Fullscreen error when displays have different scale settings

I have a commercial app that was deployed in late 2018. It runs on Windows and requires Fullscreen=true to eliminate the taskbar at the bottom of the display. The app is generally used with multiple displays with the Main display (identified as Screen 1 in the Windows display settings) used for an application that is independent of my app. I received a tech support request from a customer who is using HiDPI laptops for the Main display with a Windows scale setting of 150%. His systems have two additional displays that are not HiDPI and have a scale setting of 100%. When the display used for my app is placed to the right of the Main display through Windows Display settings, the window for my app splits across the Main display and the display to the right. Since the window is in Fullscreen mode, it cannot be dragged to the desired display to correct the placement. I created a test app in C++ to determine if this was a Windows issue. The C++ app does not exhibit this behavior. I have isolated the problem to the use of different scale settings on the displays. If they are all set to the same scale setting, the error does not occur. However, this is not an option because the text on the Main (HiDPI) display is too small to read for most folks with the scale setting at 100%. There are other issues that prevent setting the scale to 150% for all 3 monitors.

Has anyone else had this problem, and if so, is there a resolution?


Oh yes… many/most/all Xojo Developers that have to deal with TargetWindows and MultiMonitor / MultiScale. Let’s just say that the Xojo Framework is not handling this as expected, not to say it’s broken (for that kind of situation / environment).

This “FullScreen” issue is reported here: <https://xojo.com/issue/64805>
And of course quite some other Feedback Issues regarding MultiMonitor/MultiScale on Windows…

Do the positioning yourself using Declares and don’t rely on the Xojo Framework (for now)…
There is this example project: Monitors

Back to you “FullScreen” issue… have a look at the updated “Monitors - example” that I’ve attached in <https://xojo.com/issue/64805> on June 22, 2021.

I haven’t had time to clean up the “FullScreen” quick-and-dirty test and update the example project “Monitors example” version on my website… so for “FullScreen”, have a look at the one in Feedback for now.


Thank you for the link to the update for your Monitors code. Much appreciated.

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You’re welcome.
Add your Information to the Feedback Case(s)… and be it just that Xojo is aware this is affecting a lot of their customers :wink:

I ran the FullScreen test posted in https://xojo.com/issue/64805. The test code displayed the window correctly with FullScreen=true with the displays set to the scales described in my original post. :slight_smile: I plan to integrate the changes into my code. I will update when completed and tested.