Hello Keith,
KP> The linear resolution is only interesting if you want to know
> the linear dimension of an object on the screen. That ignores
> the environment the display is located in.
My understanding is that 72pt is one inch, whether on screen, on
paper or photographically reproduced on the side of a mug.
KP> Most of the time when we talk about 'point sizes', we refer to a
> media which is held at arms length (for those whos arms are
> still long enough).
I think the key word there is "we" - you're the first person I've met
who referred to 'point sizes' in that way.
KP> Objects further from the eye need larger type, objects closer
> need smaller type...
Obviously!! - but that 'larger type', by definition can't be the same
hight in points.
KP> ...the eye isn't interested in the linear dimension of an
> object, but only in the apparent angular size. When talking
> about presenting usable text to the user, we really need to know
> this angular dimension, and that takes the third parameter --
> the distance from the object to the viewer.
Interesting and valid, but not relevent to what I'm discussing.
KP> His hypothesis is that people are most comfortable when the
> computer display fills the visual field that the fovea can
> comfortably reach without head motion.
When it comes to presenting information on screen, I think the
Web browsers are on to something by letting the user increase or
decrease the type to suit their needs. Of course: then you've
got all the dumbass web 'designers' who manually set the type
size to something illegible. >:-(
KP> Given the angular size of each pixel, it's now easy to compute
> a scale factor for the screen. Linus proposed that any 1024x768
> monitor be considered "75dpi"; take that scale factor and do
> some extrapolation...
That may have been taken out of context, I don't know enough about
Linus' work to know what he had in mind. What I would much prefer is
for a way to tell X what the actual resolution of the display device
is, and have the font engine scale fonts appropriately.
Let's take two examples:
1. Archie is using an older laptop with a 10" x 7.5" LCD
(that's a 12.5" visible diagonal), fixed at an 800 x
600 pixel mode. That's 80 DPI.
2. Betty is using a newer CRT monitor with a 12" x 9"
picture (16" visible diagonal) and she runs it in a 1,152 x 864
pixel mode that she finds comfortable. That's 96 DPI.
3. Some software wants to display a heading that's 36pt (0.5") high.
Something (presumably a font engine of some sort) knows that on
on Archie's screen, that text would have to be 40 pixels high,
on Betty's it would be 48 pixels high. The result would be the
same: 36pt text, 0.5" high.
4. If the software is well written, Betty and Archie might both
have the option of making the heading smaller or larger to
suit their taste.
I have no idea what Linus is working on, but the above seems like an
obvious solution to the problem of text on displays of differing
resolution. If scaleable fonts are already available on X, it
shouldn't take a rocket scientist to build a font scaling routine
that displayed text at the correct size. Something similar could be
done with bitmapped fonts, but it would require some more work.
KP> Note that in 1990, most X users selected 75dpi as their
> "default" font size, but in 2000, most X users selected 100dpi
> -- in the same period, the "usual" monitor resolution increased
> from 1024x768 to 1280x1024 (or higher).
There's the giveaway: 1024x768 and 1280x1024 *ARE NOT RESOLUTIONS!*
they are *SCREEN MODES* 75 DPI is a resolution, 100 DPI is a
resolution.
Let's say in 1990 that I was fortunate enough to run a nice, high
resolution monochrome monitor with a 12.8" x 9.6" picture (that's 16"
visible). At 75 DPI I could drive it at 960 x 720 pixels, and load
the appropriate 75 DPI bitmapped fonts.
I type some 24 pt text, and it appears on screen in a bitmapped font
that's 25 pixels high. 24 pt is one third of one inch high. At 75
DPI, 25 pixels is also one third of one inch high. I'm happy.
Today, a monitor of the same size could be driven at a 1280 x 960
pixel mode. At 100 DPI With the appropriate bitmapped font, 18 pt
text would be rendered in a 25 pixel high font: one quarter of an
inch high.
If it were printed on a 300 DPI laser printer, I imagine it
would need a 75 dot high font. My point is this: however nice it
is that display resolutions are improving, it's no excuse for fonts
being rendered at the wrong size!
It's 03:19 here now. I'll look at the rest of your posting tomorrow
when I have time.
- Andy Ball.
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