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, 3 insertions, 3 deletions

diff --git a/bench/CubicKLMBench.cpp b/bench/CubicKLMBench.cpp
index 3c8f740bc7..1cdb068c08 100644
--- a/bench/CubicKLMBench.cpp
+++ b/bench/CubicKLMBench.cpp
@@ -22,12 +22,12 @@ public:
         fPoints[3].set(x3, y3);
 
         fName = "cubic_klm_";
-        SkScalar d[3];
+        SkScalar d[4];
         switch (SkClassifyCubic(fPoints, d)) {
-            case kSerpentine_SkCubicType:
+            case SkCubicType::kSerpentine:
                 fName.append("serp");
                 break;
-            case kLoop_SkCubicType:
+            case SkCubicType::kLoop:
                 fName.append("loop");
                 break;
             default: