[wes-k]

Smoothing is a different operation where you are simplifying the bezier curve by removing redundant(ish) points. So if you draw an almost straight line, you may have created 100 control points, and then the software simplifies it down to 4 points.

[steveruizok]

For what it’s worth, perfect freehand (the library I wrote that they’re using for the digital ink) does not use Bézier curves at all to determine the position of points or create the “stroke” polygon that wraps the input points. Curves are only used to draw the line around that stroke polygon.

I tried to incorporate simplification into the perfect freehand algorithm but eventually gave up because I could not find any “stable” algorithm that would not cause the line to jump around as you drew / added points to the end. As far as I know none exist. Most apps that use simplification solve this problem by simplifying the line only after you’ve finished drawing, however for handwriting or artistic drawing this is especially bad as it “undoes” legitimate decisions you’ve made about where to place detail. In addition, the perfect-freehand algorithm simulates pressure based on density of points, so simplifying the line (ie removing points) without creating a corresponding pressure curve will cause a reduction in line variation, which is part of the fun of using it in the first place!

I’d love to learn more about what the canva team has done here though. Freehand drawing is a fascinating problem space, even without the ml / shape recognition stuff.