Paper.js: TypeError on Path.unite

[tjunnone]

A regression between 0.9.25 and develop head:

Head is throwing the following error on calling Path.unite:
Uncaught TypeError: Cannot read property 'y' of null (propagateWinding: hor = Math.abs(curve.getTangentAtTime(t).y))
@ computeBoolean (propagateWinding(segment, _path1, _path2, monoCurves, operator);)
@ unite (return computeBoolean(this, path, 'unite');)

Both head and previous version render the actual Path fine, only the former gives this error on unite. Unite is being called on the path itself to remove any self-intersections, and the path is quite complex.

[lehni]

Please provide a test case or at least the path data that produces this error.

[tjunnone]

Sorry for not replying sooner, it's quite tricky to reproduce. The following sketch reproduces the error: http://sketch.paperjs.org/#S/ndLRTsMgFAbgVznhZl3SEEZLd4bZ1V7AxEvrBZZj1qxCw1jUNH13i07djWb1v4I/+Q4kMDBnnolpdneg2OxZzhpv0743cQ9bcPQCvekp8NupyIbawZSntut2vvNBwyKQXeSfddP5I1kNMZyoduPypna1S4O4sTa7GOVbF7PhVcNKKclVDm8a1gXytRqXSf1tUODZIFazzUYWVxqFJS83P8EPvxKq4PKiv26WFOfz/+dlVX7dXygulfiOnMexwvm8RPztlU6ujZSlZaqm//MYyBz6ZI9M3z+M7w==

Interestingly, if you supply the pathData to the Path constructor, the error does not happen. The error is only reproducible when closed: true, and you have to add the points individually.

[lehni]

Ok, this is actually an error in Curve#getTimeAt(), and can be reduced to this case

@iconexperience do you feel like looking at this?

[lehni]

Regardless of that error, the boolean code should handle the rare case where no t is found for a given length.

[lehni]

@tjunnone the reason why pathData doesn't work the same way is rounding in the formatting as string.

[lehni]

@iconexperience I have a feeling that curve.length is imprecise and too large in this case, so the offset is actually outside. Now the question is, how to handle this case?

[lehni]

Interesting... Curve.isStraight() is true for this curve, and that leads to the length being slightly larger. Then getTimeAt() uses Numerical.integrate() to calculate the length of the range and results in a different value and decides that the offset is outside of the range.

[tjunnone]

This completely fixed the issue. Lehni, you're the best!