SysWin Dark Mode

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Dark mode

Gives windows a dark title bar and rounded corners, and reads the light or dark setting.

Windows keeps two light-or-dark settings, both under Settings › Personalization › Colors: one for apps and one for the Windows shell (the taskbar and Start). A program reads the first with AppsUseDarkMode and follows it.

What Windows draws for you is the frame: the caption bar, its buttons and the border. The client area, and the controls in it, stay the colours your program paints them; EnableDarkModeForWindow changes the frame only. The frame functions work on top-level windows on Windows 11 (build 22000 and later); on older versions they return an error HRESULT and change nothing.

Importing

#import "sys/win"
using win

Example

A window that takes a dark caption bar when the user has chosen dark apps, with small rounded corners and a client area painted to match:

#import "sys/win"
#import "sys/win/gui"
using win, gui

declare function WndProc( byval hwnd as HWND, byval uMsg as UINT, byval wParam as WPARAM, byval lParam as LPARAM ) as LRESULT

dim shared as HBRUSH hBackground

function main() as long
    SetProcessDpiAwareness( PROCESS_SYSTEM_DPI_AWARE )
    dim pWindow as CWindow = "DarkDemo"
    dim hWin as HWND = pWindow.Create( NULL, "Dark mode", @WndProc )
    if AppsUseDarkMode() then
        EnableDarkModeForWindow( hWin )
        hBackground = CreateSolidBrush( BGR( 32, 32, 32 ) )
    else
        hBackground = CreateSolidBrush( GetSysColor( COLOR_WINDOW ) )
    end if
    SetWindowCornerPreference( hWin, DWMWCP_ROUNDSMALL )
    SetWindowClientSizeForDpi( hWin, 360, 160 )
    CenterWindow( hWin )
    return pWindow.DoEvents( SW_NORMAL )
end function

function WndProc( byval hwnd as HWND, byval uMsg as UINT, byval wParam as WPARAM, byval lParam as LPARAM ) as LRESULT
    select case uMsg
        case WM_ERASEBKGND
            dim rc as RECT
            GetClientRect( hwnd, @rc )
            FillRect( cast( HDC, wParam ), @rc, hBackground )
            return 1
        case WM_DESTROY
            DeleteObject( hBackground )
            PostQuitMessage( 0 )
            return 0
    end select
    return DefWindowProcW( hwnd, uMsg, wParam, lParam )
end function

end main()

Functions

Function	Does
EnableDarkModeForWindow	Draws a window's caption bar and frame in dark colours.
SetWindowCornerPreference	Chooses square, rounded or small rounded corners for a window.
AppsUseDarkMode	Returns true when the user has chosen dark mode for apps.
SystemUsesDarkMode	Returns true when the user has chosen dark mode for the Windows shell.

Reference

EnableDarkModeForWindow

function EnableDarkModeForWindow( byval hWin as HWND ) as HRESULT

Has Windows draw a window's caption bar, caption buttons and border in dark colours. It only turns dark mode on; to go back to a light frame, call DwmSetWindowAttribute with DWMWA_USE_IMMERSIVE_DARK_MODE and a BOOL of FALSE yourself.

Call it before the window is first shown, so that it never appears light first.

Parameter	Meaning
hWin	A top-level window.

Returns S_OK on success, otherwise an error HRESULT (on Windows versions without the attribute).

Example

if AppsUseDarkMode() then EnableDarkModeForWindow( hwnd )

Microsoft Learn: DwmSetWindowAttribute, DWMWINDOWATTRIBUTE

SetWindowCornerPreference

function SetWindowCornerPreference( byval hWin as HWND, byval preference as long ) as HRESULT

Chooses how the corners of a window are drawn on Windows 11.

Parameter	Meaning
hWin	A top-level window.
preference	DWMWCP_DEFAULT: as Windows decides for that kind of window. DWMWCP_DONOTROUND: square. DWMWCP_ROUND: rounded. DWMWCP_ROUNDSMALL: rounded with a smaller radius.

Returns S_OK on success, otherwise an error HRESULT.

Example

SetWindowCornerPreference( hwnd, DWMWCP_DONOTROUND )

Microsoft Learn: DWM_WINDOW_CORNER_PREFERENCE

AppsUseDarkMode

function AppsUseDarkMode() as boolean

Reports the user's choice for apps under Settings › Personalization › Colors, read from the AppsUseLightTheme value under HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize. The value is read on every call, so a program that answers WM_SETTINGCHANGE can follow a change while it runs.

Returns true for dark, false for light or when the value is not there (older Windows).

Example

if AppsUseDarkMode() then print "apps are dark" else print "apps are light"

SystemUsesDarkMode

function SystemUsesDarkMode() as boolean

Reports the user's choice for the Windows shell (the taskbar, Start and the notification area), read from the SystemUsesLightTheme value under the same key as AppsUseDarkMode. The two can differ.

Returns true for dark, false for light or when the value is not there.

Example

if SystemUsesDarkMode() then print "use a light icon for the notification area"

See also

• Category: sys/win
• Window text and styles
• Colours