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Re: Zooming

From: Jon Ferraiolo <jferraio@Adobe.COM>
Date: Thu, 08 Jun 2000 15:23:27 -0700
Message-Id: <200006082220.PAA28685@mail-345.corp.Adobe.COM>
To: "Duncanson, Ian (Ex AS01)" <IDuncans@honeywell.com.au>
Cc: "'www-svg@w3.org'" <www-svg@w3.org>
The March 3 spec says that when CSS unit identifiers are used (e.g., 3cm),
these values represent lengths in the coordinate system of nearest
viewport, and that these values should stay constant with zooming
operations. The intent of this feature is to allow such things as boxes
that have a stroke-width of 1 pixel no matter what the zoom level. What we
have learned from implementation experience is that the way this feature is
specified works pretty well as long as you only use it for length
attributes (e.g., stroke-width) but causes all sorts of bizarre results if
used for coordinate values (e.g., x and y attributes) because coordinate
values are actually just lengths from the origin of the user coordinate
system. Thus, if you want to specify x and y attributes using CSS unit
identifiers, to avoid bizarre results when zooming, you probably want to
disable zooming on the document.

There is likely to be some changes in the next draft spec to take into
account implementation experience.

Jon Ferraiolo
SVG Editor
Adobe Systems Incorporated

At 09:56 AM 10/14/99 +1000, Duncanson, Ian (Ex AS01) wrote:
>I was just wondering how zooming functionality would be implemented for both
>authoring tools and viewers of SVG files. The only mention I see in the Spec
>is the allowZoomAndPan option.
>Zooming could be achieved by modification of the coordinate system of the
>top-level object, but this doen't implicitly affect other properties which
>zoom, namely font-sizes, line widths etc. If you do tie your font-size (for
>example) to the coordinate system, then your font-size will zoom when you
>resize the element.
>The other requirement that zooming imposes is use of floating point numbers
>rather than integers for CSS and other positioning and sizing attributes.
>Use of integers implies a loss of resolution if you zoom out then back in.
>The other question that comes up in relation to zooming is what happens to
Received on Thursday, 8 June 2000 18:20:51 UTC

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