New feature: Variable width seam allowances

[Former user]

Allow different seam allowance widths around a pattern piece - e.g. Line_A_B has 1cm, Line_B_C has 2.5cm, Spl_C_D has 0cm, Line_D_A has 1.5cm seam allowance

[Roman Telezhynskyi]

Issue #76 was marked as a duplicate of this issue.

[Susan Spencer]

I submitted a proposal to the W3C working committee for SVG to allow the definition of an outset width on a per-subpath basis. Currently SVG supports generation of an outset or inset for a b-spline at a constant distance for the entire multi-path b-spline. The new proposal would allow separate outset distances for each sub-path along a b-spline, including distance=0. So path1 outset could have outsetDistance=N, path2 could have outsetDistance=M, path3 could have outsetDistance=0.

I've been invited to the SVG working group meeting in November 2016 to present and discuss the case. Perhaps low-level support for generating seam allowances and hems will be built into the SVG spec, and there will be Python elementTree() and Qt Graphics View functions to generate them easily. It will be a few years before this happens so we'll have to implement our own outset function.

[Susan Spencer]

Tavmjong Bah's blog on stroke widths and outset paths: http://tavmjong.free.fr/blog/?p=1257

[Susan Spencer]

Here is an excellent discussion at StackExchange: http://math.stackexchange.com/questions/465782/control-points-of-offset-bezier-curve

[Susan Spencer]

Tiller and Hanson's method of using a midpoint, the midpoint's tangent, the endpoints and the endpoints' tangents is summarized here: http://web.mit.edu/hyperbook/Patrikalakis-Maekawa-Cho/node222.html

Gabriel Suchowolski's method of using selective subdivisions, to improve offsets of tight curves' anomolies encountered with Tiller and Hansen, is here: http://web.mit.edu/hyperbook/Patrikalakis-Maekawa-Cho/node222.html

[Susan Spencer]

FYI, I've been invited to the W3 standards meeting in October to present the case to add this special offset feature (where each segment along a closed path can be assigned it's own offset width) into the W3 SVG standard. This feature is very useful for us, and it is a very powerful graphics concept. It's gratifying that the W3 wishes to assist us with our project, and that they see universal application. IN THE MEANTIME, we have to code this up ourselves. It will be at least a year before this feature is available in SVG libraries.

[Roman Telezhynskyi]

Sorry, but i don't see how SVG standard is related to us.

[Susan Spencer]

It won't help us out until this feature is accepted into the SVG standard for offset definition. Then it will take some time before libraries (like Qt Graphics View Framework) include the new method of defining multiple offset widths along a multisegment closed path.

[Roman Telezhynskyi]

Can you provide prove that Qt Graphics View Framework uses SVG standard?

Maybe you are talking about Qt SVG library? In this case:

Scalable Vector Graphics (SVG) is a language for describing two-dimensional graphics and graphical applications in XML. SVG 1.1 is a W3C Recommendation and forms the core of the current SVG developments in Qt. SVG 1.2 is the specification currently being developed by the SVG Working Group, and it is available in draft form. The Mobile SVG Profiles (SVG Basic and SVG Tiny) are aimed at resource-limited devices and are part of the 3GPP platform for third generation mobile phones. You can read more about SVG at About SVG.

Qt supports the static features of SVG 1.2 Tiny. ECMA scripts and DOM manipulation are currently not supported.

If your proposal will be part of SVG Tiny Qt will support it.

But i have big doubts that any changes in SVG will help us at all. Only after redesign seam allowance we will fix it.

[Roman Telezhynskyi]

Issue #451 was marked as a duplicate of this issue.

[Susan Spencer]

Good point about SVG Basic and Tiny. I'll ask about making this new feature part of SVG Tiny.

So it appears that Qt Graphics View Framework uses Qt SVG Library which is Qt's implementation of the SVG Tiny subset of the SVG standard.

It's nice that some members of the W3 working group are interested in our needs. Yes, it may be a while before the new SVG specifications are implemented in code.

[Roman Telezhynskyi]

So it appears that Qt Graphics View Framework uses Qt SVG Library

No, Qt Graphics View Framework doesn't depend on Qt SVG Library. It can use it only for export graphics scene.

[Susan Spencer]

Ok. In any case, I think it will be a good thing.

[Raina Gustafson]

@koranin and I are open to working on variable width seam allowances.

Is the existing seam allowance point to point selection functionality in the process of being replaced with line selection? I saw this topic discussed as a prerequisite for passmarks implementation, too.

[Roman Telezhynskyi]

Thing is i will take care of this feature. Read my answer here.

[Roman Telezhynskyi]

This is part of detail tool redesign.

[Susan Spencer]

Just a note, the SVG working committee released their recommendations last month. :(
So it won't be part of the SVG 2.0 standard.

[Raina Gustafson]

Too bad. Well done for trying, @tusuzu.

[Roman Telezhynskyi]

Issue #451 was marked as a duplicate of this issue.

[Roman Telezhynskyi]

Issue #535 was marked as a duplicate of this issue.

[Roman Telezhynskyi]

Merge with feature.

Resolved issue #406. New feature: Seam allowance tool -> Preview. Resolved issue #88. New feature: Variable width seam allowances. Resolved issue #280. New tool: 'Hem' in Detail mode. Resolved issue #509. Improve feature: Support internal Paths in Detail tool.

→ <<cset 22d8770e9636>>

[Roman Telezhynskyi]

Removing milestone: v0.5.0 (automated comment)