fix DWM taskbar thumbnail live app-preview for modeless WS_DLGFRAME h…#15703
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…idden dialogs The WinOS Desktop Window Manager taskbar thumbnail live preview has obviously a problem with modeless only hidden dlgs which have the WS_DLGFRAME style - the preview initially shows such dialogs, even if they were already hidden. Temporarily using the WS_EX_TOOLWINDOW style on such a problematic dlg, right before its hiding and then after the hiding immediately removing that style, does the trick (floating toolbar-wnds are not allowed on the taskbar (or in the ALT-TAB), so DWM probably will not consider them at all for such a preview...).
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@xomx The WS_EX_TOOLWINDOW have been replaced by WS_EX_DLGMODALFRAME | WS_EX_WINDOWEDGE in this commit: @ozone10 |
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@donho Also close button is smaller, same as undocked panels. IMHO this is Windows bug, IIRC there is similar issue with some QT apps, also not updating live preview. btw I cannot reproduce it on 2 machines, one with Windows 10 other 11 24H2 @xomx |
I suppose so - if I restore N++ back and minimize again, the live-preview problem is gone, hidden dlgs are not visible (until I show/hide them again). I somewhere saw a Java app having exactly this live-preview problem under Windows 10&11 and using successfully such a temporary WS_EX_TOOLWINDOW DWM-workaround, so I tried my luck in N++ and it works.
I can reproduce on Win10Ent LTSC 2021 and Win11Pro 23H2.
I noticed that even though About-dlg is also based on the
Another DWM problematic one is Find-dlg. |
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@xomx |
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@ozone10
@xomx |
:-) This is an overly optimistic expectation. Unless a miracle happens, that evidently long standing bug will remain there for good. |
I see your point, but I still want to give Microsoft a chance to fix their bug. ;) |
Ok, I will try not to behave like a spoilsport to your optimism. :-) Let's pretend the MS does not know about this problem yet. Then a simple POC & video for the report is needed: Win10 video (Win11 shows the same, but Win7SP1 in a VM is ok, so it seems to be a Win10+ bug, I do not have Win8 ready for such a test): PreviewBugPOC4.mp4Now the hard part - reporting it to them:
If anyone wants to try any of this, feel free to do it (as I will not, good luck). There is one more "dirty" possibility - somehow pretend/try to pass it off as a security issue and then write a blog post about it and try to make it go viral somehow. It is stupid but it works, nowadays people hear about it and the MS pays attention to its possible negative audience. (How to do it here - I would e.g. write something like: "It is a potential security issue because there could be a deliberately hidden dialog containing sensitive information... blablabla". Endnote: Do not ever try the MS call support for such a thing - real purpose of this 100% outsourced stuff is to get rid of thousands people annoying the MS every day with often trivial or non-existent problems. It is a filter-wall. For a person with a real technical problem to report, it is a multi-level circular Hell where the only goal is to get the caller to hang up. |
Very true :( Feedback Hub has been downloaded, and bug was reported (with the POC zip you provided) via Feedback Hub to Microsoft. Thank you very much for the very detail instructions and the POC file. |
Unfortunately this is not a sln, now I tested on another PC with Win11 25H2 (build 26200.8037), with GPU drivers from late 2025 and the problem is still there. It's a MS bug, not a GPU one. |
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That bug is also affecting Windows 10. And since Windows 10 is practically EOL and can run on many old PCs, which don't have new GPU driver I don't think that solution is correct. |
Fix #15690
The WinOS Desktop Window Manager taskbar thumbnail live preview has obviously a problem with modeless only hidden dlgs which have the WS_DLGFRAME style - the preview initially shows such dialogs, even if they were already hidden.
Temporarily using the WS_EX_TOOLWINDOW style on such a problematic dlg, right before its hiding and then after the hiding immediately removing that style, does the trick (floating toolbar-wnds are not allowed on the taskbar (or in the ALT-TAB), so DWM probably will not consider them at all for such a preview...).