Implementing overlays for ECL Thumbnails

Question

I have implemented an ECL provider which generates thumbnails of my images. I would now like to show some form of overlay to indicate whether the item is checked out (in the external system), published, and eventually add a restricted watermark.

Are there any examples of overlaying the standard checked-out or published icons on ECL items, or samples of how to use the GetThumbnailImage() method with the IList<IThumbnailOverlay> thumbnailOverlays overload that I see in the ECL API docs? Would this be an appropriate way to implement such functionality, or should I just manipulate the byte array which is returned by the GetThumbnailImage() method of my class implementing IContentLibraryContext?

Answer 1

You can get the overlay icon like this:

int actualSize;
byte[] iconData = Library.HostServices.GetIcon(
                      Library.IconBasePath,
                      null,
                      "your-icon-name",
                      16,
                      out actualSize);

As CreateThumbnailOverlay requires a stream, you need to create a memory stream. So the code will look something like this:

using (MemoryStream iconStream = new MemoryStream(iconData, false))
{
    // This implies item is a MultiMediaItem already loaded and GetContent
    // returns an actual image, if not you need to get the main thumbnail
    // image by other means
    IContentResult content = item.GetContent(null);
    try
    {
        IList<IThumbnailOverlay> overlays = new List<IThumbnailOverlay>
        {
            // maxWidth and maxHeight specifies the requested thumbnail size,
            // so this icon is placed in the lower left corner.
            Library.HostServices.CreateThumbnailOverlay(
                 0,
                 maxHeight - actualSize,
                 actualSize,
                 actualSize,
                 iconStream)
        };

        return Library.HostServices.CreateThumbnailImage(
            maxWidth,
            maxHeight,
            content.Stream,
            maxWidth,
            maxHeight,
            overlays);
    }
    finally
    {
        content.Stream.Close();
    }
}

Tridion thumbnails do not display overlays for checked out etc. This is the reason ECL doesn't add the overlays automatically.

You can of course manipulate the bytes directly - but as ECL runs in a Windows service you can't use the classes within System.Drawing. You can use the WPF classes, but these require an STA thread.

There might be a third party library you can use to manipulate images on a MTA thread, but unless you require something more than just overlaying images I would recommend sticking to the methods provided by ECL.