[LyX/master] (almost) Proper fix for caret droppings

[Jean-Marc Lasgouttes]

commit 7a28258d320db0e389de8255b442d06e47d820dd
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Sat Nov 21 20:00:26 2020 +0100

    (almost) Proper fix for caret droppings
    
    Try to find the most inner row that is overwritten by the caret. This
    allows to replace the hack in TextMetrics::draw, which did not really
    work.
    
    Note that there are still issues with emphasized caret at the
    beginning of inset, which will require some code reorganisation.
    
    Fixes current recipe of bug #12024.
---
 src/BufferView.cpp  |   19 +++++++++++++++++--
 src/TextMetrics.cpp |   12 ++----------
 2 files changed, 19 insertions(+), 12 deletions(-)

diff --git a/src/BufferView.cpp b/src/BufferView.cpp
index db9329b..62969cb 100644
--- a/src/BufferView.cpp
+++ b/src/BufferView.cpp
@@ -3295,8 +3295,23 @@ void BufferView::draw(frontend::Painter & pain, bool paint_caret)
 	 * move at all
 	 */
 	if (paint_caret) {
-		Row const & caret_row = d->cursor_.textRow();
-		caret_row.changed(true);
+		Cursor cur(d->cursor_);
+		Point p;
+		Dimension dim;
+		caretPosAndDim(p, dim);
+		while (cur.depth() > 1) {
+			if (cur.inTexted()) {
+				TextMetrics const & tm = textMetrics(cur.text());
+				if (p.x_ >= tm.origin().x_
+					&& p.x_ + dim.width() <= tm.origin().x_ + tm.dim().width())
+					break;
+			} else {
+				// in mathed
+				break;
+			}
+			cur.pop();
+		}
+		cur.textRow().changed(true);
 	}
 }
 
diff --git a/src/TextMetrics.cpp b/src/TextMetrics.cpp
index e937950..214fe89 100644
--- a/src/TextMetrics.cpp
+++ b/src/TextMetrics.cpp
@@ -1918,16 +1918,8 @@ void TextMetrics::drawParagraph(PainterInfo & pi, pit_type const pit, int const
 			LYXERR(Debug::PAINTING, "Clear rect@("
 			       << max(row_x, 0) << ", " << y - row.ascent() << ")="
 			       << width() << " x " << row.height());
-			// FIXME: this is a hack. We clear an amount equal to
-			// cursor width. This will not work if the caret has a
-			// ridiculous width like 6. (see ticket #10797)
-			// This is the same formula as in GuiWorkArea.
-			int const caret_width = lyxrc.cursor_width
-				? lyxrc.cursor_width
-				: 1 + int((lyxrc.currentZoom + 50) / 200.0);
-			pi.pain.fillRectangle(max(row_x, 0), y - row.ascent(),
-			                      width() + caret_width,
-			                      row.height(), pi.background_color);
+			pi.pain.fillRectangle(row_x, y - row.ascent(),
+			                      width(), row.height(), pi.background_color);
 		}
 
 		// Instrumentation for testing row cache (see also