...and it just came right. I see what I was doing wrong. For save to take effect I need to change the file or Eclipse just (sensibly enough) does nothing when I tell it to save. So I put a space in the XML. But if, instead, I show the image and move one of the boxes around and then save it creates a good png. Makes sense. The plugin generates it when I ask for it to be displayed, I guess, and it saves what was displayed. If I save while viewing th XML it doesn't have an image.