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 Post subject: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 10:28 am  (#1) 
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Someone told me a while back it was virtually impossible to create a circle with the paths tool that was perfect in circumference.Well i have figured out how to do it.It is very simple.

First open Gimp i am using Gimp-2.7.5 (new Partha version)
Open the layers dialog CTR + L
Open the Paths dialog Windows>Dockable Dialogs>Paths

Now create a new document - File>New
Make it any size as long as it is square - I am using 480x480
Now go to View>Guides - Also make sure snap to guides is selected
Create 6 guides and position them like so on your image
Image

Now click on the the paths tool :pathtool in your the toolbox
Create 4 new nodes/points in the center of your image Image example below
Image

Now making sure that the design option is selected in the path tool options dialog move the center of each side out from the center -image example below
Image

Now you will notice two of the nodes on the left are both already simultaneously selected.
Pull both of them by selecting one and move them in towards the other two like so - image example below
Image

You can also do this by selecting the circular selection tool :elipse
Creating a circle then doing a Select>To Path
Then stroking the path.

I just wanted to show you how to do it with just the paths tool.Now we know it is possible. :jumpclap

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 10:37 am  (#2) 
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In comparison -
Image

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 10:40 am  (#3) 
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Good for you, but I'm a simpleton. Rather just do a selection to path with a circle selection. :)

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 10:49 am  (#4) 
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Very clever, Rod. Yes, it's nice to know it can be done with the Paths tool.

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 1:35 pm  (#5) 
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Close but no cigar... There is a known pretty good approximation of the quarter of circle using the "kappa" value to compute the position of the handles (see http://www.whizkidtech.redprince.net/bezier/circle/ )(*). The method above creates a curve whose radius in the 45% diagonals is about 2% too long.

Your explanation also a bit vague at its most important point. This works if one understands that the guides should be every 120 pixels, and 120 pixels from the canvas border. But the method can be simplified:

- Make guides around the future circle, plus two middle guides. You have 9 points:
A---B---C
|   |   |
D---E---F
|   |   |
G---H---I

- With the path tool, create a segment from B to H, then go back to B and close the path. Now, due to the "xor" in the path display (at least on 2.6) you only see the two points and nothing in between. A strong faith is necessary for the following steps:
- Click on E and drag to F
- Click on E and drag to D

Out of curiosity, you can also make the initial path from D to F, and then drag E->B and E->H. And you'll notice the circle obtained is slightly different (the method has an axis bias).

You can also use the shape-path script from the Gimp registry (it uses the kappa-based curve).

(*) the mathematical proof is however a bit shallow. All it proves is that the generated curve is the one going through coordinates (sqrt(2),sqrt(2)) but it doesn't mean it's the one with the smallest global error

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 2:16 pm  (#6) 
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I am not quite sure what you just said Ofnuts but i do believe you. :)

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 2:54 pm  (#7) 
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:shock: me too.

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 3:21 pm  (#8) 
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I think this is what Ofnut was saying. I've hidden the grid so the paths are more apparent.
Image

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 5:35 pm  (#9) 
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bkh1914 wrote:
I think this is what Ofnut was saying. I've hidden the grid so the paths are more apparent.
Image
Exactly...

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 5:37 pm  (#10) 
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Now I understand.

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 7:29 pm  (#11) 
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You can also use the two-point method to make egg shapes.

Image

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Thu Dec 22, 2011 9:02 pm  (#12) 
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Or hearts (drag E to A/C)

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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Fri Dec 23, 2011 2:11 pm  (#13) 
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Clearly i will have to look into this 2 point (have faith) method more closely. ;)
Thanks guys.

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Edmund Burke nailed it when he said, "The only thing necessary for the triumph of evil is for good men to do nothing."


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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Fri Dec 23, 2011 6:51 pm  (#14) 
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Here are a few with the 2 point method. :)

Image

Image

Image

Can you think of any more?

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Edmund Burke nailed it when he said, "The only thing necessary for the triumph of evil is for good men to do nothing."


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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Sat Dec 24, 2011 7:46 am  (#15) 
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hello :gimp
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 Post subject: Re: Creating a circle with the paths tool
PostPosted: Sat Dec 24, 2011 12:14 pm  (#16) 
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Looks like a hat! :)
Cool.

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