From c7afe4f3d74f0487c913ce49abc58fe59aaeac12 Mon Sep 17 00:00:00 2001

From: Tom Gundersen <teg@jklm.no>

Date: Sun, 5 Oct 2014 15:26:54 +0200

Subject: [PATCH] terminal/screen: add support for alternate screen buffers

Hook up SM/RM 47/1047-1049 and enable alternate screen buffers for term

applications.

(David: rebased on top of -git, renamed helpers and added docs)

---

 src/libsystemd-terminal/term-internal.h |  1 +

 src/libsystemd-terminal/term-screen.c   | 89 ++++++++++++++++++++++++++++++++-

 2 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/src/libsystemd-terminal/term-internal.h b/src/libsystemd-terminal/term-internal.h

index c78b9aa70a..53713dd64d 100644

--- a/src/libsystemd-terminal/term-internal.h

+++ b/src/libsystemd-terminal/term-internal.h

@@ -646,4 +646,5 @@ struct term_screen {

         term_state state;

         term_state saved;

+        term_state saved_alt;

 };

diff --git a/src/libsystemd-terminal/term-screen.c b/src/libsystemd-terminal/term-screen.c

index c8a81658cb..54bb04752c 100644

--- a/src/libsystemd-terminal/term-screen.c

+++ b/src/libsystemd-terminal/term-screen.c

@@ -77,6 +77,7 @@ int term_screen_new(term_screen **out, term_screen_write_fn write_fn, void *writ

         screen->state.gl = &screen->g0;

         screen->state.gr = &screen->g1;

         screen->saved = screen->state;

+        screen->saved_alt = screen->saved;

         r = term_page_new(&screen->page_main);

         if (r < 0)

@@ -367,6 +368,23 @@ static void screen_restore_state(term_screen *screen, term_state *from) {

         screen->state = *from;

 }

+static void screen_reset_page(term_screen *screen, term_page *page) {

+        term_page_set_scroll_region(page, 0, page->height);

+        term_page_erase(page, 0, 0, page->width, page->height, &screen->state.attr, screen->age, false);

+}

+

+static void screen_change_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 inline void set_reset(term_screen *screen, unsigned int flag, bool set) {

         if (set)

                 screen->flags |= flag;

@@ -427,6 +445,73 @@ static void screen_mode_change(term_screen *screen, unsigned int mode, bool dec,

                 }

                 break;

+        case 47:

+                if (dec) {

+                        /*

+                         * XTERM-ASB: alternate-screen-buffer

+                         * This enables/disables the alternate screen-buffer.

+                         * It effectively saves the current page content and

+                         * allows you to restore it when changing to the

+                         * original screen-buffer again.

+                         */

+                        screen_change_alt(screen, set);

+                }

+

+                break;

+        case 1047:

+                if (dec) {

+                        /*

+                         * XTERM-ASBPE: alternate-screen-buffer-post-erase

+                         * This is the same as XTERM-ASB but erases the

+                         * alternate screen-buffer before switching back to the

+                         * original buffer. Use it to discard any data on the

+                         * alternate screen buffer when done.

+                         */

+                        if (!set)

+                                screen_reset_page(screen, screen->page_alt);

+

+                        screen_change_alt(screen, set);

+                }

+

+                break;

+        case 1048:

+                if (dec) {

+                        /*

+                         * XTERM-ASBCS: alternate-screen-buffer-cursor-state

+                         * This has the same effect as DECSC/DECRC, but uses a

+                         * separate state buffer. It is usually used in

+                         * combination with alternate screen buffers to provide

+                         * stacked state storage.

+                         */

+                        if (set)

+                                screen_save_state(screen, &screen->saved_alt);

+                        else

+                                screen_restore_state(screen, &screen->saved_alt);

+                }

+

+                break;

+        case 1049:

+                if (dec) {

+                        /*

+                         * XTERM-ASBX: alternate-screen-buffer-extended

+                         * This combines XTERM-ASBPE and XTERM-ASBCS somewhat.

+                         * When enabling, state is saved, alternate screen

+                         * buffer is activated and cleared.

+                         * When disabled, alternate screen buffer is cleared,

+                         * then normal screen buffer is enabled and state is

+                         * restored.

+                         */

+                        if (set)

+                                screen_save_state(screen, &screen->saved_alt);

+

+                        screen_reset_page(screen, screen->page_alt);

+                        screen_change_alt(screen, set);

+

+                        if (!set)

+                                screen_restore_state(screen, &screen->saved_alt);

+                }

+

+                break;

         }

 }

@@ -1966,8 +2051,7 @@ static int screen_DECSTBM(term_screen *screen, const term_seq *seq) {

                 bottom = screen->page->height;

         }

-        term_page_set_scroll_region(screen->page_main, top - 1, bottom - top + 1);

-        term_page_set_scroll_region(screen->page_alt, top - 1, bottom - top + 1);

+        term_page_set_scroll_region(screen->page, top - 1, bottom - top + 1);

         screen_cursor_clear_wrap(screen);

         screen_cursor_set(screen, 0, 0);

@@ -4143,6 +4227,7 @@ void term_screen_soft_reset(term_screen *screen) {

         screen->saved = screen->state;

         screen->saved.cursor_x = 0;

         screen->saved.cursor_y = 0;

+        screen->saved_alt = screen->saved;

         screen->page = screen->page_main;

         screen->history = screen->history_main;