I've fixed this unbearable bug when resizing a win...

# compose-desktop

[אליהו הדס]

I've fixed this unbearable bug when resizing a window in dark mode under Windows, in the next version of Nucleus that will be released. 🎉

20260309-0931-49.9082163.mp4

[Alexander Maryanovsky]

Do you mean you fixed the background showing through at the edges? How did you fix it?

[Colton Idle]

yeah whats the unbearable bug? is this the before or after the bug? lol

[אליהו הדס]

@Alexander Maryanovsky On Windows, Skiko's rendering pipeline clears the DirectX canvas to white before each frame. When the window is resized larger, the newly exposed pixels remain white for one frame — producing a visible white flash. I created a JNI module that eliminates this by adjusting Skiko's clear color to transparent for dark themes (rendered as opaque black on the DirectX surface), so the flash is invisible against a dark background. It also synchronizes the DWM caption and border colors (DWMWA_CAPTION_COLOR, DWMWA_BORDER_COLOR, DWMWA_USE_IMMERSIVE_DARK_MODE) with the title bar color for consistent Windows 11 window chrome styling.

[Alexander Maryanovsky]

Wouldn’t that just cause black bars on resize, which would be visible with a light theme?

[אליהו הדס]

I disable it in light mode

[Alexander Maryanovsky]

Ah, heh

[Alexander Maryanovsky]

Note this, though. Maybe you don’t need the hack anymore.

[Alexander Maryanovsky]

It now fills the canvas with the SkiaLayer.awt ’s background color

[אליהו הדס]

Yes ! does the latest alpha version of Compose use it?

[Alexander Maryanovsky]

yes

[אליהו הדס]

I will check this, thanks a lot

[Alexander Maryanovsky]

Hmm, I’m not sure it’s the canvas you’re referring to, though

[אליהו הדס]

I think I'll keep my hack for a little while anyway, for backward compatibility.

[Alexander Maryanovsky]

Which one did you touch?

[אליהו הדס]

I touched the GPU-level clear color — SkiaLayer.setTransparency(true) changes ContextHandler.draw() so it clears to TRANSPARENT instead of WHITE. On the DirectX surface (DXGI_ALPHA_MODE_IGNORE),
transparent renders as opaque black. I also handle the GDI level (WM_ERASEBKGND, SWP_NOCOPYBITS) and the DWM compositor (DwmExtendFrameIntoClientArea) to prevent white fills before Skiko even gets a chance
to render.
So it's a different layer from the AWT background your PR addresses 🙄 — but your fix might let me simplify or remove the setTransparency part.

[Alexander Maryanovsky]

So you’re changing the color ContextHandler.draw fills with?

[Alexander Maryanovsky]

Note there are 2 PRs. Both use the AWT background. The first one uses it to fill the canvas in ContextHandler.draw, but then we moved that to the Canvas in SkiaLayer.update, and the one in ContextHandler.draw is always filled with TRANSPARENT (0x0)

[Alexander Maryanovsky]

https://github.com/JetBrains/skiko/pull/1178

[אליהו הדס]

So you’re changing the color ContextHandler.draw fills with?

Yes, exactly. I toggle SkiaLayer.setTransparency(true) for dark themes, which makes ContextHandler.draw() clear to TRANSPARENT instead of WHITE.

Note there are 2 PRs. Both use the AWT background. The first one uses it to fill the canvas in ContextHandler.draw, but then we moved that to the Canvas in SkiaLayer.update, and the one in

ContextHandler.draw is always filled with TRANSPARENT (0x0)

so with the latest Skiko, my setTransparency(true)
hack is redundant now.

[Alexander Maryanovsky]

But now it’s always filled with TRANSPARENT

[Alexander Maryanovsky]

So it’ll be black in light theme

[אליהו הדס]

Ah yes, I see

[אליהו הדס]

I'll keep my current hack for now and drop the setTransparency once the new Skiko hits stable. Thanks!

[Alexander Maryanovsky]

I’ll talk to the team about exposing the color with which we fill in ContextHandler.draw

[Alexander Maryanovsky]

Ohhh, great news 🙂

[Alexander Maryanovsky]

So now the workaround for this that used to only work for macOS now works for Windows too, with a slight change.

[Alexander Maryanovsky]

@Composable
fun FrameWindowScope.windowBackgroundFlashingWorkaround(themeBackgroundColor: Color) {
    LaunchedEffect(window, themeBackgroundColor) {
        val awtColor = java.awt.Color(themeBackgroundColor.toArgb())
        window.background = awtColor  // for macOS 
        window.contentPane.background = awtColor  // for Windows
    }
}

[אליהו הדס]

oh it's very great

[Alexander Maryanovsky]

After setting contentPane.background I’m seeing almost no white bars on resize

[Alexander Maryanovsky]

In 1.11.0-alpha03

[אליהו הדס]

Yes, I see, there's still a little bit left. That's why I also handle the GDI level and the DWM compositor

[Alexander Maryanovsky]

I hope I didn’t break it in the 2nd PR. That won’t be seen until alpha04

[Alexander Maryanovsky]

But if I did, it just means we need to expose the clear color in ContextHandler.draw

[אליהו הדס]

Nice ! can't wait to test 😁

[Alexander Maryanovsky]

Looks like I broke it, but not too badly.
In alpha03 it’s enough to set contentPane background, in alpha04 you’ll need to set both contentPane and window background

[Alexander Maryanovsky]

(which you need to do anyway for macOS, at least previously)