player/command: add term-size/[w,h] property

There was no way for scripts to know the current size of the terminal,
which is essintial if they want to provide a good user experience even
without a window.

DOCS/interface-changes/term-size.txt

@@ -0,0 +1 @@
+add `term-size` property

DOCS/man/input.rst

@@ -2804,6 +2804,19 @@ Property list
     Any of these properties may be unavailable or set to dummy values if the
     VO window is not created or visible.
 
+``term-size``
+    The current terminal size.
+
+    This has two sub-properties.
+
+    ``term-size/w``
+        width of the terminal in cells
+    ``term-size/h``
+        height of the terminal in cells
+
+    This property is not observable. Reacting to size changes requires
+    polling.
+
 ``window-id``
     Read-only - mpv's window id. May not always be available, i.e due to window
     not being opened yet or not being supported by the VO.

player/command.c

@@ -74,6 +74,7 @@
 
 #include "osdep/io.h"
 #include "osdep/subprocess.h"
+#include "osdep/terminal.h"
 
 #include "core.h"
 
@@ -2886,6 +2887,23 @@ static int mp_property_osd_ass(void *ctx, struct m_property *prop,
     return m_property_read_sub(props, action, arg);
 }
 
+static int mp_property_term_size(void *ctx, struct m_property *prop,
+                                  int action, void *arg)
+{
+    int w = -1, h = -1;
+    terminal_get_size(&w, &h);
+    if (w == -1 || h == -1)
+        return M_PROPERTY_UNAVAILABLE;
+
+    struct m_sub_property props[] = {
+        {"w",      SUB_PROP_INT(w)},
+        {"h",      SUB_PROP_INT(h)},
+        {0}
+    };
+
+    return m_property_read_sub(props, action, arg);
+}
+
 static int mp_property_mouse_pos(void *ctx, struct m_property *prop,
                                     int action, void *arg)
 {
@@ -4092,6 +4110,7 @@ static const struct m_property mp_properties_base[] = {
     {"input-bindings", mp_property_bindings},
 
     {"user-data", mp_property_udata},
+    {"term-size", mp_property_term_size},
 
     M_PROPERTY_ALIAS("video", "vid"),
     M_PROPERTY_ALIAS("audio", "aid"),