feature/fontique: switch femtovg to parley #9466

expenses · 2025-09-19T12:33:31Z

Needs a lot of work before merging. @tronical is this the right approach at all?

internal/renderers/femtovg/itemrenderer.rs

expenses · 2025-09-22T09:03:51Z

One thing I've noticed is that there are significant performance issues with the glyph rendering, because we're parsing the font and creating the rustybuzz structures for every single glyph when we call face_ref.

Rustybuzz borrows all data internally though, making this a tricky problem to fix. Wish we had self-referential types but oh well.

tronical · 2025-09-22T10:28:19Z

Good catch. That should be fixable in femtovg, I guess. Maybe by changing the API to draw runs with same font.

internal/renderers/femtovg/fonts.rs

expenses · 2025-09-23T12:07:29Z

This is starting to look more ready. Font metrics are the main missing thing and then we can start thinking about building up parity with the current text layout.

expenses · 2025-09-23T14:37:52Z

internal/renderers/femtovg/itemrenderer.rs

+        let _overflow = text.overflow();
+        // TODO
+        let _letter_spacing = text.letter_spacing();


letter spacing I believe is handled as part of the font request stuff, but overflows need to be done.

expenses · 2025-09-23T14:39:28Z

Okay, apart from the ellipses stuff I think this is feature complete

expenses · 2025-09-23T14:44:26Z

See linebender/parley#304.

nicoburns · 2025-09-23T14:48:56Z

Rustybuzz borrows all data internally though, making this a tricky problem to fix. Wish we had self-referential types but oh well.

HarfRust (google backed fork of RustyBuzz) has an API that avoids the need for self-referential types (and is also ~3-4x faster than RustyBuzz). Alternatively, cosmic-text uses the yoke crate to store a self-referential RustyBuzz face.

tronical

Excellent progress :). A few comments inside.

internal/core/textlayout/sharedparley.rs

internal/renderers/femtovg/Cargo.toml

internal/renderers/femtovg/font_cache.rs

internal/renderers/femtovg/itemrenderer.rs

internal/core/textlayout/sharedparley.rs

tronical · 2025-09-24T06:58:12Z

pnpm-lock.yaml

I think that if you rebase your branch, this should go away :)

expenses · 2025-09-24T10:01:31Z

Rustybuzz borrows all data internally though, making this a tricky problem to fix. Wish we had self-referential types but oh well.

HarfRust (google backed fork of RustyBuzz) has an API that avoids the need for self-referential types (and is also ~3-4x faster than RustyBuzz). Alternatively, cosmic-text uses the yoke crate to store a self-referential RustyBuzz face.

Thanks @nicoburns, that'll be very helpful!

internal/renderers/femtovg/itemrenderer.rs

internal/core/textlayout/sharedparley.rs

expenses · 2025-09-24T13:43:23Z

I checked the sizes of parley stuff and boxing them does make a lot of sense:

[internal/core/textlayout/sharedparley.rs:72:5] std::mem::size_of::< parley::LayoutContext<Brush> >() = 1240
[internal/core/textlayout/sharedparley.rs:73:5] std::mem::size_of::< Contexts >() = 1904
[internal/core/textlayout/sharedparley.rs:74:5] std::mem::size_of::< RefCell<Contexts> >() = 1912
[internal/core/textlayout/sharedparley.rs:75:5] std::mem::size_of::< RefCell<Box<Contexts>> >() = 16

internal/core/textlayout/sharedparley.rs

expenses · 2025-09-24T15:01:49Z

Just rebased the feature/fontique branch again.

tronical · 2025-09-25T06:36:34Z

internal/renderers/femtovg/fonts.rs

-        mut paint: femtovg::Paint,
-    ) -> femtovg::Paint {
-        paint.set_font(&self.fonts);
-        paint.set_font_size(self.pixel_size.get());


I tried out the branch and was wondering why all the text looked so small. This call is missing, so all the glyphs have the same size. I think this should probably be done in draw_glyphs by getting the font size out of the glyph run.

Ah that makes sense!

It looks better now, but some of the kerning after the 'W' looks wrong. Before & after comparison:

Kerning looks wrong both before and after to me! (look at the kerning between H and y in Hyperlink in the sidebar for example). I'd be interested to see what text in the same font looks like in a web browser.

expenses · 2025-09-25T11:07:45Z

This PR also seems to resolve our font rendering woes (#9310). Before and after:

expenses · 2025-09-25T12:17:39Z

Here's what it looks like in the software renderer:

vs femtovg:

All in all I'm pretty happy with things.

nicoburns · 2025-09-25T12:31:33Z

Y'all should definitely look into using skrifa rather than ttf_parser for outlining glyphs. It does hinting (matching freetype), so the glyphs should look much better.

The `sharedparley` module declares a public `Layout` struct, which clashes with the `Layout` struct we use in the C++ API. The former however is entirely internal to Rust, so we can instruct cbindgen to ignore the module.

expenses requested a review from tronical September 19, 2025 12:33

tronical reviewed Sep 19, 2025

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tronical reviewed Sep 23, 2025

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expenses marked this pull request as ready for review September 23, 2025 12:06

expenses commented Sep 23, 2025

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expenses requested a review from tronical September 23, 2025 14:39

tronical reviewed Sep 24, 2025

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I think that if you rebase your branch, this should go away :)

expenses force-pushed the parley branch 2 times, most recently from d305adc to a6e0cd1 Compare September 24, 2025 08:03

expenses requested a review from tronical September 24, 2025 10:59

tronical reviewed Sep 24, 2025

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tronical approved these changes Sep 24, 2025

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expenses force-pushed the feature/fontique branch from 3547cc1 to a4278e6 Compare September 24, 2025 14:55

expenses force-pushed the parley branch from 228506a to 45423f3 Compare September 24, 2025 15:00

tronical reviewed Sep 25, 2025

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Parlay init

2b1b5f1

expenses and others added 25 commits September 25, 2025 14:35

Handle a lot more layout options

0c0009a

Use the parley cursor

c33437b

Removed unused PhysicalPoint

a5a2c31

Start combining stuff WIP

3b0a5a8

Move things into i_slint_core::textlayout::sharedparley

ebb04d2

[autofix.ci] apply automated fixes

d312751

Go back to splitting paragraphs correctly

316a4bd

Handle font_metrics via ttf_parser

de0a1ae

Move (lack of) overflow handling to sharedparley

16a1b33

[autofix.ci] apply automated fixes

f2864e8

impl Deref for Layout

24b0e9b

Be more explit about the width passed to layout being physical

8198345

Cargo fmt, rename fonts to font_cache

275293c

Use a thread local for layout context

74645aa

Use parley selection

05c4c96

fix femtovg wgpu

bab85e7

Switch femtovg branch

98e882c

max_physical_width -> max_width

b7ba9d5

Box contexts

75e351a

[autofix.ci] apply automated fixes

ad073dc

Fallback to GenericFamily::SansSerif if no font is set

c82870f

Add paint.set_font_size

58536c2

Use max_physical_height

41719fa

Fix text_size to return correct logical sizes

7a1a06e

Use femtovg from crates.io

5b2bc7c

expenses force-pushed the parley branch from 038e8e7 to 5b2bc7c Compare September 25, 2025 12:37

tronical approved these changes Sep 25, 2025

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expenses changed the title ~~feature/fontique: start switcing femtovg to parley~~ feature/fontique: switch femtovg to parley Sep 25, 2025

Fix C++ build

48be35b

The `sharedparley` module declares a public `Layout` struct, which clashes with the `Layout` struct we use in the C++ API. The former however is entirely internal to Rust, so we can instruct cbindgen to ignore the module.

expenses merged commit 13623bc into slint-ui:feature/fontique Sep 25, 2025
40 of 41 checks passed

feature/fontique: switch femtovg to parley #9466

feature/fontique: switch femtovg to parley #9466

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