More solveCubic() hardening

It really should be quite solid this time. :-)
2016-08-13 16:29:49 -07:00 · 2016-08-13 16:29:49 -07:00 · 8701fedcfe
commit 8701fedcfe
parent 5bea5f4fd6
1 changed files with 3 additions and 2 deletions
--- a/Lib/fontTools/misc/bezierTools.py
+++ b/Lib/fontTools/misc/bezierTools.py
@ -342,8 +342,9 @@ def solveCubic(a, b, c, d):
    if R2 == 0. and Q3 == 0.:
        x = round(-a1/3.0, epsilonDigits)
        return [x, x, x]
-    elif R2_Q3 <= epsilon:
-        theta = acos(max(min(R/sqrt(Q*Q*Q), 1.0), -1.0))
+    elif R2_Q3 <= epsilon * .5:
+        # The epsilon * .5 above ensures that Q3 is not zero.
+        theta = acos(max(min(R/sqrt(Q3), 1.0), -1.0))
        rQ2 = -2.0*sqrt(Q)
        a1_3 = a1/3.0
        x0 = rQ2*cos(theta/3.0) - a1_3