Designer - Shape Builder problem

[JariH]

Hello

Affinity Designer 2.6.2

I am pretty confident the Shape Builder Tool did manage this before 🥸.
I created four overlapping circles like in the picture in X-ray view. I could not build shapes like on the right side shown in shaded. Shape Builder always selects the underlying large circle as a whole, whatever setting I try. Has something changed?

Even Vector Flood Fill did the same. This used to be an easy-peasy thing unless I am doing something stupid.

[RE4LLY]

There seems to be very slight inaccuracy in the ellipse size which in return causes the blue guiding lines of the curves to not intersect which each other. However this intersection is necessary for the Shape Builder Tool and also the Vector Flood Tool to differentiate the different areas from each other.

It is definitely something the Devs should look into, so at best report this as a bug and for the time being you can avoid this issue by decreasing the size of your outer ellipse by a fraction of 0.01mm to ensure that the curves actually overlap.

[JariH]

Thanks

Decreasing the outer shapes size did the trick. I thought it was a bug, but it's a different kind. The Shape Tool seems to be working OK. However, in this case, the smaller circles were duplicated by rotating them around the centre point - there is an inaccuracy. Shapes seem to snap to each other's geometry, but not quite.

[lepr]

Not really a bug.

Affinity's Ellipse Tool was not designed to create perfect ellipses and circles - it approximates them with a path composed of 4 cubic Bézier curves -  and that can result in unwelcome tiny gaps between shapes.

@NotMyFault pointed out some time ago that a sufficiently close (at least for use in Affinity) approximation to a circle can be made by 12 cubic Bézier curves. That can be made by various tools, and my preference is the Polygon Tool with its Sides=12 and Curve=100%. (A preset can be saved for that curved polygon.)

The attached video shows Shape Builder Tool succeeding when 'improved' circles are used.

 

 

 

[JariH]

7 minutes ago, lepr said:

Ellipse Tool was not designed to create perfect ellipses and circles

Well, that's a bummer.

[Indie]

I’m following along a tutorial, and thought I was doing something wrong, but then I found this big problem when I use shape builder. My program is up-to-date. Any ideas on how to work around this? I tried to add two pieces together and it created this gargantuan weird shape.The wire diagram and the curves in my layers all look exactly right.

[George-Frazee]

On 4/15/2025 at 3:43 PM, lepr said:

Affinity's Ellipse Tool was not designed to create perfect ellipses and circles

I know this has come up many times on the forums but have the devs ever given a reason why they chose to do it this way? Feels like more work and it creates problems like the OPs intermittently.

[Alfred]

2 hours ago, George-Frazee said:

I know this has come up many times on the forums but have the devs ever given a reason why they chose to do it this way?

It isn’t a developer choice, it’s an inherent limitation of Bézier curves. Although we can achieve a very close approximation with Bézier curves, it’s mathematically impossible to draw a perfect circle.

[George-Frazee]

10 hours ago, Alfred said:

It isn’t a developer choice, it’s an inherent limitation of Bézier curves. Although we can achieve a very close approximation with Bézier curves, it’s mathematically impossible to draw a perfect circle.

Oh yeah, but I mean why not develop a separate equation specifically for circles/ellipses? I know SVGs have commands for both of these (unless those are also bezier approximations?)

I could be missing something and it's actually impossible to do without bezier curves, but that's what I'm asking here.

[Bound by Beans]

10 hours ago, Alfred said:

It isn’t a developer choice, it’s an inherent limitation of Bézier curves. Although we can achieve a very close approximation with Bézier curves, it’s mathematically impossible to draw a perfect circle.

Still, Adobe Illustrator comes much closer by using a refined 4-point Bézier approximation with optimized control point placement, minimizing visual deviation from a true circle. This method ensures that circles appear seamless and precise, even when zoomed in or stacked.

For tasks requiring high geometric accuracy in circles and ellipses, VectorStyler and Adobe Illustrator are the most precise applications. CorelDRAW also offers good precision, depending on export settings and formats. Inkscape and Affinity Designer are suitable for general design tasks but may have limitations in precision.

So, Affinity sits at the weaker end of vector design tools—and that’s kind of a trend with Affinity: weak algorithms. So... Canva, then...

[R C-R]

15 hours ago, Alfred said:

It isn’t a developer choice, it’s an inherent limitation of Bézier curves. Although we can achieve a very close approximation with Bézier curves, it’s mathematically impossible to draw a perfect circle.

As I understand it, creation of the path of a mathematically perfect circle (or ellipse) in a Cartesian coordinate system would require an infinite number of nodes because the path is defined in polar coordinates, so every angular increment, even the tiniest fraction of a degree, would require a new node for absolute accuracy. (This is a much dumbed down version of references that can be found online.)

So it amounts to what is a "good enough" approximation, which in turn depends in part on the maximum resolution & zoom factor that can be achieved using the math built into the app, the available boolean operations, how much computational load is acceptable to prevent lags, & so on.