Proposal : Layered window and full Transparent window for UWP apps.

[77376]

Proposal: Layered Windows and full Transparent Windows for UWP apps.]

Summary

Today UWP apps only support the standard Overlapped window and pop-up window. Compact overlay kinda accomplishes this but yet it can't create full transparent windows. However , a lot of times when layered & transparent windows are very useful.

Rationale

For example , that transparent windowed-floating timer helps while reading a PDF  similarly, layered window/that floating message bubbles found in android is very much useful while chatting  a lot of other scenarios are there which helps in productivity, I can't remember right now . For security reasons, this feature will have to explicitly ask the end user for permission.

Scope

Capability	Priority
This proposal will allow developers to create Layered Window & full Transparent window for UWP apps	Must
This feature will have to explicitly ask the end user for permission	Must

[AzAgarampur]

The composition engine is capable of creating a transparent window by creating a HostBackdropBrush, but by default it blurs out what's behind. Maybe we can change some internal code in Windows.UI.Composition to not use blur by default?

[stevewri]

Windowing, AppModel & Shell have a stake in this; also spoofing/security issues.

[77376]

@stevewri since developers may misuse/spoof the feature, it can be a restricted capability ; also ask the end user consent.

[77376]

@AzAgarampur enabling Layered window is the primary requirement. And transparent window (thus hiding title bar and other unnecessary elements/views) should be supported without hacks.

[AzAgarampur]

@m98770 I understand, but we really should not use layered windows with the modern hardware-accelerated XAML framework. Layered windows are designed for User32/GDI controls and windows without any hardware-acceleration. If we do enable the WS_EX_LAYERED flag on the UWP windows, the CPU, rather than the GPU, is forced to preform all the hit testing and alpha blending, causing a significant performance bottleneck.

As far as hiding the title bar, we can probably change some code within ApplicationFrame.dll which draws the modern window for UWP applications to NOT use DwmExtendFrameIntoClientArea and NOT draw a title bar and caption buttons when we specify that we don't want a title bar to be shown.

[77376]

@AzAgarampur User32/GDI controls naturally won't work on other platforms. since this is a request for UWP apps , it has to be reimplemented in XAML framework in a secured way. I'm a bit skeptical of that way of reliably hiding all the unnecessary titlebar/views/buttons.

[AzAgarampur]

Let's see what @stevewri thinks.

[ysc3839]

@AzAgarampur There's DirectComposition. And when use with WS_EX_NOREDIRECTIONBITMAP, it's similar to layered window.

https://docs.microsoft.com/en-us/archive/msdn-magazine/2014/june/windows-with-c-high-performance-window-layering-using-the-windows-composition-engine

[AzAgarampur]

@ysc3839

The composition engine is capable of creating a transparent window by creating a HostBackdropBrush, but by default it blurs out what's behind. Maybe we can change some internal code in Windows.UI.Composition to not use blur by default?

That's what I was trying to say here, because UWP already uses DirectComposition to create the HostBackdropBrush.

[mdtauk]

I had a thought in another repo that may be relevant.

I wonder if going back to Windows 7 - WinUI/Reunion could provide a driver, which provides the Rendered layer needed to handle Acrylic. WinUI apps on deployment and new OS versions could include the driver which provides the base layer render visual, via the Store.

Windows 7 and Vista before it must have had the capability for the Aero Glass rendering. Windows 8/8.1 had the Visual Composition Layer. So perhaps this is more of a Reunion ask, but if the driver handled the OS dependent stuff, the rest could all remain User level right?

[AzAgarampur]

@mdtauk Yep, the actual API can remain in user mode, but the driver could a hassle. It will need to get in between the DirectX framebuffer, and set up some form of communication from user mode to kernel mode, either rpc or ioctl.

For Windows 7, the blur is created by drawing the semi-transparent glass png file in the aero theme file. For Windows 8, since we have DirectComposition, I'm not too sure if there's a kernel-mode driver which exports some functions which we can use...

In either case, how will we get a handle to the DirectX surface of the window so we can modify it? There are undocumented api's like user32.dll's DwmGetDxSharedSurface. Hopefully somebody with kernel-mode graphics knowledge can propose something here.

[mdtauk]

For Windows 7, the blur is created by drawing the semi-transparent glass png file in the aero theme file. For Windows 8, since we have DirectComposition, I'm not too sure if there's a kernel-mode driver which exports some functions which we can use...

The DWM I think provides the transparent PNGs on top of the blurred image. The Blur is the image manipulation of the Render Buffer of the screen. The swapchain is just the render buffer minus the active window I think.

In either case, how will we get a handle to the DirectX surface of the window so we can modify it? There are undocumented api's like user32.dll's DwmGetDxSharedSurface. Hopefully somebody with kernel-mode graphics knowledge can propose something here.

Any new driver could probably just have a PNG/DDS texture in memory, which the app window/brush would display.

Edit: I am not a professional developer or have any experience with Kernel/Driver/Low Level coding

[AzAgarampur]

Yep, my bad. The PNG image is just the glass's "light shine" effect, like the bars you see spanning diagonally across the aero glass.

[selastingeorge]

@mdtauk Yep, the actual API can remain in user mode, but the driver could a hassle. It will need to get in between the DirectX framebuffer, and set up some form of communication from user mode to kernel mode, either rpc or ioctl.

For Windows 7, the blur is created by drawing the semi-transparent glass png file in the aero theme file. For Windows 8, since we have DirectComposition, I'm not too sure if there's a kernel-mode driver which exports some functions which we can use...

In either case, how will we get a handle to the DirectX surface of the window so we can modify it? There are undocumented api's like user32.dll's DwmGetDxSharedSurface. Hopefully somebody with kernel-mode graphics knowledge can propose something here.

You are right, Even The DWMEnableBlurBehind() in windows 7 was using DWMSharedSurface for acquiring the visual behind window (there is more stuff happening between) , if you try decompiling dwmapi.dll you can see those. in windows 10 there is a hack to capture the dwm thumbnail into an IDCompositionVisual, its a little confusing, Checkout the code here : https://gist.github.com/ADeltaX/aea6aac248604d0cb7d423a61b06e247

[btueffers]

Hi everyone! The Windows App SDK and this repository is focused on desktop-based apps as per our announcement. UWP apps can use the Windows App SDK by migrating their project types to desktop-based projects.

Multi-window is currently scheduled for 1.1. Transparent Windows is something being considered in the backlog for Windows App SDK see it in productboard to share further feedback!