Evaluate the mouse focus upon showing and resizing.

When a dialog is shown or resized and the mouse pointer is above the
widget the engine didn't send and mouse enter event. This partly fixes
bug #12927.

src/gui/widgets/event_handler.cpp

@@ -307,6 +307,22 @@ tpoint tevent_handler::get_mouse() const
 	return tpoint(mouse_x_, mouse_y_);
 }
 
+void tevent_handler::init_mouse_location()
+{
+	// Fix the mouse location by pushing a dummy event.
+	int x;
+	int y;
+	SDL_GetMouseState(&x, &y);
+
+	SDL_Event event;
+	event.type = SDL_MOUSEMOTION;
+	event.motion.type = SDL_MOUSEMOTION;
+	event.motion.x = x;
+	event.motion.y = y;
+
+	x = SDL_PushEvent(&event);
+}
+
 void tevent_handler::add_to_keyboard_chain(twidget* widget)
 {
 	assert(widget);

src/gui/widgets/event_handler.hpp

@@ -96,6 +96,14 @@ public:
 	/** Return the current mouse position. */
 	tpoint get_mouse() const;
 
+	/**
+	 * Initializes the location of the mouse.
+	 *
+	 * After a layout of the window the mouse location needs to be updated to
+	 * test whether it entered or left a widget.
+	 */
+	void init_mouse_location();
+
 	/**
 	 * Shows a tooltip.
 	 *

src/gui/widgets/window.cpp

@@ -566,6 +566,9 @@ void twindow::layout()
 
 	generate_dot_file("layout_finished", LAYOUT);
 	need_layout_ = false;
+
+	// The widgets might have moved so set the mouse location properly.
+	init_mouse_location();
 }
 
 void twindow::do_show_tooltip(const tpoint& location, const t_string& tooltip)