RudeWindowFixer: fix Windows taskbar always-on-top issues

Brought to you by Etienne Dechamps - GitHub

If you are looking for executables, see the GitHub releases page.

Description

Ever felt frustrated by this?

RudeWindowFixer is a small program that gets rid of known "Windows taskbar not always on top" bugs.

Specifically, it works around proven bugs in the internal Windows taskbar code where, under very specific circumstances, Windows mistakenly believes that you are using a full screen application and hides the taskbar.

Usage

Download RudeWindowFixer.exe from the GitHub releases page.
Run RudeWindowFixer.exe.
- Nothing will happen at first; this is normal. RudeWindowFixer is quietly running in the background. You can check in the Task Manager if you want to make sure.
That's it!
- You will likely want to make RudeWindowFixer.exe run on startup so that it persists across reboots.
Upvote this Microsoft bug report to hopefully get Microsoft to prioritize fixing the underlying Windows bug, which is described in detail below.

Limitations

RudeWindowFixer does not claim to fix all possible taskbar always-on-top bugs. Sadly, reverse engineering efforts (see below) revealed that the relevant Windows code paths are somewhat brittle and might be prone to variations on these problems (e.g. different triggers or problematic window state) that RudeWindowFixer might not be able to detect and fix.

Also note that all investigation and testing was done on Windows 11 21H2 22000.434; other Windows versions might behave differently.

If you notice that RudeWindowFixer does not fix the problem for you, or at least not consistently, do feel free to file an issue - it might be possible to instrument your system to gather detailed data about your problem, especially if you can reliably trigger it.

It's also theoretically possible that RudeWindowFixer could go overboard and make the taskbar show up in cases where it shouldn't - namely, on top of full screen applications (video players, games). This is unlikely to happen in practice. If you've seen it happen, do file an issue and make sure to mention the name of the full screen application the taskbar is being shown on top of.

Specific known issues that RudeWindowFixer does NOT fix

In issue #3, it was discovered that Microsoft introduced a regression in Windows 11 build 22000.556 (KB5011493). The bug is not present in build 22000.493. It appears that Microsoft has fixed it with the 22H2 update, around build 22621.1105.
- One known reproducer for this bug is:
  1. Open the Start Menu.
  2. Switch to any window using a taskbar window button.
  3. Click anywhere at the exact moment the taskbar finishes its hiding animation (assuming it's set to autohide).
    - The timing is somewhat tight so this might require a few attempts.
- This is likely the issue that this Feedback hub entry is about.
- This bug seems is completely unrelated to the other issues RudeWindowFixer is fixing (see below) - in fact it doesn't seem to involve the Rude Window Manager at all.
RudeWindowFixer currently does not address the problem of an app being treated as full screen if its dimensions exceed those of the monitor, leading the taskbar to drop behind it.

The problems in detail

Disclaimer: The following information was gathered through careful instrumentation of various window management facilities as well as reverse engineering (disassembly) of the relevant Windows code, helped by public Microsoft symbols. Reverse engineering is a difficult task where quick progress requires a fair amount of guesswork, so I wouldn't assume all the details below are exactly correct. This information applies to Windows 11 21H2 22000.434. The behaviour of other Windows versions might differ.

TL;DR

There are two known scenarios in which the taskbar can accidentally lose its "always on top" status. The following background information is required to understand both:

The taskbar "always on top" window property is controlled by a piece of internal Windows code called the Rude Window Manager.
The Rude Window Manager will only make the taskbar "always on top" on a given monitor if, among the windows located on that monitor, the top (foreground) window is not a full screen window.
Some applications create transparent full screen windows that are essentially invisible, but still count as full screen windows as far as the Rude Window Manager is concerned.

The first failure mode is fairly simple: it is triggered by the presence of an always on top transparent full screen window. This essentially confuses the Rude Window Manager, resulting in the taskbar "always on top" property being dropped.

The second failure mode is more subtle and harder to trigger, but does not require the transparent full screen window to be always on top:

A minimized window is not "located on" any monitor and is therefore never seen as the "top" window by the Rude Window Manager.
When a minimized window is activated, a race condition can occur wherein the Rude Window Manager still sees the window as minimized and therefore does not treat it as the new "top" window.
If the next window located on that monitor happens to be a (possibly transparent) full screen window, the Rude Window Manager will wrongly conclude that a full screen window is on top, and wrongly drop the taskbar "always on top" property.

The rest of this section go into each of these points in more detail.

Taskbar "always on top" behavior

During normal usage, the Windows taskbar is "always on top" of other windows. More specifically, the taskbar window (Shell_TrayWnd window class, part of explorer.exe) has the WS_EX_TOPMOST extended window style.

However, there is a case where Windows will drop the "always on top" property and will put the taskbar behind all other windows. This happens when Windows believes the user is interacting with a full screen application. This prevents the taskbar from obscuring the full screen application.

The Rude Window Manager

In internal Windows code, this full screen detection logic is implemented in an internal class called the rude window manager (twinui!CGlobalRudeWindowManager, also running in explorer.exe). Internally, the code uses the term rude monitor to refer to a monitor on which the top window is a full screen window. RudeWindowFixer is named after this terminology.

(If you are lucky enough to have access to the Windows source, you will find this code in shell\twinui\rudewindowmanager\lib\globalrudewindowmanager.cpp.)

Roughly, the rude window manager is implemented as follows:

Listen for specific window management events. Most of these events come from shell hook messages, which are generated by the kernel (win32k). For the purpose of this discussion, we are mostly interested in:
- Windows entering or exiting full screen status. These are codified using undocumented wParam values 0x35 and 0x36, respectively. These appear to be generated based on window dimension changes.
- Window activation events (HSHELL_WINDOWACTIVATED and HSHELL_RUDEAPPACTIVATED messages - note the differences between the two aren't clear, and the rude window manager treats them the same).
If one of these events occur, twinui!CGlobalRudeWindowManager::RecalculateRudeWindowState() will look at each monitor and determine if it should be considered "rude".
In the event a monitor "rudeness" changes, notifications are delivered to other components through CRudeWindowManager.
- This notably includes the code in charge of the taskbar, through Explorer!CTray::OnRudeWindowStateChange(), which calls Taskbar!TrayUI::RudenessChanged(), which calls Taskbar!TrayUI::_ResetZorder(), which finally sets or unsets the "always on top" property of the taskbar window based on the new state.

Let's focus on step (2).

What makes a monitor "rude"?

RecalculateRudeWindowState() looks at the properties of visible windows to make this determination. For the purpose of this discussion, the most relevant property is the window dimensions (i.e. its spatial coordinates and size). These are determined by RudeWindowWin32Functions::GetWindowRectForFullscreenCheck() which internally uses GetWindowRect().

(If the window has any of the WS_THICKFRAME or WS_CAPTION style bits, i.e. it has a border, then GetClientRect() is used instead and the result is converted to screen coordinates using MapWindowPoints(). This subtlety doesn't matter much for the purposes of this discussion.)

A window is deemed to be located on a monitor if its dimensions overlap with that monitor.

Within the set of windows that are on a given monitor, the window that comes at the top of the Z-order is defined as the top (foreground) window for that monitor.

The Rude Window Manager internally keeps track of a set of full screen windows. A window is added to that set upon receipt of a "full screen enter" (0x35) shell hook message. It is removed from the set upon receipt of a "full screen exit" (0x36) shell hook message.

If the top window on a given monitor is found in the set of full screen windows, then the monitor is considered rude.

Transparent full screen windows

Now, at this point, if you are not using any full screen applications (games, video players), you might wonder how this pertains to your case in any way.

Here's how: you might actually be staring at a full screen window right now. You just can't see it!

Indeed, it is possible for applications to set up windows that are:

Transparent, using the layered window mechanism (WS_EX_LAYERED extended window style), combined with transparency effects such as WS_EX_TRANSPARENT or SetLayeredWindowAttributes().
Click-through, using the same layered window mechanism. This prevents the window from capturing user input, which instead passes through to the window below it.
Not listed in window lists such as the taskbar or ALT+TAB, again using specific styles.

If a full screen window does all of the above, then it de facto becomes essentially invisible to the user; it's as if the window isn't there. This basically means you can have full screen windows on your monitor without realizing it.

Consider this: these sneaky full screen windows might be invisible to the user, but they are definitely visible to the Rude Window Manager! More specifically, the window will still be added to the Rude Window Manager's set of full screen windows.

Now, if that transparent full screen window happens to also be "always on top" (i.e. it has the WS_EX_TOPMOST extended window style), then it's game over already: the Rude Window Manager will always see that window as the top window, and since it's in its full screen window set, the monitor will be considered rude. As a result, the taskbar loses its always on top status for as long as the situation persists.

You can spot these transparent full screen windows using specialized tools such as GuiPropView or WindowInvestigator WindowMonitor. A notable example comes from the GeForce Experience overlay, which displays such a window when displaying information on some part of the screen; e.g. a corner notification, or performance statistics. WindowInvestigator also provides a TransparentFullscreenWindow tool that simulates a transparent full screen window.

This is one relatively simple scenario where the taskbar always on top state can be messed up. However, problems can still occur even if the transparent full screen window is not always on top, and is not even the current top window. Clearly, there's at least one other failure mode we're still missing. This is where things get more complicated.

Asking for trouble: rudeness state desynchronization

One fundamental problem with the way CGlobalRudeWindowManager works is that it looks at a wide set of window properties, but it is not necessarily notified when some of these properties change. Indeed the rude window manager only listens to a fairly narrow set of events (mostly window activation events). This can lead to the monitor rudeness state getting out of sync, as it might not be recomputed in response to changes to window properties.

If this happens, the taskbar might wrongly behave as if a full screen window is on top and drop itself to the background (or vice-versa), even though that is not the case.

In theory, the missed event could be a change to any kind of property the rude window manager could be interested in. RudeWindowFixer focuses on one especially problematic scenario that we're going to discuss next.

Missed changes to window dimensions

Consider the following sequence of events:

A window is activated and thus comes to the top (foreground).
CGlobalRudeWindowManager runs and calculate the new rudeness state.
The dimensions of the window that was just activated change.

A change to window dimensions is not an event CGlobalRudeWindowManager reacts to. (It will be notified if the window is becoming full screen - but as we'll see, that won't help with this particular bug.) This can lead to rudeness state getting out of sync.

A race condition: activating a minimized window

The animated screencap shown at the top of this document shows the bug being triggered by activating a minimized Firefox window. As it turns out, there is a very specific (and quite subtle!) reason why opening a minimized window can trigger a rudeness state desync.

When a minimized window is activated (e.g. by clicking on it in the taskbar, as shown in the screencap), the following occurs immediately (among other things):

The minimized (WS_ICONIC) window style is removed.
The window is moved to the foreground, i.e. the top of the Z-order.
HSHELL_WINDOWACTIVATED/HSHELL_RUDEAPPACTIVATED notifications are delivered to registered listeners, including the Rude Window Manager.
A WM_WINDOWPOSCHANGING message is sent to the window.

Now here's the important part: the window dimensions are only updated after the window has processed the WM_WINDOWPOSCHANGING message. This is because the window can make changes to the suggested dimensions while processing this message, so the final dimensions are not known until the message has been completely handled by the application.

The amount of time it takes for the change in window dimensions to take place is therefore up to the application. It is potentially unbounded, varies depending on the application, and is not necessarily deterministic. This explains why the problem is not always reproducible and seems to occur more or less often depending on the application. Firefox seems especially prone to this problem, for example. At the other extreme, you'll have a hard time triggering it with something like Notepad. For demonstration purposes, DelayedWindowPos from the WindowInvestigator toolbox can be used to simulate a window with arbitrary WM_WINDOWPOSCHANGING processing delays.

So how does this relate to the Rude Window Manager? Well, in this context, RecalculateRudeWindowState() is called on receipt of the HSHELL_WINDOWACTIVATED or HSHELL_RUDEAPPACTIVATED message, which is sent around the same time as WM_WINDOWPOSCHANGING. This means that the new rudeness state is calculated at the same time the new top window is processing the WM_WINDOWPOSCHANGING message. These two processes will therefore race against each other. If the window was quick enough to process the WM_WINDOWPOSCHANGING message in time, the Rude Window Manager will use the final dimensions and compute the correct state. Conversely, if the window is too slow to process the message, the Rude Window Manager will operate based on stale window dimensions, and potentially compute an incorrect state.

Unfortunately, the Rude Window Manager is not notified again when window dimensions finally change (unless it is becoming full screen, but let's assume that's not the case here). Therefore, that incorrect state will persist until the next event occurs - typically, when activating another window.

Dimensions of minimized windows

We still need to discuss is why this is a problem for initially minimized windows specifically. This is because, for historical reasons, Windows moves windows to an arbitrary (-32000, -32000) position when they are minimized. This position is what RecalculateRudeWindowState() will see if it "wins" the race and retrieves the window position before the application had a chance to process the WM_WINDOWPOSCHANGING message.

This is important, because a window that is at coordinates (-32000, -32000) does not overlap with any monitor. Therefore, the Rude Window Manager will not consider that window to be the top (foreground) window on any monitor. As far as the Rude Window Manager is concerned, it's as if that window does not exist at all.

In contrast, if the window is not initially minimized, then it already has proper dimensions, and the Rude Window Manager will correctly determine which monitor it's on, no matter who "wins" the race condition. This is why this bug typically only surfaces when activating an initially minimized window.

Full screen windows and minimized windows

As we just discussed, when the bug is triggered, the Rude Window Manager's assessment of which window is the top window is incorrect. Instead of treating the window that was just activated as the top window, the Rude Window Manager will wrongly believe the next window in the Z-order is the top window.

If that incorrect top window is not a full screen window, then this is not a real problem in practice: the monitor was not rude before, and it's still not rude now. The taskbar therefore keeps its "always on top" property, and everything is still fine.

We can therefore deduce that this bug only surfaces when activating a minimized window and the next window in the Z-order is a full screen window. In other words, when switching directly from a full screen window to an initially minimized window.

Switching from a transparent full screen window

Now, you might object that you're not actually using any full screen applications. Even if you are, it's actually pretty hard to switch directly from a full screen window to a minimized window. You could do it from the taskbar, but then you'd need to activate the taskbar first, since it's not shown on top of full screen applications - but then you're not switching directly from the full screen window anymore. You could also do it using ALT+TAB, but that's also indirect since you're going through the ALT+TAB window itself. (The ALT+TAB window is a bit special - it is a full screen window, but it's not treated as such by the Rude Window Manager, because it has a magic "NonRudeHWND" window property that the Rude Window Manager recognizes.)

However, these objections imply real full screen applications. Remember the transparent full screen windows that we mentioned previously? If the top window happens to be a transparent full screen window, then you might, in fact, unknowingly switch directly from that window to a minimized window by clicking its icon on the taskbar!

Because transparent full screen windows usually cannot be activated directly by the user, they will naturally tend to fall to the bottom of the window Z-order (unless they are "always on top" of course, but we've already discussed the case of always on top transparent full screen windows). The Rude Window Manager will typically not see them as top (foreground) windows. There is one notable exception, though: if all windows are minimized, i.e. the user is looking at the desktop, then a transparent fullscreen window will become the top window, and the Rude Window Monitor will wrongly conclude the monitor is rude. At this point the taskbar has already lost its "always on top" state, but that is not yet apparent to the user because there is no opaque window sitting atop the taskbar.

A notable example of a non-always-on-top transparent full screen window that can cause this problem is one of the windows created by the GeForce Experience overlay. Yes, GeForce Experience again - but note this is not the same window as the one we previously discussed. This one is not "always on top"; however, it always exists as long as the overlay feature is enabled, even when it's not being used.

If the current top window is such a transparent full screen window, and the user activates a minimized window by clicking on its icon in the taskbar, then the race we described previously will take place, the Rude Window Manager can miss the new top window, and fail to switch the monitor to the non-rude state.

Putting it all together

We now have all the information we need to reconstruct the sequence of events that trigger the second failure mode we are interested in, in addition to the simpler "always-on-top transparent full screen window" failure mode:

All windows are minimized and the user is looking at the desktop.
Unbeknownst to the user, they are also looking at a transparent clickthrough full screen window, such as the GeForce experience overlay window.
The last run of CGlobalRudeWindowManager::RecalculateRudeWindowState() concluded that the transparent full screen window is on top, and the monitor is therefore rude. The taskbar does not have the "always on top" property, but the user is unlikely to notice since they don't have any windows open.
The user activates a minimized window by clicking its taskbar icon.
CGlobalRudeWindowManager::RecalculateRudeWindowState() runs. Unfortunately, the activated window dimensions have not been updated yet. The window is still located at the "dummy" minimized position (-32000, -32000), which is not on the monitor; therefore, RecalculateRudeWindowState() ignores that window, and the computed state ends up the same as (3). The monitor is still rude and the taskbar is not "always on top".
The newly activated window finishes processing WM_WINDOWPOSCHANGING and the window dimensions are established on the monitor - but at this point it's too late.
Because the Rude Window Manager has already run, and is not triggered by a change in window dimensions, the "always on top" property is not reinstated on the taskbar, which ends up falling behind the newly activated window.

How RudeWindowFixer works

RudeWindowFixer listens to the same shell hook messages as the Rude Window Manager. When an event is received, RudeWindowFixer sets a timer for a fixed amount of time (currently 50 milliseconds). When the timer elapses, RudeWindowFixer does two things:

It goes through every visible window, looking for transparent windows.
- Currently, a window is considered transparent if it has the WS_EX_LAYERED as well as WS_EX_TRANSPARENT or WS_EX_NOACTIVATE extended window styles.
- If a transparent window is found, RudeWindowFixer will ensure it is not included in the Rude Windows Manager's set of full screen windows.
  - It does this by adding a "magic" undocumented window property ("NonRudeHWND") that the Rude Window Manager is known to look for.
  - It also sends a "full screen exit" message to the Rude Window Manager just in case the window was already in the set.
It forces the Rude Window Manager to recalculate rudeness state again by sending it a dummy message.

The above approach tackles the problem from two angles at the same time: RudeWindowFixer tries to ensure transparent windows are never treated as full screen windows, while attempting to mitigate WM_WINDOWPOSCHANGING race conditions by "poking" the Rude Window Manager again after some amount of time has elapsed.

The 50 ms timer interval should be more than enough time for the activated window to finish processing the WM_WINDOWPOSCHANGING message. (For example, Firefox takes less than ~20 ms.) Therefore, by the time the Rude Window Manager is forced to run a second time, the window should have settled unto its final position, and the Rude Window Manager should therefore be able to determine the correct top window.

Obviously the fixed delay is somewhat arbitrary, and it is entirely possible for a window to take more than 50 milliseconds to settle. A more robust solution would trigger the Rude Window Manager as soon as the WM_WINDOWPOSCHANGING message has been processed, regardless of how long that takes. This might be technically feasible using hooks, but such an approach would be complicated and would present higher potential for harmful side effects.

The delayed operation is also useful when dealing with windows that are not created as transparent, but become transparent shortly afterwards. This is the case for the GeForce Experience "DT" window, for example.

In theory, RudeWindowFixer can mitigate any issue where the Rude Window Manager is wrongly treating a transparent window as full screen, and/or races against a shell hook event, including issues that do not necessarily follow the precise sequence of events described above. Therefore, RudeWindowFixer could help even if your situation does not exactly match the one RudeWindowFixer was designed to address. However, RudeWindowFixer is unlikely to help with Rude Window Manager bugs that do not involve transparent windows (as defined above) nor shell hook message race conditions.

Tracing

RudeWindowFixer logs every event through an Event Tracing for Windows (ETW) provider. This can be used to troubleshoot RudeWindowFixer operation.

The provider GUID is F7A4605A-5EBA-46A2-8A75-D7E2FECC8D62. You can enter that GUID directly in TraceView for real time logging, or you can load the included RudeWindowFixer.wprp recording profile into the Windows Performance Recorder (WPR) for a more thorough analysis. The Provider Name will appear as RudeWindowFixer.

Developer information

RudeWindowFixer is designed to be built using CMake within the Microsoft Visual C++ 2019 toolchain native CMake support.

There are no dependencies besides the Windows SDK.

dechamps/RudeWindowFixer