user32: Implement GetDisplayConfigBufferSizes().

dlls/user32/sysparams.c

@@ -4504,14 +4504,56 @@ BOOL WINAPI PhysicalToLogicalPoint( HWND hwnd, POINT *point )
  */
 LONG WINAPI GetDisplayConfigBufferSizes(UINT32 flags, UINT32 *num_path_info, UINT32 *num_mode_info)
 {
-    FIXME("(0x%x %p %p): stub\n", flags, num_path_info, num_mode_info);
+    LONG ret = ERROR_GEN_FAILURE;
+    HANDLE mutex;
+    HDEVINFO devinfo;
+    SP_DEVINFO_DATA device_data = {sizeof(device_data)};
+    DWORD monitor_index = 0, state_flags, type;
+
+    FIXME("(0x%x %p %p): semi-stub\n", flags, num_path_info, num_mode_info);
 
     if (!num_path_info || !num_mode_info)
         return ERROR_INVALID_PARAMETER;
 
     *num_path_info = 0;
-    *num_mode_info = 0;
-    return ERROR_NOT_SUPPORTED;
+
+    if (flags != QDC_ALL_PATHS &&
+        flags != QDC_ONLY_ACTIVE_PATHS &&
+        flags != QDC_DATABASE_CURRENT)
+        return ERROR_INVALID_PARAMETER;
+
+    if (flags != QDC_ONLY_ACTIVE_PATHS)
+        FIXME("only returning active paths\n");
+
+    wait_graphics_driver_ready();
+    mutex = get_display_device_init_mutex();
+
+    /* Iterate through "targets"/monitors.
+     * Each target corresponds to a path, and each path references a source and a target mode.
+     */
+    devinfo = SetupDiGetClassDevsW(&GUID_DEVCLASS_MONITOR, DISPLAY, NULL, DIGCF_PRESENT);
+    if (devinfo == INVALID_HANDLE_VALUE)
+        goto done;
+
+    while (SetupDiEnumDeviceInfo(devinfo, monitor_index++, &device_data))
+    {
+        /* Only count active monitors */
+        if (!SetupDiGetDevicePropertyW(devinfo, &device_data, &WINE_DEVPROPKEY_MONITOR_STATEFLAGS,
+                                       &type, (BYTE *)&state_flags, sizeof(state_flags), NULL, 0))
+            goto done;
+
+        if (state_flags & DISPLAY_DEVICE_ACTIVE)
+            (*num_path_info)++;
+    }
+
+    *num_mode_info = *num_path_info * 2;
+    ret = ERROR_SUCCESS;
+    TRACE("returning %u path(s) %u mode(s)\n", *num_path_info, *num_mode_info);
+
+done:
+    SetupDiDestroyDeviceInfoList(devinfo);
+    release_display_device_init_mutex(mutex);
+    return ret;
 }
 
 /***********************************************************************