitmap(feature.Geometry);
                var bitmap = (AndroidGraphics.Bitmap)feature.RenderedGeometry[style];
                
                var dest = WorldToScreen(viewport, feature.Geometry.GetBoundingBox());
                dest = new BoundingBox(
                    dest.MinX,
                    dest.MinY,
                    dest.MaxX,
                    dest.MaxY);

                var destination = RoundToPixel(dest);
                using (var paint = new Paint())
                {
                    canvas.DrawBitmap(bitmap, new Rect(0, 0, bitmap.Width, bitmap.Height), destination, paint);
                }

                DrawOutline(canvas, style, destination);
            }
            catch (Exception ex)
            {
                Trace.WriteLine(ex.Message);
            }

        }

 public void PaintValue(Graphics graphic, Rectangle renderRect, Rectangle clipRect, IStyle style, object value)
 {
     brush.Color = ValidateValue(value);
     clipRect.Height--;
     graphic.FillRectangle(brush, clipRect);
     graphic.DrawRectangle(Pens.Black, clipRect);
 }

        public static void Draw(IViewport viewport, IStyle style, IFeature feature)
        {
            var lineString = ((LineString)feature.Geometry).Vertices;

            float lineWidth = 1;
            var lineColor = Color.White;

            var vectorStyle = style as VectorStyle;

            if (vectorStyle != null)
            {
                lineWidth = (float)vectorStyle.Line.Width;
                lineColor = vectorStyle.Line.Color;
            }

            float[] points = ToOpenTK(lineString);
            WorldToScreen(viewport, points);

            GL.LineWidth(lineWidth);
            GL.Color4((byte)lineColor.R, (byte)lineColor.G, (byte)lineColor.B, (byte)lineColor.A);
            GL.EnableClientState(All.VertexArray);
            GL.VertexPointer(2, All.Float, 0, points);
            GL.DrawArrays(All.Lines, 0, points.Length / 2);
            GL.DisableClientState(All.VertexArray);
        }

 public static ILayer CreateLineStringLayer(IStyle style = null)
 {
     return new MemoryLayer
     {
         DataSource = new MemoryProvider(
             new[] { new LineString(new[]
                 {
                     new Point(0, 0), 
                     new Point(10000, 10000),
                     new Point(10000, 0),
                     new Point(0, 10000),
                     new Point(100000, 100000),
                     new Point(100000, 0),
                     new Point(0, 100000),
                     new Point(1000000, 1000000),
                     new Point(1000000, 0),
                     new Point(0, 1000000),
                     new Point(10000000, 10000000),
                     new Point(10000000, 0),
                     new Point(0, 10000000)
                 }
             )}
         ),
         Name = "LineStringLayer",
         Style = style
     };
 }

        public static void Draw(SKCanvas canvas, IViewport viewport, IStyle style, IGeometry geometry)
        {
            var lineString = ((LineString) geometry).Vertices;

            float lineWidth = 1;
            var lineColor = new Color();

            var vectorStyle = style as VectorStyle;

            if (vectorStyle != null)
            {
                lineWidth = (float) vectorStyle.Line.Width;
                lineColor = vectorStyle.Line.Color;
            }

            var line = WorldToScreen(viewport, lineString);
            var path = ToSkia(line);

            using (var paint = new SKPaint())
            {
                paint.IsStroke = true;
                paint.StrokeWidth = lineWidth;
                paint.Color = lineColor.ToSkia();
                paint.StrokeJoin = SKStrokeJoin.Round;

                canvas.DrawPath(path, paint);
            }
        }

        public static void PositionMultiPolygon(CALayer shape, MultiPolygon multiPolygon, IStyle style, IViewport viewport)
        {
            var shapeLayer = shape as CAShapeLayer;
            var path = multiPolygon.ToUIKit(viewport);
            //var frame = ConvertBoundingBox (multiPolygon.GetBoundingBox(), viewport);
            shapeLayer.Path = path.CGPath;
            //shape.Frame = frame;
            /*
            if (viewport.Resolution > MinResolution || viewport.Resolution < MaxResolution) {
                //recalculate
                var newImage = RenderMultiPolygonOnLayer (multiPolygon, style, viewport);

                shape.Contents = newImage.Contents;
                shape.Frame = newImage.Frame;

                var resolution = ZoomHelper.ClipResolutionToExtremes (Resolutions, viewport.Resolution);

                MinResolution = ZoomHelper.ZoomOut (Resolutions, resolution);
                MaxResolution = ZoomHelper.ZoomIn (Resolutions, resolution);

            } else {
                //reposition Geometry
                var frame = ConvertBoundingBox (multiPolygon.GetBoundingBox(), viewport);
                var newFrame = new RectangleF (frame.X, (frame.Y), frame.Width, frame.Height);

                shape.Frame = newFrame;
                //shape.Frame = frame;
            }
            */
        }

 public static void Initialize(         
  IConsole console,
  ISurface surface,
  IStyle style,
  IDrawings drawing,
  IShapes shapes,
  IImages images,
  IControls controls,
  ISounds sounds,         
  IKeyboard keyboard,
  IMouse mouse,
  ITimer timer,
  IFlickr flickr,
  ISpeech speech,
  CancellationToken token)
 {
     TextWindow.Init(console);
      Desktop.Init(surface);
      GraphicsWindow.Init(style, surface, drawing, keyboard, mouse);
      Shapes.Init(shapes);
      ImageList.Init(images);
      Turtle.Init(surface, drawing, shapes);
      Controls.Init(controls);
      Sound.Init(sounds);
      Timer.Init(timer);
      Stack.Init();
      Flickr.Init(flickr);
      Speech.Init(speech);
      Program.Init(token);
 }

        public static XamlShapes.Shape RenderPoint(Point point, IStyle style, IViewport viewport,
            BrushCache brushCache = null)
        {
            XamlShapes.Shape symbol;
            var matrix = XamlMedia.Matrix.Identity;

            if (style is SymbolStyle)
            {
                var symbolStyle = style as SymbolStyle;

                if (symbolStyle.BitmapId < 0)
                    symbol = CreateSymbolFromVectorStyle(symbolStyle, symbolStyle.Opacity, symbolStyle.SymbolType);
                else
                    symbol = CreateSymbolFromBitmap(symbolStyle.BitmapId, symbolStyle.Opacity, brushCache);
                matrix = CreatePointSymbolMatrix(viewport.Resolution, symbolStyle);
            }
            else
            {
                symbol = CreateSymbolFromVectorStyle((style as VectorStyle) ?? new VectorStyle());
                MatrixHelper.ScaleAt(ref matrix, viewport.Resolution, viewport.Resolution);
            }

            MatrixHelper.Append(ref matrix, GeometryRenderer.CreateTransformMatrix(point, viewport));

            symbol.RenderTransform = new XamlMedia.MatrixTransform {Matrix = matrix};
            symbol.IsHitTestVisible = false;

            return symbol;
        }

 public CategorialThemeItem(string category, IStyle style, Bitmap symbol, object value)
 {
     label = category;
     this.style = (IStyle)style.Clone();
     Symbol = symbol;
     
     this.value = value;
 }