Create a very basic system tray icon

CMakeLists.txt

project(wintray)

add_executable(wintray WIN32
    main.cpp
    resource.rc
    wintray.exe.manifest
)

set_target_properties(wintray PROPERTIES
    CXX_STANDARD          11
    CXX_STANDARD_REQUIRED ON
)

target_link_libraries(wintray Comctl32)

config.h

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2023 Nathan Osman
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#ifndef CONFIG_H
#define CONFIG_H

#define IDI_ICON    101

#endif // CONFIG_H

main.cpp

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2023 Nathan Osman
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 */

#ifndef UNICODE
#define UNICODE
#endif

#include <windows.h>
#include <windowsx.h>

#include <commctrl.h>
#include <shellapi.h>
#include <strsafe.h>

#include "config.h"

#define ID_QUIT 101

const UINT WMAPP_NOTIFYCALLBACK = WM_APP + 1;

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam);

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow)
{
    // Create and register the window class
    const wchar_t CLASS_NAME[] = L"WndClass";

    WNDCLASS wc = { };

    wc.lpfnWndProc = WindowProc;
    wc.hInstance = hInstance;
    wc.lpszClassName = CLASS_NAME;

    RegisterClass(&wc);

    // Create a window only for notifications
    CreateWindowEx(
        0,
        CLASS_NAME,
        L"System Tray Window",
        0,
        0,
        0,
        0,
        0,
        HWND_MESSAGE,
        NULL,
        hInstance,
        NULL
    );

    // Event loop
    MSG msg = { };
    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return 0;
}

void createPopup(HWND hwnd, POINT pt)
{
    // Create the popup
    HMENU hmenu = CreatePopupMenu();

    // Create the menu item
    MENUITEMINFO mii = { };
    mii.cbSize = sizeof(mii);
    mii.fMask = MIIM_STRING | MIIM_ID;
    mii.wID = ID_QUIT;
    mii.dwTypeData = L"&Quit";
    mii.cch = wcslen(mii.dwTypeData);

    // Insert it
    InsertMenuItem(hmenu, 0, TRUE, &mii);

    // Show the menu
    int id = TrackPopupMenu(
        hmenu,
        TPM_RETURNCMD,
        pt.x,
        pt.y,
        0,
        hwnd,
        NULL
    );

    switch (id) {
    case ID_QUIT:
        PostQuitMessage(0);
        break;
    }

    DestroyMenu(hmenu);
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg) {

    case WM_CREATE:   
    {
        // Prepare the struct
        NOTIFYICONDATA nid = { };
        nid.hWnd = hwnd;
        nid.uFlags = NIF_ICON | NIF_TIP | NIF_MESSAGE;
        nid.uCallbackMessage = WMAPP_NOTIFYCALLBACK;

        // Load the icon
        LoadIconMetric(
            GetModuleHandle(nullptr),
            MAKEINTRESOURCE(IDI_ICON),
            LIM_SMALL,
            &(nid.hIcon)
        );

        // Load the tooltip
        StringCchCopy(nid.szTip, ARRAYSIZE(nid.szTip), L"Tray Icon");

        Shell_NotifyIcon(NIM_ADD, &nid);

        // Set the version
        nid.uVersion = NOTIFYICON_VERSION_4;
        Shell_NotifyIcon(NIM_SETVERSION, &nid);

        return 0;
    }

    case WMAPP_NOTIFYCALLBACK:
    {
        if (LOWORD(lParam) == WM_CONTEXTMENU) {

            // Determine the offset
            POINT pt = {
                GET_X_LPARAM(wParam),
                GET_Y_LPARAM(wParam)
            };

            createPopup(hwnd, pt);
        }

        return 0;
    }
    }

    return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

resource.rc

#include <windows.h>

#include "config.h"

IDI_ICON ICON DISCARDABLE "wintray.ico"

wintray.exe.manifest

<?xml version='1.0' encoding='UTF-8' standalone='yes'?>
<assembly xmlns='urn:schemas-microsoft-com:asm.v1' manifestVersion='1.0' xmlns:asmv3="urn:schemas-microsoft-com:asm.v3">
  <dependency>
    <dependentAssembly>
      <assemblyIdentity type="win32" name="Microsoft.Windows.Common-Controls" language="*" processorArchitecture="*" version="6.0.0.0" publicKeyToken="6595b64144ccf1df"/>
    </dependentAssembly>
  </dependency>
  <asmv3:application>
    <asmv3:windowsSettings>
      <dpiAware xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">true</dpiAware>
      <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2</dpiAwareness>
    </asmv3:windowsSettings>
  </asmv3:application>
</assembly>

wintray.ico