A nice error message when using shortcuts to change background_opacity without setting dynamic_background_opacity

Also change the default shortcuts

README.asciidoc

@@ -44,10 +44,10 @@
 :sc_scroll_page_down: pass:quotes[`ctrl+shift+page_down`]
 :sc_scroll_page_up: pass:quotes[`ctrl+shift+page_up`]
 :sc_second_window: pass:quotes[`ctrl+shift+2`]
-:sc_set_background_opacity_0_1: pass:quotes[`ctrl+shift+a → shift+-`]
-:sc_set_background_opacity_1: pass:quotes[`ctrl+shift+a → shift+1`]
-:sc_set_background_opacity_default: pass:quotes[`ctrl+shift+a → shift+d`]
-:sc_set_background_opacity_plus0_1: pass:quotes[`ctrl+shift+a → shift+=`]
+:sc_set_background_opacity_0_1: pass:quotes[`ctrl+shift+a → l`]
+:sc_set_background_opacity_1: pass:quotes[`ctrl+shift+a → 1`]
+:sc_set_background_opacity_default: pass:quotes[`ctrl+shift+a → d`]
+:sc_set_background_opacity_plus0_1: pass:quotes[`ctrl+shift+a → m`]
 :sc_set_tab_title: pass:quotes[`ctrl+shift+alt+t`]
 :sc_seventh_window: pass:quotes[`ctrl+shift+7`]
 :sc_show_scrollback: pass:quotes[`ctrl+shift+h`]

kittens/show_error/main.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+# License: GPL v3 Copyright: 2018, Kovid Goyal <kovid at kovidgoyal.net>
+
+import sys
+
+from kitty.cli import parse_args
+from ..tui.operations import styled
+
+
+OPTIONS = '''\
+--title
+default=ERROR
+The title for the error message.
+'''.format
+
+
+def real_main(args):
+    error_message = sys.stdin.buffer.read().decode('utf-8')
+    sys.stdin = open('/dev/tty')
+    msg = 'Show an error message'
+    args, items = parse_args(args, OPTIONS, '', msg, 'hints')
+    print(styled(args.title, fg_intense=True, fg='red', bold=True))
+    print()
+    print(error_message)
+    print()
+    input('Press Enter to close.')
+
+
+def main(args):
+    try:
+        real_main(args)
+    except KeyboardInterrupt:
+        pass
+    except Exception:
+        import traceback
+        traceback.print_exc()
+        input('Press Enter to close.')
+
+
+def handle_result(args, data, target_window_id, boss):
+    pass
+
+
+if __name__ == '__main__':
+    main(sys.argv)

kitty/boss.py

@@ -369,6 +369,10 @@ def set_background_opacity(self, opacity):
         window = self.active_window
         if window is None or not opacity:
             return
+        if not self.opts.dynamic_background_opacity:
+            return self.show_error(
+                    _('Cannot change background opacity'),
+                    _('You must set the dynamic_background_opacity option in kitty.conf to be able to change background opacity'))
         os_window_id = window.os_window_id
         if opacity[0] in '+-':
             opacity = background_opacity_of(os_window_id)
@@ -537,7 +541,7 @@ def get_output(self, source_window, num_lines=1):
             output += str(s.linebuf.line(i))
         return output
 
-    def _run_kitten(self, kitten, args=()):
+    def _run_kitten(self, kitten, args=(), input_data=None):
         w = self.active_window
         tab = self.active_tab
         if w is not None and tab is not None and w.overlay_for is None:
@@ -545,17 +549,22 @@ def _run_kitten(self, kitten, args=()):
             from kittens.runner import create_kitten_handler
             end_kitten = create_kitten_handler(kitten, orig_args)
             args[0:0] = [config_dir, kitten]
-            type_of_input = end_kitten.type_of_input
-            if type_of_input in ('text', 'history', 'ansi', 'ansi-history', 'screen', 'screen-history', 'screen-ansi', 'screen-ansi-history'):
-                data = w.as_text(
-                        as_ansi='ansi' in type_of_input,
-                        add_history='history' in type_of_input,
-                        add_wrap_markers='screen' in type_of_input
-                ).encode('utf-8')
-            elif type_of_input is None:
-                data = None
+            if input_data is None:
+                type_of_input = end_kitten.type_of_input
+                if type_of_input in ('text', 'history', 'ansi', 'ansi-history', 'screen', 'screen-history', 'screen-ansi', 'screen-ansi-history'):
+                    data = w.as_text(
+                            as_ansi='ansi' in type_of_input,
+                            add_history='history' in type_of_input,
+                            add_wrap_markers='screen' in type_of_input
+                    ).encode('utf-8')
+                elif type_of_input is None:
+                    data = None
+                else:
+                    raise ValueError('Unknown type_of_input: {}'.format(type_of_input))
             else:
-                raise ValueError('Unknown type_of_input: {}'.format(type_of_input))
+                data = input_data
+            if isinstance(data, str):
+                data = data.encode('utf-8')
             copts = {k: self.opts[k] for k in ('select_by_word_characters', 'open_url_with')}
             overlay_window = tab.new_special_window(
                 SpecialWindow(
@@ -593,6 +602,9 @@ def set_tab_title(self):
             args = ['--name=tab-title', '--message', _('Enter the new title for this tab below.'), 'do_set_tab_title', str(tab.id)]
             self._run_kitten('ask', args)
 
+    def show_error(self, title, msg):
+        self._run_kitten('show_error', ['--title', title], input_data=msg)
+
     def do_set_tab_title(self, title, tab_id):
         tm = self.active_tab_manager
         if tm is not None and title:

kitty/kitty.conf

@@ -501,10 +501,10 @@ map kitty_mod+u        input_unicode_character
 map kitty_mod+f2       edit_config_file
 # Open the kitty shell in a new window/tab/overlay/os_window to control kitty using commands.
 map kitty_mod+escape   kitty_shell window
-map kitty_mod+a>shift+= set_background_opacity +0.1
-map kitty_mod+a>shift+- set_background_opacity -0.1
-map kitty_mod+a>shift+1 set_background_opacity 1
-map kitty_mod+a>shift+d set_background_opacity default
+map kitty_mod+a>m set_background_opacity +0.1
+map kitty_mod+a>l set_background_opacity -0.1
+map kitty_mod+a>1 set_background_opacity 1
+map kitty_mod+a>d set_background_opacity default
 
 # Sending arbitrary text on shortcut key presses
 # You can tell kitty to send arbitrary (UTF-8) encoded text to