Modern style on windows not working with DirectX12.

[GRX005]

Bug Description

When using Skia with DirectX12, background transparency won't work at all, upon using background: transparent;, it will be just black, otherwise just simply the color defined, without the transparency in the rgba.

For example you can't use mica material(with the window-vibrancy crate) as the window background with dx12 this way, as for it to show we first need to hide the default.

Reproducible Code (if applicable)

export component MainWindow inherits Window {
background: #5758a383;
}

Environment Details

• Slint Version: 1.11.0
• Platform/OS: Windows 11
• Programming Language: Rust
• Backend/Renderer: Skia: DirectX12

Product Impact

It would be great to use modern effects like transparency with a more capable graphics API like DirectX12, to make slint more in-par with Microsoft's WinUI 3 for modern app development, but in rust.