<AWT Dev> [15] Review Request: 8231564 and 8176359

Alexey Ivanov alexey.ivanov at oracle.com
Wed Jan 29 17:27:52 UTC 2020

Hi Sergey,

The fix looks good to me.

The trick with WM_WINDOWPOSCHANGING should work to avoid covering the 
Taskbar on the secondary monitor too.


On 26/01/2020 22:43, Sergey Bylokhov wrote:
> Hello.
> Please review the fix for JDK 15.
> Bugs: 8231564: setMaximizedBounds is broken with large display scale 
> and multiple monitors
>         https://bugs.openjdk.java.net/browse/JDK-8231564
>       8176359: Frame#setMaximizedbounds not working properly in multi 
> screen environments
>         https://bugs.openjdk.java.net/browse/JDK-8176359
> Fix: http://cr.openjdk.java.net/~serb/8176359/webrev.01
> Short description:
> =================
>   The fix changes the way on how we limit the size and position of the 
> maximized window.
> Long description:
> =================
>   On Windows supports of maximized is done by the WM_GETMINMAXINFO[1] 
> message. This
> message provides MINMAXINFO[2] which has two related fields: ptMaxSize 
> and ptMaxPosition.
>   ptMaxPosition: The position of the left side of the maximized window 
> (x member) and
>                  the position of the top of the maximized window (y 
> member). For top-level
>                  windows, this value is based on the position of the 
> primary monitor.
>   ptMaxSize: The maximized width (x member) and the maximized height 
> (y member) of the
>              window. For top-level windows, this value is based on the 
> width of the primary
>              monitor.
> "For systems with multiple monitors, the ptMaxSize and ptMaxPosition 
> members describe the
> maximized size and position of the window on the primary monitor, even 
> if the window
> ultimately maximizes onto a secondary monitor. In that case, the 
> window manager adjusts
> these values to compensate for differences between the primary monitor 
> and the monitor that
> displays the window. Thus, if the user leaves ptMaxSize untouched, a 
> window on a monitor
> larger than the primary monitor maximizes to the size of the larger 
> monitor."
> My observation:
> =================
>   1. Description of "ptMaxPosition" in the documentation is wrong, 
> this value is based on the
>      actual window's monitor not a primary monitor. I have read about 
> it here[3] and confirmed
>      by the tests using three monitors setup.
>   2. ptMaxSize will be used as-is if the size is smaller than the 
> !!main!! monitor. If the size
>      is larger than the main monitor then the window manager adjusts 
> the size, like this:
>      // result = requested.w + (current.w - main.w); =>> This results 
> in the correct size if we
>      want to fully maximize the window on the current monitor, but if 
> we want to set a smaller
>      size then we will get the wrong result.
>      We can try to compensate for this adjustment like this:
>      // requested = requested.w - (current.w - main.w);
>      but this can result to the size smaller than the main screen, so 
> no adjustment will be
>      done by the window manager =>> wrong size again.
>      Note that the result does not depend on the monitor on which we 
> maximize the window.
>   3. For example for the three monitors setup: W1=600, W2=1600, 
> W3=1080. It is not possible
>      to maximize the window on W3 if the current window is on W2 
> monitor, because if we
>      request size=1080 which is bigger than 600 and it will be 
> adjusted by the window
>      manager: resulted size = 1080+(1600-600) = 2080. If we will try 
> to compensate this value:
>      size = 1080 - (1600-600) = 80, which is smaller than main monitor 
> and will be used as-is.
> Fix description:
>   1. To fix JDK-8231564 we should convert all coordinates from the 
> user's virtual space to
>      the device space.
>   2. To fix JDK-8176359 we need to translate the bounds.x/y from the 
> global virtual coordinate
>      system related to the main monitor to the coordinate system of 
> the window's actual monitor.
>   3. The current code already tried to compensate adjustment, but it 
> missed the fact that the
>      width and height should be adjusted separately, but even if that 
> be fixed, in some situations
>      this logic will be broken(see observation point 3). So instead of 
> fixing that I have passed
>      these values to the native as-is, and cut the adjustment in the  
>      just before the window is resized.
> Known issue:
>  - The current approach, as well as most of the API which uses user's 
> space coordinates, does
>    not work well if different scales are used for each screen and the 
> coordinates "overlaps".
>  - It looks like the user in the JDK-8231564 tried to avoid covers the 
> taskbar by the maximized
>    undecorated window, this is a know issue JDK-8022302.
> [1] 
> https://docs.microsoft.com/en-us/windows/win32/winmsg/wm-getminmaxinfo
> [2] 
> https://docs.microsoft.com/en-us/windows/win32/api/winuser/ns-winuser-minmaxinfo?redirectedfrom=MSDN
> [3] https://devblogs.microsoft.com/oldnewthing/20150501-00/?p=44964

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