W3C home > Mailing lists > Public > www-svg@w3.org > April 2011

RE: oddities with dasharray, markers and use

From: David Dailey <ddailey@zoominternet.net>
Date: Thu, 7 Apr 2011 16:38:03 -0400
To: "'Tony Schreiner'" <tonyschr@microsoft.com>, <www-svg@w3.org>
Cc: <yan.li@sru.edu>
Message-ID: <000c01cbf563$b16450a0$142cf1e0$@net>
Thanks for your response Tony.


On #2 - I looked at some of the discussion here, but will confess to have
not looked in great detail. It seems though that if arrow-heads are to
inherit dash array, then the author must have some way to override this. The
behavior is not what most folks would want. Is there another way? Maybe I
need to read deeper in the links you provided.


On #3 - would there be any way to have <use onclick="f(evt.target)"> not
point back to the original object? It might be nice to have uses and their
predecessors behave more like cloneNode("true"), perhaps with an attribute
that allows the author to specify whether the use is instantiated in DOM or
merely in a shadow tree. For <replicate> [1], which is sort of like <use>,
that is certainly the intention since often times the author will want only
the visual aftermath of the rendering, while in other use cases (like gaming
and 3D applications) each cloned object should have its own DOM instance. To
make <use> more forward compatible, this would make sense.


On #4 - you're right. I don't understand my question either, now that I
re-examine it.  My thinking was backward.


On #5 - if we had the ability to position markers fractionally as through
.getTotalLength(), but with markup, then browsers that are not yet
supporting <glyph> could still at least handle the use case of custom
cartographic boundary decorations of a sort that are richer than the Morse
code-like decorations afforded by dash-array.




[1] http://srufaculty.sru.edu/david.dailey/svg/SVGOpen2010/replicate.htm

From: www-svg-request@w3.org [mailto:www-svg-request@w3.org] On Behalf Of
Tony Schreiner
Sent: Wednesday, April 06, 2011 7:51 PM
To: David Dailey; www-svg@w3.org
Cc: yan.li@sru.edu
Subject: RE: oddities with dasharray, markers and use


Hi David, a few comments below:


#1 unfortunately looks like a bug in IE9 and I've forwarded for
investigation. This is specific to marker and has a simple (but odd)
workaround that should work for most scenarios: create a dummy marker and
attach it  to an unused marker attribute on the original path, e.g.:

    <marker id="Blank">

      <rect />


    <path id="P" d="M 100 50 C 100 50 150 250 200 100 250 -50 300 250 350
170 400 90 450 50 600 160" fill="none" marker-start="url(#Blank)" />

This will make the real marker-mid and marker-end from the <use> show up


#2 - There have been discussions about this from time to time. See:

- http://lists.w3.org/Archives/Public/www-svg/2010Feb/0023.html 

- http://lists.w3.org/Archives/Public/www-svg/2010Jul/0066.html

- http://www.w3.org/2010/07/20-svg-minutes.html 


After consideration and discussion with the working group IE9 slightly
deviates from the spec on the grounds that it's the more correct,
future-looking behavior. The <use> style of inheritance enables the key
scenario of being able to apply a single marker (e.g. arrowhead) to lines
with differing styles, and have it match the line. It is a minor
interoperability issue, but can be solved by explicitly setting the
properties on the primitives in the marker. I can't speak for Chrome or the


#4 - I don't understand the question. The two <use> elements with transforms
are referencing the T1 element, which does not have a stroke-dasharray.


- Tony


From: www-svg-request@w3.org [mailto:www-svg-request@w3.org] On Behalf Of
David Dailey
Sent: Sunday, April 03, 2011 2:04 PM
To: www-svg@w3.org
Cc: yan.li@sru.edu
Subject: oddities with dasharray, markers and use


Hi folks,


(I'm not sure what about this is browser bugs and what is spec bugs)


Take a look at the examples at
http://granite.sru.edu/~ddailey/svg/tracks.svg .


1.       In IE9 and ASV, the markers cannot be applied to a <use> even
though stroke-dasharray can.

2.       In Chrome (and ASV and IE9 when no use is involved), the markers
inherit the dash array of the stroke. Not elsewhere though.

3.       In Firefox (but nowhere else), if you click on the brown lines of
the dasharray or on the silver line underneath, (just the top uses and not
the second reuse), the event bubbles through to the defined path.  (this
idiosyncracy of <use> in the larger case, and whether or not the event finds
the original is rather startling to many authors, who expect the <use> to
behave more as if it is a clone when it comes to event handling - perhaps
this relates to a recent call for input concerning <use>

4.       The transform applied to the two <use>s of T1 in the lower example,
interestingly, does not translate the dasharray. This might come as a bit of
a shock to some.

5.       It would be awfully nice for cartographic purposes to be able to
apply markers at regular intervals along a path, rather than just at the
vertices (as per SVG 1.1, at least). Sure, one can do this with script, but
then the slope of the curve has to be calculated and so forth. It would
allow for a much broader class of path decorations appropriate to such
things as trails, rails, highways, borders, lake boundaries etc.


My guesses above:

1.       Is a bug in IE and ASV

2.       Is a bug in Chrome, ASV and IE

3.       Is a bug in Firefox (though I think I prefer it to how Opera,
WebKit, IE and ASV handle it)

4.       Is how the spec is written, but perhaps shouldn't be

5.       Is how the spec is written, but perhaps shouldn't be.

I'll be interested to hear others' opinions.








Received on Thursday, 7 April 2011 20:38:36 UTC

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