[LyX/2.3.x] Fix ghost caret

[Jean-Marc Lasgouttes]

commit 61c5769e3981825b5fef9aecf512679e94e0fc53
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Mon Jan 8 11:49:40 2018 +0100

    Fix ghost caret
    
    This fixes a regression in e64ea357, where a test has been (badly)
    tightened to avoid that two consecutive rows may be redrawn to get rid
    of caret ghosts. The test prohibited empty rows from being redrawn.
    
    Moreover, improve the test of cursor boundary to avoid the case where
    cursor position is already 0.
    
    Fixes bug #10952.
    
    (cherry picked from commit 66c677b9463feb0687a8228603f86eddd4e859fd)
---
 src/BufferView.cpp |   13 ++++++++++---
 1 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/BufferView.cpp b/src/BufferView.cpp
index 23d0055..36ac46c 100644
--- a/src/BufferView.cpp
+++ b/src/BufferView.cpp
@@ -2978,8 +2978,14 @@ namespace {
 
 bool sliceInRow(CursorSlice const & cs, Text const * text, Row const & row)
 {
+       /* The normal case is the last line. The previous line takes care
+        * of empty rows (e.g. empty paragraphs). Cursor boundary issues
+        * are taken care of when setting caret_slice_ in
+        * BufferView::draw.
+        */
        return !cs.empty() && cs.text() == text && cs.pit() == row.pit()
-               && row.pos() <= cs.pos() && cs.pos() < row.endpos();
+              && ((row.pos() == row.endpos() && row.pos() == cs.pos())
+                 || (row.pos() <= cs.pos() && cs.pos() < row.endpos()));
 }
 
 }
@@ -3164,8 +3170,9 @@ void BufferView::draw(frontend::Painter & pain, bool 
paint_caret)
        // Remember what has just been done for the next draw() step
        if (paint_caret) {
                d->caret_slice_ = d->cursor_.top();
-               if (d->cursor_.boundary()
-                   || d->cursor_.top().pos() == d->cursor_.top().lastpos())
+               if (d->caret_slice_.pos() > 0
+                   && (d->cursor_.boundary()
+                       || d->caret_slice_.pos() == d->caret_slice_.lastpos()))
                        --d->caret_slice_.pos();
        } else
                d->caret_slice_ = CursorSlice();