[vte] modes: Add DECSDM mode

[Christian Persch <chpe src gnome org>]

commit ce715e7b9859f62fc881c2ddd64cab7e3a2fbc7a
Author: Christian Persch <chpe src gnome org>
Date:   Mon Oct 19 00:16:36 2020 +0200

    modes: Add DECSDM mode

 src/modes-private.hh | 12 +++++-------
 src/modes.hh         |  1 +
 2 files changed, 6 insertions(+), 7 deletions(-)
---
diff --git a/src/modes-private.hh b/src/modes-private.hh
index 2dab1f8d..255a968e 100644
--- a/src/modes-private.hh
+++ b/src/modes-private.hh
@@ -415,15 +415,13 @@ MODE_FIXED(DECLRMM, 69, ALWAYS_RESET) /* aka DECVSSM */
 MODE_FIXED(DECXRLM,    73, ALWAYS_RESET)
 
 /*
- * DECSDM - sixel display mode
+ * DECSDM - sixel display mode (scrolling)
  *
- * Default: reset
- *
- * References: VT525
+ * Default: set
  *
- * Probably not worth implementing.
+ * References: ?
  */
-/* MODE_FIXED(DECSDM,    80, ALWAYS_RESET) ! Conflicts with WY161 */
+MODE(DECSDM, 80) /* Note: Conflicts with WY161 */
 
 /*
  * DECKPM - key position mode
@@ -799,7 +797,7 @@ MODE_FIXED(WYTEK,  38, ALWAYS_RESET)
  *
  * References: WY370
  */
-MODE_FIXED(WY161,  80, ALWAYS_RESET)
+/* MODE_FIXED(WY161,  80, ALWAYS_RESET) ! Conflicts with DECSDM */
 
 /*
  * WY52 - 52 lines mode
diff --git a/src/modes.hh b/src/modes.hh
index 48b1b2ce..ce480143 100644
--- a/src/modes.hh
+++ b/src/modes.hh
@@ -226,6 +226,7 @@ public:
 
         constexpr Private() : Self{eDEC_AUTOWRAP,
                                    eDEC_TEXT_CURSOR,
+                                   eDECSDM,
                                    eVTE_BIDI_SWAP_ARROW_KEYS,
                                    eXTERM_ALTBUF_SCROLL,
                                    eXTERM_META_SENDS_ESCAPE} { }