Crisp font somehow?

[tower120]

I tried all slint renderers. And not a single one produce truly crisp font, like the one in Firefox, or native windows 10 applications.
I looked at screenshots of your examples - the same everywhere.

It is not that font completely blurry, but difference with the same text, rendered in Firefox as html, and rendered by slint as application - is staggering.

Many rust GUI libraries suffer from this, but for example zed's GPUI and iced have very crisp font. I would say ideally crisp - exactly as native windows applications.

[tronical]

As you've noticed, we indeed have different renderers, and they use slightly different ways of rasterizing glyphs. I can outline a bit what they do. Perhaps that helps in understanding the differences that you may see, and how it compares to other toolkits:

(this is a snapshot of where we are today, and that might change/improve in the future)

1. The Slint software renderer uses fontdue to rasterise glyphs. We use this primarily to target low-end systems, and so when used on desktop systems, the output will look different than what CoreText on macOS, DirectWrite on Windows, and FreeType on Linux produce.

2. The FemtoVG renderer uses its own path renderer to render the outlines into glyph textures, without hinting. The output tends to look quite good at large glyph sizes, but it tends to be blurry at smaller sizes. Since this doesn't use the OS provided libraries (CoreText, DW, FT), the output differs from what you can see in native applications.

3. The Qt renderer delegates the glyph rendering to Qt, which in turn uses CoreText/DirectWrite/FreeType. The output should be identical to other applications on macOS/Windows/Linux.

4. The Skia renderer also delegates the glyph rendering to CoreText/DirectWrite/FreeType, and the output should be identical to other applications. If you see a difference here, I'd be rather surprised, to be honest.

I suspect that GPUI uses its own rasteriser, and iced - AFAICS - uses basically swash. Technically, those do produce different output than the native OS provided libraries. I'm interested in switching Slint's use of FemtoVG over to use swash, for an overall better quality.

Generally, for desktop systems I believe it's best to use the OS provided APIs to rasterise glyphs, to respect system wide settings (such as cleartype). I value consistency with the rest of the system over the individual quality per app, but I recognise that this is subjective.

I recently also ran across this post that describes the differences between macOS and Windows in an interesting detail: https://x.com/luciascarlet/status/1857909771757867082

[MrRinkana]

Am I understanding it correctly that one can run OS-native text rendering in slint? How does one do that? Text quality ootb is really terrible... Heres an example on linux desktop wayland no scaling (on that screen), I just resized the window and text is unacceptable..

[tronical]

Yes, there are two ways: You can enable the renderer-skia Cargo feature - that will result in freetype based glyph rendering and it should look good. Alternatively, in the master branch of Slint we've changed the rasterisation for the femtovg renderer (the default) to use swash, which in my experience produces also higher-quality glyphs at low resolutions.

[tower120]

Here is example of what I see at 10pt with skia renderer:

As you can see letters looks hazy. This is obviously nowhere near to built-in win32 applications (like explorer),
or even "consistent" VSCode renderer.

And to be honest - I did not tried Qt backend - since I don't have Qt installed - and I don't want to deal
with their license just to use Qt as render backend.

---

Skia renderer has anti-aliasing settings. In skia_safe::Font these are:

        font.set_subpixel(true);
        font.set_edging(Edging::SubpixelAntiAlias);
        font.set_hinting(FontHinting::Normal);

(In native Skia - you should also set pixel geometry - but I don't know how to do that in skia_safe).
They must be set explicitly. Without them (by default) - everything looks as bad as in old Chrome.
(frankly speaking even nowadays Chrome font somehow looks worse then rendered by Firefox - but now it at least readable)
If you use built-in skia font renderer - maybe it work without hinting (letters are not snapped to a pixel grid -
hence 1px line in glyph could take 2pxs)?

---

Does swash integration is somewhere in your roadmap?

[tronical]

As you can see letters looks hazy. This is obviously nowhere near to built-in win32 applications (like explorer),
or even "consistent" VSCode renderer.

That's quite odd indeed. If you open the .slint file in VS code and click on "Show Preview" does the resulting text look also that way?

Does swash integration is somewhere in your roadmap?

Nobody is actively working on it.

[tower120]

That's quite odd indeed. If you open the .slint file in VS code and click on "Show Preview" does the resulting text look also that way?

I would say - it is more or less the same... Maybe that's not just glyphs, but their layout too ... Some letters looks cramped together.

The rest of the vscode does not look that way.

[z3ugma]

See for example the spacing between Counter in the "Counter: 42". There's a narrow gap between the C and the o glyph and then a huge gap between o and u