OmniGraffle is a superb piece of vector-diagram drawing software. It's easy to create complex, multi-layered diagrams very quickly in OmniGraffle. However, it did take me a while to work out how to produce curved line joints that connect objects. I'll show you how to do it in this article.
When creating my Add-on Stats dashboard widget, I couldn't find an online tutorial for creating a widget bar icon. Apple's Designing Widgets page lists some basic information about the dimensions of the icon's contents and the size and orientation of the icon's drop shadow, but nothing about the dimensions of the icon itself or how to create the curved glass effect used by most other icons on the widget bar. After some trial and error, I developed the following tutorial for creating widget bar icons.