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Consider rational bezier curves instead of bezier curves #66

carewolf opened this issue Nov 9, 2017 · 2 comments


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commented Nov 9, 2017

Rational bezier curves are curves where the control point(s) has an extra weight.
There are two stong benefit of rational bezier curves over basic bezier curves:
a) They can represent all conic arcs accurately. This makes arc a special case of bezier curves, and possible to represent it internally as a single bezier curve.
b) They are stable under projection transformation. You do not currently have 3D transforms in the library, but if you had, then bezier curves would be broken by them, and need to split or rasterized after a projection transform, but rational bezier curves can be transformed under any 3D transform and still be a rational bezier curve.


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commented Nov 27, 2017

I've given thoughts to this at times. I'd do it in addition rather than instead (if you don't need the computational overhead of a rational Bezier, no need to pay for it).

Given that I'd keep the basic Beziers and that, to me, NURBS would add even more value, do you think there's a significant enough benefit to having rational Beziers instead of NURBS?

The obvious answer is the same as I provided for keeping simple Beziers (only pay for what you want/need). But I also need to take into account keeping the API as compact as possible. Additionally, if adopted, this will be a TS initially such that if user feedback is that they want rational Beziers in addition to NURBS (and that they want to have standardized 2D graphics) it would almost certainly be added.

I lean strongly towards NURBS. After simple Beziers, NURBS are the next most used/required feature in the realm of "curves" in my experience.

As a follow up, if you agree that NURBS are better to have than rational Beziers, are you willing to create a fork, implement a NURBS figure_item using cairo, and the submit a pull request that I could integrate? (It'd need to be under the same license as this project, i.e. the BSL 1.0). The biggest reason that something like this isn't yet in the proposal is that I haven't been able to spare the cycles to implement a NURBS figure item using cairo's line and cubic Bezier interface. It'd actually be several figure items, of course. One to begin it, control points, knots, and an end marker.

If you can spare the cycle to work on an implementation, that would be awesome and I'd gladly make time to work with you on API design issues, etc.

Best regards,


@mikebmcl mikebmcl self-assigned this Nov 27, 2017

@mikebmcl mikebmcl added the question label Nov 27, 2017


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commented Nov 27, 2017

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