W3C home > Mailing lists > Public > www-svg@w3.org > August 2001

RE: [Moderator Action] marker-mid and Bezier paths

From: Ian Tindale <ian_tindale@yahoo.co.uk>
Date: Fri, 24 Aug 2001 08:09:11 +0100
To: <www-svg@w3.org>
Message-ID: <NFBBJAKBAMNBCEAHLICEIEDGCIAA.ian_tindale@yahoo.co.uk>
> ----- Forwarded message from Mark Nahabedian <naha@ai.mit.edu> -----
> X-Envelope-From: www-svg-request@tux.w3.org  Thu Aug 23 10:24:35 2001
> Old-Date: Thu, 23 Aug 2001 10:24:25 -0400 (EDT)
> From: Mark Nahabedian <naha@ai.mit.edu>
> To: www-svg@w3.org
> Cc: naha@ai.mit.edu
> X-Diagnostic: Not on the accept list
> Subject: [Moderator Action] marker-mid and Bezier paths
> X-Diagnostic: Mail coming from a daemon, ignored
> X-Envelope-To: www-svg
> X-UIDL: 34b38dacf9e91d1c53e562badc9bfcd3
<snipped stuff>
> It seems to me that restricting markers to be rendered only at path
> vertices is unreasonable.  One often wants an arrow (or whatever) in
> the middle of a graph arc rather than at either end.  It's
> unreasonable to expect a midpoint to be synthesized for this purpose
> since doing so would require one to predict all of the points along
> the path and find the middle one.  This effort is typically beyond the
> scope or ability of the software generating the SVG (typically in an
> XSLT transformation).
> ----- End forwarded message -----

This is an interesting point. How about another way of doing 'markers' - a
way which although might violate existing mechanisms, would be useful:

1] Specify the orientation of a marker, in perhaps two modes - relative to
an outer container, or relative to the current direction of a line (with
programmatic offsets possible).

2] Specify the offset from a point along a line (typically the start or end)
such that a zero offset means that the marker is where we'd expect it, at
the end or start of a line, but a positive offset 'pushes it along the line'
in effect (or use a negative offset to 'push it back', if we placed it at
the end initially). Then you could specify an absolute value or relative
percentage along the line, at which point the marker would appear.

If there were a container structure such as a 'markerset' which could
accommodate intervals and equidistance or some other non-linear distribution
functions, we could specify that a certain amount of markers be generated
automatically, along a line, according to the line's length, without having
to have prior knowledge of how many markers will be needed. Plus, this could
be made non-scaleable, in that if reduced, the distribution interval stays
the same, or something.

Hence, we could pile in as many markers as we like, such that we can have
curvy lines that appear to have those little triangles distributed along
them, like those weather charts used to have years ago, that the forecaster
used to point at and explain what a 'front' is every time.

Maybe for SVG two and a half?
Cheers. Ian Tindale.
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Received on Friday, 24 August 2001 03:09:16 UTC

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