googlefonts · m4rc1e · Mar 1, 2022 · Feb 28, 2022
diff --git a/bin/gftools-ufo-fix-instances.py b/bin/gftools-ufo-fix-instances.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""
+Fix designspace instances so they are gf spec complaint:
+https://github.com/googlefonts/gf-docs/tree/main/Spec#fvar-instances
+
+Usage:
+
+gftools ufo-fix-instances family.designspace
+"""
+from fontTools.designspaceLib import DesignSpaceDocument, InstanceDescriptor
+from copy import deepcopy
+from gftools.fix import WEIGHT_VALUES
+import sys
+
+
+def build_instances(ds):
+    """Generate Designspace instances which are gf spec complaint"""
+    instances = []
+    axes = ds.axes
+    wght_axis = next((a for a in axes if a.tag == "wght"), None)
+    wght_vals = list(range(int(wght_axis.minimum), int(wght_axis.maximum + 100), 100))
+    italic_axis = next((a for a in axes if a.tag in ["slnt", "ital"]), None)
+    for wght in wght_vals:
+        inst = InstanceDescriptor()
+        coords = {a.tag: a.default for a in axes}
+        coords["wght"] = float(wght)
+        inst.location = coords
+        inst.styleName = WEIGHT_VALUES[wght]
+        instances.append(inst)
+
+    if italic_axis:
+        italics = deepcopy(instances)
+        for inst in italics:
+            inst.styleName = f"{inst.styleName} Italic".replace(
+                "Regular Italic", "Italic"
+            )
+            inst.location[italic_axis.tag] = italic_axis.minimum
+        instances += italics
+    return instances
+
+
+def main():
+    if len(sys.argv) != 2:
+        print(__doc__)
+        return
+    ds_path = sys.argv[1]
+    ds = DesignSpaceDocument()
+    ds.read(ds_path)
+    instances = build_instances(ds)
+    ds.instances = instances
+    ds.write(ds_path)
+
+
+if __name__ == "__main__":
+    main()