sd-terminal: support alternate page switching

This adds rmcup/smcup support.

1 files changed, 60 insertions, 2 deletions

diff --git a/src/libsystemd-terminal/term-screen.c b/src/libsystemd-terminal/term-screen.c
index 145dcdaee..f9352ad94 100644
--- a/src/libsystemd-terminal/term-screen.c
+++ b/src/libsystemd-terminal/term-screen.c
@@ -370,6 +370,26 @@ static inline void set_reset(term_screen *screen, unsigned int flag, bool set) {
                 screen->flags &= ~flag;
 }
 
+static int screen_DECSC(term_screen *screen, const term_seq *seq);
+static int screen_DECRC(term_screen *screen, const term_seq *seq);
+
+static inline void screen_clear_alt(term_screen *screen) {
+        term_page_set_scroll_region(screen->page_alt, 0, screen->page->height);
+        term_page_erase(screen->page_alt, 0, 0, screen->page->width, screen->page->height, &screen->attr, screen->age, false);
+}
+
+static inline void screen_set_alt(term_screen *screen, bool set) {
+        if (set) {
+                screen->page = screen->page_alt;
+                screen->history = NULL;
+        } else {
+                screen->page = screen->page_main;
+                screen->history = screen->history_main;
+        }
+
+        screen->page->age = screen->age;
+}
+
 static void screen_mode_change(term_screen *screen, unsigned int mode, bool dec, bool set) {
         switch (mode) {
         case 1:
@@ -423,6 +443,44 @@ static void screen_mode_change(term_screen *screen, unsigned int mode, bool dec,
                 }
 
                 break;
+        case 47:
+                if (dec)
+                        screen_set_alt(screen, set);
+
+                break;
+        case 1047:
+                if (dec) {
+                        if (!set)
+                                screen_clear_alt(screen);
+
+                        screen_set_alt(screen, set);
+                }
+
+                break;
+        case 1048:
+                if (dec) {
+                        if (set)
+                                screen_DECSC(screen, seq);
+                        else
+                                screen_DECRC(screen, seq);
+                }
+
+                break;
+        case 1049:
+                if (dec) {
+                        /* TODO: should DEC{S,R}C be done per-page, rather than per-screen? */
+                        if (set) {
+                                screen_DECSC(screen, seq);
+                                screen_clear_alt(screen);
+                        }
+
+                        screen_set_alt(screen, set);
+
+                        if (!set)
+                                screen_DECRC(screen, seq);
+                }
+
+                break;
         }
 }
 
@@ -1235,7 +1293,7 @@ static int screen_DECRARA(term_screen *screen, const term_seq *seq) {
         return 0;
 }
 
-static int screen_DECRC(term_screen *screen, const term_seq *seq) {
+int screen_DECRC(term_screen *screen, const term_seq *seq) {
         /*
          * DECRC - restore-cursor
          * Restores the terminal to the state saved by the save cursor (DECSC)
@@ -1454,7 +1512,7 @@ static int screen_DECSASD(term_screen *screen, const term_seq *seq) {
         return 0;
 }
 
-static int screen_DECSC(term_screen *screen, const term_seq *seq) {
+int screen_DECSC(term_screen *screen, const term_seq *seq) {
         /*
          * DECSC - save-cursor
          * Save cursor and terminal state so it can be restored later on.