The text in the button may tear when resizing the window

[lzm-build]

Bug Description

What is the bug?

The text in the button may tear when resizing the window.

What behavior did you expect, and what happened instead?

Normal rendering.

Steps to reproduce the issue?

git clone https://github.com/slint-ui/slint-rust-template.git
cd slint-rust-template
cargo run

Screencast_20260303_085031.webm

Reproducible Code (if applicable)

import { Button, VerticalBox } from "std-widgets.slint";

export component AppWindow inherits Window {
    in-out property <int> counter: 42;
    callback request-increase-value();
    default-font-size: 30px;
    VerticalBox {
        Text {
            text: "Counter: \{root.counter}";
        }

        Button {
            text: "Increase value";
            clicked => {
                root.request-increase-value();
            }
        }
    }
}

Environment Details

• Slint Version: 1.15.1
• Platform/OS: Fedora Linux 43 (KDE Plasma Desktop Edition)
• Programming Language: Rust
• Backend/Renderer: default

Product Impact

No response

[lzm-build]

Text in HorizontalBox and VerticalBox may also tear when the window is resized.

[wuwbobo2021]

Please check what backend and renderer are being used in your environment; check https://docs.slint.dev/latest/docs/slint/guide/backends-and-renderers/backends_and_renderers, https://docs.rs/slint/latest/slint/struct.BackendSelector.html.

[lzm-build]

@wuwbobo2021
Among the provided backend and renderer, testing found that font tearing only occurs with the following cfg:

slint = {version = "1.15.1", default-features = false, features = ["backend-winit-wayland", "renderer-femtovg", "compat-1-2"]}

and

slint = {version = "1.15.1", default-features = false, features = ["backend-winit-x11", "renderer-femtovg", "compat-1-2"]}