EvView: Fix cursor movement when logical and visual line order differs

Make sure not to move the caret in the wrong direction when restoring
the visual line X offset, in case the visual and logical order is
slightly different.

The algorithm used to move the cursor on the next line and restore the
X position across lines works as follows:

1. Move `cursor_offset` to the next line by incrementing it until
   reaching a line break;
2. Find the Y coordinate corresponding to the new cursor_offset;
3. Find the text closest to the new Y coordinate and the previous X
   coordinate.
4. Move cursor_offset to the text at this new (X, Y) location.

The issue lies in step 3, which can find a position on a different line
than expected in case several lines have a nearly the same Y position.

Evince references:
* https://gitlab.gnome.org/GNOME/evince/issues/889
* https://gitlab.gnome.org/GNOME/evince/merge_requests/81
* https://gitlab.gnome.org/GNOME/evince/commit/dddd98b4c7922e2906bba6a31afa07837ae6c39c

1 files changed, 10 insertions, 0 deletions

diff --git a/libview/ev-view.c b/libview/ev-view.c
index 61505728..2db3eb2b 100644
--- a/libview/ev-view.c
+++ b/libview/ev-view.c
@@ -5406,6 +5406,7 @@ ev_view_move_cursor (EvView         *view,
 	gint            prev_page;
 	cairo_region_t *damage_region;
 	gboolean        clear_selections = FALSE;
+	const gboolean  forward = count >= 0;
 
 	if (!view->caret_enabled || view->rotation != 0)
 		return FALSE;
@@ -5475,9 +5476,18 @@ ev_view_move_cursor (EvView         *view,
 		return TRUE;
 
 	if (step == GTK_MOVEMENT_DISPLAY_LINES) {
+		const gint prev_cursor_offset = view->cursor_offset;
+
 		position_caret_cursor_at_location (view,
 						   MAX (rect.x, view->cursor_line_offset),
 						   rect.y + (rect.height / 2));
+		/* Make sure we didn't move the cursor in the wrong direction
+		 * in case the visual order isn't the same as the logical one,
+		 * in order to avoid cursor movement loops */
+		if ((forward && prev_cursor_offset > view->cursor_offset) ||
+		    (!forward && prev_cursor_offset < view->cursor_offset)) {
+			view->cursor_offset = prev_cursor_offset;
+		}
 		if (!clear_selections &&
 		    prev_offset == view->cursor_offset && prev_page == view->cursor_page) {
 			gtk_widget_error_bell (GTK_WIDGET (view));