Re: UI ideas for quadratic and elliptic curves?

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

------------------------------------------------------------------------------
Crystal Reports - New Free Runtime and 30 Day Trial
Check out the new simplified licensing option that enables unlimited
royalty-free distribution of the report engine for externally facing
server and web deployment.
http://p.sf.net/sfu/businessobjects
_______________________________________________
Inkscape-devel mailing list
Inkscape-devel@...
https://lists.sourceforge.net/lists/listinfo/inkscape-devel