implement sdl_get_monitor_dpi

Author: allefant

src/sdl/sdl_system.c

@@ -355,6 +355,13 @@ static void sdl_destroy_mouse_cursor(ALLEGRO_MOUSE_CURSOR *cursor)
    ASSERT(sdl_cursor);
    SDL_FreeCursor(sdl_cursor->cursor);
    al_free(sdl_cursor);
+
+   static int sdl_get_monitor_dpi(int adapter)
+{
+   float ddpi, hdpi, vdpi;
+   if (SDL_GetDisplayDPI(adapter, &ddpi, &hdpi, &vdpi) < 0)
+      return 72; // we can't indicate "unknown" so return something reasonable
+   return hdpi;
 }
 
 static int sdl_get_num_display_modes(void)
@@ -411,7 +418,7 @@ ALLEGRO_SYSTEM_INTERFACE *_al_sdl_system_driver(void)
    vt->get_num_video_adapters = sdl_get_num_video_adapters;
    vt->get_monitor_info = sdl_get_monitor_info;
    vt->create_mouse_cursor = sdl_create_mouse_cursor;
-   vt->destroy_mouse_cursor = sdl_destroy_mouse_cursor;
+   vt->get_monitor_dpi = sdl_get_monitor_dpi;
    /*vt->get_cursor_position = sdl_get_cursor_position;
    vt->grab_mouse = sdl_grab_mouse;
    vt->ungrab_mouse = sdl_ungrab_mouse;*/