1 files changed, 77 insertions, 0 deletions
diff --git a/Lib/fontTools/pens/hashPointPen.py b/Lib/fontTools/pens/hashPointPen.py
new file mode 100644
index 00000000..9aef5d87
--- /dev/null
+++ b/Lib/fontTools/pens/hashPointPen.py
@@ -0,0 +1,77 @@
+# Modified from https://github.com/adobe-type-tools/psautohint/blob/08b346865710ed3c172f1eb581d6ef243b203f99/python/psautohint/ufoFont.py#L800-L838
+import hashlib
+
+from fontTools.pens.basePen import MissingComponentError
+from fontTools.pens.pointPen import AbstractPointPen
+
+
+class HashPointPen(AbstractPointPen):
+    """
+    This pen can be used to check if a glyph's contents (outlines plus
+    components) have changed.
+
+    Components are added as the original outline plus each composite's
+    transformation.
+
+    Example: You have some TrueType hinting code for a glyph which you want to
+    compile. The hinting code specifies a hash value computed with HashPointPen
+    that was valid for the glyph's outlines at the time the hinting code was
+    written. Now you can calculate the hash for the glyph's current outlines to
+    check if the outlines have changed, which would probably make the hinting
+    code invalid.
+
+    > glyph = ufo[name]
+    > hash_pen = HashPointPen(glyph.width, ufo)
+    > glyph.drawPoints(hash_pen)
+    > ttdata = glyph.lib.get("public.truetype.instructions", None)
+    > stored_hash = ttdata.get("id", None)  # The hash is stored in the "id" key
+    > if stored_hash is None or stored_hash != hash_pen.hash:
+    >    logger.error(f"Glyph hash mismatch, glyph '{name}' will have no instructions in font.")
+    > else:
+    >    # The hash values are identical, the outline has not changed.
+    >    # Compile the hinting code ...
+    >    pass
+    """
+
+    def __init__(self, glyphWidth=0, glyphSet=None):
+        self.glyphset = glyphSet
+        self.data = ["w%s" % round(glyphWidth, 9)]
+
+    @property
+    def hash(self):
+        data = "".join(self.data)
+        if len(data) >= 128:
+            data = hashlib.sha512(data.encode("ascii")).hexdigest()
+        return data
+
+    def beginPath(self, identifier=None, **kwargs):
+        pass
+
+    def endPath(self):
+        self.data.append("|")
+
+    def addPoint(
+        self,
+        pt,
+        segmentType=None,
+        smooth=False,
+        name=None,
+        identifier=None,
+        **kwargs,
+    ):
+        if segmentType is None:
+            pt_type = "o"  # offcurve
+        else:
+            pt_type = segmentType[0]
+        self.data.append(f"{pt_type}{pt[0]:g}{pt[1]:+g}")
+
+    def addComponent(
+        self, baseGlyphName, transformation, identifier=None, **kwargs
+    ):
+        tr = "".join([f"{t:+}" for t in transformation])
+        self.data.append("[")
+        try:
+            self.glyphset[baseGlyphName].drawPoints(self)
+        except KeyError:
+            raise MissingComponentError(baseGlyphName)
+        self.data.append(f"({tr})]")