Is there a built-in way to tell how many lines are in a window in a given face?

Is there a built-in way to tell how many lines are in a window in a given face?

[Zachary Kanfer]

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If I want to know how wide a window is, in terms of characters of a given
face, I can use #'window-max-chars-per-line (
https://www.gnu.org/software/emacs/manual/html_node/elisp/Window-Sizes.html#index-window_002dmax_002dchars_002dper_002dline
).

But if I want to know how tall a window is in terms of characters of a
given face, I don't think there's a built-in method to do so. At least, I
can't seem to find it.

So I wrote one. This would be nice to get into Emacs if I haven't missed
any existing functionality. My code :

(defun zck--window-max-lines-per-window (face &optional window)
  "Calculate how many lines of text with face FACE can fit in WINDOW."
  (truncate (window-body-height window t)
            (window-font-height window face)))

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Re: Is there a built-in way to tell how many lines are in a window in a given face?

[Eli Zaretskii]

> From: Zachary Kanfer <zkanfer@gmail.com>
> Date: Sat, 15 Apr 2017 01:14:43 -0400
> 
> (defun zck--window-max-lines-per-window (face &optional window)
> "Calculate how many lines of text with face FACE can fit in WINDOW."
> (truncate (window-body-height window t)
> (window-font-height window face)))

This doesn't take line-spacing into account, I think.

What are the use cases where you need these metrics of the window?
I'm not sure I understand the need for these facilities; e.g., why not
do all your calculations in pixels?  Or maybe fit-window-to-buffer
will do what you want?

Re: Is there a built-in way to tell how many lines are in a window in a given face?

[Zachary Kanfer]

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Thanks for the response. I'll look into line-spacing.

What I'm doing is making a presentation mode (
https://bitbucket.org/zck/zpresent.el;, available on Melpa) that presents
from Emacs. I want to be able to, for example, make a title slide that
looks like this (monospaced font required for this to look right):

+--------------------------------+
|                                |
|                                |
|                                |
|       Title goes here!         |
|                                |
|    $DATE         by $PERSON    |
|                                |
|                                |
+--------------------------------+

I'm certainly open to other ways of making this look right. I don't think
doing calculations in pixels would work, unless there's a way to insert
text at a specific pixel inside Emacs. And even if there were, that seems
like a bunch more work to basically reproduce LaTeX.

On Sat, Apr 15, 2017 at 3:44 AM, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Zachary Kanfer <zkanfer@gmail.com>
> > Date: Sat, 15 Apr 2017 01:14:43 -0400
> >
> > (defun zck--window-max-lines-per-window (face &optional window)
> > "Calculate how many lines of text with face FACE can fit in WINDOW."
> > (truncate (window-body-height window t)
> > (window-font-height window face)))
>
> This doesn't take line-spacing into account, I think.
>
> What are the use cases where you need these metrics of the window?
> I'm not sure I understand the need for these facilities; e.g., why not
> do all your calculations in pixels?  Or maybe fit-window-to-buffer
> will do what you want?
>

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Re: Is there a built-in way to tell how many lines are in a window in a given face?

[Eli Zaretskii]

> From: Zachary Kanfer <zkanfer@gmail.com>
> Date: Sat, 15 Apr 2017 16:27:12 -0400
> Cc: emacs-devel@gnu.org
> 
> What I'm doing is making a presentation mode (https://bitbucket.org/zck/zpresent.el;, available on Melpa) that
> presents from Emacs. I want to be able to, for example, make a title slide that looks like this (monospaced
> font required for this to look right):
> 
> +--------------------------------+
> | |
> | |
> | |
> | Title goes here! |
> | |
> | $DATE by $PERSON |
> | |
> | |
> +--------------------------------+
> 
> I'm certainly open to other ways of making this look right. I don't think doing calculations in pixels would work,
> unless there's a way to insert text at a specific pixel inside Emacs. And even if there were, that seems like a
> bunch more work to basically reproduce LaTeX.

Thanks, but I don't think I have a clear understanding how the above
is related to your zck--window-max-lines-per-window.  Let me guess:

Is it correct that you want to calculate how many empty lines to
insert before inserting the Title line, such that the text is
vertically centered in the window?  If so, then I'd begin by inserting
newlines until pos-at-point tells me I'm at the right vertical pixel
coordinate, which can be calculated given the pixel height of the
window and the number of lines you want to be centered in the window
multiplied by what window-font-height returns.  Does this work for
you?