[visitor] Add register_attr(s) example

Lib/fontTools/misc/visitor.py

@@ -7,7 +7,7 @@ class Visitor(object):
     defaultStop = False
 
     @classmethod
-    def register(celf, clazzes, attrs=(None,)):
+    def _register(celf, clazzes, attrs=(None,)):
         assert celf != Visitor, "Subclass Visitor instead."
         if "_visitors" not in celf.__dict__:
             celf._visitors = {}
@@ -34,6 +34,20 @@ class Visitor(object):
 
         return wrapper
 
+    @classmethod
+    def register(celf, clazzes):
+        return celf._register(clazzes)
+
+    @classmethod
+    def register_attr(celf, clazzes, attrs):
+        return celf._register(clazzes, attrs)
+
+    @classmethod
+    def register_attrs(celf, clazzes_attrs):
+        for clazz, attrs in clazzes_attrs:
+            celf._register(clazz, attrs)
+        return lambda _: None
+
     @classmethod
     def _visitorsFor(celf, thing, _default={}):
         typ = type(thing)

Tests/misc/visitor_test.py

@@ -1,31 +1,86 @@
 from fontTools.misc.visitor import TTVisitor
+import fontTools.ttLib as ttLib
 import fontTools.ttLib.tables.otBase as otBase
 import fontTools.ttLib.tables.otTables as otTables
 
 
 class ScalerVisitor(TTVisitor):
-
     def scale(self, v):
         return v // 2
 
+
+@ScalerVisitor.register_attrs(
+    (
+        (ttLib.getTableClass("head"), ("unitsPerEm", "xMin", "yMin", "xMax", "yMax")),
+        (
+            ttLib.getTableClass("hhea"),
+            (
+                "ascent",
+                "descent",
+                "lineGap",
+                "advanceWidthMax",
+                "minLeftSideBearing",
+                "minRightSideBearing",
+                "xMaxExtent",
+            ),
+        ),
+        (
+            ttLib.getTableClass("OS/2"),
+            (
+                "xAvgCharWidth",
+                "ySubscriptXSize",
+                "ySubscriptYSize",
+                "ySubscriptXOffset",
+                "ySubscriptYOffset",
+                "ySuperscriptXSize",
+                "ySuperscriptYSize",
+                "ySuperscriptXOffset",
+                "ySuperscriptYOffset",
+                "yStrikeoutSize",
+                "yStrikeoutSize",
+                "yStrikeoutPosition",
+                "sTypoAscender",
+                "sTypoDescender",
+                "sTypoLineGap",
+                "usWinAscent",
+                "usWinDescent",
+                "sxHeight",
+                "sCapHeight",
+            ),
+        ),
+    )
+)
+def visit(visitor, obj, attr, value):
+    setattr(obj, attr, visitor.scale(value))
+
+
+@ScalerVisitor.register_attr(ttLib.getTableClass("hmtx"), "metrics")
+def visit(visitor, obj, attr, metrics):
+    for g in metrics:
+        advance, lsb = metrics[g]
+        metrics[g] = visitor.scale(advance), visitor.scale(lsb)
+
+
+# GPOS
+
+
 @ScalerVisitor.register(otTables.ValueRecord)
 def visit(visitor, obj):
-    attrs = ['XAdvance', 'YAdvance', 'XPlacement', 'YPlacement']
+    attrs = ["XAdvance", "YAdvance", "XPlacement", "YPlacement"]
     for attr in attrs:
         v = getattr(obj, attr, None)
         if v is not None:
             v = visitor.scale(v)
             setattr(obj, attr, v)
-    return False
+
 
 @ScalerVisitor.register(otTables.Anchor)
 def visit(visitor, obj):
-    attrs = ['XCoordinate', 'YCoordinate']
+    attrs = ["XCoordinate", "YCoordinate"]
     for attr in attrs:
         v = getattr(obj, attr)
         v = visitor.scale(v)
         setattr(obj, attr, v)
-    return False
 
 
 from fontTools.ttLib import TTFont