The Eclipse IDE ecosystem includes a highly advanced 2D graphics library called Draw2D (comes as part of GEF, the Graphical Editing Framework), which rests on top of the SWT Canvas widget.
I got a chance to play around with it today and even do a spike in Glimmer DSL for SWT for supporting a Draw2D DSL. I finished a rough version in about an hour or two. Check out the samples I created below.
Spike 1 (Rectangle and contained Polygon + Drag & Drop Movement):
Screenshot:
Spike 2 (Rectangle and contained Ellipse + Drag & Drop Movement):
Screenshot:
Spike 3 (Multiple Rectangles and Ellipses within a GridLayout of 8 columns + Drag & Drop Movement):
Screenshot: