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Re: Minutes, 12 August 2009 SVG telcon

From: Anthony Grasso <anthony.grasso@cisra.canon.com.au>
Date: Thu, 13 Aug 2009 14:09:30 +1000
Message-ID: <4A8391FA.6030303@cisra.canon.com.au>
To: W3C SVG Comments List <www-svg@w3.org>
Hi WG,

Regarding ISSUE-2291 that was raised at yesterdays telcon.

It might be worth keeping in mind that that OpenVG specification [1] in Section 
6.4 specifies that the pixel (x, y) has its center at the point (x + 0.5, y + 
0.5) - i.e. 0,0 is the bottom left of the bottom left.

Given the choice of the different variations out there, I'd prefer to go with 
Alex's assumption and say that 0,0 should be the top left of the top left.

Regards,

Anthony

[1] http://www.khronos.org/registry/vg/specs/openvg-1.1.pdf

Chris Lilley wrote:
> 
> Pinned clip module
> 
>    [16]http://dev.w3.org/SVG/modules/pinnedclip/publish/
> 
>      [16] http://dev.w3.org/SVG/modules/pinnedclip/publish/
> 
>    CM: Notice Doug checked it into public repository
> 
>    DS: Alex Danilo sent it to me, so checked it in
>    ... in case we need it for SVG2
> 
>    CM: Does he plan to work on it?
> 
>    DS: Will check
>    ... One of the ogg theora people raised the issue offlist, asking if
>    SVG talks about pixel orientation, where the pixel starts (top
>    left,centre) and pinned clip covers that
>    ... asked him to comment on public list
> 
>    CL: We really need to decide as different rendering libraries are
>    off by 0.5 pixel because of this
>    ... Prefer to look at this and decide the majority solution
> 
>    ED: Opera does centre
> 
>    DS: Should be a SHOULD, but we should pick one
> 
>    CL;: Would like to see a test, then picj what most do
> 
>    DS: Alex said that top left is assumed, so 0,0 is the top left of
>    the top left (quotes from an email)
> 
>    CL: Please get permission to forward that email
> 
>    DS: And the tests he is talking about
> 
>    CL: Would changing be an issue for Opera, is there content that
>    relies on centre pixel positioning?
> 
>    <ed>
>    data:image/svg+xml;charset=utf-8;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3
>    dy53My5vcmcvMjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9yZy8x
>    OTk5L3hsaW5rIj4NCgk8bGluZSB4MT0iMTAiIHkxPSIxMCIgeDI9IjEwMCIgeTI9IjEw
>    IiBzdHJva2U9ImJsYWNrIi8%2BDQoJPGxpbmUgeDE9IjEwIiB5MT0iMjAuNSIgeDI9Ij
>    EwMCIgeTI9IjIwLjUiIHN0cm9rZT0iYmxhY2siLz4NCjwvc3ZnPg%3D%3D
> 
>    ED: Don't think so. Made a test ....
> 
>    <ed> <line x1="10" y1="10" x2="100" y2="10" stroke="black"/>
> 
>    <ed> <line x1="10" y1="20.5" x2="100" y2="20.5" stroke="black"/>
> 
>    Safari, Opera and Firefox seem to use pixel centres
> 
>    JW: One will give sharp lines, the other gives sharp edges on
>    rectangles
> 
>    ED: Wonder if shape-rendering affects it
> 
>    CM: Shape-rendering set to geometric-precision makes one blurry
> 
>    (We find opoosite results on Mac and on Windows)
> 
>    (some disagrement vs platform, browser version, lcd type ...)
> 
>    macbook vs macbook pro seems tobe different
> 
>    ED: Opera versions should be the same on all platforms modulo
>    floating point libraries
> 
>    ISSUE: Whether a given integer coordinate is pixel centre or pixel
>    top-left needs to be determined
> 
>    <trackbot> Created ISSUE-2291 - Whether a given integer coordinate
>    is pixel centre or pixel top-left needs to be determined ; please
>    complete additional details at
>    [17]http://www.w3.org/Graphics/SVG/WG/track/issues/2291/edit .
> 
>      [17] http://www.w3.org/Graphics/SVG/WG/track/issues/2291/edit
> 
Received on Thursday, 13 August 2009 04:10:13 GMT

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