terminal/screen: adjust screen age only on update

Instead of increasing the screen-age on redraw, we now increase it only on
real updates. This is effectively the same, but avoids increased age
counters on backbuffer rendering. Therefore, we can now check age counters
against fronbuffers safely, while rendering frames in background.

1 files changed, 9 insertions, 1 deletions

diff --git a/src/libsystemd-terminal/term-screen.c b/src/libsystemd-terminal/term-screen.c
index 3f7ef1cf3c..145dcdaee5 100644
--- a/src/libsystemd-terminal/term-screen.c
+++ b/src/libsystemd-terminal/term-screen.c
@@ -3735,6 +3735,12 @@ unsigned int term_screen_get_height(term_screen *screen) {
         return screen->page->height;
 }
 
+uint64_t term_screen_get_age(term_screen *screen) {
+        assert_return(screen, 0);
+
+        return screen->age;
+}
+
 int term_screen_feed_text(term_screen *screen, const uint8_t *in, size_t size) {
         uint32_t *ucs4_str;
         size_t i, j, ucs4_len;
@@ -3743,6 +3749,8 @@ int term_screen_feed_text(term_screen *screen, const uint8_t *in, size_t size) {
 
         assert_return(screen, -EINVAL);
 
+        ++screen->age;
+
         /* Feed bytes into utf8 decoder and handle parsed ucs4 chars. We always
          * treat data as UTF-8, but the parser makes sure to fall back to raw
          * 8bit mode if the stream is not valid UTF-8. This should be more than
@@ -4258,7 +4266,7 @@ int term_screen_draw(term_screen *screen,
         }
 
         if (fb_age)
-                *fb_age = screen->age++;
+                *fb_age = screen->age;
 
         return 0;
 }