[varLib.avar] Sketch of code to reconstruct mappings from binary

https://github.com/Lorp/fencer/issues/25

Lib/fontTools/varLib/avar.py

@@ -1,10 +1,104 @@
 from fontTools.varLib import _add_avar, load_designspace
+from fontTools.varLib.varStore import VarStoreInstancer
+from fontTools.misc.fixedTools import fixedToFloat as fi2fl
 from fontTools.misc.cliTools import makeOutputFileName
+from itertools import product
 import logging
 
 log = logging.getLogger("fontTools.varLib.avar")
 
 
+def _denormalize(v, axis):
+    return axis.defaultValue + v * (
+        (axis.maxValue if v >= 0 else axis.minValue) - axis.defaultValue
+    )
+
+
+def mappings_from_avar(font, denormalize=True):
+    fvarAxes = font["fvar"].axes
+    axisMap = {a.axisTag: a for a in fvarAxes}
+    axisTags = [a.axisTag for a in fvarAxes]
+    axisIndexes = {a.axisTag: i for i, a in enumerate(fvarAxes)}
+    if "avar" not in font:
+        return {}, {}
+    avar = font["avar"]
+    axisMaps = {
+        tag: seg
+        for tag, seg in avar.segments.items()
+        if seg and seg != {-1: -1, 0: 0, 1: 1}
+    }
+    mappings = []
+
+    if getattr(avar, "majorVersion", 1) == 2:
+        varStore = avar.table.VarStore
+        regions = varStore.VarRegionList.Region
+        inputLocations = set()
+        for varData in varStore.VarData:
+            regionIndices = varData.VarRegionIndex
+            for regionIndex in regionIndices:
+                peakLocation = {}
+                corners = []
+                region = regions[regionIndex]
+                for axisIndex, axis in enumerate(region.VarRegionAxis):
+                    if axis.PeakCoord == 0:
+                        continue
+                    axisTag = axisTags[axisIndex]
+                    peakLocation[axisTag] = axis.PeakCoord
+                    corner = []
+                    if axis.StartCoord != 0:
+                        corner.append((axisTag, axis.StartCoord))
+                    if axis.EndCoord != 0:
+                        corner.append((axisTag, axis.EndCoord))
+                    corners.append(corner)
+                corners = set(product(*corners))
+                inputLocations.update(corners)
+
+        inputLocations = [
+            dict(t)
+            for t in sorted(
+                inputLocations,
+                key=lambda t: (len(t), tuple(axisIndexes[tag] for tag, _ in t)),
+            )
+        ]
+
+        varIdxMap = avar.table.VarIdxMap
+        instancer = VarStoreInstancer(varStore, fvarAxes)
+        for location in inputLocations:
+            instancer.setLocation(location)
+            outputLocation = {}
+            for axisIndex, axisTag in enumerate(axisTags):
+                varIdx = axisIndex
+                if varIdxMap is not None:
+                    varIdx = varIdxMap[varIdx]
+                delta = instancer[varIdx]
+                if delta != 0:
+                    v = location.get(axisTag, 0)
+                    v = v + fi2fl(delta, 14)
+                    v = max(-1, min(1, v))
+                    outputLocation[axisTag] = v
+            mappings.append((location, outputLocation))
+        # Filter out empty mappings
+        mappings = [io for io in mappings if io[1]]
+
+    if denormalize:
+        for tag, seg in axisMaps.items():
+            if tag not in axisMap:
+                raise ValueError(f"Unknown axis tag {tag}")
+            denorm = lambda v: _denormalize(v, axisMap[tag])
+            axisMaps[tag] = {denorm(k): denorm(v) for k, v in seg.items()}
+
+        for i, (inputLoc, outputLoc) in enumerate(mappings):
+            inputLoc = {
+                tag: _denormalize(val, axisMap[tag]) for tag, val in inputLoc.items()
+            }
+            outputLoc = {
+                tag: _denormalize(val, axisMap[tag]) for tag, val in outputLoc.items()
+            }
+            mappings[i] = (inputLoc, outputLoc)
+
+    return axisMaps, mappings
+
+
 def main(args=None):
     """Add `avar` table from designspace file to variable font."""
 
@@ -24,7 +118,11 @@ def main(args=None):
     )
     parser.add_argument("font", metavar="varfont.ttf", help="Variable-font file.")
     parser.add_argument(
-        "designspace", metavar="family.designspace", help="Designspace file."
+        "designspace",
+        metavar="family.designspace",
+        help="Designspace file.",
+        nargs="?",
+        default=None,
     )
     parser.add_argument(
         "-o",
@@ -45,6 +143,12 @@ def main(args=None):
         log.error("Not a variable font.")
         return 1
 
+    if options.designspace is None:
+        from pprint import pprint
+
+        pprint(mappings_from_avar(font))
+        return
+
     axisTags = [a.axisTag for a in font["fvar"].axes]
 
     ds = load_designspace(options.designspace)