From 47c858a2f2b97c1e21daf83b7b226d1eef2d2061 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sun, 23 Jul 2023 17:14:01 -0600
Subject: [PATCH] [varLib.avarPlanner] Add axis-limit sanitization

---
 Lib/fontTools/varLib/avarPlanner.py | 99 ++++++++++++++++++++++++++++-
 1 file changed, 97 insertions(+), 2 deletions(-)

diff --git a/Lib/fontTools/varLib/avarPlanner.py b/Lib/fontTools/varLib/avarPlanner.py
index 3e6c7173e..ba3375b47 100644
--- a/Lib/fontTools/varLib/avarPlanner.py
+++ b/Lib/fontTools/varLib/avarPlanner.py
@@ -10,6 +10,8 @@ __all__ = [
     "planWeightAxis",
     "planWidthAxis",
     "planAxis",
+    "sanitizeWeight",
+    "sanitizeWidth",
     "measureBlackness",
     "measureWidth",
     "makeDesignspaceSnippet",
@@ -114,10 +116,103 @@ def measureWidth(glyphset, glyphs=None):
 
 
 def sanitizeWidth(userTriple, designTriple, pins, measurements):
+    if len(set(userTriple)) < 3:
+        return True
+
+    minVal, defaultVal, maxVal = (
+        measurements[designTriple[0]],
+        measurements[designTriple[1]],
+        measurements[designTriple[2]],
+    )
+
+    calculatedMinVal = userTriple[0] * (minVal / defaultVal)
+    calculatedMaxVal = userTriple[2] * (maxVal / defaultVal)
+
+    log.info("Original axis limits: %g:%g:%g", *userTriple)
+    log.info(
+        "Calculated axis limits: %g:%g:%g",
+        calculatedMinVal,
+        userTriple[1],
+        calculatedMaxVal,
+    )
+
+    if (
+        abs(calculatedMinVal - userTriple[0]) / userTriple[1] > 0.05
+        or abs(calculatedMaxVal - userTriple[2]) / userTriple[1] > 0.05
+    ):
+        log.warning("Calculated width axis min/max do not match user input.")
+        log.warning(
+            "  Suggested axis limits: %g:%g:%g",
+            calculatedMinVal,
+            userTriple[1],
+            calculatedMaxVal,
+        )
+
+        return False
+
     return True
 
 
 def sanitizeWeight(userTriple, designTriple, pins, measurements):
+    if len(set(userTriple)) < 3:
+        return True
+
+    minVal, defaultVal, maxVal = (
+        measurements[designTriple[0]],
+        measurements[designTriple[1]],
+        measurements[designTriple[2]],
+    )
+
+    logMin = math.log(minVal)
+    logDefault = math.log(defaultVal)
+    logMax = math.log(maxVal)
+
+    t = (userTriple[1] - userTriple[0]) / (userTriple[2] - userTriple[0])
+    y = math.exp(logMin + t * (logMax - logMin))
+    t = (y - minVal) / (maxVal - minVal)
+    calculatedDefaultVal = userTriple[0] + t * (userTriple[2] - userTriple[0])
+
+    log.info("Original axis limits: %g:%g:%g", *userTriple)
+    log.info(
+        "Calculated axis limits: %g:%g:%g",
+        userTriple[0],
+        calculatedDefaultVal,
+        userTriple[2],
+    )
+
+    if abs(calculatedDefaultVal - userTriple[1]) / userTriple[1] > 0.05:
+        log.warning("Calculated axis default does not match user input.")
+        log.warning(
+            "  Suggested axis limits, changing default: %g:%g:%g",
+            userTriple[0],
+            calculatedDefaultVal,
+            userTriple[2],
+        )
+
+        t = (userTriple[2] - userTriple[0]) / (userTriple[1] - userTriple[0])
+        y = math.exp(logMin + t * (logDefault - logMin))
+        t = (y - minVal) / (defaultVal - minVal)
+        calculatedMaxVal = userTriple[0] + t * (userTriple[1] - userTriple[0])
+        log.warning(
+            "  Suggested axis limits, changing maximum: %g:%g:%g",
+            userTriple[0],
+            userTriple[1],
+            calculatedMaxVal,
+        )
+
+        t = (userTriple[0] - userTriple[2]) / (userTriple[1] - userTriple[2])
+        y = math.exp(logMax + t * (logDefault - logMax))
+        t = (y - maxVal) / (defaultVal - maxVal)
+        calculatedMinVal = userTriple[2] + t * (userTriple[1] - userTriple[2])
+        log.warning(
+            "  Suggested axis limits, changing minimum: %g:%g:%g",
+            calculatedMinVal,
+            userTriple[1],
+            userTriple[2],
+        )
+
+        return False
+
     return True
 
 
@@ -309,7 +404,7 @@ def planWidthAxis(
         glyphs=glyphs,
         designUnits=designUnits,
         pins=pins,
-        sanitizeFunc=sanitizeWeight if sanitize else None,
+        sanitizeFunc=sanitizeWidth if sanitize else None,
     )
 
 
@@ -411,7 +506,7 @@ def main(args=None):
     options = parser.parse_args(args)
 
     configLogger(
-        level=("DEBUG" if options.verbose else "ERROR" if options.quiet else "INFO")
+        level=("DEBUG" if options.verbose else "WARNING" if options.quiet else "INFO")
     )
 
     font = TTFont(options.font)