wayland: text renders with wrong font size on startup until hover (regression from v2.7.4)

[gbonnema]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

When opening a window that contains a widget.List as its content, items are rendered with an incorrect (much larger) font size on startup. Moving the mouse cursor over a list item triggers a re-render that corrects the font and layout.

On v2.7.4, the same code renders correctly on startup without any mouse interaction.

This is similar to the previously fixed #645 ("Initial window display is blank on Gnome until hover or resize"), but that issue was resolved in 2020 and this appears to be a new regression in v2.8.0.

How to reproduce

1. Save the example code below as main.go in a new directory
2. Initialize and build for v2.8.0:

   go mod init fyne28test
   go get fyne.io/fyne/v2@v2.8.0
   go mod tidy
   CGO_ENABLED=1 go build -o list-test-280 .
   

3. Build for v2.7.4 (same directory):

   go get fyne.io/fyne/v2@v2.7.4
   go mod tidy
   CGO_ENABLED=1 go build -o list-test-274 .
   

4. Run ./list-test-280
5. Observe: items appear with an incorrect (much larger) font size
6. Move the mouse cursor over a list item — the font and layout correct themselves
7. Close the window, run ./list-test-274
8. Observe: the list renders correctly on startup without any mouse interaction

Screenshots

Example code

package main

import (
	"fmt"

	"fyne.io/fyne/v2"
	"fyne.io/fyne/v2/app"
	"fyne.io/fyne/v2/widget"
)

func main() {
	a := app.New()
	w := a.NewWindow("List font test")
	w.Resize(fyne.NewSize(400, 300))

	data := make([]string, 20)
	for i := range data {
		data[i] = fmt.Sprintf("Item %d", i)
	}

	list := widget.NewList(
		func() int { return len(data) },
		func() fyne.CanvasObject { return widget.NewLabel("template") },
		func(id widget.ListItemID, obj fyne.CanvasObject) {
			obj.(*widget.Label).SetText(data[id])
		},
	)

	w.SetContent(list)
	w.ShowAndRun()
}

Fyne version

v2.8.0 (works correctly on v2.7.4)

Go compiler version

go1.23.0 linux/amd64

Operating system and version

Ubuntu-based (Pop!_OS), Linux 6.16.3, GNOME desktop, Wayland

Additional Information

The terminal prints the following warning on startup (not seen on v2.7.4):

*** This application has not been migrated to the fyne.Do threading model ***
*** The next major Fyne release will remove this safety! ***
*** Read more at https://docs.fyne.io/started/goroutines ***

Setting fyneDo = true in FyneApp.toml does not resolve the issue.

The application does not use any goroutines for UI updates; all widget construction and SetContent happen on the main goroutine before ShowAndRun.

In a more complex application where the widget.List is wrapped inside a custom focusable widget, the same underlying issue manifests as a completely blank list area (no items rendered at all) until hover. This suggests the initial layout/theme pass is incomplete, with the severity depending on the widget hierarchy.

[MaxGyver83]

I can't reproduce this on my system (Arch Linux with dwm/X11). Maybe this issue is Wayland specific!?

[gbonnema]

Thanks for checking — that matches what we see here.

Same minimal repro on Fyne v2.8.0, Pop!_OS / Cosmic, session type Wayland:

• FYNE_PLATFORM=wayland: incorrect (much larger) list font/spacing on startup; corrects after hover, or after a screenshot forces a redraw.
• FYNE_PLATFORM=x11 (XWayland on the same Wayland session): renders correctly on startup.

So this does look Wayland-specific on our side. Screenshot: top window is X11 (correct; title missing (x11) only due to a rebuild race when launching — process was still started with FYNE_PLATFORM=x11), bottom is Wayland (oversized until redraw).

[andydotxyz]

Are you sure this is list related? That seems very strange given that it seems to be dependent on the window/render context.

[gbonnema]

Good point — it does not appear to be List-specific.

On the same Wayland session, a window whose only content is widget.NewLabel(...) starts blank. Taking a screenshot forces a redraw and the label then appears (same as hover/screenshot/tiling correcting the List case).

So List was just how we first noticed it; this looks like a Wayland window/render initial-paint issue. Happy to retitle if that helps.

[dweymouth]

I cannot reproduce either on Kubuntu Wayland

[Niotras]

Hi, i do have the same problem in simple app taht is just a window with buttons. (not list specific this bug)

I am on an CachyOS 7.1.5-1 Hyprland Wayland

[andydotxyz]

I cannot replicate on Weston - will try to get a VM running pop or similar

[andydotxyz]

I have run it in Hyprland and not got this problem - so perhaps there is a configuration required as well?
Of note is that the screenshot above appears to have window borders but the default is tiling...

[Niotras]

Hi,
i think this is only happening if you have a scaling applied to the monitor you are starting the application on with hyprland.
https://wiki.hypr.land/Configuring/Basics/Monitors/