this contour crashes crossingsRemoved

[mbutterick]

I am making a Path using this contour as a component and passing it through crossingsRemoved(). The two off-curve points are key. Once the upper point gets one unit to the right of the lower point, it triggers this assertion in addNeighbor.

[mbutterick]

BTW if I disable the assert, nothing bad seems to happen, so I can’t tell if the assert is protecting against a stricter condition than necessary, or if there is some subtle logic or math error happening deeper. Considering that the error seems very sensitive to the exact relative positions of the handles, I suspect the latter.

[hfutrell]

Wow, I've never seen that assert hit before!

I am not sure why it's happening here. addNeighbor is called on a per-intersection basis and it does not appear that the path self-intersects so I'm unsure why it is called at all.

I'll try to reproduce this issue soon.

[mbutterick]

This contour also crashes crossingsRemoved — seemingly related to having four points at the same Y coordinate on the top edge. Is there a way I can print a text-based representation of a path that would make reconstructing the test case easier? (Because these errors seem to be very sensitive to point position)

[hfutrell]

@mbutterick if you have the debugger paused at the assert, try navigating the stack up to AugmentedGraph.init(...) and type:

po path1.components.map { $0.curves }

This should print out the curves that make up the contour and I can make a test case directly from that.

[mbutterick]

Seems likely it’s a different bug so I’ll post a separate issue (see #81)

[mbutterick]

Here’s a test case that produces same error. Slightly different shape on top but the problematic inflected curve at the bottom is the same.

Text:

path.components.map { $0.curves } =
[[BezierKit.CubicCurve(p0: (275.0, 656.0), p1: (325.0, 656.0), p2: (324.0, 594.0), p3: (372.0, 594.0)), BezierKit.CubicCurve(p0: (372.0, 594.0), p1: (406.0, 594.0), p2: (426.0, 616.0), p3: (426.0, 645.0)), BezierKit.CubicCurve(p0: (426.0, 645.0), p1: (426.0, 691.0), p2: (377.0, 713.0), p3: (329.0, 713.0)), BezierKit.CubicCurve(p0: (329.0, 713.0), p1: (228.0, 713.0), p2: (240.0, 656.0), p3: (275.0, 656.0))]]
path.crossingsRemoved().components.map { $0.curves } =
[[BezierKit.CubicCurve(p0: (275.0, 656.0), p1: (300.5, 656.0), p2: (312.7349, 639.8738000000001), p3: (324.96979999999996, 624.0701239999999)), BezierKit.CubicCurve(p0: (324.96979999999996, 624.0701239999999), p1: (336.7249, 608.8862), p2: (348.48, 594.0), p3: (372.0, 594.0)), BezierKit.CubicCurve(p0: (372.0, 594.0), p1: (406.0, 594.0), p2: (426.0, 616.0), p3: (426.0, 645.0)), BezierKit.CubicCurve(p0: (426.0, 645.0), p1: (426.0, 691.0), p2: (377.0, 713.0), p3: (329.0, 713.0)), BezierKit.CubicCurve(p0: (329.0, 713.0), p1: (228.0, 713.0), p2: (240.0, 656.0), p3: (275.0, 656.0))]]

Visual:

[hfutrell]

@mbutterick I am unfortunately not able to reproduce the issue. Here is the code I'm running trying to hit the assert with your first path:

        let mutablePath = CGMutablePath()
        mutablePath.move(to: CGPoint(x: 0, y: 62))
        mutablePath.addCurve(to: CGPoint(x: 97, y: 0),
                      control1: CGPoint(x: 50, y: 62),
                      control2: CGPoint(x: 49, y: 0))
        mutablePath.addLine(to: CGPoint(x: 78, y: 102))
        mutablePath.addLine(to: CGPoint(x: 0, y: 62))
        let path = Path(cgPath: mutablePath)
        let result = path.crossingsRemoved()
        assert(path == result)

Here is the code I'm running to try to reproduce the issue with the second path

        let points = [CGPoint(x: 275.0, y: 656.0), CGPoint(x: 325.0, y: 656.0), CGPoint(x: 324.0, y: 594.0), CGPoint(x: 372.0, y: 594.0),
                      CGPoint(x: 406.0, y: 594.0), CGPoint(x: 426.0, y: 616.0), CGPoint(x: 426.0, y: 645.0),
                      CGPoint(x: 426.0, y: 691.0), CGPoint(x: 377.0, y: 713.0), CGPoint(x: 329.0, y: 713.0),
                      CGPoint(x: 228.0, y: 713.0), CGPoint(x: 240.0, y: 656.0), CGPoint(x: 275.0, y: 656.0)]
        let path = Path(components: [PathComponent(points: points, orders: [3, 3, 3, 3])])
        let result = path.crossingsRemoved()
        assert(path == result)

Everything seems ok on my end. If you run these code snippets are things working ok on your end?

I might need more information, like what branch you are using, OS version, XCode version, hardware things are running (especially 32 vs 64 bit).

[mbutterick]

Sorry, that was my error. My copy of BezierKit was a little behind the current one. I’ve updated and the issue no longer recurs.

[hfutrell]

good to know BezierKit is at least improving over time :)