[issue #2002] Ensure that absolute LineHeight is always > 0.0

[joshuamegnauth54]

Fixes #2002.

The gist of the problem is that LineHeight::to_absolute in conjunction with other widgets may inadvertently return 0.0. This triggers a panic in cosmic_text's Buffer regardless of the renderer.

The original issue has a minimal example. My patch just ensures that absolute LineHeight is > 0.0 to avoid the panic.

[B0ney]

Awesome! The patch fixed the issue for me.

[hecrj]

Since this is a limitation of a dependency used in the renderers, I believe the fix should live there.

[joshuamegnauth54]

Hmm, the panic is in cosmic_text, but the panic is expected and part of its public API:

    /// Create a new [`Buffer`] with the provided [`FontSystem`] and [`Metrics`]
    ///
    /// # Panics
    ///
    /// Will panic if `metrics.line_height` is zero.
    pub fn new(font_system: &mut FontSystem, metrics: Metrics) -> Self {
        let mut buffer = Self::new_empty(metrics);
        buffer.set_text(font_system, "", Attrs::new(), Shaping::Advanced);
        buffer
    }

So it's the caller's responsibility (iced in this case) to ensure that line height is > 0.0.

Edit: I understand your concerns of course, but I think cosmic_text won't remove the panics since a lot of its public API documents panics for invalid values. Buffer has a few of them.

[hecrj]

@joshuamegnauth54 For sure! I meant that the fix should live in iced_wgpu and iced_tiny_skia instead of iced_core. Basically, after calling to_absolute.

[joshuamegnauth54]

Alright, that makes sense! I'll look into it soon.

[joshuamegnauth54]

I updated the WGPU and Tiny Skia renders. cargo test --all passes and b0ney's code works too.

Let me know if there's anything else I should do.

[joshuamegnauth54]

Okay, so I moved the LineHeight logic to allocate and removed the previous checks. Everything still works!

[hecrj]

Almost! This should look the same as the wgpu code:

Suggested change

	key.line_height,
	(key.line_height * 1.2).max(f32::MIN_POSITIVE),
	key.size,
	key.line_height.max(f32::MIN_POSITIVE),

You can test the tiny-skia backend by setting the ICED_BACKEND=tiny-skia env variable.

[joshuamegnauth54]

Alright, I just committed the requested changes.

Also, I've been recompiling iced with default-features=false to test Tiny Skia. 😅 That env var is very helpful.

[hecrj]

Awesome! Thanks.