Frame size in specified font

[Matthias Meulien <meulien@club.lemonde.fr>]

Hi,

How to know the size of a frame in line and columns of a SPECIFIED
font ? 

Only idea : create a new frame using the specified font and with the
same pixel dimension ; call frame-size then delete the new frame...

It would be useful in fixing the following problems.

First, in the calendar/diary, the modeline stuff isn't visually
satisfying when the `mode-line' face use a font different from the
frame font: the function `calendar-set-mode-line' use `frame-width'
which return the width of the (current) frame measured in columns of
its font characters. The value should depend of the `mode-line' face
font.

Note for the `calendar.el' maintainer. 
Why `update-calendar-mode-line' don't call `calendar-set-mode-line' ?

Second, look at the speedbar frame creation function. Speedbar's frame
height is calculated from the associated frame height using
`frame-height'. So if `speedbar-frame-parameters' specify a new font,
the speedbar frame parameter `height' won't be initialized to the
height (pixel speaking) of the frame speedbar is attached !

Sorry for my poor English.
-- 
Matthias