Relating to the datepicker widget I should once again acknowledge
the basic work of Elanor (calendar widget) and Bernd (additions to
the calendar widget) and hints/comments by Bernd.
[The algorithms I used are translated to LCB from the LCS of Raspi
stack "calendar 1-3-6-12" (Aug 2015).]
The main interesting thing for me when writing this widget was to
see that the following is possible (and *very* comfortable in LCB):
1. Paint the canvas for a fixed fontSize (say 13) "pixel-exact".
2. Then use simply an affine transform to scale the display (you have
to reverse the transform for the mouse positions to get the clicks).
You set this transform via the property pickerScale.