How does Emacs know the background color?

How does Emacs know the background color?

[Michael Herman]

I am using a special mode for handling e-mail called post.el.  In
post.el there are different faces depending on the background being
'light' or 'dark'.  When I launch emacs -nw from within an xterm with
a white background, emacs uses the face for a dark background.

How does emacs determine what the background is?

When I use -rv for the xterm, emacs still thinks the background is
dark.

On a sort of related note, is there a way to tell how emacs was
launched from the command line?  I'd like to modify my .emacs to
change settings depending on whether I used emacs -nw or not.

Thanks.

-- 
Michael Herman

Re: How does Emacs know the background color?

[John Rabkin]

On Sun, 16 Feb 2003 08:10:38 +0000, Michael Herman wrote:

> I am using a special mode for handling e-mail called post.el.  In post.el
> there are different faces depending on the background being 'light' or
> 'dark'.  When I launch emacs -nw from within an xterm with a white
> background, emacs uses the face for a dark background.
> 
> How does emacs determine what the background is?
> 
> When I use -rv for the xterm, emacs still thinks the background is dark.
> 
> On a sort of related note, is there a way to tell how emacs was launched
> from the command line?  I'd like to modify my .emacs to change settings
> depending on whether I used emacs -nw or not.
> 
> Thanks.

I'm a newbie myself. The first thing I ever wrote (2 weeks ago) in elisp was:

(defun reversed_colors () 
  "Sets the background to black and the foreground to white"
  (set-background-color "black")
  (set-foreground-color "white")
  )

(if (equal window-system 'x) 
    (reversed_colors)
  )

It's in my ~/.emacs file and works fine.

> How does emacs determine what the background is?

Try evaluating (set-background-color "black")

-- 
"Cut your own wood and it will warm you twice"
	Regards, Yoni Rabkin

Re: How does Emacs know the background color?

[Kevin Rodgers]

Michael Herman wrote:

> On a sort of related note, is there a way to tell how emacs was
> launched from the command line?  I'd like to modify my .emacs to
> change settings depending on whether I used emacs -nw or not.

Check the window-system variable.  But it would be better to check the specific

display characteristics you're interested in instead.

-- 
<a href="mailto:&lt;kevin.rodgers&#64;ihs.com&gt;">Kevin Rodgers</a>

RE: How does Emacs know the background color?

[Zaretskii Eli]

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> From: Michael Herman [mailto:michael-lists@thehermans.org] 
> Sent: Sunday, February 16, 2003 4:11 PM
> 
> I am using a special mode for handling e-mail called post.el.  In
> post.el there are different faces depending on the background being
> 'light' or 'dark'.  When I launch emacs -nw from within an xterm with
> a white background, emacs uses the face for a dark background.
> 
> How does emacs determine what the background is?

It looks for an environment variable defined by xterm.  See startup.el
for more details.


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