[thelist] A pixel is not a pixel

[Arlen.P.Walker at jci.com]

A couple of recent threads contained notes that pixels were the only way to
achieve cross-platform consistency. Anyone who has seriously wedded
themselves to this idea needs to have a look at Opera 5 for the Mac, which
in fact renders pixel text on a Mac considerably smaller than pixel text on
a Windows machine. Opera doesn't appear to consider this a bug, and in
reading the CSS spec, they appear to be justified in that assertion, as the
CSS spec asserts that the user agent (AKA browser) should in fact *not*
consider a pixel as a screen pixel, but rather as a hypothetical unit
approximately equal to 1/90th of an inch.

Which means that if the user agent is not given the video density of the
monitor attached, it will assume the platform standard (72 pixels per inch
for MacOS) and resize the value accordingly. (BTW, for the more technically
inclined: Since almost the beginning of time, MacOS internally has
contained fields purporting to be the horizontal and vertical dpi values of
the attached screen. I think some video driver writers even use them. But
Apple doesn't; Quickdraw, and therefore MacOS, always assumes 72. No idea
if this has changed under OS X, as I haven't had the time to take it apart,
yet.)

Pixels aren't your saviour. Get used to the idea that your wonderful
pixel-perfect beautifully-colored layout will *only* be that way on your
own screen, and start designing by rules, rather than pixels.

If anyone's got an "in" with the W3C, here's what's needed:
1) A way to read the rendering assumptions of the browser (96dpi, 72dpi,
whatever)
2) A "minimum-font-size" attribute, which functions as a limit beneath
which the user agent should ignore font sizing declarations
3) A way of reading the current rendering size of an object specified in
relative measurements. (200% of what? How big's an em? That sort of thing.

These should all be part of the standard, so that if/when a browser decides
to support it we can use them to help our pages understand the conditions
they're about to be subjected to.

(If I seem to be ranting there at the end, it's because I just ran into
*another* site designed by someone who knows better than *I* do what size I
want my browser window set at. My apologies if I carried the rancor along
with me. Maybe I should code up an extra for the Mozilla project; a
preference button that replaces that particular piece of, um, javascript
code with a quick redirect to the top of the history stack.)

Have fun,
Arlen
Chief Managing Director In Charge, Department of Redundancy Department
DNRC 224

Arlen.P.Walker at JCI.Com
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