Allow viewing the current contents of the alternate screen in a new window.

Fixes #933

kitty/boss.py

@@ -790,6 +790,10 @@ class Boss:
                 return w.as_text()
             if arg == '@ansi_screen':
                 return w.as_text(as_ansi=True)
+            if arg == '@alternate':
+                return w.as_text(alternate_screen=True)
+            if arg == '@ansi_alternate':
+                return w.as_text(as_ansi=True, alternate_screen=True)
 
         if args[0].startswith('@') and args[0] != '@':
             stdin = data_for_at(args[0]) or None

kitty/config_data.py

@@ -827,7 +827,8 @@ k('scroll_end', 'kitty_mod+end', 'scroll_end', _('Scroll to bottom'))
 k('show_scrollback', 'kitty_mod+h', 'show_scrollback', _('Browse scrollback buffer in less'), long_text=_('''
 You can send the contents of the current screen + history buffer as stdin to an arbitrary program using
 the placeholders @text (which is the plain text) and @ansi (which includes text styling escape codes).
-For only the current screen, use @screen or @ansi_screen.
+For only the current screen, use @screen or @ansi_screen. For the secondary screen, use
+@alternate and @ansi_alternate.
 For example, the following command opens the scrollback buffer in less in a new window::
 
     map kitty_mod+y new_window @ansi less +G -R

kitty/screen.c

@@ -1684,6 +1684,21 @@ as_text_non_visual(Screen *self, PyObject *args) {
     as_text_generic(args, self, range_line_, self->lines, self->columns);
 }
 
+static inline PyObject*
+as_text_generic_wrapper(Screen *self, PyObject *args, Line*(get_line)(Screen *, int)) {
+    as_text_generic(args, self, get_line, self->lines, self->columns);
+}
+
+static PyObject*
+as_text_alternate(Screen *self, PyObject *args) {
+    LineBuf *original = self->linebuf;
+    self->linebuf = original == self->main_linebuf ? self->alt_linebuf : self->main_linebuf;
+    PyObject *ans = as_text_generic_wrapper(self, args, range_line_);
+    self->linebuf = original;
+    return ans;
+}
+
+
 static PyObject*
 screen_wcswidth(PyObject UNUSED *self, PyObject *str) {
     if (PyUnicode_READY(str) != 0) return NULL;
@@ -2169,6 +2184,7 @@ static PyMethodDef methods[] = {
     MND(set_pending_timeout, METH_O)
     MND(as_text, METH_VARARGS)
     MND(as_text_non_visual, METH_VARARGS)
+    MND(as_text_alternate, METH_VARARGS)
     MND(tab, METH_NOARGS)
     MND(backspace, METH_NOARGS)
     MND(linefeed, METH_NOARGS)

kitty/window.py

@@ -436,10 +436,13 @@ class Window:
             self.screen.reset_callbacks()
         self.screen = None
 
-    def as_text(self, as_ansi=False, add_history=False, add_wrap_markers=False):
+    def as_text(self, as_ansi=False, add_history=False, add_wrap_markers=False, alternate_screen=False):
         lines = []
-        add_history = add_history and not self.screen.is_using_alternate_linebuf()
+        add_history = add_history and not self.screen.is_using_alternate_linebuf() and not alternate_screen
-        f = self.screen.as_text_non_visual if add_history else self.screen.as_text
+        if alternate_screen:
+            f = self.screen.as_text_alternate
+        else:
+            f = self.screen.as_text_non_visual if add_history else self.screen.as_text
         f(lines.append, as_ansi, add_wrap_markers)
         if add_history:
             h = []