[vte/wip/egmont/bidi: 13/16] emulation, bidi: Add keyboard swapping mode

[Egmont Koblinger <egmontkob src gnome org>]

commit e3eb675e2ac433c209393585dfd95e9fd646e605
Author: Egmont Koblinger <egmont gmail com>
Date:   Sat Jun 1 15:58:52 2019 +0200

    emulation,bidi: Add keyboard swapping mode
    
    If the corresponding mode is enabled and the cursor stands within an
    RTL paragraph, the Left and Right keys of the keyboard swap their
    generated escape sequence.

 src/vte.cc | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)
---
diff --git a/src/vte.cc b/src/vte.cc
index 9ed4c27b..5fe01789 100644
--- a/src/vte.cc
+++ b/src/vte.cc
@@ -5090,6 +5090,52 @@ Terminal::widget_key_press(GdkEventKey *event)
                /* If the above switch statement didn't do the job, try mapping
                 * it to a literal or capability name. */
                 if (handled == FALSE) {
+                        if (G_UNLIKELY (m_enable_bidi &&
+                                        m_modes_private.VTE_BIDI_SWAP_ARROW_KEYS() &&
+                                        (keyval == GDK_KEY_Left ||
+                                         keyval == GDK_KEY_Right ||
+                                         keyval == GDK_KEY_KP_Left ||
+                                         keyval == GDK_KEY_KP_Right))) {
+                                /* In keyboard arrow swapping mode, the left and right arrows need swapping
+                                 * if the cursor stands inside a (possibly autodetected) RTL paragraph. */
+                                ensure_row();
+                                VteRowData const *row_data = find_row_data(m_screen->cursor.row);
+                                bool rtl;
+                                if ((row_data->attr.bidi_flags & (VTE_BIDI_FLAG_IMPLICIT | 
VTE_BIDI_FLAG_AUTO))
+                                                              == (VTE_BIDI_FLAG_IMPLICIT | 
VTE_BIDI_FLAG_AUTO)) {
+                                        /* Implicit paragraph with autodetection. Need to run the BiDi 
algorithm
+                                         * to get the autodetected direction.
+                                         * m_ringview is for the onscreen contents and the cursor may be 
offscreen.
+                                         * Better leave that alone and use a temporary ringview for the 
cursor's row. */
+                                        vte::base::RingView ringview;
+                                        ringview.set_ring(m_screen->row_data);
+                                        ringview.set_rows(m_screen->cursor.row, 1);
+                                        ringview.set_width(m_column_count);
+                                        ringview.update();
+                                        rtl = ringview.get_bidirow(m_screen->cursor.row)->base_is_rtl();
+                                } else {
+                                        /* Not an implicit paragraph with autodetection, no autodetection
+                                         * is required. Take the direction straight from the stored data. */
+                                        rtl = !!(row_data->attr.bidi_flags & VTE_BIDI_FLAG_RTL);
+                                }
+                                if (rtl) {
+                                        switch (keyval) {
+                                        case GDK_KEY_Left:
+                                                keyval = GDK_KEY_Right;
+                                                break;
+                                        case GDK_KEY_Right:
+                                                keyval = GDK_KEY_Left;
+                                                break;
+                                        case GDK_KEY_KP_Left:
+                                                keyval = GDK_KEY_KP_Right;
+                                                break;
+                                        case GDK_KEY_KP_Right:
+                                                keyval = GDK_KEY_KP_Left;
+                                                break;
+                                        }
+                                }
+                        }
+
                        _vte_keymap_map(keyval, m_modifiers,
                                         m_modes_private.DEC_APPLICATION_CURSOR_KEYS(),
                                         m_modes_private.DEC_APPLICATION_KEYPAD(),