Zoomed layers result in blurry text

[pepperoni505]

Describe the bug
When zooming using the Pan Zoom demo on the website, it appears the font doesn't get properly updated to the zoom level, and still renders at the quality of the initial depth.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.egui.rs/
2. Open the Pan Zoom demo
3. Zoom in
4. Observe text

Expected behavior
The text would not be blurry

Screenshots

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Safari
• Version: Whatever the demo is running (presumably latest?)

Additional context

[jb55]

it would be great if we had something like https://sluglibrary.com/ for rendering text

EDIT: nm apparently open source projects can't implement this because the technique is patented (very lame). so another approach would be mesh based fonts.

Thinking about this some more, a quick fix might be to have a way to set the resolution of the glyph texture so that zooming up to a certain level remains crisp?

[jb55]

I went down a rabbit hole today looking into this. I was curious how browsers deal with glyph sizes when it comes to pinch zooming and found a few interesting comments by @pcwalton:

Honestly, there are so few different glyphs on a typical page, and CPUs are so fast, that it usually isn't that hard to just rerender every glyph on CPU and aggressively reuse glyph images in order to hit 60 FPS during pinch zoom, at least for Latin text. CJK may be a different story, but I kind of doubt it.

https://news.ycombinator.com/item?id=32113767

I imagine the fastest thing you could do is use an algorithm similar to slug to generate these glyph atlases on the gpu while you're zooming. The downside of this is that a gpu algo is not going to cover all of the features that something like swash will be providing?

Perhaps the best approach is some kind of glyph caching system that supports various sizes.

With the plan to switch to cosmic-text:

• Cosmic Text for font rendering #3378

I noticed there is a SwashCache:

• https://docs.rs/cosmic-text/latest/cosmic_text/struct.SwashCache.html

so maybe we can use that to cache glyphs at various sizes when we need them for a particular zoom level?

there is still the issue of what the texture atlas would look like in this setup, perhaps you would need something like

• https://github.com/nical/etagere

for building these dynamically? I'm just thinking out loud here since I have yet to dive into the internals of egui's glyph atlas and caching. would be curious to hear @emilk 's thoughts on how we might do this.

....

After doing some more digging it looks like glyphon does exactly this:

• https://github.com/grovesNL/glyphon

and I noticed there is egui-glyphon also:

• https://github.com/StratusFearMe21/egui-glyphon

...

I've updated egui-glyphon for 0.30.0 to see if I can get a proof of concept working:

• Cosmic Text for font rendering #3378 (comment)