Re: ps-print-color-p and the background colour of Emacs' frame

[Vinicius Jose Latorre <viniciusjl@ig.com.br>]

Christian Schlauer wrote:
> Vinicius Jose Latorre <viniciusjl@ig.com.br> writes:
>   
>> Christian Schlauer wrote:
>
> [...]
>   
>>> There is only an inaccurate doc string:
>>>
>>> ,----[ C-h v ps-default-bg RET ]
>>> | It's used only when `ps-print-color-p' is non-nil.
>>> `----
>>>
>>> Correct is "It's used only when `ps-print-color-p' is not nil or
>>> black-white." -- see below:
>>>       
>> Humm, isn't black-white a non-nil (not nil) value?
>>
>>     
>>> ,----[ C-h v ps-print-color-p RET ]
>>> | ps-print-color-p is a variable defined in `ps-print.el'.
>>> | | Valid values are:
>>> | |    nil		Do not print colors.
>>> | |    t		Print colors.
>>> | |    black-white	Print colors on black/white printer.
>>> | | Any other value is treated as t.
>>> | | You can customize this variable.
>>> `----
>>>       
>
> `black-white' is a non-nil value, but ps-default-bg isn't used when
> ps-print-color-p is `black-white' -- the following is tested with
> Emacs 22.1.50:
>
> | ps-print-color-p | Background colour in PS file when    |
> |                  | `ps-default-bg' is `frame-parameter? |
> |------------------+--------------------------------------|
> | t                | yes                                  |
> | black-white      | no                                   |
> | nil              | no                                   |
>
> So the doc-string of ps-default-bg *could* say "It is used iff
> `ps-print-color-p' is t."
>   

Ok, now I see what you mean.

I've just updated ps-print.el in trunk, Emacs 22 branch and Emacs 
Unicode branch.

Now ps-default-bg and ps-default-fg has:

    This variable is used only when `ps-print-color-p' (which see) is 
neither nil
    nor black-white.

> But there is this nasty "Any other value is treated as t." in the
> doc-string of ps-print-color-p, as quoted above. That suggests that
> the only way to *avoid* the background colour in the PS file is to set
> ps-print-color-p to `nil' or `black-white' -- if I set it to `foo',
> that would be treated as t according to the doc-string. That's why I
> ended up with the above formulation. My suggestions are:
>
> 1. Either write "It is used unless `ps-print-color-p' is nil or
>    black-white." in the doc-string of ps-default-bg (I tested that,
>    see the table above) or
>
> 2. get rid of the "Any other value is treated as t." in the doc-string
>    of ps-print-color-p.
>
> It seems to me that (2) makes most sense: I can't seem to set
> ps-print-color-p to anything else than t/black-white/nil. I tried
>
> M-x set-variable RET ps-print-color-p RET foo RET
>
> and
>
> M-x set-variable RET ps-print-color-p RET 4 RET
>
> but that doesn't work. And
>
> M-x customize-variable RET ps-print-color-p RET
>
> shows a `Value Menu' consisting of t/black-white/nil. So how could the
> user set it to any other value? 

Through Emacs Lisp:

(setq ps-print-color-p 4)

(setq ps-print-color-p (or (some-fun 10) 4))

(defun my-settings ()
   ;; ... some settings ...
   (setq ps-print-color 'my-setting))

(defun my-print (...)
   (let ((ps-print-color-p 'use-this-value))
     (ps-print-buffer-with-face ...)))