RFR: JDK-8255439: System Tray icons get corrupted when windows scaling changes

[Harshitha Onkar]

On Fri, 29 Apr 2022 00:36:15 GMT, Sergey Bylokhov <serb at openjdk.org> wrote:

>> In Windows when desktop scaling was changed the tray icons was distorted/blurred a bit each time scaling changes.
>> 
>> With the proposed fix, the tray icon scales according to on-the-fly DPI scale settings. A test case has been added which adds a MRI icon to system tray, to observe the icon scaling when DPI is changed. Since the scale cannot be programmatically changed (for dynamic on-the-fly scale changes), I have used a manual test case to test this scenario.
>> 
>> When DPI changes usually two messages are sent by windows -
>> 
>> - [WM_DPICHANGED](https://docs.microsoft.com/en-us/windows/win32/hidpi/wm-dpichanged)
>> - [WMPOSCHANGING](https://docs.microsoft.com/en-us/windows/win32/winmsg/wm-windowposchanging)
>> 
>> I'm triggering an update on tray icons on receiving WMPOSCHANGING msg through the Tray icon's Window Procedure. Triggering an update on WM_DPICHANGED was still causing the icons to be distorted, hence WMPOSCHANGING is being used as the message to trigger the update.
>
> Did you have a chance to check why the WM_DPICHANGED does not work, any specific cases? It is used by checking the scale change for windows in AWT, and no issues were reported for that as far as I know.

@mrserb  I wanted to add few more details about various window messages received during DPI changes. The order in which messages are received- 

1. WM_DPICHANGED - if update is triggered at this point, the tray icons get distorted
2. WM_POSCHANGING - if update is triggered at this point, tray icons are rendered without any distortion.
3. WM_POSCHANGED - message received when tray icon is removed or exited.

Kevin (@kevinrushforth) mentioned the usage of `WM_WINDOWPOSCHANGING` in JavaFX. Adding him to this PR conversation for suggestions.

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PR: https://git.openjdk.java.net/jdk/pull/8441