[LyX/master] Center correctly top labels like Abstract.

[Jean-Marc Lasgouttes]

commit 294e4884ee29585d311177406cd31499e6d81877
Author: Jean-Marc Lasgouttes <lasgouttes at lyx.org>
Date:   Tue Aug 25 10:25:14 2020 +0200

    Center correctly top labels like Abstract.
    
    They used to take the paragraph indentation into account.
    
    Fixes bug #11939.
---
 src/RowPainter.cpp |   12 ++++++++++--
 src/TextMetrics.h  |   18 +++++++++---------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/src/RowPainter.cpp b/src/RowPainter.cpp
index 6e4cf31..c8b9157 100644
--- a/src/RowPainter.cpp
+++ b/src/RowPainter.cpp
@@ -458,8 +458,16 @@ void RowPainter::paintTopLevelLabel() const
 
 	double x = x_;
 	if (layout.labeltype == LABEL_CENTERED) {
-		x += (tm_.width() - row_.left_margin - row_.right_margin) / 2;
-		x -= fm.width(str) / 2;
+		/* Currently, x points at row_.left_margin (which contains the
+		 * indent). First remove that, and then center the title with
+		 * respect to the left and right margins.
+		 */
+		int const leftm = row_.isRTL() ? tm_.rightMargin(row_.pit())
+		                               : tm_.leftMargin(row_.pit());
+		int const rightm = row_.isRTL() ? tm_.leftMargin(row_.pit())
+			                            : tm_.rightMargin(row_.pit());
+		x += leftm - row_.left_margin + (tm_.width() - leftm -rightm) / 2
+			- fm.width(str) / 2;
 	} else if (row_.isRTL()) {
 		x = xo_ + tm_.width() - row_.right_margin - fm.width(str);
 	}
diff --git a/src/TextMetrics.h b/src/TextMetrics.h
index 353d289..6484967 100644
--- a/src/TextMetrics.h
+++ b/src/TextMetrics.h
@@ -123,6 +123,15 @@ public:
 	/// current text height.
 	int height() const { return dim_.height(); }
 
+	/**
+	 * Returns the left beginning of the text.
+	 * This information cannot be taken from the layout object, because
+	 * in LaTeX the beginning of the text fits in some cases
+	 * (for example sections) exactly the label-width.
+	 */
+	int leftMargin(pit_type pit, pos_type pos) const;
+	int leftMargin(pit_type pit) const;
+
 	///
 	int rightMargin(ParagraphMetrics const & pm) const;
 	int rightMargin(pit_type const pit) const;
@@ -136,15 +145,6 @@ private:
 	///
 	ParagraphMetrics & parMetrics(pit_type, bool redo_paragraph);
 
-	/**
-	 * Returns the left beginning of the text.
-	 * This information cannot be taken from the layout object, because
-	 * in LaTeX the beginning of the text fits in some cases
-	 * (for example sections) exactly the label-width.
-	 */
-	int leftMargin(pit_type pit, pos_type pos) const;
-	int leftMargin(pit_type pit) const;
-
 	/// the minimum space a manual label needs on the screen in pixels
 	int labelFill(Row const & row) const;