Changing opacity of child window without using WS_EX_LAYERED

Question

I have a window and then I create a child window using the following code:

HWND childHwnd = CreateWindowExA(WS_EX_LAYERED, "Test", "Test", WS_CHILD, 0, 0, 500, 500, mainHwnd, NULL, instance, NULL);

After it has been created I can control the opacity using:

static COLORREF color = RGB(255, 0, 0);
SetLayeredWindowAttributes(childHwnd, color, 127, LWA_ALPHA);

It works fine but I also have to support Windows 7 and MSDN says the following:

Windows 8: The WS_EX_LAYERED style is supported for top-level windows and child windows. Previous Windows versions support WS_EX_LAYERED only for top-level windows.

I have installed Windows 7 in a VM and sadly it doesn't works. What could be the workaround to achieve the same opacity control over a child window in Windows 7?

I also tried to make it a standalone window and just follow the position of the parent window but the user experience is not that good when the window gets moved fast.

There's no "workaround", it's simply not supported. If you want a transparent effect from a child window on Windows 7 you'll need to render it that way yourself. — Jonathan Potter, Dec 05 '22 at 07:12
Little point trying to support an ancient OS like win 7. I mean, it's time to drop support for win 8.1 so win 7 should be long gone. — David Heffernan, Dec 06 '22 at 20:38

score 0 · Answer 1 · edited Dec 08 '22 at 08:45

According to the documentation:

Using Layered Windows

In order to use layered child windows, the application has to declare itself Windows 8-aware in the manifest.

I suggest you refer to this answer:

https://stackoverflow.com/a/42570249/11872808

In Windows 7, you could try to use the SetWindowRgn() function.

I suggest you refer to this question:

Creating a Transparent Child window on top of non-transparent Parent Window (win32)

Changing opacity of child window without using WS_EX_LAYERED

1 Answers1