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Re: [SVGMobile12] SVGT12-207: 7.3 The initial coordinate system lacks conformance criteria

From: Jon Ferraiolo <jonf@adobe.com>
Date: Tue, 9 May 2006 16:11:15 -0700
Message-ID: <6ECA24BE410D994496A2AE995367C5C8AED906@namail3.corp.adobe.com>
To: "Ian Hickson" <ian@hixie.ch>
Cc: <www-svg@w3.org>

This is the official response from the SVG WG to your Last Call comment
at the following URL:

We agree with your comment and have made editorial changes to better
indicate what user agents must do. Here is the new text:

7.3 The initial coordinate system

For the 'svg' element, the SVG user agent must establish an initial
viewport coordinate system and an initial user coordinate system such
that the two coordinates systems are identical. The origin of both
coordinate systems must be at the origin of the viewport, and one unit
in the initial coordinate system must equal one "pixel" (i.e., a px unit
as defined in [ CSS2 lengths]) in the viewport. In most cases, such as
stand-alone SVG documents or SVG document fragments embedded (by
reference or inline) within XML parent documents where the parent's
layout is determined by CSS [CSS2] or XSL [XSL], the SVG user agent must
establish the initial viewport  coordinate system (and therefore the
initial user coordinate system) such that its origin is at the top/left
of the viewport, with the positive x-axis pointing towards the right,
the positive y-axis pointing down, and text rendered with an "upright"
orientation, which means glyphs are oriented such that Roman characters
and full-size ideographic characters for Asian scripts have the top edge
of the corresponding glyphs oriented upwards and the right edge of the
corresponding glyphs oriented to the right.

If the SVG implementation is part of a user agent which supports styling
XML documents using CSS2-compatible px units, then the SVG user agent
should get its initial value for the size of a px unit in real world
units to match the value used for other XML styling operations;
otherwise, if the user agent can determine the size of a px unit from
its environment, it should use that value; otherwise, it should choose
an appropriate size for one px unit. In all cases, the size of a px must
be in conformance with the rules described in [ CSS2 lengths].

Example 07_02 below shows that the initial coordinate system has the
origin at the top/left with the x-axis pointing to the right and the
y-axis pointing down. The initial user coordinate system has one user
unit equal to the parent (implicit or explicit) user agent's "pixel".

Thank you very much for your thorough review and excellent feedback.
Please tell us within two weeks if you are not satisfied with this

Jon Ferraiolo


From: Ian Hickson <ian@hixie.ch> 
Date: Wed, 28 Dec 2005 15:36:54 +0000 (UTC)
To: www-svg@w3.org 
Message-ID: <Pine.LNX.4.62.0512281534430.7669@dhalsim.dreamhost.com> 

Section 7.3 The initial coordinate system's first pargraph describes a 
model, but does not require implementations to use that model.

Please change section 7.3 such that the paragraph makes clear testable 
requirements on implementations, so that it is possible to determine
user agents must do, or, alternatively, link the assertions in this 
section to the sections that actually contain the relevant conformance 
criteria that result in these assertions being true statements.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
Received on Tuesday, 9 May 2006 23:11:42 UTC

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