Re: Display certain glyphs with paddings on the side

["Clément Pit-Claudel" <cpitclaudel@gmail.com>]

On 2019-12-03 14:13, Eli Zaretskii wrote:
>> Cc: emacs-devel@gnu.org
>> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
>> Date: Tue, 3 Dec 2019 13:43:33 -0500
>>
>>> No, character composition does nothing to the width of glyphs on
>>> display.  We take the width from the glyph metrics reported by the
>>> font.
>>
>> For the OP's purpose, I think character composition is "enough", in the sense that it can be used to display a glyphs with padding on the sides (as far as I know, composition can't be used to shrink a glyph, however).
>>
>> Concretely, I'm think of this:
>>
>> 　　(insert (compose-string "a" 0 1 '(?\s (br . bl) ?\s (bc . bc) ?我)))
>>
>> If I'm reading the spec correctly, this should draw the character 我 with padding on both sides to reach the width of two spaces (assuming the choice of fonts is such as 我 is narrower than two spaces to being with).
> 
> This isn't really workable in practice. 

Sorry, my point wasn't that the OP should do that; rather, I was pointing out that the display engine was powerful enough to achieve the desired result.

Ideally, what I'd love to have is a mode that implements a grid-like layout, where each character occupies an exact multiple of the base character width, regardless of which font it comes from.

Deciding what this multiple should be for each character could be done in various ways; for my purposes (and for OP's case as well, I think), it would be enough to use one cell for halfwidth characters, two for fullwidth characters, and add a few exceptions for things like TAB and zero-width spaces (I'm using the terms fullwidth and halfwidth in the sense of https://www.unicode.org/reports/tr11/).

Should I open a bug report about this?

Cheers,
Clément.