custom-theme-set-faces compatible with tty

Question

I have created an emacs-23 custom theme using customize-create-theme. It works fine under X (Linux gnome desktop). However, when running under a tty (within gnome-terminal) some of the colors are wrong.

It is not the accuracy of the colors which are a problem (although it would be nice to match them under both situations) but the fact that some are so off as to be unworkable. For example, function names which appear green under X are invisible under the tty, although keywords which appear gold under X also appear gold (or at least some kind of yellow) under the tty.

Perhaps under the tty colors can't be matched exactly and so something similar is being substituted? If so, this doesn't seem to work all the time.

How can I fix this? Is it possible to specify, either in the 'customize' GUI or in the ~/.emacs.d/my-theme.el file, that certain faces only apply to frames displayed on X and others are only for the tty, or something similar?

(I'm interested in getting this, the built-in emacs theming system working rather than using some external color theme system.)

Answer 1

You can tell whether or not the current frame is associated with a graphical window by examining the variable window-system. The link has the documentation, but it looks like:

window-system is a variable defined in `C source code'.
Its value is nil

Documentation:
Name of window system through which the selected frame is displayed.
The value is a symbol--for instance, `x' for X windows.
The value is nil if the selected frame is on a text-only-terminal.

So, you can wrap the current theme inside an

(if window-system
    ;; current theme configuration
)

and then when in an xterm, create a new one that you like, and put that in the else (or another if statement, or unless and when)

Answer 2

If a color is unavailable on a frame, emacs should try and pick something "close", but that's often very wrong on limited color displays. You should ask emacs how many colors it thinks it has in gnome-terminal either using M-x list-colors-display (to actually view the colors) or run (display-color-cells) in the scratch buffer. If it says you only have 8, you might want to consider changing your TERM environment variable to something like xterm-256color before you start emacs (though I'm not sure how well this actually works in gnome-terminal; I use xterm).

So that might help emacs be able to find a color that's closer, but if it's still wrong, you'll want to do something more drastic, like set the colors based on the window system.

If you're not using daemon mode, you can use something like

(if window-system
    (set-face-foreground 'font-lock-function-name-face "LightSkyBlue"))

If you use M-x describe-face, it will ask which face you want to describe, defaulting to the one currently at point. You can get the name (and usually the color) from there.

If you are using daemon mode, then you'll want different colors for each frame, in which case you'll need to set the color for the frame in the new frame hook, something more like:

(defun set-new-frame-colors (frame)
   "Set colors based on frame type."
   (if (window-system frame)
       (set-face-forgeground 'font-lock-function-name-face "LightSkyBlue" frame)
       (set-face-forgeground 'font-lock-function-name-face "blue" frame)))
(add-hook 'after-make-frame-functions 'set-new-frame-colors)

Alternatively, instead of checking (window-system frame), you could check (length (defined-colors frame)) and base it on how many colors are supported by the system, so that you can have different colors for 8-color vs. 256-color terminals.