Create window_focused callback

ui/drivers/cocoa/ui_cocoa_window.m

@@ -70,11 +70,21 @@ void ui_window_cocoa_set_droppable(void *data, bool droppable)
    }
 }
 
+bool ui_window_cocoa_focused(void *data)
+{
+   ui_window_cocoa_t *cocoa = (ui_window_cocoa_t*)data;
+   CocoaView *cocoa_view    = (CocoaView*)cocoa->data;
+   if ([[cocoa_view window] isMainWindow] == YES)
+      return true;
+   return false;
+}
+
 const ui_window_t ui_window_cocoa = {
    ui_window_cocoa_destroy,
    ui_window_cocoa_set_focused,
    ui_window_cocoa_set_visible,
    ui_window_cocoa_set_title,
    ui_window_cocoa_set_droppable,
+   ui_window_cocoa_focused,
    "cocoa"
 };

ui/drivers/null/ui_null_window.c

@@ -42,11 +42,17 @@ static void ui_window_null_set_droppable(void *data, bool droppable)
 {
 }
 
+static bool ui_window_null_focused(void *data)
+{
+   return true;
+}
+
 const ui_window_t ui_window_null = {
    ui_window_null_destroy,
    ui_window_null_set_focused,
    ui_window_null_set_visible,
    ui_window_null_set_title,
    ui_window_null_set_droppable,
+   ui_window_null_focused,
    "null"
 };

ui/drivers/win32/ui_win32_window.c

@@ -79,11 +79,18 @@ void ui_window_win32_set_droppable(void *data, bool droppable)
    DragAcceptFiles(window->hwnd, droppable);
 }
 
+bool ui_window_win32_focused(void *data)
+{
+   ui_window_win32_t *window = (ui_window_win32_t*)data;
+   return (GetForeGroundWindow() == window->hwnd);
+}
+
 const ui_window_t ui_window_win32 = {
    ui_window_win32_destroy,
    ui_window_win32_set_focused,
    ui_window_win32_set_visible,
    ui_window_win32_set_title,
    ui_window_win32_set_droppable,
+   ui_window_win32_focused,
    "win32"
 };

ui/ui_companion_driver.h

@@ -38,6 +38,7 @@ typedef struct ui_window
    void (*set_visible)(void *data, bool visible);
    void (*set_title)(void *data, char *buf);
    void (*set_droppable)(void *data, bool droppable);
+   bool (*focused)(void *data);
    const char *ident;
 } ui_window_t;