I need it for two connected lines at arbitrary angles.
My approach to the math is to envision two lines parallel to the original and at a distance equal to the radius of the fillet. Then find the point of intersection of the two new lines, which will be the centre of the fillet arc. Next, envision perpendiculars to the original lines which will provide the end points of the arc.
My hope is to simplify the math to provide formulas for the three essential points in terms of the end points of the original lines, and then have my script use the formulas directly in drawing the arc and trimming the original lines.
I guess it's more of an analytic geometry question than a programming question. I'm making progress but my math is rusty. If anyone is adept at this sort of thing I'd appreciate their input.