Sams Teach Yourself Emacs in 24 Hours
Hour 12: Visible Editing Utilities
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Sams Teach Yourself Emacs in 24 Hours |
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Hour 12: Visible Editing Utilities |
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Today's monitors have the capability to show text in different colors, fonts, and shapes. Why not use this to make the text more readable?
Note - The font, the color, and the shape are, together, referred to as the face. |
Using the face to help show the meaning of the text is what font-lock mode does. Using information built in to the major mode with which you edit a given text, font-lock mode knows enough about your text to show keywords in one face, comments in another, text literals in a third, and so on. An example of this can be seen in Figure 12.7. To make is easy for you to see it in a black-and-white printed book, I configured, for this figure, font-lock mode to show text literals in italic, keywords in bold, and comments in inverse video. In the default setup for font-lock-mode .ifferent colors would be used instead.
The colors used in GNU Emacs 20 can be configured by customizing the group called font-lock-highlighting-faces; in GNU Emacs 19 and in XEmacs, you have to stick with the default fonts chosen, because configuring in these setups is much more difficult than using customize.
Figure
12.7
Font-lock
mode works
with information built in to your major modes.
If you want font-lock mode enabled for all the major modes that know about font-lock and you are using GNU Emacs, simply insert the following line into your .emacs file:
){kind=link}
(global-font-lock-mode)
If, on the other hand, you do not want it loaded for all modes or you use XEmacs, you have to explicitly enable it for each major mode, using a construct like the following:
(add-hook 'c-mode-hook 'turn-on-font-lock)
c-mode should be replaced with the major mode that you want to start font-lock mode for by default. Thus, if you want font-lock mode to be started by default in html-helper-mode, c-mode, and emacs-lisp-mode, insert the following into your .emacs file:
(add-hook 'html-helper-mode-hook 'turn-on-font-lock) (add-hook 'c-mode-hook 'turn-on-font-lock) (add-hook 'emacs-lisp-mode-hook 'turn-on-font-lock)
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Note - This method is described in detail in Hour 24, "Installing Emacs Add-Ons." It does require that the given major mode define a hook called major-mode-hook, but this should always be the case. Font-lock mode can be turned on or off explicitly by pressing M-x and typing font-lock-mode. |
To make your buffer look nice, font-lock mode must do some pretty hard work. In most situations you will hardly notice, but if you have a very slow computer or a very large file, this might be a problem for you. To make everyone happy, font-lock mode offers different levels of fontification. What is fontified at a given level depends on the major mode. To find the truth, you have to either look in the Lisp file or try it out. By default, font-lock mode works in full-fontification-mode, but using the variable font-lock-maximum-decoration you can change this. To set font-lock mode to a low fontification level, insert the following into your .emacs file:
(setq font-lock-maximum-decoration 1)
Even with fast computers, font-lock mode can be slow given, for example, a file with the size of 100MB. Thus font-lock mode can be configured to not do fontifications when a new file is opened with a size above a given value. This value is configured using the variable font-lock-maximum-size. Its default value is 256KB, which should be enough in most situations.
If you, however, sometimes read a file into Emacs that's larger than this size, you can either set the value higher or force Emacs to fontify your buffer, using the function font-lock-fontify-buffer.
The fontification can sometimes be done wrong due to the fact that font-lock mode tries to be as lazy as possible (that is, whenever you insert a character, it does not fontify your whole buffer). In these situations, press M-g M-g (font-lock-fontify-block), which should fix it. In situations where this also fails, use the function font-lock-fontify-buffer.
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Sams Teach Yourself Emacs in 24 Hours |
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Hour 12: Visible Editing Utilities |
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