implement input iteraction

inc/gfx/layout.h

@@ -11,11 +11,11 @@
 class layout {
     class Slot {
     private:
-        int pos_;
-        int size_;
-        canvas *canvas_ = 0;
+        int pos_ = 0;
+        int size_ = 0;
+        canvas *canvas_ = nullptr;
     public:
-        node *content;
+        node *content = nullptr;
         friend layout;
     };
 
@@ -35,6 +35,7 @@ private:
 public:
     static const int maxslots = 10;
     Slot slots[maxslots];
+    node *cursor;
 
     layout(screen& s) : maxwidth_(s.getWidth()), maxheight_(s.getHeight()), screen_(s) {