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

[Christian Schlauer <cs-muelleimer-rubbish.bin@arcor.de>]

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."

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?

-- 
Christian Schlauer