view.lcd_display library Null safety

Widget to draw the LCD Display, using a CustomPainter and direct drawing commands. The main eleven-digit display doesn't use a font; the individual segments are drawn.

The structure of this module is pretty straightforward:
LcdDisplay is the main widget. It uses Flutter's CustomPainter to do direct drawing of the different visual elements. The most interesting part of that is the 7 segment digits, which are drawn with Digit. There's a Digit instance for each character of our alphabet, which includes the digits from 0 to f, as well as some other characters used by the 16C, e.g. for the flashing "running" message. A Digit is comprised of some number of Segments, each of which is a Flutter Path, one for each of the seven segments, plus the decimal point and the tail that completes a comma.

Drawing a Digit involves some trig, like this:
(More is available under Segments.)


Draw a digit, by drawing the individual Segments.
A widget that looks like an LCD display. It uses Flutter's CustomPainter to directly draw the visual elements, notably using 7-segment Digit instances. LcdDisplay listens to events from Model.display.
Singleton to do the math of where tho display the digit segments. These segments are based on a 72-pixel high digit whose upper-left hand corner is at 0,0. it is expected that the client will scale and translate the Canvas accordingly.