Window transparency in Windows 11

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Window transparency in Windows 11

T B 66

Hi, I had a working example on windows 8 of a transparent window, I don't remember exactly if it used UpdateLayeredWindow or AlphaBlend, the idea was to use crKey as the transparency color. I have only the exe file, and if I open it on windows 11 there is no transparency. What could be causing this behaviour ? I have tried:

        //UpdateLayeredWindow(hwnd, hdc, &ptDest, &client, hdc1, &ptSrc, RGB(0, 0, 0), &blendFunc, ULW_COLORKEY);
        AlphaBlend(hdc, 0, 0, rect.right - rect.left, rect.bottom - rect.top, hdc1, 0, 0, rect.right - rect.left, rect.bottom - rect.top, blendFunc);

Thankyou in advance!

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Answer 1

Castorix31 90,686

UpdateLayeredWindow works on Windows 11 : I had uploaded a test in WinUI 3/C# : https://github.com/castorix/WinUI3_SwapChainPanel_Layered

and people told me it worked on Windows 11 but that I needed to add DwmSetWindowAttribute for borders/shadow

Or you can also test this sample I had posted in C++, which could have borders because I did not use DwmSetWindowAttribute :

https://learn.microsoft.com/en-us/answers/questions/639888/how-to-make-transparent-window-using-updatelayered?orderby=newest

[Edit] I just saw this thread was from you : so this sample, with the same jpg and white transparent color, is not transparent on Windows 11 ?

T B 66 Reputation points

2023-05-13T20:21:15.65+00:00
Hey, you came to the rescue again :)

That example is working indeed. I am working in Unreal Engine though, I made a working code with your help from the previous post, I lost the code, but the exe is there and not working on w 11. Anyway, now I am pinpointing this code

pBitmap->GetHBITMAP(Gdiplus::Color(255, 255, 255), &hBitmap);

which in my code is

HBITMAP hBitmap = CreateCompatibleBitmap(hdc, rect.right - rect.left, rect.bottom - rect.top); HBITMAP hBmpOld = (HBITMAP)SelectObject(hdc, hBitmap); FillRect(hdc,&rect,CreateSolidBrush(RGB(0,0,0))); SelectObject ( hdc, hBitmap );
Castorix31 90,686 Reputation points

2023-05-13T21:01:07.3166667+00:00

The original line get the hBitmap from pBitmap with white as background color

But your code creates a black rectangle... (with twice SelectObject(hdc, hBitmap)...)
T B 66 Reputation points

2023-05-13T21:04:48.5866667+00:00
Probably this is why I get this error

Access violation reading location 0x00007FF6ECE92640.

static int __cdecl invoke_main() { return WinMain( reinterpret_cast<HINSTANCE>(&__ImageBase), nullptr, _get_narrow_winmain_command_line(), __scrt_get_show_window_mode()); }

I deleted the FillRect, I noticed it shouldn't be there.

Edit: this error above was caused by DeleteDC(hdc1); where HDC hdc1 = CreateCompatibleDC(hdc);

Also this code makes the same error:

SetLayeredWindowAttributes(hwnd, 0x00000000, 127, 0x00000001);

Castorix31 90,686

If I draw for example a blue ellipse on a black background as transparent color, I get a transparent ellipse :

					HDC hDC = GetDC(hWnd);
					RECT rect;
					GetClientRect(hWnd, &rect);
					HBITMAP hBitmap = CreateCompatibleBitmap(hDC, rect.right - rect.left, rect.bottom - rect.top);
					HDC hDCMem = CreateCompatibleDC(hDC);
					HBITMAP hBmpOld = (HBITMAP)SelectObject(hDCMem, hBitmap);
					HBRUSH hBrush = CreateSolidBrush(RGB(0, 0, 0));
					HBRUSH hBrushEllipse = CreateSolidBrush(RGB(0, 0, 255));
					HBRUSH hBrushEllipseOld = (HBRUSH)SelectObject(hDCMem, hBrushEllipse);
					FillRect(hDCMem, &rect, hBrush);
					Ellipse(hDCMem, rect.left, rect.top, rect.right, rect.bottom);
					DeleteObject(hBrush);
					SelectObject(hDCMem, hBrushEllipseOld);
					SelectObject(hDCMem, hBmpOld);
					DeleteDC(hDCMem);
					ReleaseDC(hWnd, hDC);
					SetPicture(hWnd, hBitmap, RGB(0, 0, 0));

User's image

T B 66 Reputation points

2023-05-14T17:03:47.58+00:00

Your example works in visual studio, I will test it tommorow in Unreal Engine, though my guess is that in my project, after I make the changes, I don't set the DC or hwnd so they don't have any effect.
T B 66 Reputation points

2023-05-14T21:26:18.2333333+00:00

So in Unreal Engine I did hwnd = GetActiveWindow(); and then the above code and it didn't paint this over
T B 66 Reputation points

2023-05-16T09:56:31.8333333+00:00

I tried SetLayeredWindowAttributes with LWA_ALPHA, but I need LWA_COLORKEY which doesn't work. I tried SetWindowLong with WS_EX_LAYERED, DwmEnableBlurBehindWindow, UpdateLayeredWindow with ULW_COLORKEY, also CreateDIBSection then AlphaBlend. After all this I called SetWindowPos, ShowWindow and DwmExtendFrameIntoClientArea. Nothing works ...

Reading the source code I found

if window is ALPHA_BLENDED & transparency per pixel

WindowExStyle |= WS_EX_COMPOSITED;

Last thing I have to try is to change PixelFormat like here, not sure how yet.

From the unity forum , they say to UNCHECK "Use DXGI Flip Model Swapchain for D3D11", not sure how.

What do you think ?
T B 66 Reputation points

2023-05-17T09:48:25.53+00:00

I think it's about the shaders, PCD3D_SM5 and PCD3D_ES31 doesn't seem to work. I try to compile OPENGL_ES31 and GLSL_430
T B 66 Reputation points

2023-05-17T19:01:16.1033333+00:00

it works with vulkan

Answer 2

T B 66

I am still looking for an answer. This code works on windows 8 when using RHI SM5 and ES31, but on windows 11 only with vulkan. I am using Unreal Engine. Any idea how to fix this ? Same thing using UpdateLayeredWindow

        DwmExtendFrameIntoClientArea(hwnd, &margins);
        SetLayeredWindowAttributes( hwnd, 0x00000000, FMath::TruncToInt( 1 * 255.0f ), LWA_ALPHA );

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Window transparency in Windows 11

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