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

Re: Making pt a non-physical unit

From: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Date: Sat, 16 Jan 2010 10:02:22 +0100
Message-ID: <cb7bb73a1001160102s3000b9c6s9d6c44fe261ee025@mail.gmail.com>
To: "Tab Atkins Jr." <jackalmage@gmail.com>
Cc: Brad Kemper <brad.kemper@gmail.com>, "robert@ocallahan.org" <robert@ocallahan.org>, www-style <www-style@w3.org>
On Sat, Jan 16, 2010 at 7:33 AM, Tab Atkins Jr. <jackalmage@gmail.com> wrote:
>> For screens, I suspect most (or at least a huge portion of) Web authors would expect 1px to be 1 device pixel. And with this, many may go into all their style sheets and HTML files, and wherever something is measured in pixels, they'd add the same measurement as true-px. And not be too happy about it. Because despite what we decree from  our ivory towers, they expect a pixel to be a pixel and not to be told that the pixel they authored wasn't REALLY the pixel they wanted, because we know best what they REALLY meant (I'm not saying I feel that way, but rather that I anticipate this sort of reaction). And because they really want their 1024px-wide layout to fit on a 1024 pixel-wide monitor, even if it has 140 dpi (138 is half way to (96 x 2), so anything in that range would be rounded to two device pixels per px, right?).
> If you're on a 140dpi screen, and have a mere 1024px resolution,
> you're looking at a pretty small screen.  You, the user, would
> probably appreciate mapping a CSS pixel to multiple device pixels.
> Though, at 140dpi the jury's still out.  I suspect we'll stay with a
> 1-1 mapping until a decent bit past the halfway point, just because of
> inertia.
> Do you think this is somehow maintainable?  What about when screens
> are 300 dpi?  1000dpi?  Do you still expect 1 CSS px to be one device
> pixel?  I expect that would render most current webpages unreadable.
> We all know that transitioning from a 1-1 mapping to a 1-2 mapping
> will be painful.  It's the largest transition of all; how could it not
> be?  That doesn't mean it's not necessary, or the correct course of
> action.

Precisely. Rather than making a difference of print vs screen
rendering, we should consider low vs high resolution, where 'high' is
somewhere above the 192dpi threshold, optionally corrected as
indicated below.

If print vs screen is to be considered, I'd rather see it influence
whether viewing distance should be considered or not, where print
sizing would be unaffected by (assumed) viewing distance, in contrast
with screens and projections, where an estimate of the viewing
distance can be done from the device size (an information typically
available from the o/s). For example, an iPhone with a 160dpi (=5/3
the CSS dpi) is usually held a 3/4 the distance of a typical monitor,
thus leading to a 1.25 (rounded to 1) correspondence between CSS and
actual dpi.

Giuseppe "Oblomov" Bilotta
Received on Saturday, 16 January 2010 09:03:15 UTC

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