From 7d19265ba02aa0f7dcd14b34bb3f04add8584ad8 Mon Sep 17 00:00:00 2001
From: Jean-Marc Lasgouttes <lasgouttes@lyx.org>
Date: Wed, 22 Jul 2015 11:05:02 +0200
Subject: [PATCH] Do not break row at inset boundary if possible

The first change is to concentrate on the last ro elements that contain separators and try to break it a a width that is shorter than both
- its current width (we want to break it, after all)
- the amount of space available.

This simple heuristic seems to give good results.
---
 src/Row.cpp | 49 ++++++++++++++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 17 deletions(-)

diff --git a/src/Row.cpp b/src/Row.cpp
index 0974265328..a619874b93 100644
--- a/src/Row.cpp
+++ b/src/Row.cpp
@@ -382,13 +382,44 @@ void Row::shortenIfNeeded(pos_type const keep, int const w)
 	Elements::iterator const end = elements_.end();
 	int wid = left_margin;
 
+	// The last breakable element that has been found and its x position.
+	Elements::iterator last_brk = elements_.end();
+	int last_wid = 0;
+
 	Elements::iterator cit = beg;
 	for ( ; cit != end ; ++cit) {
-		if (cit->endpos >= keep && wid + cit->dim.wid > w)
+		if (cit->countSeparators() && cit->pos >= keep) {
+			last_brk = cit;
+			last_wid = wid;
+		}
+		if (wid + cit->dim.wid > w)
 			break;
 		wid += cit->dim.wid;
 	}
 
+	/* We have found a suitable separable element. This is the common case.
+	 * Try to break it cleanly (at word boundary) at a length that is both
+	 * - less than the available space on the row
+	 * - shorter than the natural width of the element, in order to enforce
+	 *   break-up.
+	 */
+	if (last_brk != end
+		&& last_brk->breakAt(min(w - last_wid, last_brk->dim.wid - 2), false)) {
+		end_ = last_brk->endpos;
+		/* after breakAt, there may be spaces at the end of the
+		 * string, but they are not counted in the string length
+		 * (QTextLayout feature, actually). We remove them, but do not
+		 * change the endo of the row, since the spaces at row break
+		 * are invisible.
+		 */
+		last_brk->str = rtrim(last_brk->str);
+		last_brk->endpos = last_brk->pos + last_brk->str.length();
+		dim_.wid = last_wid + last_brk->dim.wid;
+		// If there are other elements, they should be removed.
+		elements_.erase(next(last_brk, 1), end);
+		return;
+	}
+
 	if (cit == end) {
 		// This should not happen since the row is too long.
 		LYXERR0("Something is wrong cannot shorten row: " << *this);
@@ -402,22 +433,6 @@ void Row::shortenIfNeeded(pos_type const keep, int const w)
 		wid -= cit->dim.wid;
 	}
 
-	// Try to break this row cleanly (at word boundary)
-	if (cit->breakAt(w - wid, false)) {
-		end_ = cit->endpos;
-		// after breakAt, there may be spaces at the end of the
-		// string, but they are not counted in the string length
-		// (qtextlayout feature, actually). We remove them, but do not
-		// change the endo of the row, since the spaces at row break
-		// are invisible.
-		cit->str = rtrim(cit->str);
-		cit->endpos = cit->pos + cit->str.length();
-		dim_.wid = wid + cit->dim.wid;
-		// If there are other elements, they should be removed.
-		elements_.erase(next(cit, 1), end);
-		return;
-	}
-
 	if (cit != beg) {
 		// There is no separator, but several elements have been
 		// added. We can cut right here.
-- 
2.39.2