Improve accuracy of cubic classification

- Updates the logic to reflect the Loop-Blinn paper instead of the GPU
  gems website.
- Removes the threshold for detecting local cusps. The serpentine
  codepath works for these cusps anyway, so what we really want to know
  is whether the discriminant is negative.
- Makes sure to not scale the inflection function by 1/0.
- Shifts the inflection function coefficients in d[] so they match the
  paper.
- Stores the cubic discriminant in d[0].

Bug: skia:
Change-Id: I909a522a0fd27c9c8dfbc27d968bc43eeb7a416f
Reviewed-on: https://skia-review.googlesource.com/13304
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/PathOpsCubicIntersectionTest.cpp b/tests/PathOpsCubicIntersectionTest.cpp
index 638ecb008c..66becf304a 100644
--- a/tests/PathOpsCubicIntersectionTest.cpp
+++ b/tests/PathOpsCubicIntersectionTest.cpp
@@ -646,11 +646,11 @@ static void selfOneOff(skiatest::Reporter* reporter, int index) {
         c[i] = cubic.fPts[i].asSkPoint();
     }
     SkScalar loopT[3];
-    SkScalar d[3];
+    SkScalar d[4];
     SkCubicType cubicType = SkClassifyCubic(c, d);
     int breaks = SkDCubic::ComplexBreak(c, loopT);
     SkASSERT(breaks < 2);
-    if (breaks && cubicType == SkCubicType::kLoop_SkCubicType) {
+    if (breaks && cubicType == SkCubicType::kLoop) {
         SkIntersections i;
         SkPoint twoCubics[7];
         SkChopCubicAt(c, twoCubics, loopT[0]);