Mitigate the instability of autoKern

successfully reducing individual patches as a result

Author: dummy-index

xkcd-script/font/xkcd-script.otf

@@ -77,7 +77,7 @@ def autokern(font):
     font.addLookup('kerning', 'gpos_pair', (), [['kern', [['latn', ['dflt']]]]])
     font.addLookupSubtable('kerning', 'kern')
 
-    def kern(sep, left, right, **kwargs):
+    def kern(sep, left, right, damper=None, **kwargs):
         """Wraps font.autoKern: expands accented variants and leading/trailing ligatures."""
         def expand(chars, left_side):
             expanded = _expand_with_variants(font, chars)
@@ -94,7 +94,16 @@ def expand(chars, left_side):
                     expanded.append(name)
                     seen.add(name)
             return expanded
-        font.autoKern('kern', sep, expand(left, left_side=True), expand(right, left_side=False), **kwargs)
+        lefts = expand(left, left_side=True)
+        rights = expand(right, left_side=False)
+        font.autoKern('kern', sep, lefts, rights, **kwargs)
+        if damper and damper != 1.0:
+            for l in lefts:
+                tuples = font[l].getPosSub('kern')
+                new_table = []
+                for tup in tuples:
+                    if tup[1] == 'Pair' and tup[2] in rights:
+                        font[l].addPosSub('kern', *(tup[2:5] + (int(tup[5] * damper),) + tup[6:]))
 
     def getkern(left, right):
         c = font[left]
@@ -119,29 +128,25 @@ def getkern(left, right):
     kern(80+a, ['x'], set(lower) - {'i', 'j'}, onlyCloser=True)
     kern(100+a, ['f', 't'], set(lower) - {'i', 'j'}, onlyCloser=True)
     # Set *Y altogether first: CY, OY, etc. will have appropriate values set in the latter part.
-    kern(120, roman, ['Y', 'T'], onlyCloser=True)
+    # CY is a notable example where it is better to use the smaller separation value.
+    kern(105, roman, ['Y', 'T'], onlyCloser=True, damper=0.75)
+    kern(35, caps, ['f'], onlyCloser=True, touch=True, damper=0.9)
     # F/E are separated from T/J so they can use a tighter target gap.
-    kern(130, ['F'], set(roman) - {'f', 'j'}, onlyCloser=True)
+    kern(110, ['F'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
     # Since F and z mesh together and the kerning becomes too large,
-    # reuse the kerning value of the round letterforms.
+    # reuse the kerning value of one of the round letterforms.
     diff_Fo_Fz = getkern('F', 'o') - getkern('F', 'z')
-    kern(130 + diff_Fo_Fz, ['F'], ['z'], onlyCloser=True)
-    kern(100, ['E'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    kern(140, ['E'], ['V'], onlyCloser=True)
-    kern(150, ['T', 'J'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    kern(120, ['T', 'J'], ['O', 'R'], onlyCloser=True)
-    kern(120, ['Y'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    kern(100, ['V'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    # C: loosen from the default (was too tight for Ct/Cf/Cj).
-    kern(65, ['C'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    kern(30, ['C'], ['V', 't', 'v'], onlyCloser=True, touch=True)
-    kern(60, ['O', 'P'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    # For some reason, touch=True creates an unnatural gap in Pe.
-    kern(40, ['P'], ['X', 'a', 'd', 'g', 'q'], onlyCloser=True, touch=True)
-    kern(80, ['D'], set(roman) - {'f', 'j'}, onlyCloser=True)
-    kern(40, ['L'], set(roman) - {'f', 'j'}, onlyCloser=True, touch=True)
-    kern(40, caps, ['f'], onlyCloser=True, touch=True)
-    kern(180, roman, ['j'], onlyCloser=True)
+    kern(110 + int(diff_Fo_Fz / 0.75), ['F'], ['z'], onlyCloser=True, damper=0.75)
+    kern(90, ['E'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(115, ['T', 'J'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(105, ['Y'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(95, ['V'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(65, ['C'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(40, ['E', 'C'], ['V'], onlyCloser=True, touch=True)
+    kern(60, ['O', 'P'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(70, ['D'], set(roman) - {'j'}, onlyCloser=True, damper=0.75)
+    kern(150, roman, ['j'], onlyCloser=True, damper=0.75)
+    kern(40, ['L'], roman, onlyCloser=True, touch=True, damper=0.9)
 
 
 autokern(font)