Rounded corners are the most immediately noticeable feature of Windows 11 Geometry. On Windows 11, the system automatically rounds top-level window corners for all inbox apps, including all UWP apps, and most other apps. However, some Win32 apps might not be rounded. This topic describes how to round your Win32 app's main window corners if the system does not round them automatically.

Note

By design, apps are not rounded when maximized, snapped, running in a Virtual Machine (VM), running on a Windows Virtual Desktop (WVD), or running as a Windows Defender Application Guard (WDAG) window.

The Notepad app on Windows 11 with rounded corners.
Why isn't my app rounded?

If your app's main window doesn't receive automatic rounding, it's because you've customized your frame in a way that prevents it. Apps fall into three main categories from the perspective of the Desktop Window Manager (DWM):

Apps that are rounded by default.

This includes apps that want a complete system-provided frame and caption-controls (min/max/close buttons), like Notepad. It also includes apps that provide enough information to the system so it can properly round them, such as setting the WS_THICKFRAME and WS_CAPTION window styles or providing a 1-pixel non-client area border that the system can use to round the corners.

Apps that are not rounded by policy, but can be rounded.

Apps in this category generally want to customize the majority of the window frame but still want the system-drawn border and shadow, such as Microsoft Office. If your app is not rounded by policy, it could be caused by one of the following things:
Lack of frame styles
Empty non-client area
Other customizations, such as extra non-child windows used for custom shadows

Changing one of these things will break automatic rounding. Although we did try to round as many apps as possible with our system heuristics, there are some combinations of customizations that we can't predict so we provided a manual opt-in API for those cases. If you address these issues in your app or call the opt-in API, described in the following section, then it's possible for the system to round your app's window. Note, however, that the API is a hint to the system and does not guarantee rounding, depending on the customizations.

Apps that cannot ever be rounded, even if they call the opt-in API.

These apps have no frame or borders, and typically have heavily customized UI. If your app does one of the following, it cannot be rounded:
Per-pixel alpha layering
Window regions

For example, an app might use per-pixel alpha layering to draw transparent pixels around its main window to achieve a custom shadow effect, which makes the window no longer a rectangle and therefore the system cannot round it.