UI ideas for quadratic and elliptic curves?

[bulia byak]

Krzysztof is working on Node tool as his GSoC task, and as part of the
refactoring we may be able to add support for editing quadratic and
elliptic segments in paths. Is anyone aware of how other software
supports these beasts from UI viewpoint - what handles are used and
how? Any pointers will be appreciated.

--
bulia byak
Inkscape. Draw Freely.
http://www.inkscape.org

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[Aaron Spike-2]

bulia byak wrote:
> Krzysztof is working on Node tool as his GSoC task, and as part of the
> refactoring we may be able to add support for editing quadratic and
> elliptic segments in paths. Is anyone aware of how other software
> supports these beasts from UI viewpoint - what handles are used and
> how? Any pointers will be appreciated.

Nathan and Marco have done some work in lib2geom experimenting with
various user interactions for elliptic segments. I would recommend
chatting with Nathan and testing some of the toy implementations in
lib2geom.

Aaron Spike

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[Daniel Pope]

bulia byak wrote:
> Krzysztof is working on Node tool as his GSoC task, and as part of the
> refactoring we may be able to add support for editing quadratic and
> elliptic segments in paths. Is anyone aware of how other software
> supports these beasts from UI viewpoint - what handles are used and
> how? Any pointers will be appreciated.

I used some software once that had these, though I can't remember the
name of it. SomethingDraw I think. In that your paths were either/or -
you would use either a bezier tool, or a quadratic tool, or an
elliptical segment tool.

A dedicated elliptical path drawing tool would be fairly useful imho.
You could draw shapes with one tool or another and combine them with
boolean operations.

One use case that would come in handy would be if you could convert a
rounded rectangle to a path with elliptic segments for corners so that
you could scale each corner individually without distorting the
rectangle's sides.

Dan

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[Krzysztof Kosiński]

2009/6/17 Daniel Pope <mauve@...>:
> I used some software once that had these, though I can't remember the
> name of it. SomethingDraw I think. In that your paths were either/or -
> you would use either a bezier tool, or a quadratic tool, or an
> elliptical segment tool.

This is wrong. We can have any of those segments in any path: SVG
allows to mix them freely. Not to mention it would be very confusing,
because we would now have several modes of the node tool, and modes
are bad. I didn't think about drawing such paths yet - for now it's
sufficient if we can change the type of a segment to either quad or
arc and edit it.

Now actual UI ideas. For quadratic beziers, it's rather easy: we have
something like two cubic bezier handles glues together. It's a bit
harder for elliptical arcs. The ellipse-fitting toy from 2geom uses
three points on the arc, but it's hard to get the shape you want with
this kind of control. The ellipse tool uses the bounding rectangle,
but this approach doesn't make much sense for paths when the ends of
the arc are fixed. Here are my initial ideas:

a) Ellipse's major and minor axis end with handles. Dragging on one of
the handles would leave the second handle of the same axis in place
and update the handles of the other axis appropriately. Unwieldy for
shallow arcs.

b) Draw the entire ellipse as a helper path, allow dragging any part
of it and do the "expected thing". Not very precise, unwieldy for
shallow arcs.

c) Use the ellipse's foci and a point on the arc as handles. Dragging
any of the handles would have to change the position of at least one
other handle, so they wouldn't be independent, unwieldy for shallow
arcs.

d) Use a point on the arc with one handle which specifies the
direction of the normal at that point. The point would be independent,
but there would be keys to drag the point along the arc without
changing the shape with the tangent point following. Pros: can edit
very shallow arcs with ease. Cons: might not work well for arcs larger
than 180 degrees, I don't know how to do this mathemathically :), not
sure about interaction with smooth and symmetric nodes.

Regards, Krzysztof

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[Daniel Pope]

Krzysztof Kosiński wrote:
> This is wrong. We can have any of those segments in any path: SVG
> allows to mix them freely.

I'm aware of that, but just because the SVG format allows something it's
not necessarily easier for users. SVG also allows horizontal and
vertical segments too, but what Inkscape currently implements is a good
approximation[1] to the superset of all shapes without introducing
different user interfaces for each of the 6 segment types.

> Not to mention it would be very confusing,
> because we would now have several modes of the node tool, and modes
> are bad.

"Modal interfaces are bad" is only a loose usability guideline. What is
good usability can only be measured by how people interact with an
interface. Modal interfaces only present a problem when it's not obvious
which mode you're in. We have modes for other tools, and tools
themselves are modes of the user interface.

In any case, what I was suggesting was no change to the node tool except
that it allows you to scale the axes of elliptic segments, and an
additional pen tool for creating elliptic/straight paths alongside the
existing tool for creating cubic/straight paths. Quadratic segments
aren't compelling for me.

Dan

[1] I recall cubics can approximate elliptical segments to an accuracy
of greater than 99%.

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[Pajarico]

>From my point of view (an user) is hard to tell since I don't know
what these new curve types offer or what can I gain by using them. I
have basic knowledge of them but I don't know what's the advantage of
having more than one, care to explain?

I think FontLab has a way to edit different curve types. PostScript
fonts are cubic while TrueType are quadratic. Maybe the free Fontforge
has support for both too? last I checked it let you export fonts in
both formats. However, font editors are one of a kind since you are
editing one type of curve *or* the other, you can't mix both (maybe
I'm wrong and native file formats support this (FontLab has support
for Spiro curves too, how does it store them?). I need to know if this
will have a "one thing or the other" treatment --i.e.:if  the user
sets this exclusively for each document or not.

If all the types will be editable at the same time on the canvas
--like it's done now with bezier and spiro paths--, it might be worth
checking 3D and CAD apps like Maya, 3D Studio Max or Autocad, since
some of them support various types of curves (like bezier and nurbs,
but I'm not sure if the case is the same here).

Regards.

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[Alexandre Prokoudine]

On Thu, Jun 18, 2009 at 2:41 AM, Pajarico wrote:

> Maybe the free Fontforge has support for both too?

Yes, you set this in preferences

 last I checked it let you export fonts in
> both formats. However, font editors are one of a kind since you are
> editing one type of curve *or* the other, you can't mix both (maybe
> (FontLab has support for Spiro curves too, how does it store them?).

What? v6 is out already? :-D

Alexandre

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[Krzysztof Kosiński]

> SVG also allows horizontal and vertical segments too

They are no different than ordinary line segments beyond shortening
the representation a bit, so it doesn't make much sense to treat them
specially. On the other hand elliptical and quadratic beziers would
allow users to edit the paths differently: it's rather hard to create
a circular or elliptical shape with cubic beziers without resorting to
boolean operations on ellipses. I'm not instisting on supporting those
kinds of segments, but if we can come up with a good UI to edit them,
why not provide this?

Regards, Krzysztof Kosiński

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[Ratajski Stefan]

Hello,

I write a user manual on PDF inkscape 0.46. In this book are screenshots
of Inkscape. I would like to publish the book.
I'd like to have your permission.
Please, who is my contact?

Best Regards

Stefan Ratajski
ratajski@...





Maximilian Albert schrieb:

> Hallo Stefan,
>
>     seit Januar 2009 schreibe ich an einem Benutzerhandbuch für
>     Inkscape 0.46 als eBook. Voraussichtlich bin ich in 2 -3 Monaten
>     damit fertig.
>     Anfangs habe ich das Buch nur aus Spaß geschrieben. Nun denke ich
>     aber an einer Veröffentlichung.
>
>
> Cool, klingt gut.
>  
>
>     Da ich Screenshots des Programmes verwendet habe, wollte ich Euch
>     um eine offizielle Zustimmung bitten.
>
>
> Hmm, ich fürchte, da bin ich ehrlich gesagt der falsche
> Ansprechpartner (habe bisher keinen eigenen Screenshot zur Verfügung
> gestellt). Ich weiß auch offen gestanden gar nicht genau, unter
> welcher Lizenz die stehen - das sollte eigentlich auf der Webseite
> vermerkt sein, ist es aber nicht. Ich vermute aber so was wie
> "Creative Commons". Alexandre könnte das aber wissen, ansonsten würde
> ich vorsichtshalber doch nochmal auf der Mailingliste rumfragen (ich
> glaube, es wurde vor einiger Zeit schon einmal gefragt - vielleicht
> findes Du ja was im Archiv). Je nachdem unter welcher Lizenz Du das
> eBook veröffentlichen möchtest, hängt es dann davon ab, ob Du die
> Screenshots verwenden darfst oder nicht. Grundsätzlich werden aber die
> Künstler nichts dagegen haben, denke ich. Aber absichern würde ich
> mich auf jeden Fall, sonst kann es, wenn's doof läuft, passieren, daß
> Du hinterher ungewollt ein Menge Ärger am Hals hast.
>
> Viel Erfolg und viele Grüße,
> Max
>

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