W3C home > Mailing lists > Public > www-style@w3.org > January 2010

Re: Making pt a non-physical unit

From: Robert O'Callahan <robert@ocallahan.org>
Date: Tue, 12 Jan 2010 22:22:41 +1300
Message-ID: <11e306601001120122l5ec974d9u6ef851e7d2e1bb2c@mail.gmail.com>
To: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Cc: "Linss, Peter" <peter.linss@hp.com>, www-style W3C Group <www-style@w3.org>
On Tue, Jan 12, 2010 at 9:23 PM, Giuseppe Bilotta <
giuseppe.bilotta@gmail.com> wrote:

> The ratio between logical and true physical units would be influenced
> by factors such as monitor resolution, assumed viewing distance, zoom
> level, etc. Lacking information, these would be assumed to be at a 1:1
> ratio (at the default zoom level), using whatever reference is
> available from the (visual) media: screen pixel for monitor display,
> printer metrics for print media, etc.

That's OK as long as you're not upset when browsers don't generally use 1:1.
As I explained previously, for Firefox we want the browser to be consistent
with user and system settings, and unless the user has indicated otherwise,
we want 1px to be one screen pixel for performance and quality reasons.

 Additionally, CSS could introduce the proposed true physical units
> (truept, truein, truecm, etc) which ought to be rendered, to the best
> of the UA knowledge, as the actual given lengths measured _on the
> physical object_. (Thus, a poster-specific CSS could use true physical
> units and express lengths in feet, etc). An important point about
> these units is that they would NOT be influenced by zoom levels.

This is not what we want. Zooming should always work. If page has a "life
size" diagram, then it should be "life size" at the default zoom level, and
zooming in by 2x should make it 2x "life size".

The question at this point would be whether a 'truepx' should be
> introduced as well, and whether it should be equal to 1/96truein or
> rather the smallest representable physical unit on the device (single
> screen pixel, single printer dot, etc).

I don't think that is a meaningful or useful unit. What would you use it

I think your proposal is OK modulo the caveats above.

"He was pierced for our transgressions, he was crushed for our iniquities;
the punishment that brought us peace was upon him, and by his wounds we are
healed. We all, like sheep, have gone astray, each of us has turned to his
own way; and the LORD has laid on him the iniquity of us all." [Isaiah
Received on Tuesday, 12 January 2010 09:23:14 UTC

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