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#65803
29.1; Noto Sans Mono CJK JP has doubled-width on Windows
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Message #83 received at 65803 <at> debbugs.gnu.org (full text, mbox):
Eli Zaretskii <eliz <at> gnu.org> writes:
>> From: Po Lu <luangruo <at> yahoo.com>
>> Cc: shingo.fg8 <at> gmail.com, 65803 <at> debbugs.gnu.org
>> Date: Sun, 10 Sep 2023 13:55:47 +0800
>>
>> Eli Zaretskii <eliz <at> gnu.org> writes:
>>
>> > No, the purpose of FRAME_COLUMN_WIDTH is much more than just "the
>> > width of ASCII characters". It is used as the canonical character
>> > width of the frame, for gazillion purposes. One example which
>> > triggered this bug is :align-to display spec, something utterly
>> > unrelated to ASCII characters.
>>
>> However, the column width has hitherto been defined to the average width
>> of the frame font's ASCII characters. At least outside W32, that is.
>
> No! Once again, for fixed-pitch fonts the average width is taken from
> the font. Here, from ftfont.c:
>
> if (spacing != FC_PROPORTIONAL
> #ifdef FC_DUAL
> && spacing != FC_DUAL
> #endif /* FC_DUAL */
> )
> font->min_width = font->average_width = font->space_width
> = (scalable ? ft_face->max_advance_width * size / upEM + 0.5
> : ft_face->size->metrics.max_advance >> 6);
> else
> {
> int n;
>
> font->min_width = font->average_width = font->space_width = 0;
> for (i = 32, n = 0; i < 127; i++)
> if (FT_Load_Char (ft_face, i, FT_LOAD_DEFAULT) == 0)
> {
> int this_width = ft_face->glyph->metrics.horiAdvance >> 6;
>
> if (this_width > 0
> && (! font->min_width || font->min_width > this_width))
> font->min_width = this_width;
> if (i == 32)
> font->space_width = this_width;
> font->average_width += this_width;
> n++;
> }
> if (n > 0)
> font->average_width /= n;
> }
>
> This clearly only calculates the average width for proportional fonts,
> and otherwise takes the average width from the font's max_advance
> width without calculating anything. Or what am I missing?
>
>> > But other font back-ends don't compute average_width for fixed-pitch
>> > fonts, so are you only talking about proportional fonts here?
>>
>> I'm talking about fonts in general: since fixed pitch fonts are meant to
>> incorporate uniformly sized glyphs, the width of the space glyph should
>> represent the average width of any subset of the font's glyphs. In this
>> particular case, Fontconfig doesn't deem the font in question a fixed
>> pitch font, and thus Emacs measures the average width of each ASCII
>> character itself.
>
> See above: other backends only calculate the average width for
> proportional fonts. So what you say doesn't fit my reading of the
> code.
Because if spacing is not FC_PROPORTIONAL or FC_DUAL, we know in advance
that max_advance_width or max_advance are identical to the average of
all ASCII glyphs. Such special treatment is an optimization, nothing
more. max_advance_width is the advance width (in em space) of the
widest glyph when the font is scalable, and max_advance is that in pixel
space if not.
This bug report was last modified 1 year and 281 days ago.
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