Text render bug using tiny-skia

[Daillusorisch]

Is your issue REALLY a bug?

• My issue is indeed a bug!
• I am not crazy! I will not fill out this form just to ask a question or request a feature. Pinky promise.

Is there an existing issue for this?

• I have searched the existing issues.

Is this issue related to iced?

• My hardware is compatible and my graphics drivers are up-to-date.

What happened?

When two groups of text with different lengths are scrolled together, the shorter group leaves a wrong rendering after the text.

It only happened on tiny-skia in my pc. I am on windows10, latest rustc(1.82)

Can be reproduct using this code

use iced::{
    widget::{column, container, row, scrollable, text},
    Element, Length,
};
struct A {
    text: String,
    text2: String,
}

impl Default for A {
    fn default() -> Self {
        let mut text = String::new();
        let mut text2 = String::new();
        for _ in 0..100 {
            text.push_str("J:iijji::..2131ji12j3jijiji.iji.ji.j.ij.ij.ij.i.ji.j.i\n");
            text2.push_str("J2:iijji::..2131ji12j3jijiji.iji.ji.j.ij.ij.ij.i.ji.j.i\n");
            text2.push_str("J3:iijji::..2131ji12j3jijiji.iji.ji.j.ij.ij.ij.i.ji.j.i\n");
            text2.push_str("J4:iijji::..2131ji12j3jijiji.iji.ji.j.ij.ij.ij.i.ji.j.i\n");
        }
        Self { text, text2 }
    }
}

impl A {
    fn view(&self) -> Element<()> {
        let col = container(column![text!("col {}", self.text), text!("{}", self.text)])
            .center_x(Length::Fill);

        let col1 = container(column![
            text!("col 1{}", self.text2),
            text!("{}", self.text2)
        ])
        .center_x(Length::Fill);

        container(scrollable(row![col, col1]))
            .width(iced::Length::Fill)
            .height(iced::Length::Fill)
            .into()
    }
}

fn main() {
    let _ = iced::run("test", (), A::view);
}

Cargo.toml

[package]
// your package

[dependencies]
iced = { version = "0.13", default-features=false , features = ["tiny-skia","auto-detect-theme"] }

compile, scroll and see

What is the expected behavior?

There shouldn't be any of those weird trails.

Version

crates.io release

Operating System

Windows

Do you have any log output?

No response

[Daillusorisch]

Sadly, I found it happend even just scroll one column text :(

[sokorototo]

There seems to be an issue with Scrollable when paired with tiny-skia. I'm also on Windows, but I'm not sure if that's a variable too

[SoulSharer]

I just found that its due to a layer damage calculation in:

iced/tiny_skia/src/layer.rs

Lines 197 to 220 in a687a83

	let text = damage::diff(
	&previous.text,
	&current.text,
	|item| {
	item.as_slice()
	.iter()
	.filter_map(Text::visible_bounds)
	.map(|bounds| bounds * item.transformation())
	.collect()
	},
	|text_a, text_b| {
	damage::list(
	text_a.as_slice(),
	text_b.as_slice(),
	|text| {
	text.visible_bounds()
	.into_iter()
	.map(|bounds| bounds * text_a.transformation())
	.collect()
	},
	|text_a, text_b| text_a == text_b,
	)
	},
	);

It is probably due to float imprecision, I tested fix on my side, everything seems to be okay with additional 1 pixel padding.