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Hi,
I don't believe this is a bug (for the most part, I shall explain shortly), but Illustrator uses a Winding (Non-Zero) Fill Mode by default, whereas we use 'Alternate (Even-Odd)' by default on objects. This means that depending on the direction a curve object was drawn in will result on a parts of the object appearing filled in when normally using Winding. This website here does a nice job of explaining what these mean and how they work.

So essentially with the O shape, if you apply a fill and set the Fill Mode to be Winding you don't get the hole, however with the Fill Mode set to Alternate you do! This is because each curve was drawn in a different direction. See Designer (Windows) below:

Winding.thumb.png.4ad7de9f205a6d5ac169bfbe9729e6d6.pngAlternate.thumb.png.3bb7a6d422a3b574e29078beb37566c3.png

 

You can see this in Illustrator by just reversing the curve direction of one of the Curves in the O object. See below:

ReversePathDirectionOn.thumb.png.f0bcac78d9bb97f923d1b5ede0e36a8d.pngReversePathDirectionOff.thumb.png.57ee789e6f2a69bec797ea4e63b9fbaf.png

Now unfortunately I'm not sure what CnC or other vector software you are using that shows the SVG importing like that, However you could double check this by trying the following: Create a single O objects drawing both the inner and outer shapes in a clockwise direction and then subtract them to create the O, and then create another O object but this time draw the inner shape clockwise and the outer shape anti-clockwise. I bet the one with the both clockwise drawn paths will fail to cut like you want. 

Now where the issue with Designer comes in, is that it is not possible to change the direction of a single path in a Curves object. There is the option on the context toolbar to 'Reverse Curves', but what this does is change the direction of all the paths in the Curves object, meaning you can't actually get it to the state you would want using this option. This issue is logged with development however.

I hope this makes sense to you! It was a bit awkward to try and describe the behaviour, and without knowing or trying your CnC software it is a little bit of a shot in the dark!

Hope that helps :)

 

 

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1 hour ago, Sean P said:

Now where the issue with Designer comes in, is that it is not possible to change the direction of a single path in a Curves object. There is the option on the context toolbar to 'Reverse Curves', but what this does is change the direction of all the paths in the Curves object, meaning you can't actually get it to the state you would want using this option. This issue is logged with development however.

I haven’t tried this (or I would know the answer!) but can’t you work around the problem by dividing the Curves object, reversing the interior curve and then combining the pieces again? :/

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36 minutes ago, αℓƒяє∂ said:

I haven’t tried this (or I would know the answer!) but can’t you work around the problem by dividing the Curves object, reversing the interior curve and then combining the pieces again? :/

That should work, but may take a bit of trial and error without knowing the direction of the curve (which is not possible to see on a closed curve).

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7 hours ago, αℓƒяє∂ said:

I haven’t tried this (or I would know the answer!) but can’t you work around the problem by dividing the Curves object, reversing the interior curve and then combining the pieces again? :/

That worked,

Since we have an option to choose either;
Couldn't you just make the winding non zero option to be the default in svg export ?

Or strip the choice and give every export format its own default,best suited, version

 

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@sean Thanks for the detailed reply!  At least now I understand what's going on.  Of all the very many things I tried, having the two curves drawn in opposite directions wasn't one of them!  While I agree this isn't a bug exactly, it's definitely a userbility issue in my opinion.

I tried a test, two nested shapes, repeat four times drawn as:  1:clockwise/clockwise  2:anti-clockwise/anticlockwise  3:clockwise/anti-clockwise, 4:anti-clockwise/clockwise.

Case 1 & 2 did not 'cut-out' the interior as was desired.  3 & 4 both did, so the takeaway is to ensure in such cases that it doesn't matter which is outer or inner, just that the direction is not he same.  

While I have yet to import these test shapes into the CNC tool, I'm confident the results will be the same as was rendered when importing into an alternative app on the iPad as I did for this test.  Thanks again, I'm glad the mystery is solved now.

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If you're running your svg through an optimiser for use on the web, be careful of the option 'remove non-essential styles'.

If it can't be deselected in the optimiser then open the svg file in a plaintext/code editor and add  style="fill-rule:evenodd;"  back in after the viewBox attribute and hit save.

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