Layout glitch

[ahmet-sakar]

Description

When the application window is minimized and then restored (or maximized), a weird layout glitch occurs. The UI components do not redraw correctly, leaving parts of the interface blank or misaligned.

Steps to Reproduce

1. Run the application (flectar-mail.exe).
2. Minimize the window to the taskbar.
3. Restore the window.

Visuals

Actual Behavior

The layout glitches out, elements fail to render, and the interface doesn't refresh properly. Terminal logs show it uses vello-cpu / blitz-paint for rendering.

Expected Behavior

The UI layout should adjust and redraw correctly when the window state changes.

Environment

• OS: Windows 10/11 (cmd.exe environment)
• Renderer: vello-cpu / blitz

[iamdarkle]

Hi, thank you for the report. Just a quick question: is this a one-off occurrence, or does it happen consistently every time those steps are carried out?

[ahmet-sakar]

Everytime

[iamdarkle]

Thanks for confirming that this happens every time. This appears to be an upstream Slint software-renderer problem triggered when Windows restores or resizes the window. We’re tracking the matching upstream report at slint-ui/slint#13537.

Could you please test the GPU renderer and tell us whether the problem still occurs?

set "FLECTAR_RENDERER=gpu" && target\debug\flectar-mail.exe

Please also include the Windows version shown by winver. The GPU renderer can be used as a temporary workaround if it resolves the problem.

[ahmet-sakar]

You're welcome,

I compiled and tested the app. When I tested it using the GPU, I didn't notice any visual issues upon launching the app.

Visual

Problems

Import

Solve

crates/flectar-mail-core/src/files/service.rs

use crate::files as files;
use crate::files::{AttachmentFile, ConnectionSettings, FileClient, FileNode, PAGE_SIZE};

GPU Initialization

Have a shatter

2026-09-22.17-30-58.mp4

Debug log

FLECTAR_RENDERER {"event":"requested","gpu_supported":true,"pid":24440,"preferred":"gpu","requested":"gpu"}
FLECTAR_RENDERER {"active":"gpu","blitz":"vello-gpu","event":"selected","pid":24440,"preferred":"gpu","requested":"gpu","shared_device":null,"slint":"femtovg-wgpu","wgpu_initialized":null}
GPU initialization failed; restarting once in CPU / Low Memory mode: The rendering backend does not support rendering notifiers.
FLECTAR_RENDERER {"event":"requested","gpu_supported":true,"pid":20368,"preferred":"gpu","requested":"cpu"}
FLECTAR_RENDERER {"active":"cpu","blitz":"vello-cpu","event":"selected","pid":20368,"preferred":"gpu","requested":"cpu","shared_device":false,"slint":"software","wgpu_initialized":false}

Environment

• OS: Windows 11 Pro 25H2, Build 10.0.26200.9457
• CPU / Architecture: x64 / x86_64
• GPU: AMD RX580 8 GB - DX12
• Cargo Version: 1.92.0-nightly (2025-09-16)
• Rustup Version: 1.28.2
• Python Version: 3.12.4

[iamdarkle]

Thanks for taking the time to build and test this, and for including the video and logs.

I checked the renderer log, and the GPU renderer didn't actually stay active. It was selected initially, but initialization then failed:

GPU initialization failed; restarting once in CPU / Low Memory mode:
The rendering backend does not support rendering notifiers.

Flectar Mail then restarted using Slint software renderer. That means the window shown after the restart was still CPU-rendered.
This also explains why the app could look fine when it first opened. The original problem only happens after minimizing and restoring the window, the initial software-rendered frame is normally complete.

Slint has now reproduced that exact sequence in its own Gallery example and identified the cause. A targeted fix is under review in slint-ui/slint#13566. I'll keep this issue open until we can update Slint and verify the fix here.

I also saw the animation stutter in the video. That is expected when running an unoptimized debug build with cargo run and is separate from the minimize/restore problem. A release build created with cargo run --release should give a more representative result.