Fix caret painting

The trick is to remember in BufferView what has been done at the
previous draw, so that the row that contained the caret can be
repainted if needed.

To this end, add an argument paint_caret to BufferView, although
painting the caret is not the job of the BufferView (at this point).

BufferView::needRepaint will act as an interface with
TextMetrics::drawParagraph to know whether the painting of a given
row should be forced.

Currently everything is done at the top row level, so that, if the
caret is in a large table, the whole table will have to be repainted.
It is not clear yet that this is necessary.

src/BufferView.cpp

@@ -235,7 +235,7 @@ struct BufferView::Private
 		last_inset_(0), clickable_inset_(false),
 		mouse_position_cache_(),
 		bookmark_edit_position_(-1), gui_(0),
-		horiz_scroll_offset_(0)
+		horiz_scroll_offset_(0), repaint_caret_row_(false)
 	{
 		xsel_cache_.set = false;
 	}
@@ -312,6 +312,12 @@ struct BufferView::Private
 	/// a slice pointing to the start of the row where cursor was
 	/// at previous draw event
 	CursorSlice last_row_slice_;
+
+	/// a slice pointing to where the cursor has been drawn after the current
+	/// draw() call.
+	CursorSlice caret_slice_;
+	/// indicates whether the caret slice needs to be repainted in this draw() run.
+	bool repaint_caret_row_;
 };
 
 
@@ -2761,7 +2767,7 @@ void BufferView::updatePosCache()
 	// this is the "nodraw" drawing stage: only set the positions of the
 	// insets in metrics cache.
 	frontend::NullPainter np;
-	draw(np);
+	draw(np, false);
 }
 
 
@@ -2972,6 +2978,23 @@ void BufferView::setCurrentRowSlice(CursorSlice const & rowSlice)
 }
 
 
+namespace {
+
+bool sliceInRow(CursorSlice const & cs, Text const * text, Row const & row)
+{
+	return !cs.empty() && cs.text() == text && cs.pit() == row.pit()
+		&& row.pos() <= cs.pos() && cs.pos() <= row.endpos();
+}
+
+}
+
+
+bool BufferView::needRepaint(Text const * text, Row const & row) const
+{
+	return d->repaint_caret_row_ && sliceInRow(d->caret_slice_, text, row);
+}
+
+
 void BufferView::checkCursorScrollOffset(PainterInfo & pi)
 {
 	CursorSlice rowSlice = d->cursor_.bottom();
@@ -3060,7 +3083,7 @@ void BufferView::checkCursorScrollOffset(PainterInfo & pi)
 }
 
 
-void BufferView::draw(frontend::Painter & pain)
+void BufferView::draw(frontend::Painter & pain, bool paint_caret)
 {
 	if (height_ == 0 || width_ == 0)
 		return;
@@ -3071,6 +3094,16 @@ void BufferView::draw(frontend::Painter & pain)
 	int const y = tm.first().second->position();
 	PainterInfo pi(this, pain);
 
+	CursorSlice const & bottomSlice = d->cursor_.bottom();
+	/**  A repaint of the previous cursor row is needed if
+	 * 1/ the caret will be painted and is is not the same than the
+	 *    already painted one;
+	 * 2/ the caret will not be painted, but there is already one on
+	 * screen.
+	 */
+	d->repaint_caret_row_ = (paint_caret && bottomSlice != d->caret_slice_)
+		|| (! paint_caret && !d->caret_slice_.empty());
+
 	// Check whether the row where the cursor lives needs to be scrolled.
 	// Update the drawing strategy if needed.
 	checkCursorScrollOffset(pi);
@@ -3082,9 +3115,14 @@ void BufferView::draw(frontend::Painter & pain)
 		// however, the different coordinates of insets and paragraphs
 		// needs to be updated.
 		LYXERR(Debug::PAINTING, "Strategy: NoScreenUpdate");
-		pi.full_repaint = true;
-		if (pain.isNull())
+		pi.full_repaint = false;
+		if (pain.isNull()) {
+			pi.full_repaint = true;
 			tm.draw(pi, 0, y);
+		} else if (d->repaint_caret_row_) {
+			pi.full_repaint = false;
+			tm.draw(pi, 0, y);
+		}
 		break;
 
 	case SingleParUpdate:
@@ -3147,6 +3185,12 @@ void BufferView::draw(frontend::Painter & pain)
 	}
 	LYXERR(Debug::PAINTING, "Found new anchor pit = " << d->anchor_pit_
 		<< "  anchor ypos = " << d->anchor_ypos_);
+
+	// Remember what has just been done for the next draw() step
+	if (paint_caret)
+		d->caret_slice_ = bottomSlice;
+	else
+		d->caret_slice_ = CursorSlice();
 }
 
 

src/BufferView.h

@@ -46,6 +46,7 @@ class PainterInfo;
 class ParIterator;
 class ParagraphMetrics;
 class Point;
+class Row;
 class TexRow;
 class Text;
 class TextMetrics;
@@ -132,6 +133,9 @@ public:
 	/// Only to be called with good y coordinates (after a bv::metrics)
 	bool needsFitCursor() const;
 
+	/// returns true if this row needs to be repainted (to erase caret)
+	bool needRepaint(Text const * text, Row const & row) const;
+
 	// Returns the amount of horizontal scrolling applied to the
 	// top-level row where the cursor lies
 	int horizScrollOffset() const;
@@ -308,7 +312,7 @@ public:
 	void cursorPosAndHeight(Point & p, int & h) const;
 
 	///
-	void draw(frontend::Painter & pain);
+	void draw(frontend::Painter & pain, bool paint_caret);
 
 	/// get this view's keyboard map handler.
 	Intl & getIntl();

src/MetricsInfo.h

@@ -130,7 +130,7 @@ public:
 	bool selected;
 	/// Whether the spell checker is enabled for the parent
 	bool do_spellcheck;
-	///
+	/// True when it can be assumed that the screen has been cleared
 	bool full_repaint;
 	/// Current background color
 	ColorCode background_color;

src/TextMetrics.cpp

@@ -1881,7 +1881,8 @@ void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int const
 		// Row signature; has row changed since last paint?
 		row.setCrc(pm.computeRowSignature(row, *bv_));
 		bool row_has_changed = row.changed()
-			|| bv_->hadHorizScrollOffset(text_, pit, row.pos());
+			|| bv_->hadHorizScrollOffset(text_, pit, row.pos())
+			|| bv_->needRepaint(text_, row);
 
 		// Take this opportunity to spellcheck the row contents.
 		if (row_has_changed && pi.do_spellcheck && lyxrc.spellcheck_continuously) {

src/frontends/qt4/GuiWorkArea.cpp

@@ -1170,9 +1170,10 @@ void GuiWorkArea::paintEvent(QPaintEvent * ev)
 	}
 
 	GuiPainter pain(viewport(), pixelRatio());
-	d->buffer_view_->draw(pain);
+	d->buffer_view_->draw(pain, d->cursor_visible_);
 
-	d->cursor_->draw(pain);
+	if (d->cursor_visible_)
+		d->cursor_->draw(pain);
 	ev->accept();
 }