Win32: Improve monitor enumeration

This changes enumeration to add as a GLFW monitor any active adapter
without displays, even if other active adapters do have displays.

Related to #441.
Fixes #960.

README.md

@@ -165,6 +165,7 @@ information on what to include when reporting a bug.
 - [Win32] Bugfix: Mouse capture logic lost secondary release messages (#954)
 - [Win32] Bugfix: The 32-bit Vulkan loader library static was not searched for
 - [Win32] Bugfix: Vulkan libraries have a new path as of SDK 1.0.42.0 (#956)
+- [Win32] Bugfix: Monitors with no display devices were not enumerated (#960)
 - [X11] Replaced `_GLFW_HAS_XF86VM` compile-time option with dynamic loading
 - [X11] Bugfix: `glfwGetVideoMode` would segfault on Cygwin/X
 - [X11] Bugfix: Dynamic X11 library loading did not use full sonames (#941)

src/win32_monitor.c

@@ -94,7 +94,6 @@ void _glfwPollMonitorsWin32(void)
     _GLFWmonitor** disconnected = NULL;
     DWORD adapterIndex, displayIndex;
     DISPLAY_DEVICEW adapter, display;
-    GLFWbool hasDisplays = GLFW_FALSE;
 
     disconnectedCount = _glfw.monitorCount;
     if (disconnectedCount)
@@ -105,30 +104,6 @@ void _glfwPollMonitorsWin32(void)
                _glfw.monitorCount * sizeof(_GLFWmonitor*));
     }
 
-    // HACK: Check if any active adapters have connected displays
-    //       If not, this is a headless system or a VMware guest
-
-    for (adapterIndex = 0;  ;  adapterIndex++)
-    {
-        ZeroMemory(&adapter, sizeof(DISPLAY_DEVICEW));
-        adapter.cb = sizeof(DISPLAY_DEVICEW);
-
-        if (!EnumDisplayDevicesW(NULL, adapterIndex, &adapter, 0))
-            break;
-
-        if (!(adapter.StateFlags & DISPLAY_DEVICE_ACTIVE))
-            continue;
-
-        ZeroMemory(&display, sizeof(DISPLAY_DEVICEW));
-        display.cb = sizeof(DISPLAY_DEVICEW);
-
-        if (EnumDisplayDevicesW(adapter.DeviceName, 0, &display, 0))
-        {
-            hasDisplays = GLFW_TRUE;
-            break;
-        }
-    }
-
     for (adapterIndex = 0;  ;  adapterIndex++)
     {
         int type = _GLFW_INSERT_LAST;
@@ -145,8 +120,6 @@ void _glfwPollMonitorsWin32(void)
         if (adapter.StateFlags & DISPLAY_DEVICE_PRIMARY_DEVICE)
             type = _GLFW_INSERT_FIRST;
 
-        if (hasDisplays)
-        {
         for (displayIndex = 0;  ;  displayIndex++)
         {
             ZeroMemory(&display, sizeof(DISPLAY_DEVICEW));
@@ -155,6 +128,9 @@ void _glfwPollMonitorsWin32(void)
             if (!EnumDisplayDevicesW(adapter.DeviceName, displayIndex, &display, 0))
                 break;
 
+            if (!(display.StateFlags & DISPLAY_DEVICE_ACTIVE))
+                continue;
+
             for (i = 0;  i < disconnectedCount;  i++)
             {
                 if (disconnected[i] &&
@@ -174,8 +150,10 @@ void _glfwPollMonitorsWin32(void)
 
             type = _GLFW_INSERT_LAST;
         }
-        }
-        else
+
+        // HACK: If an active adapter does not have any display devices
+        //       (as sometimes happens), add it directly as a monitor
+        if (displayIndex == 0)
         {
             for (i = 0;  i < disconnectedCount;  i++)
             {