RFR: JDK-8255439: System Tray icons get corrupted when windows scaling changes [v2]

[Harshitha Onkar]

On Sat, 7 May 2022 13:01:53 GMT, Kevin Rushforth <kcr at openjdk.org> wrote:

>> Harshitha Onkar has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   resized instruction window and formatted line lengths
>
> The fix looks good to me, but someone more familiar with the code will need to review it. I can confirm that the new test program fails without the fix and passes with the fix. One problem with the test is that it doesn't exit for me, regardless of whether the test passes or fails (or times out).
> 
> To partially answer Sergey's question, the problem with just using `WM_DPICHANGED` to trigger the update is that the scale of the default screen transform used by `WTrayIconPeer::updateNativeImage` hasn't yet been updated to reflect that new DPI scale. I don't know _why_ that is the case here, but it is. I do know that in JavaFX we stopped relying on `WM_DPICHANGED` for anything related to HiDPI several years ago when fixing some multi-monitor HiDPI issues in [JDK-8146920](https://bugs.openjdk.java.net/browse/JDK-8146920).
> 
> To show that triggering the update on `WM_DPICHANGED` is insufficient, I applied the patch from this PR, added some debugging output, and modified the fix to also update the image on a `WM_DPICHANGED` event. Here is the output when I start the program with a screen scale of 1.25 and then change it to 1.5:
> 
> 
> WM_WINDOWPOSCHANGING
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WTrayIconPeer::updateNativeImage : scale = (1.25, 1.25)
> WM_DPICHANGED
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WM_WINDOWPOSCHANGING
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WTrayIconPeer::updateNativeImage : scale = (1.25, 1.25)  <----- This is from the WM_DPICHANGED event
> WTrayIconPeer::updateNativeImage : scale = (1.25, 1.25)
> WM_WINDOWPOSCHANGING
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WTrayIconPeer::updateNativeImage : scale = (1.5, 1.5)    <----- Transform has now been updated
> WM_WINDOWPOSCHANGING
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WTrayIconPeer::updateNativeImage : scale = (1.5, 1.5)
> WM_WINDOWPOSCHANGING
> AwtTrayIcon::UpdateTrayIconHandler
> SystemTray::updateTrayIcons
> WTrayIconPeer::updateNativeImage : scale = (1.5, 1.5)
> 
> 
> So I think the fix using `WM_WINDOWPOSCHANGING` to trigger the update is good. I left a couple minor comments inline.

@kevinrushforth Thank you for taking time to look into the fix and providing informative feedback. 
I'll check the test case exit issues and add the suggested changes.

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