[solved] How to taper a winding shape?

theozh · Postby **theozh** » Thu May 04, 2017 5:12 am

I would like to make a given winding shape thinner from one to the other end. For example a question mark. The dot can be scaled independently.

Surely, some LPE can do this. But which one?
LPE Pattern along path? Perspective/Envelope? Power stroke? Taper Stroke? Envelope Deformation?
My guess is that I probably need the center line of the upper part of the question mark and then scale it gradually along this center line. But how can I get this done?
With the question marks I maybe could interpolate two circles along a curved path...? But in general, I don't want to redraw the path, because they can have completely different shapes.
Currently, I don't have any good idea. Thank you for any hints.

There was a similiar title earlier but somehow different:
viewtopic.php?f=5&t=18550&p=70257

: QuestionMarkTaper.png (4.84 KiB) Viewed 2143 times

Moini · Postby **Moini** » Thu May 04, 2017 7:24 am

theo, can you post another picture of the desired result? (or is this the result?)

tylerdurden · Postby **tylerdurden** » Thu May 04, 2017 8:51 am

Maybe PaP LPE?

Lazur · Postby **Lazur** » Thu May 04, 2017 8:52 am

Hi.

If I understand right you want to modify a "pre-existing" shape as if it was drawn atop a core path with a path effect.
Only tool I can think capable of something similar is the tweak tool.

The other way around, if you already had a core path the powerstroke is the "intended solution", which can simulate round nibbed pens with different widths at given points along the path, no matter how crude it may be. (There is not much control over the interpolation being used between the "key counterpoints"-handles.)

Theoretically with transformations you can make it appear if your pen was ellipse-nibbed, but that's about it.
Inkscape doesn't have the "kalliculator" tool.
related topic

Postby **brynn** » Thu May 04, 2017 1:31 pm

Far from ideal, but Envelope Deform, either extension or path effect, could move in that direction. Nothing precise about it.

theozh · Postby **theozh** » Thu May 04, 2017 3:48 pm

Thank you all.
@Moini, if I knew how to draw it...
@tylerdurden, yes that's basically the effect, but you are starting with a core/center path which I do not have with my given shape.
@Lazur, below result was realized with the tweak tool, well a bit exaggerated, bumpy and handmade.
@brynn, I don't know yet how to use the Envelope Deform in this special situation but I'll further try with it.

I think the main problem is that I do not have a core/center path to modify the object. Maybe I have to draw/introduce it by hand?

Although, there is an extension Centerline-trace which should generate centerline from bitmap shapes:
https://github.com/fablabnbg/inkscape-centerline-trace
But so far I haven't gotten it to work to test. Need to install python-PIL first.

: QuestionMarkTaper2.png (14.69 KiB) Viewed 2078 times

theozh · Postby **theozh** » Thu May 04, 2017 10:05 pm

Maybe I am a step further?!
I used the LPE Envelope Deformation on the yellow square and split my shape into two paths and link the red one as "left bend path" and the blue as "right bend path" and disable top&bottom paths and then deform the square by "edit-on-canvas".

However, I haven't managed to get rid of the distortions at the begin and the end. I suspect that this has something to do with the angle of the handles. But couldn't remove it also with the usage of top&bottom bend path.
Maybe someone else knows what to do here?

: TaperShape.png (26.81 KiB) Viewed 2042 times

tylerdurden · Postby **tylerdurden** » Fri May 05, 2017 12:17 am

theozh wrote:@tylerdurden, yes that's basically the effect, but you are starting with a core/center path which I do not have with my given shape.

FWIW, I started with a hershey font, but that looked lumpy even after smoothing... maybe another style would work better. (Maybe you are not using text anyway?)

theozh · Postby **theozh** » Fri May 05, 2017 12:30 am

tylerdurden wrote:... maybe another style would work better. (Maybe you are not using text anyway?)

Actually, I was not starting with any font but with a bitmap image. The question mark is just to illustrate with a simple example. I would like to keep it general for basically any shape.

theozh · Postby **theozh** » Fri May 05, 2017 4:23 am

OK, here comes a solution...
maybe not THE most convenient direct-single-step-LPE solution, but at least A solution ;-)

.

- Select your arbitrary path (black)
- Make sure node #1 is at the desired starting position
- Use LPE "Pattern Along Path" and pattern the yellow diamond along the black path which gives the red path
- Do a Boolean difference between the black and the red path.
Done! :-)

: TaperShape2.png (39.12 KiB) Viewed 1988 times

edit:
with the above procedure the thickest Pattern along path is not necessarily at the position where one would like it to be, because the outer/upper path is longer then the inner/lower one.

To define the position with thickest pattern
- split your path at the desired positions
- change path direction going away from node(s) #1
- combine path again (Ctrl+K)
- LPE "Pattern along path" the yellow triangle
- ... rest see above...

: TaperShape3.png (11.38 KiB) Viewed 1984 times

Lazur · Postby **Lazur** » Fri May 05, 2017 6:47 am

That's quite clever!

Postby **brynn** » Fri May 05, 2017 11:01 pm

Well possibly I should have thought of this earlier. I'm blaming age :-p Possibly the Bezier Envelope extension would be better? https://github.com/shlomif/Bezier-Envelope-for-Inkscape I'm thinking use a kind of.....what's that....trapezoid? Or maybe symmetrical trapezoid. Where the top is wider, the 2 sides are angled inwards towards the bottom, and mirroring each other, and the bottom is a very short line.

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