1. Since you incorporated snap on endpoints could you extend the fuctionality a bit further to snap on divisions? Say halves for midpoint, or any other division thirds, fourths, etc.
2. In the tool tip that follows the cursor when drawing straight lines, instead of showing pixels for lenght, to show paper (cm) or scaled unit (m 1:100, m 1:50, m 1:200, etc).
Don't get me wrong I'm not looking for precision drawing, just a visual aid of how long the line is
3. when rotating canvas the compass to adjust on that rotation, so 0 angle of line to be always parallel with canvas top and bottom edges
Black Ink is ideal for mimicking hand drawn technical drawings and architectural renderings, very fast and very responsive.