Allow changing font size in a running terminal using keyboard shortcuts.

Fixes #57

kitty/boss.py

@@ -14,6 +14,7 @@ from time import monotonic
 from queue import Queue, Empty
 from gettext import gettext as _
 
+from .config import MINIMUM_FONT_SIZE
 from .constants import (
     viewport_size, set_boss, wakeup, cell_size, MODIFIER_KEYS,
     main_thread, mouse_button_pressed, mouse_cursor_pos
@@ -86,6 +87,7 @@ class Boss(Thread):
         self.pending_ui_thread_calls = Queue()
         self.write_dispatch_map = {}
         set_boss(self)
+        self.current_font_size = opts.font_size
         cell_size.width, cell_size.height = set_font_family(opts)
         self.opts, self.args = opts, args
         self.glfw_window = glfw_window
@@ -228,6 +230,28 @@ class Boss(Thread):
         self.pending_resize = False
         glfw_post_empty_event()
 
+    def increase_font_size(self):
+        self.change_font_size(min(self.opts.font_size * 5, self.current_font_size + self.opts.font_size_delta))
+
+    def decrease_font_size(self):
+        self.change_font_size(max(MINIMUM_FONT_SIZE, self.current_font_size - self.opts.font_size_delta))
+
+    def restore_font_size(self):
+        self.change_font_size(self.opts.font_size)
+
+    def change_font_size(self, new_size):
+        if new_size == self.current_font_size:
+            return
+        self.current_font_size = new_size
+        cell_size.width, cell_size.height = set_font_family(
+            self.opts, override_font_size=self.current_font_size)
+        self.sprites.do_layout(cell_size.width, cell_size.height)
+        self.queue_action(self.resize_windows_after_font_size_change)
+
+    def resize_windows_after_font_size_change(self):
+        self.tab_manager.resize()
+        glfw_post_empty_event()
+
     def tabbar_visibility_changed(self):
         self.tab_manager.resize(only_tabs=True)
         glfw_post_empty_event()

kitty/config.py

@@ -17,10 +17,11 @@ from .layout import all_layouts
 from .utils import safe_print, to_color
 
 key_pat = re.compile(r'([a-zA-Z][a-zA-Z0-9_-]*)\s+(.+)$')
+MINIMUM_FONT_SIZE = 6
 
 
 def to_font_size(x):
-    return max(6, float(x))
+    return max(MINIMUM_FONT_SIZE, float(x))
 
 
 cshapes = {
@@ -153,6 +154,7 @@ type_map = {
     'scrollback_pager': shlex.split,
     'scrollback_in_new_tab': to_bool,
     'font_size': to_font_size,
+    'font_size_delta': float,
     'cursor_shape': to_cursor_shape,
     'cursor_opacity': to_opacity,
     'open_url_modifiers': to_open_url_modifiers,

kitty/fonts/core_text.py

@@ -19,7 +19,7 @@ def install_symbol_map(val, font_size, dpi):
         symbol_map[ch] = family_map[family]
 
 
-def set_font_family(opts, ignore_dpi_failure=False):
+def set_font_family(opts, override_font_size=None, ignore_dpi_failure=False):
     global cell_width, cell_height, baseline, CellTexture, WideCellTexture, underline_thickness, underline_position
     try:
         dpi = get_logical_dpi()
@@ -37,11 +37,12 @@ def set_font_family(opts, ignore_dpi_failure=False):
         if ans == 'auto' and (bold or italic):
             ans = get_family(False, False)
         return ans
+    font_size = override_font_size or opts.font_size
 
     for bold in (False, True):
         for italic in (False, True):
-            main_font[(bold, italic)] = Face(get_family(bold, italic), bold, italic, True, opts.font_size, dpi)
+            main_font[(bold, italic)] = Face(get_family(bold, italic), bold, italic, True, font_size, dpi)
-    install_symbol_map(opts.symbol_map, opts.font_size, dpi)
+    install_symbol_map(opts.symbol_map, font_size, dpi)
     mf = main_font[(False, False)]
     cell_width, cell_height = mf.cell_size()
     CellTexture = ctypes.c_ubyte * (cell_width * cell_height)

kitty/fonts/freetype.py

@@ -71,10 +71,10 @@ def font_units_to_pixels(x, units_per_em, size_in_pts, dpi):
     return ceil_int(x * ((size_in_pts * dpi) / (72 * units_per_em)))
 
 
-def set_font_family(opts):
+def set_font_family(opts, override_font_size=None):
     global current_font_family, current_font_family_name, cff_size, cell_width, cell_height, CharTexture, baseline
     global underline_position, underline_thickness
-    size_in_pts = opts.font_size
+    size_in_pts = override_font_size or opts.font_size
     current_font_family = get_font_files(opts)
     current_font_family_name = opts.font_family
     dpi = get_logical_dpi()

kitty/kitty.conf

@@ -15,6 +15,10 @@ bold_italic_font auto
 # Font size (in pts)
 font_size        11.0
 
+# The amount the font size is changed by (in pts) when increasing/decreasing
+# the font size in a running terminal.
+font_size_delta 2
+
 # The foreground color
 foreground       #dddddd
 
@@ -215,6 +219,10 @@ map ctrl+shift+l        next_layout
 map ctrl+shift+.        move_tab_forward
 map ctrl+shift+,        move_tab_backward
 
+# Miscellaneous
+map ctrl+shift+equal    increase_font_size
+map ctrl+shift+minus    decrease_font_size
+map ctrl+shift+backspace restore_font_size
 
 # Symbol mapping (special font for specified unicode code points). Map the
 # specified unicode codepoints to a particular font. Useful if you need special