From: Kai Ma <justksqsf@gmail.com>
To: Eli Zaretskii <eliz@gnu.org>
Cc: emacs-devel@gnu.org
Subject: Re: Text shadows
Date: Sun, 12 Mar 2023 16:24:17 +0800 [thread overview]
Message-ID: <EC1A0CE7-AA3E-40A3-8CFC-09897E0954F0@gmail.com> (raw)
In-Reply-To: <83mt4iv3xa.fsf@gnu.org>
> On Mar 12, 2023, at 15:12, Eli Zaretskii <eliz@gnu.org> wrote:
>
>> From: Kai Ma <justksqsf@gmail.com>
>> Date: Sun, 12 Mar 2023 12:06:28 +0800
>>
>> Recently, I implemented the “text shadows” feature for Cairo-powered windowing systems, including X11 and Wayland. See [1] if you wonder what that looks like.
>
> Which parts of the feature implementation really require Cairo? IOW,
> why cannot this be available to non-Cairo builds as well?
Theoretically, nothing. I targeted Cairo because (I think) it is the most popular option on GNU/Linux.
Speaking of this specific implementation, gaussian_blur() relies on a specific Cairo image format ARGB32, (this assumption could be easily removed), and then it is used by ftcrfont_draw() to generate shadows.
I don’t know whether non-Cairo builds (non-cairo X, win32) can/should use gaussian_blur() though, since I’m not familiar with them.
>> This feature adds a new face attribute :shadow, and accepts values like:
>>
>> - FLOAT how much blurring?
>> - (FLOAT . COLOR) additionally, specifies a color for the shadow
>> - (FLOAT COLOR OFFSET) additionally, specifies an offset (x . y)
>
> I think at least in some GUI systems the offset is specified as radius
> and angle.
The shadow is generated by this process:
- draw glyphs (in the shadow color) onto a blank canvas;
- apply the blurring function;
- copy the “shadow” back to the original canvas at the specified x-y coordinate.
So I don’t think radius and angle is relevant here.
>> I’m writing to ask if the community is interested in accepting this feature into mainline Emacs? If so, I will improve things and make a formal patch.
>
> Yes, I think we'd like to support this feature. But it looks to me
> like the current WIP is incomplete, as it doesn't handle the change in
> glyph metrics due to the shadowing, see below.
Thanks!
> It is best to submit a feature-request bug report using
> report-emacs-bug, and then continue the discussion on our issue
> tracker.
Will do after I fix the glyph metrics.
>> 1. The shadows sometimes should be drawn outside the glyph extents, but they aren’t drawn.
>> 2. Previously drawn shadows are not cleared, and they even accumulate. This can be observed with blink-cursor-mode enabled.
>
> This probably means you need further changes in the layout part of the
> display code, in xdisp.c, to account for the changes in the glyph
> metrics due to the shadow attribute. See, for example, how the 'box'
> face attribute is handled there.
Thanks for this pointer. I will work this out first, and then let’s continue the discussion on the bug tracker.
— Kai
next prev parent reply other threads:[~2023-03-12 8:24 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-12 4:06 Text shadows Kai Ma
2023-03-12 4:18 ` Kai Ma
2023-03-12 7:12 ` Eli Zaretskii
2023-03-12 8:24 ` Kai Ma [this message]
2023-03-12 8:46 ` Po Lu
2023-03-12 9:23 ` Kai Ma
2023-03-12 10:33 ` Po Lu
2023-03-12 9:14 ` Eli Zaretskii
2023-03-12 9:55 ` Kai Ma
2023-03-12 11:33 ` Eli Zaretskii
2023-03-12 11:49 ` Kai Ma
2023-03-12 12:36 ` Eli Zaretskii
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