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May 21, 2013: defining a keyboard shortcut for a unicode symbol showing tensor product
In KDE system settings -> Keyboard -> Advanced, it is possible to activate:
- CTRL+ALT+BACKSPACE to restart X. If my memory is correct, it was enabled by default in KDE3.
- but also the “compose key”, e.g. choosing the two “Windows” keys (with a Windows OS logo). It allows to combine characters, for example the keyboard sequence “Window”,”+”, “-” yields “±”. This is pretty intuitive.
Entering new shortcuts concerns X, not KDE. This is explained here. X is here listening for our actions, not KDE (as it can be shown by typing “$ xev” in a console).
In the X system, apart from classical keys, we have two important ones to recall: the “modifier keys”, and a “compose key” (that we have just activated).
Key modification
There are four level of key modification easily activated:
- unshifted, for example “;” on my keyboard.
- shifted, for example “.”.
- ALTGR, for example “×”
- ALTGR+shift, for example “⋅”.
In fact, there are six level per key, that can be displayed with:
$ xmodmap -pk
(“$ man xmodmap” for more information, of course).
Levels 1, 2, 5, and 6 correspond to: unshifted, shifted, ALTGR, ALTGR+shift. According to the previously mentioned page, levels 3 and 4 do not seem to be accessible directly (I have not examined the subject further on).
For example, the character I use for vector product is obtained by ALTGR+”.”. Its unicode is 00D7:
$ unicode × U+00D7 MULTIPLICATION SIGN UTF-8: c3 97 UTF-16BE: 00d7 Decimal: × × Category: Sm (Symbol, Math) Bidi: ON (Other Neutrals)
I can then find the corresponding key in X configuration with:
$ xmodmap -pk|grep x00D7
59 0x003b (semicolon) 0x002e (period) 0x003b (semicolon) 0x002e (period) 0x00d7 (multiply) 0x10022c5 (U22C5) 0x00d7 (multiply) 0x10022c5 (U22C5)
Note that unicode “code points” (see here) are in hexadecimal form. U22C5 corresponds to the scalar product sign obtained with ALTGR+SHIFT+”.”:
$ unicode 22C5 U+22C5 DOT OPERATOR UTF-8: e2 8b 85 UTF-16BE: 22c5 Decimal: ⋅ ⋅ Category: Sm (Symbol, Math) Bidi: ON (Other Neutrals)
It is possible to redefine the character corresponding to a keyboard press with xmodmap. Today I will rather use key composition to be able to enter a tensor product sign.
Key composition
The characters that can be obtained with the compose key are stored at /usr/share/X11/locale/en_US.UTF-8/Compose. It is possible to add composition sequences in ~/.XCompose. An example of such a file is given here, where there are already a lot of mathematical symbols. To get the tensor product sign:
$ unicode 2297 U+2297 CIRCLED TIMES UTF-8: e2 8a 97 UTF-16BE: 2297 Decimal: ⊗ ⊗ Category: Sm (Symbol, Math) Bidi: ON (Other Neutrals)
for more convenience, I change the line:
<Multi_key> <parenleft> <x> <x> <parenright> : "⊗" U2297 # CIRCLED TIMES
to
<Multi_key> <o> <x> : "⊗" U2297 # CIRCLED TIMES
even if it overwrites the following sequence in /usr/share/X11/locale/en_US.UTF-8/Compose:
<Multi_key> <o> <x> »······: "¤" currency # CURRENCY SIGN
After restarting an application (an “X client”), e.g. Konsole, the new composition sequence works correctly; there is no need to log out or to restart X.
I have observed that at least two characters after <Multi_key> are necessary for the composition to work correctly. For example, the following one does not work:
<Multi_key> <e> : "Э" U042D # CYRILLIC CAPITAL LETTER E
contrary to:
<Multi_key> <e> <e> : "Э" U042D # CYRILLIC CAPITAL LETTER E
Other useful combinations in the file given at here
-
Greek characters:\begin_inset Separator latexpar\end_inset
<Multi_key> <asterisk> <p> : "π" U03C0 # GREEK SMALL LETTER PI
where <asterisk> is “*”. All greek letters are obtained with a “*” followed by a letter. - Square root: <Multi_key> <s> <q>
Note about number of characters (i.e. number of cursor positions) behind a unicode character when using a monospace font
I have discovered recently that some unicode characters take two character width when used with a fixed size font (“monospace” font), instead of one. This is typically the case in a terminal. With a variable size font, they appear as one character as expected. It is not specially related to their size: for example,
- ⨀, i.e. U+2A00, obtained with “compose key” + “(“ + “o” + “)”, takes two character width.
- whereas ㉑, i.e. U+3251, obtained with “compose key” + “(“ + “2” + “1” + “)”, takes one character width.
Yet they have the same size, as it is seen from a snapshot of my KDE Konsole:\begin_inset Separator latexpar\end_inset
There is a larger tensor product available as ⨂ corresponding to sign U+2A02, but as it takes two character width in Konsole, I prefer to use U2297.
Update on September 12, 2014, on (K)ubuntu 14.04
The compositions in file /usr/share/X11/locale/en_US.UTF-8/Compose are taken into account, but not my ~/.XCompose file, as well in ‘konsole‘ as in ‘xterm‘ or ‘gnome-terminal‘. After some experiments, I have finally found that using the program named ‘im-config‘ is enough:
$ which im-config /usr/bin/im-config $ wajig whichpkg /usr/bin/im-config im-config: /usr/bin/im-config $ wajig describe -v im-config im-config: Input method configuration framework im-config package provides the framework to configure and to switch the input method on X Window System. This input method is the essential mechanism for Japanese, Chinese and Korean (CJK) languages to enter their non-ASCII native characters. Many modern input methods such as IBus support not only one of these CJK languages but support almost all languages simultaneously by dynamically switching keyboard modes with GUI helper program. By installing this package, the most desirable input method and its backend conversion engine are automatically configured with both the X Window System Input Method (XIM), GTK+ input method module, Qt input method module, and clutrer input method module. You can further customize your input method with ’im-config’ command.
To know the current configuration:
$ im-config -m default ibus ibus
And to list the available configurations:
$ im-config -l ibus xim
The solution I have found is to switch to xim input method:
$ im-config -n xim
Note that it is necessary to logout for the new configuration to be taken into account.