I've tried to find a handwriting system, that is suitable for "infinite" media(paper) and to small one(touchpads on mobile devices, etc). And, finally, made it. It is too simple, so i've, probably, rediscovered already known. Original "inplace" version can be "ported" to four-positional joystick, found on some old phones and to "infinite" paper (done). It is (almost) direction-insensitive, "recognizing" program can "synchronize" it's coordinates with yours at first stroke on every word.
In short (in-place version): letters "starts" and "ends" in the arbitrary chosen "centre" (near the point, where the "pen" first lands on writing surface), and are distinguished by the direction of pen's "horizontal" movement near the 2 points at "vertical" extremes. We recognize 5 variants at each (--, -+, 0, +-, ++). That gives us 25 distinct letters. Not enough for natlangs, but almost perfect for lojban. Also, 2 "special" features (horizontal strokes in 2 directions) are available somewhere. I've used them for "'" and "y". Natlangs can use it to extend the letter space to at least 36. Another extension is possible by adding "microletters" at the bottom/top parts of some full-size letters. I've wanted to use it for lojban's diphthong, but that complicates the writing program, so that is postponed.
The system is easily adopted to infinite paper, by adding "time" to the "horizontal" axis on the "lower->upper" part of trajectory. Each letter, then, can be described as 2 points with cubic spline lines between them and to/from first/last points of adjacent letters.
The choice of "y" and "'" have made "y'y" indistinguishable from "y" on paper, which can be fixed in several ways, not described here.
Program generated result is in the picture. "Vertical" axis is skewed -25° (stolen from the daughter's exercise book), "time" goes from left to right. The choice of axis is arbitrary, at the bottom you can see xrulyvalsi, written with polar coordinates (i cant read it, but only 2 "features" are indistinguishable, some tweaking can, probably, fix it).