Hi Seamly enthusiasts,

As a new user I have been enjoying playing around with Seamly! My first impressions are of a terrific product.

I have a question about a behavior that was surprising to me, and wondered whether it’s a bug or a feature.

The cubic Bezier splines tool seems to use the wrong control point angle for segments beyond the first one. It seems to use the reciprocal angle of the previous control point rather than the one that is set.

Here’s a minimal example. The spline ABC (dashed, light blue) uses control points AB_cp1 and AB_cp2 for the first segment and BC_cp1 and BC_cp2 for the second segment. Based on experience with other software and in mathematics more generally, I expected the resulting curve to be identical to the union of the two single-segment cubic splines AB and BC (same control points; dotted purple). However, the second segment of the bezier spline is quite different, and the effective control point at B is not actually BC_cp1.

It turns out that the second segment is taking the *length* of the assigned control point (B to BC_cp1) but the effective control point angle *angle* is 180 plus `angle(B, AB_cp2)`

.

My question: is this the expected behavior? If I want different control point angles in my patterns, should I just use a sequence of individual cubic Bezier curves, like the purple dashed line?

Thanks very much!

Edit: here’s an annotated version of the above diagram, to clarify which are the intended and resulting curves.