I should have warned readers (if there were any!) of the scheduled 2 months family time through December and January, as we visited with all the various branches of the family around New Zealand. Now back in action, installed deep in the bush at Karekare, and visiting with Beryl Plimmer's group at the University of Auckland.
The first day of coding on return was a little rusty (editor commands forgotten, basic maths skills lost), but I managed to add a couple of incremental functions - an interactive ellipse class to join the rectangle, and upgrading of the basic line class to allow interactive editing.
After this, time to get stuck in and add support for a fundamental new concept that I dreamt up during a jetlagged night in Singapore. I've decided that the stack view of layers should be a first class object, interchangeable with collections of layer references. In order to make this obvious to users, I think this equivalence should be visible in a graphical transition from collection to stack. That's relatively straightforward, but still lots of geometric detail to be figured out in the animation. A quarter of yesterday spent on false starts for representing that geometry sensibly, and another quarter thinking that I had created a sublte reference contention problem in my animation thread (in fact, had just forgotten to initialise the reference at all).
An interesting consequence of the 2 month break is reluctance to get my hands dirty in refactoring code that I was blithely chucking around at the start of December. Perfectly happy now to make incremental changes or add features, but the core architecture has now acquired substantial viscosity after being "paged out" of my head. Hopefully the fluidity will be recovered before too long.