give up on quad root if infinite

src/core/SkGeometry.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGeometry.h"
 #include "SkMatrix.h"
 #include "SkNx.h"
@@ skipping 72 matching lines @@
 int SkFindUnitQuadRoots(SkScalar A, SkScalar B, SkScalar C, SkScalar roots[2]) {
     SkASSERT(roots);
 
     if (A == 0) {
         return valid_unit_divide(-C, B, roots);
     }
 
     SkScalar* r = roots;
 
     SkScalar R = B*B - 4*A*C;
-    if (R < 0 || SkScalarIsNaN(R)) {  // complex roots
+    if (R < 0 || !SkScalarIsFinite(R)) {  // complex roots
+        // if R is infinite, it's possible that it may still produce
+        // useful results if the operation was repeated in doubles
+        // the flipside is determining if the more precise answer
+        // isn't useful because surrounding machinery (e.g., subtracting
+        // the axis offset from C) already discards the extra precision
+        // more investigation and unit tests required...
         return 0;
     }
     R = SkScalarSqrt(R);
 
     SkScalar Q = (B < 0) ? -(B-R)/2 : -(B+R)/2;
     r += valid_unit_divide(Q, A, r);
     r += valid_unit_divide(C, Q, r);
     if (r - roots == 2) {
         if (roots[0] > roots[1])
             SkTSwap<SkScalar>(roots[0], roots[1]);
@@ skipping 1467 matching lines @@
         matrix.preScale(SK_Scalar1, -SK_Scalar1);
     }
     if (userMatrix) {
         matrix.postConcat(*userMatrix);
     }
     for (int i = 0; i < conicCount; ++i) {
         matrix.mapPoints(dst[i].fPts, 3);
     }
     return conicCount;
 }