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, 16 insertions, 8 deletions

diff --git a/src/core/SkAnalyticEdge.cpp b/src/core/SkAnalyticEdge.cpp
index 7cb6493f8b..e2da09023d 100644
--- a/src/core/SkAnalyticEdge.cpp
+++ b/src/core/SkAnalyticEdge.cpp
@@ -20,6 +20,14 @@ bool SkAnalyticEdge::updateLine(SkFixed x0, SkFixed y0, SkFixed x1, SkFixed y1,
     SkASSERT(fWinding == 1 || fWinding == -1);
     SkASSERT(fCurveCount != 0);
 
+    // We don't chop at y extrema for cubics so the y is not guaranteed to be increasing for them.
+    // In that case, we have to swap x/y and negate the winding.
+    if (y0 > y1) {
+        SkTSwap(x0, x1);
+        SkTSwap(y0, y1);
+        fWinding = -fWinding;
+    }
+
     SkASSERT(y0 <= y1);
 
     SkFDot6 dx = SkFixedToFDot6(x1 - x0);
@@ -48,10 +56,10 @@ bool SkAnalyticEdge::updateLine(SkFixed x0, SkFixed y0, SkFixed x1, SkFixed y1,
     return true;
 }
 
-bool SkAnalyticEdge::update(SkFixed last_y) {
+bool SkAnalyticEdge::update(SkFixed last_y, bool sortY) {
     SkASSERT(last_y >= fLowerY); // we shouldn't update edge if last_y < fLowerY
     if (fCurveCount < 0) {
-        return static_cast<SkAnalyticCubicEdge*>(this)->updateCubic();
+        return static_cast<SkAnalyticCubicEdge*>(this)->updateCubic(sortY);
     } else if (fCurveCount > 0) {
         return static_cast<SkAnalyticQuadraticEdge*>(this)->updateQuadratic();
     }
@@ -147,10 +155,10 @@ bool SkAnalyticQuadraticEdge::updateQuadratic() {
     return success;
 }
 
-bool SkAnalyticCubicEdge::setCubic(const SkPoint pts[4]) {
+bool SkAnalyticCubicEdge::setCubic(const SkPoint pts[4], bool sortY) {
     fRiteE = nullptr;
 
-    if (!fCEdge.setCubicWithoutUpdate(pts, kDefaultAccuracy)) {
+    if (!fCEdge.setCubicWithoutUpdate(pts, kDefaultAccuracy, sortY)) {
         return false;
     }
 
@@ -174,10 +182,10 @@ bool SkAnalyticCubicEdge::setCubic(const SkPoint pts[4]) {
 
     fSnappedY = fCEdge.fCy;
 
-    return this->updateCubic();
+    return this->updateCubic(sortY);
 }
 
-bool SkAnalyticCubicEdge::updateCubic() {
+bool SkAnalyticCubicEdge::updateCubic(bool sortY) {
     int     success;
     int     count = fCurveCount;
     SkFixed oldx = fCEdge.fCx;
@@ -205,14 +213,14 @@ bool SkAnalyticCubicEdge::updateCubic() {
 
         // we want to say SkASSERT(oldy <= newy), but our finite fixedpoint
         // doesn't always achieve that, so we have to explicitly pin it here.
-        if (newy < oldy) {
+        if (sortY && newy < oldy) {
             newy = oldy;
         }
 
         SkFixed newSnappedY = SnapY(newy);
         // we want to SkASSERT(snappedNewY <= fCEdge.fCLastY), but our finite fixedpoint
         // doesn't always achieve that, so we have to explicitly pin it here.
-        if (fCEdge.fCLastY < newSnappedY) {
+        if (sortY && fCEdge.fCLastY < newSnappedY) {
             newSnappedY = fCEdge.fCLastY;
             count = 0;
         }