为贴图添加透明多边形

这是一个问题，我一直试图解决一段时间，并决定寻求帮助。我正在创建一个ESRI ArcGIS桌面插件，允许用户绘制多边形，然后将其添加到地图中。我能够捕获多边形并将其添加到地图中，问题是透明度。目前和默认情况下，它是100%不透明度和固体。我想让它的不透明度在50%左右，这样用户就可以看到它背后的数据。

这是我到目前为止的代码:

     public static void AddPolygonToMap(IActiveView ActiveViewInstance, IGeometry NewGeo)
    {
        //Local Variable Declaration
        var fillShapeElement = default(IFillShapeElement);
        var element = default(IElement);
        var graphicsContainer = default(IGraphicsContainer);
        var simpleFilleSymbol = default(ISimpleFillSymbol);
        var newRgbColor = default(IRgbColor);
        var lineSymbol = default(ILineSymbol);
        //Use the IElement interface to set the Envelope Element's geo
        element = new PolygonElement();
        element.Geometry = NewGeo;
        //QI for the IFillShapeElement interface so that the symbol property can be set
        fillShapeElement = element as IFillShapeElement;
        //Create a new fill symbol
        simpleFilleSymbol = new SimpleFillSymbol();
        //Create a new color marker symbol of the color black;
        newRgbColor = new RgbColor();
        newRgbColor.Red = 0;
        newRgbColor.Green = 0;
        newRgbColor.Blue = 0;
        //Create a new line symbol so that we can set the width outline
        lineSymbol = new SimpleLineSymbol();
        lineSymbol.Color = newRgbColor;
        lineSymbol.Width = 2;
        //Setup the Simple Fill Symbol
        simpleFilleSymbol.Color = newRgbColor;
        simpleFilleSymbol.Style = esriSimpleFillStyle.esriSFSHollow;
        simpleFilleSymbol.Outline = lineSymbol;
        fillShapeElement.Symbol = simpleFilleSymbol;
        //QI for the graphics container from the active view allows access to basic graphics layer
        graphicsContainer = ActiveViewInstance as IGraphicsContainer;
        //Add the new element at Z order 0
        graphicsContainer.AddElement((IElement)fillShapeElement, 0);
        //Show the new graphic
        ActiveViewInstance.Refresh();
    }

我知道这是可能的，我相信它只是少了一两行，但任何帮助将是非常感激的。

V/r

,

Josh

For graphic elements, 0 for transparent and 255 for opaque are the only supported values.