Coalesce neighboring symbol maps for better lookup performance

kitty/fonts/render.py

@@ -25,8 +25,29 @@ else:
 current_faces = None
 
 
+def coalesce_symbol_maps(maps):
+    if not maps:
+        return maps
+    items = tuple((k, maps[k]) for k in sorted(maps))
+    ans = [items[0]]
+
+    def merge(prev_item, item):
+        s, e = item[0]
+        pe = prev_item[0][1]
+        ans[-1] = ((prev_item[0][0], max(pe, e)), prev_item[1])
+
+    for item in items[1:]:
+        current_item = ans[-1]
+        if current_item[1] != item[1] or item[0][0] > current_item[0][1] + 1:
+            ans.append(item)
+        else:
+            merge(current_item, item)
+
+    return dict(ans)
+
+
 def create_symbol_map(opts):
-    val = opts.symbol_map
+    val = coalesce_symbol_maps(opts.symbol_map)
     family_map = {}
     count = 0
     for family in val.values():

kitty_tests/fonts.py

@@ -11,7 +11,9 @@ from kitty.fast_data_types import (
     test_render_line, test_sprite_position_for, wcwidth
 )
 from kitty.fonts.box_drawing import box_chars
-from kitty.fonts.render import render_string, setup_for_testing, shape_string
+from kitty.fonts.render import (
+    coalesce_symbol_maps, render_string, setup_for_testing, shape_string
+)
 
 from . import BaseTest
 
@@ -122,3 +124,7 @@ class Rendering(BaseTest):
         finally:
             sys.stderr = orig
         self.assertIn('LastResort', buf.getvalue())
+
+    def test_coalesce_symbol_maps(self):
+        q = {(2, 3): 'a', (4, 6): 'b', (5, 5): 'b', (7, 7): 'b', (9, 9): 'b', (1, 1): 'a'}
+        self.ae(coalesce_symbol_maps(q), {(1, 3): 'a', (4, 7): 'b', (9, 9): 'b'})