RFR: 8372415: Stage size should match visual window bounds

[Michael Strauß]

On Mon, 24 Nov 2025 14:28:47 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> On Windows, the `Stage.width` and `Stage.height` correspond to the window size as returned by `GetWindowRect`.
> 
> Up until Windows 10, the size of a window was identical to its visual borders. However, since Windows 10 has introduced thin visual window borders, the window manager adds an invisible border of a few pixels around the window to make it easier to resize the window. Since `GetWindowRect` returns the window size _including_ these invisible borders, the location and size of a `Stage` isn't exactly what we'd expect.
> 
> For example, if we place a `Stage` at `setX(0)` and `setY(0)`, the window appears with a small distance from the screen edge, and the window size extends a few pixels beyond its visual borders (in the following images, the screenshot size corresponds to the window size; note the invisible padding around the edges):
> <img width="300" alt="window-size-1" src="https://github.com/user-attachments/assets/76ea6861-885f-4bea-aeb7-e8e6464b7199" />
> 
> What we actually want is to have the visual borders line up with the edges of the screen, and have the window size correspond to the visual borders:
> <img width="295" alt="window-size-2" src="https://github.com/user-attachments/assets/ca6bed73-e4e7-4df6-9491-d82792bb0866" />
> 
> The implementation is quite simple: instead of `GetWindowRect`, we use `DwmGetWindowAttribute(DWMA_EXTENDED_FRAME_BOUNDS)`. This gives us the bounds of the visual window borders. If this function fails, we fall back to `GetWindowRect` (now, I don't know why `DwmGetWindowAttribute(DWMA_EXTENDED_FRAME_BOUNDS)` would ever fail... maybe an old Windows version in a remote desktop scenario?).

I've added a comment to clarify that `m_minSize`, `m_maxSize`, and `m_insets` are specified with respect to the extended frame bounds.

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PR Comment: https://git.openjdk.org/jfx/pull/1982#issuecomment-3604540834