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Minutes, 22 December 2011 SVG WG telcon

From: Erik Dahlstrom <ed@opera.com>
Date: Thu, 22 Dec 2011 22:36:10 +0100
To: "public-svg-wg@w3.org" <public-svg-wg@w3.org>
Message-ID: <op.v6wuakb6geuyw5@mbp-2.local>


and as text below:


       [1] http://www.w3.org/

                                - DRAFT -

                    SVG Working Group Teleconference

22 Dec 2011



    See also: [3]IRC log

       [3] http://www.w3.org/2011/12/22-svg-irc


           +61.2.980.5.aaaa, heycam, [IPcaller], +, ed,
           cyril, Tav




      * [4]Topics
          1. [5]mesh gradients
          2. [6]SVG2 requirements
      * [7]Summary of Action Items

    <trackbot> Date: 22 December 2011

    <cyril> yes, don't tell me I woke up early for nothing :)

    <scribe> scribeNick: ed

mesh gradients

    <Tav> [8]http://tavmjong.free.fr/SVG/MESH/Mesh_Boundaries.html

       [8] http://tavmjong.free.fr/SVG/MESH/Mesh_Boundaries.html

    TB: i've been looking at cyril's comments on the problems with mesh
    ... as can be seen in the examples in the link above, there are
    discontinuity in the gradient
    ... scroll down, and you can see the same problem for linear
    gradients too
    ... look at where the red line breaks

    <cyril> mach banding effect I think

    TB: probably the brain is geared towards finding discontinuities

    CM: where there's a bend in the line, it looks brigther

    <cyril> [9]http://en.wikipedia.org/wiki/Mach_banding

       [9] http://en.wikipedia.org/wiki/Mach_banding

    CC: not sure it's this exactly, but it's related

    TB: with mesh gradients you have the control points along the sides,
    that not only control the shape but also the spread
    ... next figure shows the same discontinuities as for the linear
    gradients but with mesh gradients
    ... i've moved the control points in the figure with the purple
    curve, giving a smoother look
    ... if you change the controlpoints you change two things at once,
    both shape and color
    ... the mesh in this case is still a rectangle

    CC: would be nice to show the controlpoints in the example, for
    understanding it better

    TB: will add that
    ... now in "Understanding Coons Patches"
    ... shows controlpoints, and what you get
    ... if you move controlpoints further you get discontinuities
    ... you can never have a derivative of 0 at the edge of a patch

    CC: what if you put the controlpoint in horizontal?

    TB: can't do that
    ... they're in colorspace
    ... 1/3 of the way up and 1/3 of the way down
    ... it's not a controlpoint for the mesh, it's for the color

    CM: are you illustrating the rate of the change?

    TB: something like that yes

    CM: so the color moves quicker at the start of the curve

    TB: i've plotted what happens when you move the controlpoints

    CC: are you using the same controlpoints for the upper and lower
    parts of the curve

    TB: yes

    CC: you use linear interpolation since you have two colors, you'd
    have bilinear if you had one color in each corner

    TB: just illustrating that it's possible to reduce the effect
    ... once you move the controlpoint outside the mesh it overlaps
    ... if you introduce a tensor
    ... you could change the the way the colors inside the mesh are
    ... doesn't affect the edges
    ... i've looked at the cairo code and it exploits this to compute
    the gradient, divides the patch from top to bottom using the tensor
    points so that you have a series of bezier curves taht are no wider
    than a pixel
    ... and then it draws each bezier curve in turn

    CC: illustrator doesn't use coons patches
    ... probably tensor product patches with tensor derivatives
    ... with bicubic interpolation

    TB: what they show in illustration...
    ... is shown as one patch but is actually many patches
    ... the boundaries don't correspond to the object, but to the edges
    to the mesh
    ... some examples have rough shapes that can't be described by a
    simple bezier

    CM: clipping is another trick

    TB: when we discussed it previously there was a request to use the
    mesh as a clip or by itself

    CC: but then tehre would be a problem with the stroke
    ... not sure if we decided to do it as a paintserver or not

    TB: anyway, that's the state atm

    CM: does messing with the controlpoints help for eliminating the

    TB: a bit
    ... by adding extra patches it's possible to smooth it out

    CC: i've experimented with corel draw, looks like they do something
    very similar to illustrator

    CM: could the subdivision of patches be useful to define in the
    ... could we describe this simply, and would we want to enable that
    by an attribute for example?

    CC: i think they're approximating, not sure there's a single way to
    do this
    ... depends on quality etc

    TB: leaning towards letting the author handle it
    ... if you have a regular gradient you owuld not use meshes, or they
    would subdivide
    ... i'm going to read the paper cyril linked to again

    CC: let's discuss this at the F2F
    ... coons patches are fine and you can do good things with them, but
    there are limitations, and authoring tools solve them atm, but we
    may want to introduce something like that in the future

    TB: we might want to smooth out linear gradients too
    ... using catmull-rom curves

SVG2 requirements




      [11] http://mpeg.chiariglione.org/meetings/geneva11-1/geneva_press.htm

    CC: this is from MPEG
    ... one track for MPEG1, since patents are phasing out
    ... other option is AVC standard but with a baseline where patent
    holders agree to make it free
    ... that's not yet decided
    ... there are big interests, political and economical

    CM: what's your sense of these two possible ways forward?

    CC: first option is clear in terms of patent conflicts
    ... if there were other patents they would have been claimed before
    ... thing is it won't be good quality
    ... building on mpeg1 is unclear, due to patents
    ... other option H264 / AVC one, it would be compatible with most
    exisitng codecs
    ... but it's a big question for the stakeholders

    TB: what does google support in their browser?

    CC: on pc it's different from on android
    ... think they're talking about dropping 264 on pc, and android

    TB: what's the fallback?

    CC: webm
    ... but the licensing isn't clear either
    ... mpeg issued a call for patents covering webm, and got responses
    (3 digits)

    CM: the responses will be published yes?

    CC: i think so, next year maybe

    CM: in terms of requirements i don't think we should be reuqiring
    codecs at this point

    <cyril> [12]http://www.webm-ccl.org/

      [12] http://www.webm-ccl.org/

    CM: it's something that should be done for the whole web platform

    CC: apple and microsoft are missing from the webm licensing members

    <cyril> SVG WG supports the goal, including for the whole web
    platform, but it does not seem feasible at the moment

    RESOLUTION: SVG WG supports the goal, including for the whole web
    platform, but it does not seem feasible at the moment



    CM: next tooltip elements
    ... this has come up before
    ... i've never really been satisfied with the tooltips in tiny so
    ... not clear to me what's a good solution
    ... he wants a way to generate tooltips

    TB: doesn't browsers differ today with what's displayed as a
    tooltip, <title> or xlink:title

    CM: yes I think you're right TB
    ... html is a bit different because it has a title attribute
    ... i think our title element has a broader meaning than @title in
    ... people are used to what it does in html
    ... i think we should look into the issue for svg2
    ... agree with DOH that using metadata with role isn't the right way
    to do this

    CC: maybe a should req?



    <heycam> SVG 1.1 also says "Alternate presentations are possible,
    both visual and aural, which display the ‘desc’ and ‘title’ elements
    but do not display ‘path’ elements or other graphics elements. This
    is readily achieved by using a different (perhaps user) style

    CM: the document has both <title> and <desc> duplicating the content

    ED: don't think any of the browser display <desc> as a tooltip

    CM: think we can improve on the requirements for tooltips, to align
    with html implementation
    ... so that they're shown under the same circumstances
    ... we can investigate more when we look into the issue

    RESOLUTION: SVG2 will have stronger requirements for when to display



    CM: this was discussed in an FXTF meeting IIRC
    ... perhaps more generic, with images and fill

    ED: probably the proposal from zynga, with masks for mouse events

    CC: we could discuss this with alex at the F2F

    <scribe> ACTION: ED to summarize the discussions about hittesting
    with alpha from the FX list [recorded in

    <trackbot> Created ACTION-3190 - Summarize the discussions about
    hittesting with alpha from the FX list [on Erik Dahlström - due



    CM: doug is requesting an event for when the link changes
    ... html already has the hashchanged events

    CC: this should be part of the harmonization with html, right?

    CM: not sure if we said before if we decided on document level
    events and such
    ... think we should consider all the documentwide events
    ... in html, and make them apply to svg
    ... where it makes sense

    <cyril> "SVG 2 will have HTML document wide events (including
    hashchange) apply to SVG documents when they make sense"

    RESOLUTION: SVG 2 will consider adding HTML document wide events
    (including hashchange) in SVG documents where they make sense



    CM: DND in html5 is dragsources and dragtargets, and getting things
    from other applications
    ... not with moving elements around
    ... we should try to get the html5 dnd functionality
    ... not sure about the dnd for moving things in the document
    ... probably better to focus on improving the DOM apis for getting
    the mouse cursor in the variious cooridnate systems, to ease moving
    things around that way

    ED: aligning with html5 on this sounds good to me



    ED: and improving the DOM apis too

    <scribe> ACTION: CM to investigate how html5 drag&drop could be used
    in svg [recorded in

    <trackbot> Sorry, amibiguous username (more than one match) - CM

    <trackbot> Try using a different identifier, such as family name or
    username (eg. charles, cmccorma)

    <scribe> ACTION: heycam to investigate how html5 drag&drop could be
    used in svg [recorded in

    <trackbot> Created ACTION-3191 - Investigate how html5 drag&drop
    could be used in svg [on Cameron McCormack - due 2011-12-29].

    <scribe> ACTION: heycam to investigate what document wide events
    would make sense to apply to svg documents too [recorded in

    <trackbot> Created ACTION-3192 - Investigate what document wide
    events would make sense to apply to svg documents too [on Cameron
    McCormack - due 2011-12-29].

    RESOLUTION: SVG2 may require drag&drop functionality, and we'll
    investigate html5's functionality for that

    trackbot, end telcon

Summary of Action Items

    [NEW] ACTION: CM to investigate how html5 drag&drop could be used in
    svg [recorded in
    [NEW] ACTION: ED to summarize the discussions about hittesting with
    alpha from the FX list [recorded in
    [NEW] ACTION: heycam to investigate how html5 drag&drop could be
    used in svg [recorded in
    [NEW] ACTION: heycam to investigate what document wide events would
    make sense to apply to svg documents too [recorded in

    [End of minutes]

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Found ScribeNick: ed
Inferring Scribes: ed
Default Present: +61.2.980.5.aaaa, heycam, [IPcaller], +
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Present: +61.2.980.5.aaaa heycam [IPcaller] + ed cyril T
Agenda: [30]http://lists.w3.org/Archives/Public/public-svg-wg/2011OctDe
Found Date: 22 Dec 2011
Guessing minutes URL: [31]http://www.w3.org/2011/12/22-svg-minutes.html
People with action items: cm ed heycam

      [31] http://www.w3.org/2011/12/22-svg-minutes.html

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Erik Dahlstrom, Core Technology Developer, Opera Software
Co-Chair, W3C SVG Working Group
Personal blog: http://my.opera.com/macdev_ed
Received on Thursday, 22 December 2011 21:36:29 UTC

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