On Mon, Jun 26, 2006 at 15:47 -0700, George Williams wrote:
> On Tue, 2006-06-20 at 07:37, Ralf Stubner wrote:
> > >> It seems to me that it would be more useful to create a little tooltip
> > >> type window when moving the control points with the mouse rather than
> > >> putting this into Point Info.
> > I think it would be good if this information were available when working
> > in the 'Point Info' dialog, too. I often change the parameters directly
> > there, since it is difficult to change the position of a control point
> > without changing the slope.
> OK, this patch will, I hope, provide curvature info. Both in the Point
> Info dlg, and as a popup info window when moving control points with the
Thanks a lot! I started to play with it, and it does indeed look useful.
It is to early for definite statements, though. I have found a few
points concerning usability, though:
* The curvatures are really small, even for something like an 'o'. This
isn't to surprising, since curvature is the inverse of the radius of
the approximating circle. Since this radius is typically of the order
of 1 em or 1000 units, curvature is typically of the order 1/1000.
Since I find it easier to compare, say, 3.4 with 2.3 than 0.0034 with
0.0023 I simply modified the curvature function to return 1000 times
the curvature. IMO the better solution would be to multiply curvature
with the number of units per em, which is equivalent to measuring the
radius of the approximating circle in em instead of font units. I
think this is more natural. I just don't know in which variable this
value is stored ...
* It can happen that the tool-tip hides the node which control point I am
currently changing. I don't know how difficult it is to change this.
Maybe it is better to wait a little bit with this.
* I could imagine that there are users who will find this tool-tip a bit
to technical. It might be useful to provide a possibility to disable
it. Preferences is probably to static for most users. Maybe something
like the 'View -> Fill'.
> > Anyway, I think for getting some experience with this feature, it would
> > be best if one could simply have the curvature before and after the
> > spline node displayed somewhere.
> And its difference, since that's what you are trying to minimize.
That's a very good idea.
> > Have you looked at Hobby splines used by Metafont and Metapost?
> > I think it would be really interesting to have something like this in
> > ff. I have no idea how a UI could look like, though. With these splines
> > you simply specify a series of points, maybe with slopes specified, and
> > the result are really good looking curves.
> Um, isn't the UI just the freehand tool?
I don't see how the freehand tool fits. It is closer to just placing a
series of curve points on the canvas. FF already uses some algorithm
to draw splines through them. Hobby splines would be a different
algorithm for that. However, the interesting part there starts when you
specify the tangents at some points.
> Ikarus files consist of a bunch of on curve points, and they
> deliberately do not specify what splines to use to join those points.
That does sound similar.
> There would have to be a conversion back to Beziers at some point
Hobby splines are Bezier curves AFAIK. It is just an algorithm to
choose the control points in such a way that a pleasing curve results.
At least that's what I have gathered so far.