W3C home > Mailing lists > Public > www-svg@w3.org > January 2014

Re: The (new, enhanced) viewbox property

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Tue, 7 Jan 2014 14:08:57 -0800
Message-ID: <CAAWBYDDP=WDj1j027mu0Ct3aO-U0_w+TQQ7o00UEyuFew0JVOg@mail.gmail.com>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
Cc: www-svg <www-svg@w3.org>
On Tue, Jan 7, 2014 at 4:14 AM, Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de> wrote:
> Tab Atkins Jr.:
>>No, CSS applies, the language as it stands, not any obsolete snapshots
>>of the standard like 2.0.
>
> No, SVG 1.1 clearly references the CSS 2.0 recommendation.

Doesn't matter.  The living CSS is what is actually used.  That
reference is a spec bug, nothing more.

>>Once again, you misunderstand what was actually defined by CSS.  I'm
>>far past the point of hoping to educate you on this matter, but for
>>the edification of other readers, here's how CSS deals with units:
>
> Well, as an experimental physicist I know what an absolute unit of
> length is

So does everyone else in this thread and the relevant working groups.
That's not relevant here.

>>It turns out that authors commonly assume that there is a fixed ratio
>>between the px unit and all the physical units, especially pt.  This
>>sometimes results in page designs that work when a particular px:pt
>>ratio is used, but breaks (lines break unexpectedly, floats move
>>chaotically) when a different one is used.  This means that browsers,
>>in practice, have to fix a particular ratio of px:pt in order to
>>render the internet correctly.
>
> If this happens for projects using (X)HTML+CSS, typically those
> pages are already broken due to user-stylesheets with a required
> minimal font size. Often one has to switch off CSS interpretation for
> such projects at all to get some kind of interpretable presentation -
> in several cases however it turns out, that the content is in a similar
> way chaotic than the styling. This needs to be fixed by the authors,
> CSS cannot fix nonsense of authors.

Yes, minimum font sizes cause similar problems.  They're also opt-in,
controllable, and less common than monitors with a px:pt ratio other
than 4:3.

>>The most common ratio, and the one CSS mandates, is 4px = 3pt, due to
>>most monitors using 96 dpi for many years.
>
> I used many monitors in the past years, none of them had 96 decive pixels
> per inch. Most older monitors have about 120 device pixels per inch (CRT),
> for notebooks I have 72, 99, 120 in use.

The ratio that Windows reported was, for many years, 96.  I'm well
aware that there were other types of ratios.  96 was by far the most
common reported ratio, which is why the 4:3 ratio was assumed by
authors.

We didn't pull this out of nowhere.

> There seems to be a need for authors to indicate, whether size matters
> or not for presentation.

Regardless of this, the 4:3 ratio can still hold.  You're attacking
the ratio, which is nonsense; the absolute size of a px is
theoretically arbitrary.

*Like I said in my previous message*, implementations are allowed to
accurately size the physical units.  Browsers have good reasons for
not doing so by default, and for nearly all pages, the result is fine.

If you'd like to have a switch in your browser that lets you calibrate
the size of the absolute units, feel free to file a bug against your
browser.  It's completely allowed by the specs to do so.  Please stop
diverting every single thread about units with your misunderstanding
over this issue.

~TJ
Received on Tuesday, 7 January 2014 22:09:44 UTC

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