iup.c behaves differently from iup.py

[behdad]

Just building Oswald font:

fontmake -o variable --output-dir Oswald.glyphs --drop-implied-oncurves --no-production-names --keep-direction OswaldFont/sources/Oswald.glyphs

produces different gvar table if varLib.iup module is Cython-compiled vs if it's not. We think the Python version is correct as it matches the Rust port.

[behdad]

If I comment out the following line (tolerance annotation in can_iup_in_between), then the .c behavior matches .py:

diff --git a/Lib/fontTools/varLib/iup.py b/Lib/fontTools/varLib/iup.py
index 0b7dcb7e9..4673a155e 100644
--- a/Lib/fontTools/varLib/iup.py
+++ b/Lib/fontTools/varLib/iup.py
@@ -167,7 +167,7 @@ def iup_delta(
 @cython.locals(
     i=cython.int,
     j=cython.int,
-    tolerance=cython.double,
+    # tolerance=cython.double,
     x=cython.double,
     y=cython.double,
     p=cython.double,

[behdad]

If I rewrite the generator as a for loop, that also makes the difference go away:

-    return all(
-        abs(complex(x - p, y - q)) <= tolerance
-        for (x, y), (p, q) in zip(deltas, interp)
-    )
+    for (x, y), (p, q) in zip(deltas, interp):
+        if not (abs(complex(x - p, y - q)) <= tolerance):
+            return False
+    return True

The .c code for the generator is suspect...

[behdad]

So does this:

diff --git a/Lib/fontTools/varLib/iup.py b/Lib/fontTools/varLib/iup.py
index 0b7dcb7e9..a393319f2 100644
--- a/Lib/fontTools/varLib/iup.py
+++ b/Lib/fontTools/varLib/iup.py
@@ -189,8 +189,9 @@ def can_iup_in_between(
     interp = iup_segment(coords[i + 1 : j], coords[i], deltas[i], coords[j], deltas[j])
     deltas = deltas[i + 1 : j]
 
+    tolerance2 = tolerance
     return all(
-        abs(complex(x - p, y - q)) <= tolerance
+        abs(complex(x - p, y - q)) <= tolerance2
         for (x, y), (p, q) in zip(deltas, interp)
     )
 

[behdad]

So does using a list comprehension:

diff --git a/Lib/fontTools/varLib/iup.py b/Lib/fontTools/varLib/iup.py
index 0b7dcb7e9..a0344bf83 100644
--- a/Lib/fontTools/varLib/iup.py
+++ b/Lib/fontTools/varLib/iup.py
@@ -189,10 +189,10 @@ def can_iup_in_between(
     interp = iup_segment(coords[i + 1 : j], coords[i], deltas[i], coords[j], deltas[j])
     deltas = deltas[i + 1 : j]
 
-    return all(
+    return all([
         abs(complex(x - p, y - q)) <= tolerance
         for (x, y), (p, q) in zip(deltas, interp)
-    )
+    ])
 
 
 @cython.locals(

Not the same, but maybe related: cython/cython#3928