Transparency issues with ImGUI

[Chaos192]

Version/Branch of Dear ImGui:

Version v1.88, Branch: Got from releases

Back-ends:

imgui_impl_DX11.cpp + imgui_impl_WIN32.cpp

Compiler, OS:

Windows 11, Visual Studio 22

Full config/build information:

Dear ImGui 1.88 WIP (18718)
--------------------------------
sizeof(size_t): 8, sizeof(ImDrawIdx): 2, sizeof(ImDrawVert): 20
define: __cplusplus=199711
define: _WIN32
define: _WIN64
define: _MSC_VER=1938
define: _MSVC_LANG=202004
define: IMGUI_HAS_VIEWPORT
define: IMGUI_HAS_DOCK
--------------------------------
io.BackendPlatformName: imgui_impl_win32
io.BackendRendererName: imgui_impl_dx11
io.ConfigFlags: 0x00000401
 NavEnableKeyboard
 ViewportsEnable
io.ConfigViewportsNoDecoration
io.ConfigInputTextCursorBlink
io.ConfigWindowsResizeFromEdges
io.ConfigMemoryCompactTimer = 60.0
io.BackendFlags: 0x00001C0E
 HasMouseCursors
 HasSetMousePos
 PlatformHasViewports
 HasMouseHoveredViewport
 RendererHasVtxOffset
 RendererHasViewports
--------------------------------
io.Fonts: 1 fonts, Flags: 0x00000000, TexSize: 512,64
io.DisplaySize: 120.00,11.00
io.DisplayFramebufferScale: 1.00,1.00
--------------------------------
style.WindowPadding: 8.00,8.00
style.WindowBorderSize: 1.00
style.FramePadding: 4.00,3.00
style.FrameRounding: 0.00
style.FrameBorderSize: 0.00
style.ItemSpacing: 8.00,4.00
style.ItemInnerSpacing: 4.00,4.00

Details:

So this is just a basic imgui window with ImGuiWindowFlags window_flags = 0; window_flags |= ImGuiWindowFlags_NoBackground; window_flags |= ImGuiWindowFlags_NoTitleBar; setup but it doesn't work. I've looked into other issues and applied their patches to imgui.cpp but they didn't solve the issue.

I am trying to use imgui as a .dll and inject into any process and create overlays and not need to use applications rendering as I don't want to have to hook. When I compile the code as an .exe it works fine and there is transparency and styling able to be applied to the imgui windows. When it's compiled as an .dll and injected into a process the imgui windows always have a black background regardless of styles.

Even in my custom project where I render textures to use as backgrounds or controls the buttons I can make transparent but the background window I cannot. The textures will render but the background will be black regardless of the texture being transparent.

Screenshots/Video:

Top is internal .dll

This is external .exe

Minimal, Complete and Verifiable Example code:

    const WNDCLASSEX wc = { sizeof(WNDCLASSEX), CS_CLASSDC, WndProc, 0L, 0L, GetModuleHandle(nullptr), nullptr, nullptr, nullptr, nullptr, _T("Chaos Dumper"), nullptr };
    ::RegisterClassEx(&wc);
    const HWND hwnd = ::CreateWindow(wc.lpszClassName, _T("Chaos Dumper"), WS_OVERLAPPEDWINDOW, 100, 100, 50, 50, NULL, NULL, wc.hInstance, NULL);

    if (!CreateDeviceD3D(hwnd))
    {
        CleanupDeviceD3D();
        ::UnregisterClass(wc.lpszClassName, wc.hInstance);
        return;
    }

    ::ShowWindow(hwnd, SW_HIDE);
    ::UpdateWindow(hwnd);

    IMGUI_CHECKVERSION();
    ImGui::CreateContext();
    ImGuiIO& io = ImGui::GetIO(); (void)io;
    io.ConfigFlags |= ImGuiConfigFlags_NavEnableKeyboard;
    io.ConfigFlags |= ImGuiConfigFlags_ViewportsEnable;

    ImGui::StyleColorsDark();

    ImGuiStyle& style = ImGui::GetStyle();
    if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
    {
        style.WindowRounding = 4.0f;
        style.Colors[ImGuiCol_WindowBg].w = 0.0f;
    }

    const HMONITOR monitor = MonitorFromWindow(hwnd, MONITOR_DEFAULTTONEAREST);
    MONITORINFO info = {};
    info.cbSize = sizeof(MONITORINFO);
    GetMonitorInfo(monitor, &info);
    const int monitor_height = info.rcMonitor.bottom - info.rcMonitor.top;

    if (monitor_height > 1080)
    {
        const float fScale = 2.0f;
        ImFontConfig cfg;
        cfg.SizePixels = 13 * fScale;
        ImGui::GetIO().Fonts->AddFontDefault(&cfg);
    }

    ImGui::GetIO().IniFilename = nullptr;

    ImGui_ImplWin32_Init(hwnd);
    ImGui_ImplDX11_Init(pd3dDevice, pd3dDeviceContext);

    const ImVec4 clear_color = ImVec4(0.45f, 0.55f, 0.60f, 1.00f);

    bool bDone = false;

    while (!bDone)
    {
        MSG msg;
        while (::PeekMessage(&msg, nullptr, 0U, 0U, PM_REMOVE))
        {
            ::TranslateMessage(&msg);
            ::DispatchMessage(&msg);
            if (msg.message == WM_QUIT)
                bDone = true;

            Renderer::Device = pd3dDevice;
            TextureService = new CTextureLoader();
            Drawing::LoadCustomTextures();
        }

        if (GetAsyncKeyState(VK_END) & 1)
            bDone = true;

        if (bDone)
            break;

        ImGui_ImplDX11_NewFrame();
        ImGui_ImplWin32_NewFrame();

        
        ImGui::NewFrame();
        {
            Drawing::Draw();
            if (ImGui::IsWindowHovered(ImGuiHoveredFlags_RootAndChildWindows)) {
                ChangeClickability(true, hwnd);
            }
            else {
                ChangeClickability(false, hwnd);
            }
        }
        ImGui::EndFrame();

        ImGui::Render();
        const float clear_color_with_alpha[4] = { clear_color.x * clear_color.w, clear_color.y * clear_color.w, clear_color.z * clear_color.w, clear_color.w };
        pd3dDeviceContext->OMSetRenderTargets(1, &pMainRenderTargetView, nullptr);
        pd3dDeviceContext->ClearRenderTargetView(pMainRenderTargetView, clear_color_with_alpha);
        ImGui_ImplDX11_RenderDrawData(ImGui::GetDrawData());

        if (io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable)
        {
            ImGui::UpdatePlatformWindows();
            ImGui::RenderPlatformWindowsDefault();
        }

        pSwapChain->Present(1, 0);

#ifndef _WINDLL
        if (!Drawing::isActive())
            break;
#endif
    }

    ImGui_ImplDX11_Shutdown();
    ImGui_ImplWin32_Shutdown();
    ImGui::DestroyContext();

    CleanupDeviceD3D();
    ::DestroyWindow(hwnd);
    ::UnregisterClass(wc.lpszClassName, wc.hInstance);

#ifdef _WINDLL
    CreateThread(nullptr, NULL, (LPTHREAD_START_ROUTINE)FreeLibrary, hCurrentModule, NULL, nullptr);
#endif
}