We want to be able to define a region by dragging the mouse across the image. That is, record (x,y) on mouse down, and (x,y) again on mouse up. The FF toolbar lets one define a rectangular region in this manner. However, we also want to define circular regions (by dragging from center to circumference). Unfortunately, in normal image viewing, moving the cursor with the mouse button down is used to pan the image.
Firefly should and is planning to support circular selections (as you described) in a similar way we support rectangular selection. When this feature is implemented, the region parameters (center x,y and radius) should be available in a callback, similar to the way the rectangular selection parameters are available now. Would it work for you?
Thanks for the information. What you propose will work. In the meantime, we’ll enter the parameters on the command line, and display the resulting circle as a DS9 region.