bug#67563: 30.0.50; Box should not extend with line-spacing

[Yuan Fu <casouri@gmail.com>]

On 12/2/23 6:06 AM, Eli Zaretskii wrote:
>> From: Yuan Fu <casouri@gmail.com>
>> Date: Thu, 30 Nov 2023 23:47:37 -0800
>>
>> If I set a box face for a button, and then set a line-space for the buffer, I expect the extra space between lines to be added outside of the box, like so:
>>
>> +-------------------------+
>> |          Box            |
>> |                         |
>> +-------------------------+
>>         extra line space
>> +-------------------------+
>> |          Box            |
>> |                         |
>> +-------------------------+
>>
>> However, right now, the bottom line of the box includes the extra line spacing, like so:
>>
>> +-------------------------+
>> |          Box            |
>> |                         |
>> +                         +
>> |      extra line space   |
>> +-------------------------+
>> +-------------------------+
>> |          Box            |
>> |                         |
>> +-------------------------+
>>
>> Screenshot:
>>
>> Ideally there should be some space between the two buttons on the two lines. Also notice the extra space above the bottom line of the box.
>>
>> I also attached a repo file to produce these buttons.
>>
>> If someone can give me some pointers, I can try to look into this.
> We currently draw the box such that its height is equal to the height
> of the screen line, and that includes line-spacing.
>
> The implementation is in x_draw_glyph_string_box and similar functions
> in other GUI backends (w32_draw_glyph_string_box etc.).
Thanks, I'll come back when I have good questions to ask.
> If you want to ad a feature where the box excludes line-space, please
> make it optional, by default off, as the current behavior is a very
> old one.
Will do. I'm sure the current behavior has its use-cases too.

Yuan