No chop at y extrema for cubics

The new Delta AA scan converter does not need the edge to be updated
with monotonic Y so chopping at y extrema is not necessary. Removing
such chopping brings ~10% performance increase to chalkboard.svg which
has tons of small cubics (the same is true for many svgs I saw).

We didn't remove the chopping for quads because that does not bring
a significant speedup. Moreover, dropping those y extremas would make
our strokecircle animation look a little more wobbly (because we would
have fewer divisions for the quads at the top and bottom of the circle).

Bug: skia:
Change-Id: I3984d2619f9f77269ed24e8cbfa9f1429ebca4a8
Reviewed-on: https://skia-review.googlesource.com/31940
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/core/SkEdgeBuilder.h b/src/core/SkEdgeBuilder.h
index b876fcf5e5..a549e15681 100644
--- a/src/core/SkEdgeBuilder.h
+++ b/src/core/SkEdgeBuilder.h
@@ -21,8 +21,19 @@ class SkPath;
 class SkEdgeBuilder {
 public:
     enum EdgeType {
+        // Used in supersampling or non-AA scan coverter; it stores only integral y coordinates.
         kEdge,
+
+        // Used in Analytic AA scan converter; it uses SkFixed to store fractional y.
         kAnalyticEdge,
+
+        // Used in Delta AA scan converter; it's a super-light wrapper of SkPoint, which can then be
+        // used to construct SkAnalyticEdge (kAnalyticEdge) later. We use kBezier to save the memory
+        // allocation time (a SkBezier is much lighter than SkAnalyticEdge or SkEdge). Note that
+        // Delta AA only has to deal with one SkAnalyticEdge at a time (whereas Analytic AA has to
+        // deal with all SkAnalyticEdges at the same time). Thus for Delta AA, we only need to
+        // allocate memory for n SkBeziers and 1 SkAnalyticEdge. (Analytic AA need to allocate
+        // memory for n SkAnalyticEdges.)
         kBezier
     };
 
@@ -76,6 +87,8 @@ public:
     void addCubic(const SkPoint pts[]);
     void addClipper(SkEdgeClipper*);
 
+    EdgeType edgeType() const { return fEdgeType; }
+
     int buildPoly(const SkPath& path, const SkIRect* clip, int shiftUp, bool clipToTheRight);
 
     inline void addPolyLine(SkPoint pts[], char* &edge, size_t edgeSize, char** &edgePtr,