I have always wanted a graphics editor with BlackBox and never had the time to work on one. I developed a module named ShapesDraw, however, that could serve to render primitive shapes for the editor.
It exports the following procedures:
Arc, a 90 degree arc
RoundedRect, a rectangle with rounded corners
Arrow, an arrow with a solid shaft
PathArrow, an arrow with a hollow interior
Pie, a segment of a pie chart
Sin, an efficient computation of sine
Cos, an efficient computation of cosine
I think the arrow routines are particularly nice, as you can specify the exact shape of the arrowheads. You can even put them on either or both ends of a Bezier curve. Integer arithmetic is used for efficiency, and angles are specified to a precision of 1/64 of one degree. The module is well-documented. It has a suite of test programs including some with animation. The BlackBox system is particularly nice, as you get resolution-independent rendering for hardcopy output. Anyone is welcome to use the module as one of the building blocks of a BlackBox editor.