[core] Fixed widget positioning logic in GUI containers.

Also added Update() implementation for GUI_Container

Author: DC-SWAT

include/SDL/SDL_gui.h

@@ -574,6 +574,7 @@ class GUI_Container : public GUI_Widget
 		GUI_Container(const char *name, int x, int y, int w, int h);
 		virtual ~GUI_Container(void);
 
+		virtual void Update(int force);
 		int ContainsWidget(GUI_Widget *widget);
 		void AddWidget(GUI_Widget *widget);
 		virtual void RemoveWidget(GUI_Widget *widget);

lib/SDL_gui/Container.cc

@@ -97,6 +97,7 @@ void GUI_Container::AddWidget(GUI_Widget *widget)
 			SDL_Rect parea = widgets[n_widgets - 1]->GetArea();
 
 			if((parea.x + parea.w + warea.w) > area.w) {
+				warea.x = 0;
 				warea.y = parea.y + parea.h;
 			} else {
 				warea.x = parea.x + parea.w;
@@ -149,6 +150,7 @@ void GUI_Container::AddWidget(GUI_Widget *widget)
 
 	widgets[n_widgets++] = widget;
 	UpdateLayout();
+	MarkChanged();
 }
 
 void GUI_Container::RemoveWidget(GUI_Widget *widget)
@@ -172,6 +174,7 @@ void GUI_Container::RemoveWidget(GUI_Widget *widget)
 	}
 	n_widgets = j;
 	UpdateLayout();
+	MarkChanged();
 }
 
 void GUI_Container::RemoveAllWidgets()
@@ -186,6 +189,7 @@ void GUI_Container::RemoveAllWidgets()
 
 	n_widgets = 0;
 	UpdateLayout();
+	MarkChanged();
 }
 
 void GUI_Container::UpdateLayout(void)
@@ -328,6 +332,29 @@ void GUI_Container::SetEnabled(int flag)
 	MarkChanged();
 }
 
+void GUI_Container::Update(int force)
+{
+	if (flags & WIDGET_HIDDEN) return;
+
+	if (flags & WIDGET_CHANGED)
+	{
+		force = 1;
+		flags &= ~WIDGET_CHANGED;
+	}
+	
+	if (force)
+	{
+		Erase(&area);
+	}
+
+	for (int i = 0; i < n_widgets; i++)
+	{
+		if(IsVisibleWidget(widgets[i])) {
+			widgets[i]->DoUpdate(force);
+		}
+	}
+}
+
 extern "C"
 {