Improve undo of consecutive insertions/deletions

The old scheme was:
 * multiple insertions are undone by groups of 20
 * multiple deletions are undone in one big block

The new scheme is to stop merging undo elements after 2 seconds of elapsed time.

Moreover, the merging of undo elements stops when the cursor has moved. Potentially, this could allow to remove many of the finishUndo() calls.

Fixes bug #9204.

src/Text.cpp

@@ -198,7 +198,7 @@ void mergeParagraph(BufferParams const & bparams,
 
 
 Text::Text(InsetText * owner, bool use_default_layout)
-	: owner_(owner), autoBreakRows_(false), undo_counter_(0)
+	: owner_(owner), autoBreakRows_(false)
 {
 	pars_.push_back(Paragraph());
 	Paragraph & par = pars_.back();
@@ -212,7 +212,7 @@ Text::Text(InsetText * owner, bool use_default_layout)
 
 
 Text::Text(InsetText * owner, Text const & text)
-	: owner_(owner), autoBreakRows_(text.autoBreakRows_), undo_counter_(0)
+	: owner_(owner), autoBreakRows_(text.autoBreakRows_)
 {
 	pars_ = text.pars_;
 	ParagraphList::iterator const end = pars_.end();
@@ -1081,15 +1081,6 @@ void Text::charInserted(Cursor & cur)
 {
 	Paragraph & par = cur.paragraph();
 
-	// Here we call finishUndo for every 20 characters inserted.
-	// This is from my experience how emacs does it. (Lgb)
-	if (undo_counter_ < 20) {
-		++undo_counter_;
-	} else {
-		cur.finishUndo();
-		undo_counter_ = 0;
-	}
-
 	// register word if a non-letter was entered
 	if (cur.pos() > 1
 	    && !par.isWordSeparator(cur.pos() - 2)

src/Text.h

@@ -382,8 +382,6 @@ private:
 	bool autoBreakRows_;
 	/// position of the text in the buffer.
 	DocIterator macrocontext_position_;
-	///
-	unsigned int undo_counter_;
 };
 
 

src/Undo.cpp

@@ -33,6 +33,7 @@
 #include "support/debug.h"
 #include "support/gettext.h"
 #include "support/lassert.h"
+#include "support/lyxtime.h"
 
 #include <algorithm>
 #include <deque>
@@ -72,7 +73,7 @@ struct UndoElement
 	            bool lc, size_t gid) :
 		kind(kin), cur_before(cb), cell(cel), from(fro), end(en),
 		pars(pl), array(ar), bparams(0),
-		lyx_clean(lc), group_id(gid)
+		lyx_clean(lc), group_id(gid), time(current_time())
 		{
 		}
 	///
@@ -80,11 +81,11 @@ struct UndoElement
 				bool lc, size_t gid) :
 		kind(ATOMIC_UNDO), cur_before(cb), cell(), from(0), end(0),
 		pars(0), array(0), bparams(new BufferParams(bp)),
-		lyx_clean(lc), group_id(gid)
+		lyx_clean(lc), group_id(gid), time(current_time())
 	{
 	}
 	///
-	UndoElement(UndoElement const & ue)
+	UndoElement(UndoElement const & ue) : time(current_time())
 	{
 		kind = ue.kind;
 		cur_before = ue.cur_before;
@@ -127,6 +128,8 @@ struct UndoElement
 	bool lyx_clean;
 	/// the element's group id
 	size_t group_id;
+	/// timestamp
+	time_t time;
 private:
 	/// Protect construction
 	UndoElement();
@@ -325,9 +328,13 @@ void Undo::Private::doRecordUndo(UndoKind kind,
 	    && samePar(stack.top().cell, cell)
 	    && stack.top().kind == kind
 	    && stack.top().from == from
-	    && stack.top().end == end) {
+	    && stack.top().end == end
+	    && stack.top().cur_after == cur_before
+	    && current_time() - stack.top().time <= 2) {
 		// reset cur_after; it will be filled correctly by endUndoGroup.
 		stack.top().cur_after = CursorData();
+		// update the timestamp of the undo element
+		stack.top().time = current_time();
 		return;
 	}