pathops coincident work

src/pathops/SkAddIntersections.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkAddIntersections.h"
 #include "SkOpCoincidence.h"
 #include "SkPathOpsBounds.h"
 
@@ skipping 490 matching lines @@
 #endif
             int coinIndex = -1;
             SkOpPtT* coinPtT[2];
             for (int pt = 0; pt < pts; ++pt) {
                 SkASSERT(ts[0][pt] >= 0 && ts[0][pt] <= 1);
                 SkASSERT(ts[1][pt] >= 0 && ts[1][pt] <= 1);
                 wt.segment()->debugValidate();
                 SkOpPtT* testTAt = wt.segment()->addT(ts[swap][pt]);
                 wn.segment()->debugValidate();
                 SkOpPtT* nextTAt = wn.segment()->addT(ts[!swap][pt]);
-                SkOpPtT* oppPrev = testTAt->oppPrev(nextTAt);
-                if (oppPrev) {
-                    testTAt->addOpp(nextTAt, oppPrev);
+                if (!testTAt->contains(nextTAt)) {
+                    SkOpPtT* oppPrev = testTAt->oppPrev(nextTAt);  //  Returns nullptr if pair 
+                    if (oppPrev) {                                 //  already shares a pt-t loop.
+                        testTAt->span()->mergeMatches(nextTAt->span());
+                        testTAt->addOpp(nextTAt, oppPrev);
+                    }
+                    if (testTAt->fPt != nextTAt->fPt) {
+                        testTAt->span()->unaligned();
+                        nextTAt->span()->unaligned();
+                    }
+                    wt.segment()->debugValidate();
+                    wn.segment()->debugValidate();
                 }
-                if (testTAt->fPt != nextTAt->fPt) {
-                    testTAt->span()->unaligned();
-                    nextTAt->span()->unaligned();
-                }
-                wt.segment()->debugValidate();
-                wn.segment()->debugValidate();
                 if (!ts.isCoincident(pt)) {
                     continue;
                 }
                 if (coinIndex < 0) {
                     coinPtT[0] = testTAt;
                     coinPtT[1] = nextTAt;
                     coinIndex = pt;
                     continue;
                 }
                 if (coinPtT[0]->span() == testTAt->span()) {
@@ skipping 12 matching lines @@
                 coincidence->add(coinPtT[0], testTAt, coinPtT[1], nextTAt);
                 wt.segment()->debugValidate();
                 wn.segment()->debugValidate();
                 coinIndex = -1;
             }
             SkASSERT(coinIndex < 0);  // expect coincidence to be paired
         } while (wn.advance());
     } while (wt.advance());
     return true;
 }