windows: Add property mapping displayID to HMONITOR. (#14494)

include/SDL3/SDL_video.h

@@ -665,6 +665,11 @@ extern SDL_DECLSPEC SDL_DisplayID SDLCALL SDL_GetPrimaryDisplay(void);
  * - `SDL_PROP_DISPLAY_WAYLAND_WL_OUTPUT_POINTER`: the wl_output associated
  *   with the display
  *
+ * On Windows:
+ *
+ * - `SDL_PROP_DISPLAY_WINDOWS_HMONITOR_POINTER`: the monitor handle (HMONITOR)
+ *   associated with the display
+ *
  * \param displayID the instance ID of the display to query.
  * \returns a valid property ID on success or 0 on failure; call
  *          SDL_GetError() for more information.
@@ -678,6 +683,7 @@ extern SDL_DECLSPEC SDL_PropertiesID SDLCALL SDL_GetDisplayProperties(SDL_Displa
 #define SDL_PROP_DISPLAY_HDR_ENABLED_BOOLEAN             "SDL.display.HDR_enabled"
 #define SDL_PROP_DISPLAY_KMSDRM_PANEL_ORIENTATION_NUMBER "SDL.display.KMSDRM.panel_orientation"
 #define SDL_PROP_DISPLAY_WAYLAND_WL_OUTPUT_POINTER       "SDL.display.wayland.wl_output"
+#define SDL_PROP_DISPLAY_WINDOWS_HMONITOR_POINTER        "SDL.display.windows.hmonitor"
 
 /**
  * Get the name of a display in UTF-8 encoding.

src/video/windows/SDL_windowsmodes.c

@@ -605,6 +605,9 @@ static void WIN_AddDisplay(SDL_VideoDevice *_this, HMONITOR hMonitor, const MONI
             internal->MonitorHandle = hMonitor;
             internal->state = DisplayUnchanged;
 
+            SDL_PropertiesID props = SDL_GetDisplayProperties(_this->displays[i]->id);
+            SDL_SetPointerProperty(props, SDL_PROP_DISPLAY_WINDOWS_HMONITOR_POINTER, hMonitor);
+
             if (!_this->setting_display_mode) {
                 SDL_VideoDisplay *existing_display = _this->displays[i];
                 SDL_Rect bounds;
@@ -665,6 +668,9 @@ static void WIN_AddDisplay(SDL_VideoDevice *_this, HMONITOR hMonitor, const MONI
     if (SDL_AddVideoDisplay(&display, false)) {
         // The mode is owned by the video subsystem
         mode.internal = NULL;
+
+        SDL_PropertiesID props = SDL_GetDisplayProperties(display.id);
+        SDL_SetPointerProperty(props, SDL_PROP_DISPLAY_WINDOWS_HMONITOR_POINTER, hMonitor);
     } else {
         SDL_free(displaydata);
     }