player: redo terminal OSD and status line handling

The terminal OSD code includes the handling of the terminal status line,
showing player OSD messages on the terminal, and showing subtitles on
terminal (the latter two only if there is no video window, or if
terminal OSD is forced).

This didn't handle some corner cases correctly. For example, showing an
OSD message on the terminal always cleared the previous line, even if
the line was an important message (or even just the command prompt, if
most other messages were silenced).

Attempt to handle this correctly by keeping track of how many lines the
terminal OSD currently consists of. Since there could be race conditions
with other messages being printed, implement this in msg.c. Now msg.c
expects that MSGL_STATUS messages rewrite the status line, so the caller
is forced to use a single mp_msg() call to set the status line.

Instead of littering print_status() all over the place, update the
status only once per playloop iteration in update_osd_msg(). In audio-
only mode, the status line might now be a little bit off, but it's
perhaps ok.

Print the status line only if it has changed, or if another message was
printed. This might help with extremely slow terminals, although in
audio+video mode, it'll still be updated very often (A-V sync display
changes on every frame).

Instead of hardcoding the terminal sequences, use
terminfo/termcap to get the sequences. Remove the --term-osd-esc option,
which allowed to override the hardcoded escapes - it's useless now.

The fallback for terminals with no escape sequences for moving the
cursor and clearing a line is removed. This somewhat breaks status line
display on these terminals, including the MS Windows console: instead of
querying the terminal size and clearing the line manually by padding the
output with spaces, the line is simply not cleared. I don't expect this
to be a problem on UNIX, and on MS Windows we could emulate escape
sequences. Note that terminal OSD (other than the status line) was
broken anyway on these terminals.

In osd.c, the function get_term_width() is not used anymore, so remove
it. To remind us that the MS Windows console apparently adds a line
break when writint the last column, adjust screen_width in terminal-
win.c accordingly.

2 files changed, 80 insertions, 14 deletions

diff --git a/common/msg.c b/common/msg.c
index 841fab30c7..2cd2e19b27 100644
--- a/common/msg.c
+++ b/common/msg.c
@@ -43,8 +43,12 @@ struct mp_log_root {
     struct mpv_global *global;
     // --- protected by mp_msg_lock
     char *msglevels;
-    bool smode; // slave mode compatibility glue
+    bool smode;         // slave mode compatibility glue
     bool module;
+    bool termosd;       // use terminal control codes for status line
+    bool header;        // indicate that message header should be printed
+    int blank_lines;    // number of lines useable by status
+    int status_lines;   // number of current status lines
     // --- semi-atomic access
     bool color;
     int verbose;
@@ -55,8 +59,6 @@ struct mp_log_root {
      * (This is perhaps better than maintaining a globally accessible and
      * synchronized mp_log tree.) */
     int64_t reload_counter;
-    int header;         // indicate if last line printed ended with \n or \r
-    int statusline;     // indicates if last line printed was a status line
 };
 
 struct mp_log {
@@ -117,6 +119,61 @@ bool mp_msg_test(struct mp_log *log, int lev)
     return lev <= log->level || (log->root->smode && lev == MSGL_SMODE);
 }
 
+// Reposition cursor and clear lines for outputting the status line. In certain
+// cases, like term OSD and subtitle display, the status can consist of
+// multiple lines.
+static void prepare_status_line(struct mp_log_root *root, char *new_status)
+{
+    FILE *f = stderr;
+    size_t old_lines = root->blank_lines;
+
+    size_t new_lines = 1;
+    char *tmp = new_status;
+    while (1) {
+        tmp = strchr(tmp, '\n');
+        if (!tmp)
+            break;
+        new_lines++;
+        tmp++;
+    }
+
+    // clear the status line itself
+    fprintf(f, "\r%s", terminal_erase_to_end_of_line);
+    // and clear all previous old lines
+    for (size_t n = 1; n < old_lines; n++)
+        fprintf(f, "%s\r%s", terminal_cursor_up, terminal_erase_to_end_of_line);
+    // skip "unused" blank lines, so that status is aligned to term bottom
+    for (size_t n = new_lines; n < old_lines; n++)
+        fprintf(f, "\n");
+
+    root->status_lines = new_lines;
+    root->blank_lines = MPMAX(root->blank_lines, new_lines);
+}
+
+static void flush_status_line(struct mp_log_root *root)
+{
+    // If there was a status line, don't overwrite it, but skip it.
+    if (root->status_lines)
+        fprintf(stderr, "\n");
+    root->status_lines = 0;
+    root->blank_lines = 0;
+}
+
+void mp_msg_flush_status_line(struct mpv_global *global)
+{
+    pthread_mutex_lock(&mp_msg_lock);
+    flush_status_line(global->log->root);
+    pthread_mutex_unlock(&mp_msg_lock);
+}
+
+bool mp_msg_has_status_line(struct mpv_global *global)
+{
+    pthread_mutex_lock(&mp_msg_lock);
+    bool r = global->log->root->status_lines > 0;
+    pthread_mutex_unlock(&mp_msg_lock);
+    return r;
+}
+
 static void set_msg_color(FILE* stream, int lev)
 {
     static const int v_colors[] = {9, 1, 3, -1, -1, 2, 8, 8, -1};
@@ -139,12 +196,21 @@ void mp_msg_va(struct mp_log *log, int lev, const char *format, va_list va)
     tmp[MSGSIZE_MAX - 2] = '\n';
     tmp[MSGSIZE_MAX - 1] = 0;
 
-    /* A status line is normally intended to be overwritten by the next
-     * status line, and does not end with a '\n'. If we're printing a normal
-     * line instead after the status one print '\n' to change line. */
-    if (root->statusline && lev != MSGL_STATUS)
-        fprintf(stderr, "\n");
-    root->statusline = lev == MSGL_STATUS;
+    char *terminate = "";
+
+    if (lev == MSGL_STATUS) {
+        if (root->termosd) {
+            prepare_status_line(root, tmp);
+            terminate = "\r";
+        } else {
+            terminate = "\n";
+        }
+        root->header = true;
+    } else {
+        flush_status_line(root);
+        size_t len = strlen(tmp);
+        root->header = len && tmp[len - 1] == '\n';
+    }
 
     if (root->color)
         set_msg_color(stream, lev);
@@ -156,10 +222,7 @@ void mp_msg_va(struct mp_log *log, int lev, const char *format, va_list va)
         }
     }
 
-    size_t len = strlen(tmp);
-    root->header = len && (tmp[len - 1] == '\n' || tmp[len - 1] == '\r');
-
-    fprintf(stream, "%s", tmp);
+    fprintf(stream, "%s%s", tmp, terminate);
 
     if (root->color)
         terminal_set_foreground_color(stream, -1);
@@ -211,7 +274,7 @@ void mp_msg_init(struct mpv_global *global)
 
     struct mp_log_root *root = talloc_zero(NULL, struct mp_log_root);
     root->global = global;
-    root->header = 1;
+    root->header = true;
     root->reload_counter = 1;
 
     struct mp_log dummy = { .root = root };
@@ -236,6 +299,7 @@ void mp_msg_update_msglevels(struct mpv_global *global)
     root->module = opts->msg_module;
     root->smode = opts->msg_identify;
     root->color = opts->msg_color && isatty(fileno(stdout));
+    root->termosd = !opts->slave_mode && isatty(fileno(stdout));
 
     talloc_free(root->msglevels);
     root->msglevels = talloc_strdup(root, global->opts->msglevels);
diff --git a/common/msg.h b/common/msg.h
index 561efe5e53..50420c9044 100644
--- a/common/msg.h
+++ b/common/msg.h
@@ -82,6 +82,8 @@ void mp_msg_uninit(struct mpv_global *global);
 void mp_msg_update_msglevels(struct mpv_global *global);
 void mp_msg_mute(struct mpv_global *global, bool mute);
 void mp_msg_force_stderr(struct mpv_global *global, bool force_stderr);
+void mp_msg_flush_status_line(struct mpv_global *global);
+bool mp_msg_has_status_line(struct mpv_global *global);
 
 struct bstr;
 int mp_msg_split_msglevel(struct bstr *s, struct bstr *out_mod, int *out_level);