[visitor_test] Make it into the start of a font rescaler

Tests/misc/visitor_test.py

@@ -1,19 +1,37 @@
+from fontTools.misc.visitor import TTVisitor
+import fontTools.ttLib.tables.otBase as otBase
+import fontTools.ttLib.tables.otTables as otTables
 
-class TestVisitor(OTVisitor):
-    pass
 
-import fontTools.ttLib.tables.otTables as otTables
+class ScalerVisitor(TTVisitor):
 
-@TestVisitor.register(otTables.Lookup)
+    def scale(self, v):
+        return v // 2
+
+@ScalerVisitor.register(otTables.ValueRecord)
 def visit(visitor, obj):
-    print(obj)
+    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']
+    for attr in attrs:
+        v = getattr(obj, attr)
+        v = visitor.scale(v)
+        setattr(obj, attr, v)
+    return False
+
+
 from fontTools.ttLib import TTFont
 import sys
 
 font = TTFont(sys.argv[1])
-gsub = font['GSUB']
 
-visitor = TestVisitor()
-visitor.visit(gsub)
+visitor = ScalerVisitor()
+visitor.visit(font)