[cffLib] Add remove_hints() and remove_unused_subroutines() methods

From subset.cff.

Lib/fontTools/cffLib/__init__.py

@@ -313,6 +313,16 @@ def desubroutinize(self):
 
         desubroutinize(self)
 
+    def remove_hints(self):
+        from .transforms import remove_hints
+
+        remove_hints(self)
+
+    def remove_unused_subroutines(self):
+        from .transforms import remove_unused_subroutines
+
+        remove_unused_subroutines(self)
+
 
 class CFFWriter(object):
     """Helper class for serializing CFF data to binary. Used by

Lib/fontTools/cffLib/transforms.py

@@ -1,4 +1,12 @@
-from fontTools.misc.psCharStrings import SimpleT2Decompiler
+from fontTools.misc.psCharStrings import (
+    SimpleT2Decompiler,
+    T2WidthExtractor,
+    calcSubrBias,
+)
+
+
+def _uniq_sort(l):
+    return sorted(set(l))
 
 
 class StopHintCountEvent(Exception):
@@ -113,3 +121,365 @@ def desubroutinize(cff):
                 del pd.rawDict["Subrs"]
     # as well as the global subrs
     cff.GlobalSubrs.clear()
+
+
+class _MarkingT2Decompiler(SimpleT2Decompiler):
+    def __init__(self, localSubrs, globalSubrs, private):
+        SimpleT2Decompiler.__init__(self, localSubrs, globalSubrs, private)
+        for subrs in [localSubrs, globalSubrs]:
+            if subrs and not hasattr(subrs, "_used"):
+                subrs._used = set()
+
+    def op_callsubr(self, index):
+        self.localSubrs._used.add(self.operandStack[-1] + self.localBias)
+        SimpleT2Decompiler.op_callsubr(self, index)
+
+    def op_callgsubr(self, index):
+        self.globalSubrs._used.add(self.operandStack[-1] + self.globalBias)
+        SimpleT2Decompiler.op_callgsubr(self, index)
+
+
+class _DehintingT2Decompiler(T2WidthExtractor):
+    class Hints(object):
+        def __init__(self):
+            # Whether calling this charstring produces any hint stems
+            # Note that if a charstring starts with hintmask, it will
+            # have has_hint set to True, because it *might* produce an
+            # implicit vstem if called under certain conditions.
+            self.has_hint = False
+            # Index to start at to drop all hints
+            self.last_hint = 0
+            # Index up to which we know more hints are possible.
+            # Only relevant if status is 0 or 1.
+            self.last_checked = 0
+            # The status means:
+            # 0: after dropping hints, this charstring is empty
+            # 1: after dropping hints, there may be more hints
+            # 	continuing after this, or there might be
+            # 	other things.  Not clear yet.
+            # 2: no more hints possible after this charstring
+            self.status = 0
+            # Has hintmask instructions; not recursive
+            self.has_hintmask = False
+            # List of indices of calls to empty subroutines to remove.
+            self.deletions = []
+
+        pass
+
+    def __init__(
+        self, css, localSubrs, globalSubrs, nominalWidthX, defaultWidthX, private=None
+    ):
+        self._css = css
+        T2WidthExtractor.__init__(
+            self, localSubrs, globalSubrs, nominalWidthX, defaultWidthX
+        )
+        self.private = private
+
+    def execute(self, charString):
+        old_hints = charString._hints if hasattr(charString, "_hints") else None
+        charString._hints = self.Hints()
+
+        T2WidthExtractor.execute(self, charString)
+
+        hints = charString._hints
+
+        if hints.has_hint or hints.has_hintmask:
+            self._css.add(charString)
+
+        if hints.status != 2:
+            # Check from last_check, make sure we didn't have any operators.
+            for i in range(hints.last_checked, len(charString.program) - 1):
+                if isinstance(charString.program[i], str):
+                    hints.status = 2
+                    break
+                else:
+                    hints.status = 1  # There's *something* here
+            hints.last_checked = len(charString.program)
+
+        if old_hints:
+            assert hints.__dict__ == old_hints.__dict__
+
+    def op_callsubr(self, index):
+        subr = self.localSubrs[self.operandStack[-1] + self.localBias]
+        T2WidthExtractor.op_callsubr(self, index)
+        self.processSubr(index, subr)
+
+    def op_callgsubr(self, index):
+        subr = self.globalSubrs[self.operandStack[-1] + self.globalBias]
+        T2WidthExtractor.op_callgsubr(self, index)
+        self.processSubr(index, subr)
+
+    def op_hstem(self, index):
+        T2WidthExtractor.op_hstem(self, index)
+        self.processHint(index)
+
+    def op_vstem(self, index):
+        T2WidthExtractor.op_vstem(self, index)
+        self.processHint(index)
+
+    def op_hstemhm(self, index):
+        T2WidthExtractor.op_hstemhm(self, index)
+        self.processHint(index)
+
+    def op_vstemhm(self, index):
+        T2WidthExtractor.op_vstemhm(self, index)
+        self.processHint(index)
+
+    def op_hintmask(self, index):
+        rv = T2WidthExtractor.op_hintmask(self, index)
+        self.processHintmask(index)
+        return rv
+
+    def op_cntrmask(self, index):
+        rv = T2WidthExtractor.op_cntrmask(self, index)
+        self.processHintmask(index)
+        return rv
+
+    def processHintmask(self, index):
+        cs = self.callingStack[-1]
+        hints = cs._hints
+        hints.has_hintmask = True
+        if hints.status != 2:
+            # Check from last_check, see if we may be an implicit vstem
+            for i in range(hints.last_checked, index - 1):
+                if isinstance(cs.program[i], str):
+                    hints.status = 2
+                    break
+            else:
+                # We are an implicit vstem
+                hints.has_hint = True
+                hints.last_hint = index + 1
+                hints.status = 0
+        hints.last_checked = index + 1
+
+    def processHint(self, index):
+        cs = self.callingStack[-1]
+        hints = cs._hints
+        hints.has_hint = True
+        hints.last_hint = index
+        hints.last_checked = index
+
+    def processSubr(self, index, subr):
+        cs = self.callingStack[-1]
+        hints = cs._hints
+        subr_hints = subr._hints
+
+        # Check from last_check, make sure we didn't have
+        # any operators.
+        if hints.status != 2:
+            for i in range(hints.last_checked, index - 1):
+                if isinstance(cs.program[i], str):
+                    hints.status = 2
+                    break
+            hints.last_checked = index
+
+        if hints.status != 2:
+            if subr_hints.has_hint:
+                hints.has_hint = True
+
+                # Decide where to chop off from
+                if subr_hints.status == 0:
+                    hints.last_hint = index
+                else:
+                    hints.last_hint = index - 2  # Leave the subr call in
+
+        elif subr_hints.status == 0:
+            hints.deletions.append(index)
+
+        hints.status = max(hints.status, subr_hints.status)
+
+
+def _cs_subset_subroutines(charstring, subrs, gsubrs):
+    p = charstring.program
+    for i in range(1, len(p)):
+        if p[i] == "callsubr":
+            assert isinstance(p[i - 1], int)
+            p[i - 1] = subrs._used.index(p[i - 1] + subrs._old_bias) - subrs._new_bias
+        elif p[i] == "callgsubr":
+            assert isinstance(p[i - 1], int)
+            p[i - 1] = (
+                gsubrs._used.index(p[i - 1] + gsubrs._old_bias) - gsubrs._new_bias
+            )
+
+
+def _cs_drop_hints(charstring):
+    hints = charstring._hints
+
+    if hints.deletions:
+        p = charstring.program
+        for idx in reversed(hints.deletions):
+            del p[idx - 2 : idx]
+
+    if hints.has_hint:
+        assert not hints.deletions or hints.last_hint <= hints.deletions[0]
+        charstring.program = charstring.program[hints.last_hint :]
+        if not charstring.program:
+            # TODO CFF2 no need for endchar.
+            charstring.program.append("endchar")
+        if hasattr(charstring, "width"):
+            # Insert width back if needed
+            if charstring.width != charstring.private.defaultWidthX:
+                # For CFF2 charstrings, this should never happen
+                assert (
+                    charstring.private.defaultWidthX is not None
+                ), "CFF2 CharStrings must not have an initial width value"
+                charstring.program.insert(
+                    0, charstring.width - charstring.private.nominalWidthX
+                )
+
+    if hints.has_hintmask:
+        i = 0
+        p = charstring.program
+        while i < len(p):
+            if p[i] in ["hintmask", "cntrmask"]:
+                assert i + 1 <= len(p)
+                del p[i : i + 2]
+                continue
+            i += 1
+
+    assert len(charstring.program)
+
+    del charstring._hints
+
+
+def remove_hints(cff):
+    for fontname in cff.keys():
+        font = cff[fontname]
+        cs = font.CharStrings
+        # This can be tricky, but doesn't have to. What we do is:
+        #
+        # - Run all used glyph charstrings and recurse into subroutines,
+        # - For each charstring (including subroutines), if it has any
+        #   of the hint stem operators, we mark it as such.
+        #   Upon returning, for each charstring we note all the
+        #   subroutine calls it makes that (recursively) contain a stem,
+        # - Dropping hinting then consists of the following two ops:
+        #   * Drop the piece of the program in each charstring before the
+        #     last call to a stem op or a stem-calling subroutine,
+        #   * Drop all hintmask operations.
+        # - It's trickier... A hintmask right after hints and a few numbers
+        #    will act as an implicit vstemhm. As such, we track whether
+        #    we have seen any non-hint operators so far and do the right
+        #    thing, recursively... Good luck understanding that :(
+        css = set()
+        for g in font.charset:
+            c, _ = cs.getItemAndSelector(g)
+            c.decompile()
+            subrs = getattr(c.private, "Subrs", [])
+            decompiler = _DehintingT2Decompiler(
+                css,
+                subrs,
+                c.globalSubrs,
+                c.private.nominalWidthX,
+                c.private.defaultWidthX,
+                c.private,
+            )
+            decompiler.execute(c)
+            c.width = decompiler.width
+        for charstring in css:
+            _cs_drop_hints(charstring)
+        del css
+
+        # Drop font-wide hinting values
+        all_privs = []
+        if hasattr(font, "FDArray"):
+            all_privs.extend(fd.Private for fd in font.FDArray)
+        else:
+            all_privs.append(font.Private)
+        for priv in all_privs:
+            for k in [
+                "BlueValues",
+                "OtherBlues",
+                "FamilyBlues",
+                "FamilyOtherBlues",
+                "BlueScale",
+                "BlueShift",
+                "BlueFuzz",
+                "StemSnapH",
+                "StemSnapV",
+                "StdHW",
+                "StdVW",
+                "ForceBold",
+                "LanguageGroup",
+                "ExpansionFactor",
+            ]:
+                if hasattr(priv, k):
+                    setattr(priv, k, None)
+    remove_unused_subroutines(cff)
+
+
+def _pd_delete_empty_subrs(private_dict):
+    if hasattr(private_dict, "Subrs") and not private_dict.Subrs:
+        if "Subrs" in private_dict.rawDict:
+            del private_dict.rawDict["Subrs"]
+        del private_dict.Subrs
+
+
+def remove_unused_subroutines(cff):
+    for fontname in cff.keys():
+        font = cff[fontname]
+        cs = font.CharStrings
+        # Renumber subroutines to remove unused ones
+
+        # Mark all used subroutines
+        for g in font.charset:
+            c, _ = cs.getItemAndSelector(g)
+            subrs = getattr(c.private, "Subrs", [])
+            decompiler = _MarkingT2Decompiler(subrs, c.globalSubrs, c.private)
+            decompiler.execute(c)
+
+        all_subrs = [font.GlobalSubrs]
+        if hasattr(font, "FDArray"):
+            all_subrs.extend(
+                fd.Private.Subrs
+                for fd in font.FDArray
+                if hasattr(fd.Private, "Subrs") and fd.Private.Subrs
+            )
+        elif hasattr(font.Private, "Subrs") and font.Private.Subrs:
+            all_subrs.append(font.Private.Subrs)
+
+        subrs = set(subrs)  # Remove duplicates
+
+        # Prepare
+        for subrs in all_subrs:
+            if not hasattr(subrs, "_used"):
+                subrs._used = set()
+            subrs._used = _uniq_sort(subrs._used)
+            subrs._old_bias = calcSubrBias(subrs)
+            subrs._new_bias = calcSubrBias(subrs._used)
+
+        # Renumber glyph charstrings
+        for g in font.charset:
+            c, _ = cs.getItemAndSelector(g)
+            subrs = getattr(c.private, "Subrs", None)
+            _cs_subset_subroutines(c, subrs, font.GlobalSubrs)
+
+        # Renumber subroutines themselves
+        for subrs in all_subrs:
+            if subrs == font.GlobalSubrs:
+                if not hasattr(font, "FDArray") and hasattr(font.Private, "Subrs"):
+                    local_subrs = font.Private.Subrs
+                else:
+                    local_subrs = None
+            else:
+                local_subrs = subrs
+
+            subrs.items = [subrs.items[i] for i in subrs._used]
+            if hasattr(subrs, "file"):
+                del subrs.file
+            if hasattr(subrs, "offsets"):
+                del subrs.offsets
+
+            for subr in subrs.items:
+                _cs_subset_subroutines(subr, local_subrs, font.GlobalSubrs)
+
+        # Delete local SubrsIndex if empty
+        if hasattr(font, "FDArray"):
+            for fd in font.FDArray:
+                _pd_delete_empty_subrs(fd.Private)
+        else:
+            _pd_delete_empty_subrs(font.Private)
+
+        # Cleanup
+        for subrs in all_subrs:
+            del subrs._used, subrs._old_bias, subrs._new_bias