Sidebar background blinking on scrollbar mouse hover

[akashjasani]

Screen.Recording.2025-04-30.at.12.08.00.AM.mov

I'm experiencing an issue with the sidebar in my app. When I hover the mouse over the sidebar or its scrollbar, the background of the sidebar starts blinking. I've attached a video showing the official macOS UI example, which demonstrates the same issue I'm encountering.

How can I resolve this? The sidebar background should remain stable and not blink on mouse hover.

[akashjasani]

Any idea? How can i fix this kind issue

[Adrian-Samoticha]

All of us maintainers currently have very low bandwidth, and it’s difficult to allocate time for fixing a bug when it’s impossible to tell how long that would take. You can, however, greatly speed up the resolution of this issue by attempting to look into the issue yourself and reporting any insight you gain.

[GroovinChip]

@akashjasani Are you still encountering this issue? If so, please provide the following details:

• What version of macOS does this happen on?
• What version of Flutter does this happen with?

[SchillingSebastian]

This is still present in the sample project under macOs 15.6.1 and Flutter 3.9.2

[SchillingSebastian]

I nailed it further down to the TransparentMacOSSidebar widget which is rendered in the window.dart

macos_ui/lib/src/layout/window.dart

Lines 326 to 332 in b1ecd80

	: TransparentMacOSSidebar(
	state: sidebarState,
	child: DecoratedBox(
	decoration: const BoxDecoration(
	color: Color.fromRGBO(0, 0, 0, 1.0),
	backgroundBlendMode: BlendMode.clear,
	),

This somehow interferes in repaints/widget updates and creates this flickering. It might be related to the blend mode and the updates happening there.
Why is there event this DecoratedBox with 100% opacity?
Removing the DecoratedBox and directly pass the Column resolves the flickering for me, but it makes the sidebar a tint darker.

[Adrian-Samoticha]

The DecoratedBox is there precisely to remove this dark tint (which I believe is caused by some Cupertino widget, but I’m not quite sure—either way, it’s not present in native applications). I guess the flickering is caused by that DecoratedBox not being rendered when the user hovers over the scrollbar, but I have no clue as to why that is.