tooling: improve STAT table patching. See issue #308

misc/fontbuildlib/stat.py

@@ -7,42 +7,70 @@ from fontTools.otlLib.builder import buildStatTable
 OT_ELIDABLE_AXIS_VALUE_NAME = 0x0002
 
 def rebuildStatTable(font, designspace):
+  #
+  # Changing this code? See discussion at https://github.com/rsms/inter/issues/308
+  #
   if not 'fvar' in font:
     raise Exception('missing fvar table in font')
   axes = [dict(tag=a.axisTag, name=a.axisNameID) for a in font['fvar'].axes]
-  locations = None
+
+  # isMultiAxis is true when compiling the multi-axis VF,
+  # false when compiling e.g. Inter-roman.var.ttf
+  isMultiAxis = False
   if len(axes) > 1:
-    # TODO: Compute locations automatically.
-    # Currently specific to Inter w/ hard-coded values.
-    locations = [
-      { 'name': 'Regular', 'location': { 'wght': 400, 'slnt': 0 },
-        'flags': OT_ELIDABLE_AXIS_VALUE_NAME },
-      { 'name': 'Italic', 'location': { 'wght': 400, 'slnt': -10.0 } },
-    ]
+    isMultiAxis = True
+
   axisTagToName = dict()
   for axis in designspace.axes:
     axisTagToName[axis.tag] = axis.name
+
   weightAxisName = axisTagToName['wght']
   slantAxisName = axisTagToName.get('slnt', 'Slant')
-  weightAxis = None
-  for a in axes:
-    if a['tag'] == 'wght':
-      weightAxis = a
-      break
+  regularWeightValueEntry = None
+
   weightValues = []
+  slantValues = []
+  extremeSlantValue = 0
   for instance in designspace.instances:
-    for axisName, value in instance.location.items():
-      if axisName == slantAxisName:
-        # skip italic/oblique/slant
-        continue
-      weightValue = {
-        'name':  instance.styleName,
-        'value': instance.location[weightAxisName],
+    weightValue = instance.location[weightAxisName]
+    slantValue = instance.location.get(slantAxisName, 0)
+    if slantValue != 0:
+      # slanted (we only make one entry: "Italic")
+      if isMultiAxis and weightValue == 400:
+        extremeSlantValue = slantValue
+        slantValues.append({
+          'name': instance.styleName,
+          'value': slantValue,
+        })
+    else:
+      # upright
+      v = {
+        'name': instance.styleName,
+        'value': weightValue,
       }
-      if weightValue['value'] == 400:
-        weightValue['flags'] = OT_ELIDABLE_AXIS_VALUE_NAME
-      weightValues.append(weightValue)
-  weightAxis['values'] = weightValues
+      if weightValue == 400:
+        v['flags'] = OT_ELIDABLE_AXIS_VALUE_NAME
+        v['linkedValue'] = 700  # style link to "Bold"
+        regularWeightValueEntry = v
+      weightValues.append(v)
+
+  # "Regular" entry for the slant axis, linked with the "Italic" entry
+  if isMultiAxis:
+    slantValues.append({
+      'name': regularWeightValueEntry['name'],
+      'value': 0,
+      'flags': OT_ELIDABLE_AXIS_VALUE_NAME,
+      'linkedValue': extremeSlantValue,
+    })
+
+  for a in axes:
+    tag = a['tag']
+    if tag == 'wght':
+      a['values'] = weightValues
+    elif tag == 'slnt' and len(slantValues) > 0:
+      a['values'] = slantValues
+
+  buildStatTable(font, axes)
 
   # axisNameToTag = dict()
   # for axis in designspace.axes:
@@ -57,5 +85,3 @@ def rebuildStatTable(font, designspace):
   #   if instance.styleName == "Regular":
   #     loc['flags'] = OT_ELIDABLE_AXIS_VALUE_NAME
   #   locations.append(loc)
-
-  buildStatTable(font, axes, locations)