Re: How much is one em (image size unit)?

[Akib Azmain Turja]

Fu Yuan <casouri@gmail.com> writes:

>> 在 2023年4月1日，上午5:35，Akib Azmain Turja <akib@disroot.org> 写道：
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>>>> From: Akib Azmain Turja <akib@disroot.org>
>>>> Cc: Manuel Giraud <manuel@ledu-giraud.fr>
>>>> Date: Fri, 31 Mar 2023 22:32:49 +0600
>>>> 
>>>>> Akib Azmain Turja <akib@disroot.org> writes:
>>>>> 
>>>>>> I'm trying to show an image such that it has same height as the text and
>>>>>> resizes relatively with text scale.  I've achieved this with the 'em'
>>>>>> unit as described in (elisp)Image Descriptors.  But 1 em seems to be
>>>>>> pretty smaller than the font size.  How to figure out correct value in
>>>>>> em unit such that image and the text has correct height?
>>>>> 
>>>>> Hi,
>>>>> 
>>>>> FWIW, your example works for me and scales accordingly when I zoom.
>>>> 
>>>> But 1 em is pretty smaller than the default font size.  I want to make
>>>> the image height and the text height same.
>>> 
>>> Maybe this page will help you:
>>> 
>>>  https://learn.microsoft.com/en-us/typography/opentype/spec/ttch01
>>> 
>> 
>> Thanks, but I couldn't understand much.  Say the line height is X em,
>> then how can I figure out that X?
>
> 1 em equals to the text height. If your 1 em looks smaller than the text 
> height, something might be wrong. Perhaps post a screenshot of what you get?
>
> Yuan 

I have found the size of em unit, it's actually the font size (as in the
the SIZE argument of font-spec).  So, line height in em is:

#+begin_src emacs-lisp
(/ (float (default-font-height)) (font-get (font-spec :name (face-font 
'default)) :size))
#+end_src

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