Chinese Character Stroke Order
A web app that steps through the stroke order of a Chinese character, then checks each stroke as you draw it yourself.
Every Chinese character is written with its strokes in a fixed order.
The Hanzi Writer library draws the characters and grades the quiz. Its strokes come from the Make Me a Hanzi data set. The data stores each stroke as an outline to fill and as a center line through it. In the quiz, Hanzi Writer compares your line with the center line of the stroke you are on. It checks the average distance between them, where your line starts and ends, its direction, its shape and its length. If your line fits a later stroke better, the check gets stricter, since you have probably skipped a stroke. After one miss, the correct stroke flashes as a hint.
The app loads each of the 9,574 characters in the data from a CDN when you pick it. For a character outside the data, the CDN can take tens of seconds to answer that the file does not exist. The app ships the list of covered characters, so it can tell you right away when it has no strokes for a character.