Windows 10 Aero Undocumented API https://blog.ysc3839.com/archives/2017/10/win10-aero-undocumented-api.html

example.c

HMODULE hUser = GetModuleHandleA("user32.dll");
if (hUser)
{
	pfnSetWindowCompositionAttribute setWindowCompositionAttribute = (pfnSetWindowCompositionAttribute)GetProcAddress(hUser, "SetWindowCompositionAttribute");
	if (setWindowCompositionAttribute)
	{
		ACCENT_POLICY accent = { ACCENT_ENABLE_BLURBEHIND, 0, 0, 0 };
		WINDOWCOMPOSITIONATTRIBDATA data;
		data.Attrib = WCA_ACCENT_POLICY;
		data.pvData = &accent;
		data.cbData = sizeof(accent);
		setWindowCompositionAttribute(hWnd, &data);
	}
}

structs.h

#pragma once

typedef enum _WINDOWCOMPOSITIONATTRIB
{
	WCA_UNDEFINED = 0,
	WCA_NCRENDERING_ENABLED = 1,
	WCA_NCRENDERING_POLICY = 2,
	WCA_TRANSITIONS_FORCEDISABLED = 3,
	WCA_ALLOW_NCPAINT = 4,
	WCA_CAPTION_BUTTON_BOUNDS = 5,
	WCA_NONCLIENT_RTL_LAYOUT = 6,
	WCA_FORCE_ICONIC_REPRESENTATION = 7,
	WCA_EXTENDED_FRAME_BOUNDS = 8,
	WCA_HAS_ICONIC_BITMAP = 9,
	WCA_THEME_ATTRIBUTES = 10,
	WCA_NCRENDERING_EXILED = 11,
	WCA_NCADORNMENTINFO = 12,
	WCA_EXCLUDED_FROM_LIVEPREVIEW = 13,
	WCA_VIDEO_OVERLAY_ACTIVE = 14,
	WCA_FORCE_ACTIVEWINDOW_APPEARANCE = 15,
	WCA_DISALLOW_PEEK = 16,
	WCA_CLOAK = 17,
	WCA_CLOAKED = 18,
	WCA_ACCENT_POLICY = 19,
	WCA_FREEZE_REPRESENTATION = 20,
	WCA_EVER_UNCLOAKED = 21,
	WCA_VISUAL_OWNER = 22,
	WCA_HOLOGRAPHIC = 23,
	WCA_EXCLUDED_FROM_DDA = 24,
	WCA_PASSIVEUPDATEMODE = 25,
	WCA_USEDARKMODECOLORS = 26,
	WCA_CORNER_STYLE = 27,
	WCA_PART_COLOR = 28,
	WCA_DISABLE_MOVESIZE_FEEDBACK = 29,
	WCA_LAST = 30
} WINDOWCOMPOSITIONATTRIB;

typedef struct _WINDOWCOMPOSITIONATTRIBDATA
{
	WINDOWCOMPOSITIONATTRIB Attrib;
	PVOID pvData;
	SIZE_T cbData;
} WINDOWCOMPOSITIONATTRIBDATA;

typedef enum _ACCENT_STATE
{
	ACCENT_DISABLED = 0,
	ACCENT_ENABLE_GRADIENT = 1,
	ACCENT_ENABLE_TRANSPARENTGRADIENT = 2,
	ACCENT_ENABLE_BLURBEHIND = 3,
	ACCENT_ENABLE_ACRYLICBLURBEHIND = 4, // RS4 1803
	ACCENT_ENABLE_HOSTBACKDROP = 5, // RS5 1809
 	ACCENT_INVALID_STATE = 6
} ACCENT_STATE;

typedef struct _ACCENT_POLICY
{
	ACCENT_STATE AccentState;
	DWORD AccentFlags;
	DWORD GradientColor;
	DWORD AnimationId;
} ACCENT_POLICY;

typedef BOOL (WINAPI *pfnGetWindowCompositionAttribute)(HWND, WINDOWCOMPOSITIONATTRIBDATA*);

typedef BOOL (WINAPI *pfnSetWindowCompositionAttribute)(HWND, WINDOWCOMPOSITIONATTRIBDATA*);

Very useful, thanks a bunch! <3

Any reason why the ACCENT_ENABLE_ACRYLICBLURBEHIND setting would cause immense performance dropoff? I can't find any information as to how to improve that.

It is an internal function which emulates the behaviour of the AcrylicBrush from the new WinUI toolkit. For some reason it has these performance issues and is only used for the taskbar, which makes it go by unnoticed since the taskbar is static. I've been waiting for a couple of windows builds now since over a year and this hasn't been adressed yet sadly. I was looking into WinUI and found a way to couple WinUI with a classic Win32 application, which worked nicely, the only thing that didn't work tho was the looked after AcrylicBrush which depends on the HostBackdropBrush (you can look all of these up on MSDN) :/

@KitsuneAlex that makes sense, thanks for the information. I wish M$ would give us an API to do it nicely :/

This is amazing, thank you so much!

I heard rumors that this works on Windows 11 again? I will give this a try later and give a little update with some information if it works :)

It works for me. (Windows 11 Build 22000)

NICE ONE! Time to uncomment that code :^)

I'd like to know what WINDOWCOMPOSITIONATTRIB enumerations can do. Is there any documentation on that?

@like-me there is no public documentation on this which is why this gist exists :)