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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
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cwendling authored and raveit65 committed Sep 4, 2018
1 parent f4a7715 commit a7d0b8dfb7993a7f8938c4a89c1df68001bfd456
Showing with 10 additions and 0 deletions.
  1. +10 −0 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));

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