[GIS] How to draw transparent polygons with ArcObjects

arcgis-10.1arcobjectscnettransparency

How do I draw transparent polygons in ArcObjects? I mean is it possible to set alpha channel?

Best Answer

Transparency is not a property of a polygon itself, rather it is a property of the layer containing the polygon (like symbology). Take your polygon data, and store it in an IFeatureLayer. From IFeatureLayer, get ILayerEffects, which is an interface of IFeatureLayer. Transparency (0% to 100%) is a property of ILayerEffects.

Also, note this from ESRI documentation:

When you set Transparency for a FeatureLayer, a TransparencyDisplayFilter is created and applied to the layer. You can accomplish the same effect by manually creating a new TransparencyDisplayFilter using IDisplayFilter, and then assigning it to a layer using IDisplayFilterManager.

Related Solutions

ArcObjects – Create and Draw a Transparent Polygon

As per ArcObjects docs

IColor.Transparency Property: Transparency is the degree to which a color is opaque. True transparency is only supported at the layer level. For graphic elements, 0 for transparent and 255 for opaque are the only supported values. Use either the ILayerEffects or ITransparencyRenderer interfaces to set layer transparency. For layer transparency to work properly the display device must be set to "True Color (32 bit)".

ArcObjects – Setting Command Button Image to a Partially Transparent Bitmap in ArcGIS 10.0

To maintain partial alpha channel transparency, an IPictureDisp object must be created using some unmanaged code, described in this post on Ryan Gregg's blog.

Copy the C# (mirror) or VB.NET (mirror) code to a new code file and add it to your project. Then, instead of the technique in the previously-mentioned answer, set ICommandItem.FaceID to the return value of PictureDispConverter.ToIPictureDisp, passing in your original bitmap.

For example:

UID uid = new UIDClass();
uid.Value = ThisAddIn.IDs.MyButton;
ICommandItem cmdItem = ArcMap.Application.Document.CommandBars.Find(uid, true, true);
cmdItem.FaceID = PictureDispConverter.ToIPictureDisp(Resources.MyButtonEnabledState);

The partially-transparent areas of the original bitmap should be maintained.

Best Answer

Related Solutions

ArcObjects – Create and Draw a Transparent Polygon

ArcObjects – Setting Command Button Image to a Partially Transparent Bitmap in ArcGIS 10.0

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