Gui: add some helpers:

- clear() function on LineEdit
 - setDefault/Destructive flags on Button
 - check if focus is set on a Widget

Nasal/canvas/gui/Widget.nas

@@ -108,6 +108,12 @@ gui.Widget = {
 
     return me;
   },
+  #
+  hasActiveFocus:func
+  {
+      return me.getCanvas()._focused_widget == me;
+  },
+  #
   listen: func(type, cb)
   {
     me._view._root.addEventListener("cb." ~ type, cb);

Nasal/canvas/gui/widgets/Button.nas

@@ -7,6 +7,8 @@ gui.widgets.Button = {
     m._down = 0;
     m._checkable = 0;
     m._flat = cfg.get("flat", 0);
+    m._isDefault = cfg.get("default", 0);
+    m._destructive = cfg.get("destructive", 0);
 
     if( style != nil and !m._flat )
       m._setView( style.createWidget(parent, cfg.get("type", "button"), cfg) );
@@ -54,6 +56,16 @@ gui.widgets.Button = {
 
     return me;
   },
+  setDefault: func(isDefault)
+  {
+    me._isDefault = isDefault;
+    return me;
+  },
+  setDestructive: func(isDestructive)
+  {
+    me._destructive = isDestructive;
+    return me;
+  },
 # protected:
   _setView: func(view)
   {

Nasal/canvas/gui/widgets/LineEdit.nas

@@ -19,6 +19,11 @@ gui.widgets.LineEdit = {
   },
   setText: func(text)
   {
+     if (text == nil) {
+       me.clear();
+       return me;
+     }
+
     me._text = utf8.substr(text, 0, me._max_length);
     me._cursor = utf8.size(me._text);
     me._selection_start = me._cursor;
@@ -29,6 +34,16 @@ gui.widgets.LineEdit = {
 
     return me;
   },
+  clear: func
+  {
+    me._text = "";
+    me._cursor = 0;
+    me._selection_start = 0;
+    me._selection_end = 0;
+
+    if( me._view != nil )
+      me._view.setText(me, "");
+  },
   text: func()
   {
     return me._text;