Introduced a Screen (sub) module and divided app into multiple screens.

common/gui/screen.c

@@ -0,0 +1,58 @@
+#include "screen.h"
+
+
+static SCREEN_STRUCT* screen_list = NULL;
+static SCREEN_STRUCT* screen_current = NULL;
+
+
+SCREEN_STRUCT* gui_screen_get_current() {
+	return screen_current;
+}
+
+void gui_screen_update() {
+	if(screen_current!=NULL) {
+		screen_current->on_update(screen_current);	
+	}
+}
+
+
+
+bool gui_screen_navigate(SCREEN_STRUCT* screen) {
+	if(screen==NULL) return false;
+	screen->next = NULL;
+	if(screen_current!=NULL) {
+		screen_current->on_leave(screen_current);
+		screen_current->next = screen;
+	} else {
+		screen_list=screen;
+	}
+	screen->on_enter(screen);
+	screen_current = screen;	
+	return true;
+}
+
+
+
+bool gui_screen_back() {
+	if(screen_list==NULL) return false;
+	SCREEN_STRUCT* current = screen_list;
+	SCREEN_STRUCT* last = NULL;
+	while(current->next != NULL) {
+		last = current;
+		current = current->next;
+	}
+	if(last==NULL) return false; //There's only a single screen.
+	if(current!=screen_current) return false; //List corrupted?
+	current->on_leave(current);
+	last->next=NULL;
+	last->on_enter(last);
+	screen_current=last;	
+	return true;
+}
+
+
+
+
+
+
+