Optimized Fl_Group::clear() and Fl_Scroll::clear() as discussed in

fltk.development in "Fl_Group::clear SLOW!" on Feb. 06/07, 2010 (no STR)


git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@7038 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

CHANGES

@@ -1,5 +1,8 @@
 CHANGES IN FLTK 1.3.0
 
+	- Optimized Fl_Group::clear() and Fl_Scroll::clear() as
+	  discussed in fltk.development in "Fl_Group::clear SLOW!"
+	  on Feb. 06/07, 2010 (no STR)
 	- Replaced _WIN32 symbols that had come with UTF-8 and the
 	  new Fl_Table widget with WIN32
 	- Fixed a buffer overflow in fl_utf8from_mb() (STR #2279)

src/Fl_Group.cxx

@@ -382,24 +382,33 @@ Fl_Group::Fl_Group(int X,int Y,int W,int H,const char *l)
   This method differs from the remove() method in that it
   affects all child widgets and deletes them from memory.
 */
+/* Implementation note:
+  This is optimized and does not remove children _during_ the loop.
+  However, deleting one child may also delete other children in the
+  group because a child widget can destroy other children in the same
+  group in its destructor or simply remove them from the parent group.
+  Because of this we must walk forwards through the array of children.
+  The allocated array_ of children is freed after the loop.
+*/
 void Fl_Group::clear() {
   savedfocus_ = 0;
   resizable_ = this;
   init_sizes();
   // okay, now it is safe to destroy the children:
-  while (children_) {
-    Fl_Widget* o = child(0);	// *first* child widget
-    if (o->parent() == this) {	// should always be true
-      remove(o);		// remove child widget first
-      delete o;			// then delete it
-    } else {			// this should never happen !
-#ifdef DEBUG_CLEAR
-      printf ("Fl_Group::clear() widget:%p, parent: %p != this (%p)\n",
-	      o, o->parent(), this); fflush(stdout);
-#endif // DEBUG_CLEAR
-      remove(o);		// remove it
+  int i;
+  for (i=0; i<children_; i++) {	// delete all children
+    Fl_Widget* o = child(i);	// get child widget
+    if (o->parent()==this) {	// should always be true
+      o->parent_ = 0;		// reset child's parent
+      delete o;			// delete it
     }
   }
+  // now free the array_ of children (if any)
+  if (children_ > 1) {
+    free((void*)array_);
+  }
+  array_ = 0;
+  children_ = 0;
 }
 
 /**
@@ -469,6 +478,8 @@ void Fl_Group::add(Fl_Widget &o) {insert(o, children_);}
   This method differs from the clear() method in that it only affects
   a single widget and does not delete it from memory.
 */
+// Note: if you change this, be sure to do similar changes in
+// Fl_Group::clear() as well, if applicable.
 void Fl_Group::remove(Fl_Widget &o) {
   if (!children_) return;
   int i = find(o);

src/Fl_Scroll.cxx

@@ -32,13 +32,16 @@
 
 /** Clear all but the scrollbars... */
 void Fl_Scroll::clear() {
-  for (int i=children() - 1; i >= 0; i --) {
-    Fl_Widget* o = child(i);
-    if (o != &hscrollbar && o != &scrollbar) {
-      remove(o);
-      delete o;
-    }
-  }
+  // Note: the scrollbars are removed from the group before
+  // calling Fl_Group::clear() to take advantage of the
+  // optimized widget removal. Finally they are added
+  // to the Fl_Scroll's group again.
+  // This is MUCH faster than removing each widget.
+  remove(scrollbar);
+  remove(hscrollbar);
+  Fl_Group::clear();
+  add(hscrollbar);
+  add(scrollbar);
 }
 
 /** Insure the scrollbars are the last children */