How does Emacs render glyphs?

How does Emacs render glyphs?

[Roland Lutz]

Hi,

I've been fiddling with Pango text rendering and noticed that the output 
looks kind of weird.  Using the same font and size, glyphs rendered via 
Pango appear to be one pixel shorter and slightly narrower than in Emacs:

https://hedmen.org/vera-11-emacs.png
https://hedmen.org/vera-11-pango.png

Since I very much prefer the way Emacs renders text, I'd like to replicate 
this behavior.  Do I assume correctly that Emacs uses Pango internally? 
Are there specific parameters I need to pass to Pango in order to achieve 
this result?

Roland

Re: How does Emacs render glyphs?

[Eli Zaretskii]

> Date: Sun, 24 Nov 2024 16:03:29 +0100 (CET)
> From: Roland Lutz <rlutz@hedmen.org>
> 
> Hi,
> 
> I've been fiddling with Pango text rendering and noticed that the output 
> looks kind of weird.  Using the same font and size, glyphs rendered via 
> Pango appear to be one pixel shorter and slightly narrower than in Emacs:
> 
> https://hedmen.org/vera-11-emacs.png
> https://hedmen.org/vera-11-pango.png
> 
> Since I very much prefer the way Emacs renders text, I'd like to replicate 
> this behavior.  Do I assume correctly that Emacs uses Pango internally? 

No, I don't think Emacs uses Pango, at least not directly.  Emacs
built with Cairo might use Pango indirectly; all the other
configurations AFAIK do not.

Po Lu, please correct me if I'm wrong.

Re: How does Emacs render glyphs?

[Po Lu]

Eli Zaretskii <eliz@gnu.org> writes:

>> Date: Sun, 24 Nov 2024 16:03:29 +0100 (CET)
>> From: Roland Lutz <rlutz@hedmen.org>
>> 
>> Hi,
>> 
>> I've been fiddling with Pango text rendering and noticed that the output 
>> looks kind of weird.  Using the same font and size, glyphs rendered via 
>> Pango appear to be one pixel shorter and slightly narrower than in Emacs:
>> 
>> https://hedmen.org/vera-11-emacs.png
>> https://hedmen.org/vera-11-pango.png
>> 
>> Since I very much prefer the way Emacs renders text, I'd like to replicate 
>> this behavior.  Do I assume correctly that Emacs uses Pango internally? 
>
> No, I don't think Emacs uses Pango, at least not directly.  Emacs
> built with Cairo might use Pango indirectly; all the other
> configurations AFAIK do not.
>
> Po Lu, please correct me if I'm wrong.

No, Emacs doesn't use Pango.  The discrepancy observed by the OP is
probably the product of inconsistencies between either hinting or glyph
metrics rounding (but it's hard to say from this description who is in
the wrong).

Re: How does Emacs render glyphs?

[Roland Lutz]

On Mon, 25 Nov 2024, Po Lu wrote:
> No, Emacs doesn't use Pango.  The discrepancy observed by the OP is
> probably the product of inconsistencies between either hinting or glyph
> metrics rounding (but it's hard to say from this description who is in
> the wrong).

Thank you!  This was the hint that allowed me to solve this.

When rendering glyphs via FreeType and disabling hinting, I get the 
desired result.  For reference, here is the regular FreeType output 
(with hinting):

https://hedmen.org/vera-11-freetype.png

Roland