fix hair fuzz

If the end and control points of a quad, conic, or cubic are the same,
adjust all of them when stretching the curve to account for a square
or round end cap. If all of the points are the same, move all but the
last.

Enlarge the clip check to account for the cap.

The clip bug was detected by ASAN.

R=reed@google.com, msarett@google.com
BUG=571214
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1547483003

Review URL: https://codereview.chromium.org/1547483003

1 files changed, 14 insertions, 6 deletions

diff --git a/src/core/SkScan_Hairline.cpp b/src/core/SkScan_Hairline.cpp
index c59521abc7..12553a4a54 100644
--- a/src/core/SkScan_Hairline.cpp
+++ b/src/core/SkScan_Hairline.cpp
@@ -428,11 +428,15 @@ void extend_pts(SkPath::Verb prevVerb, SkPath::Verb nextVerb, SkPoint* pts, int
         } while (tangent.isZero() && --controls > 0);
         if (tangent.isZero()) {
             tangent.set(1, 0);
+            controls = ptCount - 1;  // If all points are equal, move all but one
         } else {
             tangent.normalize();
         }
-        first->fX += tangent.fX * capOutset;
-        first->fY += tangent.fY * capOutset;
+        do {    // If the end point and control points are equal, loop to move them in tandem.
+            first->fX += tangent.fX * capOutset;
+            first->fY += tangent.fY * capOutset;
+            ++first;
+        } while (++controls < ptCount);
     }
     if (SkPath::kMove_Verb == nextVerb || SkPath::kDone_Verb == nextVerb) {
         SkPoint* last = &pts[ptCount - 1];
@@ -444,11 +448,15 @@ void extend_pts(SkPath::Verb prevVerb, SkPath::Verb nextVerb, SkPoint* pts, int
         } while (tangent.isZero() && --controls > 0);
         if (tangent.isZero()) {
             tangent.set(-1, 0);
+            controls = ptCount - 1;
         } else {
             tangent.normalize();
         }
-        last->fX += tangent.fX * capOutset;
-        last->fY += tangent.fY * capOutset;
+        do {
+            last->fX += tangent.fX * capOutset;
+            last->fY += tangent.fY * capOutset;
+            --last;
+        } while (++controls < ptCount);
     }
 }
 
@@ -466,8 +474,8 @@ void hair_path(const SkPath& path, const SkRasterClip& rclip, SkBlitter* blitter
     const SkRect* outsetClip = nullptr;
 
     {
-        const SkIRect ibounds = path.getBounds().roundOut().makeOutset(1, 1);
-
+        const int capOut = SkPaint::kButt_Cap == capStyle ? 1 : 2;
+        const SkIRect ibounds = path.getBounds().roundOut().makeOutset(capOut, capOut);
         if (rclip.quickReject(ibounds)) {
             return;
         }