On 9/8/25 11:10, William F Pokorny wrote:
> Thinking aloud, it might be possible to allow x<0 control points - ONLY 
> - where both on curve points and off curve control points are forced to 
> be always ascending (>= previous) in y. This, probably, would cover the 
> 'useful' x<0 control point cases while preventing the curve from 
> crossing into -x?  I'll try to play with this thought some more when I 
> again have time - need to run.

I spent some time on this idea and, on seeing some issues where entire 
segments would just blink out of existence, I went back to trying more 
parser legal point sets and found similar weirdness. :-(

There exists internal cylinder bounding of segments intended to reduce 
the number of calls to the solvers. My guess is that code isn't 
completely solid, but who knows.

Attached an image where the top row uses the currently legal point set of:

     <+1.5,-0.01> // C0
     <+0.4, 0.0>  // P1
     <+0.3, 0.5>  // P2
     <+0.4, 0.9>  // P3
     <+1.5,+0.91> // C4

and the shape breaks apart(a)(b). In the bottom row I changed that last 
control point to:

    <+1.5,+0.901> // C4

and the entire top segment drops out.

So yep...

Bill P.

(a) Curve going negative can already happen without negative control 
points.

(b) In yuqk the parts of the sor there all look good. In v3.8 beta 2, 
the results for top segment are noisy; Likely solver differences.

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