- From: Tavmjong Bah <tav.w3c@gmail.com>
- Date: Sun, 26 May 2013 22:19:49 +0200
- To: Paul LeBeau <paul.lebeau@gmail.com>
- Cc: www-svg@w3.org
Added an agenda request for this. Inkscape almost matches Batik (two markers are different) but this isn't too surprising as we have traditionally used Batik as the authoritative guide. Inkscape does put markers on a rect... but with start/end markers on one corner. Tav On Sun, 2013-05-26 at 22:04 +1200, Paul LeBeau wrote: > I've put up a document showing the current problems with orient=auto > markers here: > > > http://paullebeau.com/svg2/markers/ > > > > At the bottom of that page is a copy of my proposed clarifications to > the SVG 2 spec. It is a slightly expanded version of what I had in my > first email. > > > Paul > > > > > > > On 26 May 2013 15:57, Paul LeBeau <paul.lebeau@gmail.com> wrote: > Sure. I'll put together something to show what I mean. > > > P > > > > > On 26 May 2013 10:03, Dirk Schulze <dschulze@adobe.com> wrote: > Hi Paul, > > You said that the implementations are very quirky and > inconsistent. It would be extremely helpful if you > have tests that you can share with the community. > Quite often there edge cases not respected by > implementations and specifications because of a lack > of tests. Do you have some test cases? > > I did not have the time to review your analysis but > will do it before the next F2F meeting. > > Greetings, > Dirk > > On May 25, 2013, at 10:25 AM, Paul LeBeau > <paul.lebeau@gmail.com> wrote: > > > Hi all > > > > When I was implementing my SVG renderer, the Marker > section was one of the head-scratchiest parts of the > spec to try and understand and get right. It did not > help that pretty much all SVG renderers have bugs (or > "quirks") in their marker handling so there wasn't any > consensus to go on. > > > > I notice the SVG 2 spec is a bit better, but I think > the section on "auto" oriented markers is still a bit > confusing. > > > > 'auto' > > A value of 'auto' indicates that the marker is > oriented such that its positive x-axis is pointing in > the direction of the path at the point it is placed. > > > > If the marker is a segment marker, then the > direction the marker is oriented is, if considering > the incoming and outgoing directions as unit vectors, > in the direction of the sum of these two vectors. If > this sum is zero, then the marker is oriented in the > incoming direction. > > > > Is this a typo? Seems like this should be referring > to a vertex marker. > > > > If the marker is on the first or last vertex of a > closed subpath, [..snip..] > > > > I think it is not obvious in all cases what the > "first" and "last" vertex is. If the last point in > the subpath does not coincide with the first point, we > are told to draw a line to the start point. In this > case, which point is the "last" point? Also should we > be drawing a start marker, an end marker, or both? > > > > My feeling that in a closed subpath, there is > conceptually no real start or end point. All vertexes > should be considered mid points and only midpoint > markers should be rendered. So my proposed > replacement for this section would be as follows: > > ------------------------------------------ > > 'auto' > > A value of 'auto' indicates that the marker is > oriented such that its positive x-axis is pointing in > the direction of the path at the point it is placed. > > > > If the marker is a vertex marker, then the direction > the marker is oriented is, if considering the incoming > and outgoing directions as unit vectors, in the > direction of the sum of these two vectors. If this sum > is zero, then the marker is oriented in the incoming > direction. > > > > If there are two or more consecutive points in a > path that coincide exactly (both their x and y values > are the same) then all the consecutive coinciding > points should be treated as if they were a single > vertex. > > > > If the marker is on the first vertex of a closed > subpath, then the outgoing direction is taken from the > first path segment and the incoming direction is taken > from: > > • the last path segment of the subpath, if the > last point coincides with the first point, or > > • the line drawn from the last point to the > start point, if they do not coincide. > > For closed subpaths, the marker definition to be > rendered for all vertexes is the marker specified by > marker-mid. No start or end markers should be applied. > > ------------------------------------------ > > > > That last paragraph might be a bit controversial, > but for closed subpaths I think it makes sense. As I > said, from my testing, renderers rarely agree on how > markers are positioned at the start/end of closed > subpaths, so I don't think making this change would > affect too many people. > > > > I also have a suggestion for an enhancement: > > ------------------------------------------ > > 'auto-start' > > A value of 'auto-start' behaves exactly the same as > 'auto' except for the treatment of the start marker. > If a subpath is not closed, then the start marker is > positioned so that it points in the exact opposite > direction (inverse vector) to the first path segment. > > ------------------------------------------ > > > > The idea is that would allow for the easy creation > of double-ended arrows, for example, without having to > define two markers. > > > > This is my first contribution to this list, so if I > am an idiot, go easy on me! :) > > > > Paul > > > > > > > -- > Phone: +64 3 9423700 / Mobile: +64 21 1666127 > Skype: paul.lebeau / XMPP: paul.lebeau@gmail.com > Twitter: @paullebeau > > > > > -- > Phone: +64 3 9423700 / Mobile: +64 21 1666127 > Skype: paul.lebeau / XMPP: paul.lebeau@gmail.com > Twitter: @paullebeau
Received on Sunday, 26 May 2013 20:20:20 UTC