Crop the fast path dashed lines to the cull rect

Without:

maxrss  loops   min     median  mean    max     stddev  samples         config  bench
  56M   1       13.3ms  13.6ms  13.6ms  14.2ms  2%      Ooooo.....      8888    GM_dashing5_bw
  56M   13      390us   417us   416us   459us   5%      ooooO..o.o      gpu     GM_dashing5_bw
  56M   1       13.4ms  13.9ms  14.1ms  15ms    3%      Oooo..ooOo      8888    GM_dashing5_aa
  56M   13      402us   421us   416us   425us   2%      Ooo.ooOOOO      gpu     GM_dashing5_aa

With:

  40M   1       1.53ms  1.54ms  1.54ms  1.55ms  0%      oo.O...o..      8888    GM_dashing5_bw
  40M   12      407us   412us   415us   445us   3%      ...Oo.....      gpu     GM_dashing5_bw
  40M   1       1.7ms   1.7ms   1.7ms   1.72ms  0%      o.O.......      8888    GM_dashing5_aa
  43M   13      405us   409us   409us   415us   1%      ooo.Ooo..o      gpu     GM_dashing5_aa

The GM images (including the new one) are the same with and without this CL.

BUG=428296

Review URL: https://codereview.chromium.org/699623003

1 files changed, 5 insertions, 4 deletions

diff --git a/src/utils/SkDashPath.cpp b/src/utils/SkDashPath.cpp
index 3c4aef343d..02de98f1d6 100644
--- a/src/utils/SkDashPath.cpp
+++ b/src/utils/SkDashPath.cpp
@@ -115,14 +115,15 @@ static bool cull_path(const SkPath& srcPath, const SkStrokeRec& rec,
     SkScalar minX = pts[0].fX;
     SkScalar maxX = pts[1].fX;
 
-    if (maxX < bounds.fLeft || minX > bounds.fRight) {
-        return false;
-    }
-
     if (dx < 0) {
         SkTSwap(minX, maxX);
     }
 
+    SkASSERT(minX < maxX);
+    if (maxX < bounds.fLeft || minX > bounds.fRight) {
+        return false;
+    }
+
     // Now we actually perform the chop, removing the excess to the left and
     // right of the bounds (keeping our new line "in phase" with the dash,
     // hence the (mod intervalLength).