关于分辨率的问题，补充一篇文章

zhangmms

Solving the Linux DPI Puzzle
by Billy Biggs , Sun Dec 5 2004
Linux
applications use the DPI reported by the X server when converting from
font point size to pixels. "Sans 10" will be a smaller number of pixels
if your X server is configured at 75 DPI than if it is at 100 DPI.
How the XFree86 and Xorg servers calculate DPI
The DPI of the X server is determined in the following manner:
   1. The -dpi command line option has highest priority.
   2. If this is not used, the DisplaySize setting in the X config file is used to derive the DPI, given the screen resolution.
   3. If no DisplaySize is given, the monitor size values from DDC are used to derive the DPI, given the screen resolution.
   4. If DDC does not specify a size, 75 DPI is used by default.
You can check what DPI your X server is set to by running xdpyinfo | grep resolution in a terminal window.
How X applications choose DPI
For
traditional fonts on X, the DPI was chosen as either 75 or 100
depending on which set of fonts was listed first in your X font path.
Xft/fontconfig
added a new DPI parameter as an X resource (Xft.dpi). If set, this
value is used by both Qt 3 and GTK+ 2 when rendering. If it is not set,
Xft, GTK+-2 and Qt 3 will all fall back to using the DPI reported by
the X display.
GNOME also offers an interface to set the Xft
DPI. If "gnome-settings-daemon" is running, this will advertise the DPI
value set in the gnome-font-properties dialog to GNOME applications via
XSETTINGS, and set the Xft.dpi X resource. Any Qt application started
after gnome-settings-daemon is running will use the Xft.dpi value
configured by GNOME.
Problem: choosing default font sizes
Having a standardized DPI is important for choosing good default font sizes.
Windows
machines use the DPI value as a way of globally changing font size.
Windows XP defaults to 96 DPI. Changing to large font mode increases
the DPI to 120. Users can also specify a custom DPI value. The default
application font on Windows is "Tahoma 8".
MacOS X standardizes
on 72 DPI, which means that fonts are smaller on the Mac at the same
point size as on Windows. The default font on my MacOS X laptop is
"Lucida Grande 13".
GTK+ uses a default application font of "Sans 10". This size seems to be chosen assuming a screen configured to 96 DPI.
DPI in practice
The DPI used on a Linux desktop is defined by the following:

1. If gnome-settings-daemon is running, it defaults to 96 DPI, and all
GTK+/Qt applications will use this value. Your fonts will appear as
intended.
   2. Otherwise, some distributions launch X using "-dpi 100". Fonts will appear as intended.

3. If your monitor announces a size via DDC, X will derive its DPI
from these values. These values are unreliable, and regardless, this is
not a good way to determine font sizes. The result is fonts which are
usually either too big or too small.
   4. Your X server uses 75 DPI, and your fonts are all too small.
In
one weekend supporting tvtime and Eclipse on IRC, I saw the following
DPI values from various users, all of whom were using the default X
setup from their distribution: 75x75, 85x80, 100x100, 117x115, and
133x133.
Proposal
I strongly believe that fonts on Linux
should pick a standard default DPI value, and thereby standardize the
pixel sizes of fonts on Linux desktops. Applications and desktop
systems cannot reliably choose default font sizes without this. My
proposal is that we standardize this value in Xft.dpi so that it does
not affect the DPI reported by the X server for applications which may
find this information useful.
The proposal is as follows:
   1. Decide on 96 DPI as the default, since this is already quite popular and matches all default GNOME desktops.
   2. Distributions should set the X resource "Xft.dpi" in an Xresources file sourced by all X servers.
Here is the code for inclusion in the Xresources file:
     Xft.dpi: 96.0
Should the X server DPI match the Xft DPI?
There
are conflicting ideas about whether screen DPI is useful or not.
Configuring Xft to use the default value of 96.0 is much less
controversial, as it only applies to fonts.
Why is a fixed default DPI better than an autodetected one?
An
obvious criticism of this proposal is that it is proposing a single and
arbitrary DPI, which seems to go against the whole concept of "dots per
inch". Having a DPI value calculated based on the monitor size is
appealing.
The reasons why I believe a fixed DPI is a good idea are as follows:

1. User interfaces are designed in terms of pixels. Having a standard
default fixed DPI makes it possible for application and desktop
developers to choose reasonable default fonts that will be readable
even at low DPI.
   2. Font hints are specified for certain popular
font sizes. Changing the DPI can affect the appearance of text, not
just its size.
   3. DPI applies well to printing, but not well to
the screen. If I project my laptop display on a screen for a
presentation, the theoretical DPI has clearly changed, but I do not
want all of my fonts to suddenly change with it. DPI values for
computer screens are simply convention and not meaningful.
   4. Other operating systems like Windows and MacOS choose arbitrary DPI values rather than auto-calculate it.
我没有按照文章的观点把xft的分辨率设成固定的96dpi，而是与物理dpi一致。需要修改xft的默认字体大小。
               
               
               

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