Why does ADM create new Windows themes, when it's set to use a (or two) default theme(s) ?

[Jay-o-Way]

I use the settings where I use standard "Windows Light" and "Windows Dark" themes. Seems simple to apply, but ADM still creates its own versions, like "ADMUnmanagedLight". Why?

[Armin2208]

@Spiritreader

[Spiritreader]

Because it would create require more maintainable code just for an edge case, which in the end doesn't matter for the user experience of "your theme is being switched to what you expect it to look like".
Creating extra edge case handling for this is unnecessary code bloat in this specific instance.

The reason why we have an UnmanagedLight and UnmanagedDark theme in the first place is because of ignore flags. Ignore flags generally aren't supported by default Windows themes, but they are if you create your own custom themes.

If you set an ignore flag, Windows will report "Custom" as selected theme, because the theme you chose to apply with more than 0 ignore flags may not exactly match that configuration, if you, for example, chose to ignore wallpapers.

In order to still keep track of where it comes from, AutoDarkMode injects its own UnmanagedOriginalName into the theme ini file, which can then be read from the Custom.theme to let Auto Dark Mode know which original theme this was pulled from.
This is crucial for theme state synchronization (e.g knowing which theme is actually active).

Here is the relevant logic for theme state synchronization in Windows theme mode:

    /// <summary>
    /// This method is responsible for updating the internal UnmanagedActiveThemePath variable. <br/>
    /// Without this ADM would have no idea if the applied theme is correct. <br/>
    /// We append an UnmanagedOriginalName entry to each of adm's light or dark unmanaged theme
    /// file. <br/> That tells us on what theme file it was based on. This way we can prevent unnecessary theme switches <br/>
    /// Appending this extra parameter is done in ThemeHandler.ApplyTheme
    /// </summary>
    /// <param name="config">current adm config object</param>
    public void RefreshThemes(AdmConfig config)
    {
        if (config.WindowsThemeMode.Enabled)
        {
            try
            {
                UnmanagedActiveThemePath = RegistryHandler.GetActiveThemePath();

                // for unmanaged with flags we need to set the unmanagedactivethemepath to our internal names
                // This is because when using apply flags, the theme is reported as custom. However, our UnmanagedOriginalName
                // persists because we have set it originally when applying the theme, so if we read that then we are aware of the origin theme
                if (config.WindowsThemeMode.ApplyFlags != null && config.WindowsThemeMode.ApplyFlags.Count > 0)
                {
                    string customPath = Path.Combine(Helper.PathThemeFolder, "Custom.theme");
                    bool unmanagedCustom = UnmanagedActiveThemePath.Equals(customPath);
                    if (unmanagedCustom)
                    {
                        UnmanagedActiveThemePath = "";
                        // retrieve theme names from configuration file and then compare them to the custom path
                        (_, _, string displayNameLight) = ThemeFile.GetDisplayNameFromRaw(config.WindowsThemeMode.LightThemePath);
                        (_, _, string displayNameDark) = ThemeFile.GetDisplayNameFromRaw(config.WindowsThemeMode.DarkThemePath);
                        string sourceThemeNameCustom = ThemeFile.GetOriginalNameFromRaw(customPath);
                        if (sourceThemeNameCustom == displayNameDark)
                        {
                            UnmanagedActiveThemePath = Helper.PathUnmanagedDarkTheme;
                        }
                        else if (sourceThemeNameCustom == displayNameLight)
                        {
                            UnmanagedActiveThemePath = Helper.PathUnmanagedLightTheme;
                        }
                        Logger.Debug($"refresh theme state with apply flags enabled, active theme: {(UnmanagedActiveThemePath == "" ? "undefined" : UnmanagedActiveThemePath)}");
                    }
                }
                // for unmanaged without applyflags
                else
                {
                    bool unmanagedLight = UnmanagedActiveThemePath.Equals(Helper.PathUnmanagedLightTheme);
                    bool unmanagedDark = UnmanagedActiveThemePath.Equals(Helper.PathUnmanagedDarkTheme);

                    // check if an unmanaged theme is active. If so, extract the original name from the theme path
                    // This way, we know which origin theme is active and don't have to switch
                    if (unmanagedLight)
                    {
                        string displayNameUnmanaged = ThemeFile.GetOriginalNameFromRaw(Helper.PathUnmanagedLightTheme);
                        (_, _, string displayNameSource) = ThemeFile.GetDisplayNameFromRaw(config.WindowsThemeMode.LightThemePath);
                        if (displayNameUnmanaged != displayNameSource)
                        {
                            Logger.Debug($"detected change in unmanaged light theme, new origin: {config.WindowsThemeMode.LightThemePath}");
                            UnmanagedActiveThemePath = "";
                        }
                    }
                    if (unmanagedDark)
                    {
                        string displayNameUnmanaged = ThemeFile.GetOriginalNameFromRaw(Helper.PathUnmanagedDarkTheme);
                        (_, _, string displayNameSource) = ThemeFile.GetDisplayNameFromRaw(config.WindowsThemeMode.DarkThemePath);
                        if (displayNameUnmanaged != displayNameSource)
                        {
                            Logger.Debug($"detected change in unmanaged light theme, new origin: {config.WindowsThemeMode.DarkThemePath}");
                            UnmanagedActiveThemePath = "";
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Logger.Error(ex, "could not retrieve active theme path: ");
            }
        }
        else
        {
            // we're only reading here, so we can't apply the theme fix safely
            ManagedThemeFile.SyncWithActiveTheme(patch: false, keepDisplayNameAndGuid: false, logging: true);
        }
    }

[Jay-o-Way]

Okay. But I don't have any ignore flags. I just want the default light and dark themes, along with light and dark mode. That's it. Do you see how, for a user, this is strange?

[Armin2208]

Normally, a user wouldn't care about that. What's now the difference of having one or two adm managed themes? Is this hurting your productivity? Do you even notice it? Do you see this on daily bases?

[Jay-o-Way]

Well, yes, actually. It seems to interfere with other themes too. Sometimes I have a theme with several images (slide show) and every time ADM starts, the slideshow is stuck on one and the same image on both my screens. Not even speaking of having two very different themes on two virtual desktops...

[Spiritreader]

Okay. But I don't have any ignore flags. I just want the default light and dark themes, along with light and dark mode. That's it. Do you see how, for a user, this is strange?

I have explained this.
Because it would create require more maintainable code just for an edge case, which in the end doesn't matter for the user experience. You can never fully guarantee that a Windows default theme will actually be correctly set by the API. Whereas we can control custom themes. It's strange, but Windows is strange, and it makes no sense to put the blame on this implementation.

Oh and also, I just remembered. We use a custom color patching mechanism that improves the experience when theme switching the taskbar. In order to realize this, we have to modify the active theme. So at that point we again need the unmanaged theme files.

Well, yes, actually. It seems to interfere with other themes too. Sometimes I have a theme with several images (slide show) and every time ADM starts, the slideshow is stuck on one and the same image on both my screens.

That is a different issue altogether. Slide shows will always reset when a theme is applied because we're applying Windows themes to change the theme. It's a Windows limitation when setting themes.
It's unrelated to unmanaged themes. If you don't want that behavior, you need to use PowerToys, OR, well, create custom themes and use ignore flags.

Not even speaking of having two very different themes on two virtual desktops...

That is also a Windows limitation because there's no stable API nuget package that works on every Windows version, because the interface definition is different on almost every single build. In addition, it's impossible to have multi-monitor and multi-virtual-desktop wallpapers at the same time because Windows has no implementation for it.