add documentation

diagram for pathops change

TBR=caryclark@google.com
Bug: skia:8049
Change-Id: I2bbd04f1efad53e1197a45baf3ce98f0eb550512
Reviewed-on: https://skia-review.googlesource.com/132664
Commit-Queue: Cary Clark <caryclark@skia.org>
Auto-Submit: Cary Clark <caryclark@skia.org>
Reviewed-by: Cary Clark <caryclark@skia.org>

1 files changed, 17 insertions, 16 deletions

diff --git a/src/pathops/SkOpAngle.cpp b/src/pathops/SkOpAngle.cpp
index 194260f658..9decb272b1 100644
--- a/src/pathops/SkOpAngle.cpp
+++ b/src/pathops/SkOpAngle.cpp
@@ -167,7 +167,8 @@ bool SkOpAngle::after(SkOpAngle* test) {
 //        SkASSERT(lrOpposite != trOpposite);
         return COMPARE_RESULT(10, lrOpposite);
     }
-    // if a pair couldn't be ordered, there's not enough information to determine the sort
+    // If a pair couldn't be ordered, there's not enough information to determine the sort.
+    // Refer to:  https://docs.google.com/drawings/d/1KV-8SJTedku9fj4K6fd1SB-8divuV_uivHVsSgwXICQ
     if (fUnorderable || lh->fUnorderable || rh->fUnorderable) {
         // limit to lines; should work with curves, but wait for a failing test to verify
         if (!fPart.isCurve() && !lh->fPart.isCurve() && !rh->fPart.isCurve()) {
@@ -178,25 +179,25 @@ bool SkOpAngle::after(SkOpAngle* test) {
             int trShare = fOriginalCurvePart[0] == rh->fOriginalCurvePart[0];
             // if only one pair are the same, the third point touches neither of the pair
             if (ltShare + lrShare + trShare == 1) {
-                if (ltShare) {
-                    int lrOOrder = lh->allOnOriginalSide(rh);
-                    int trOOrder = rh->allOnOriginalSide(this);
-                    // result must be 0 and 1 or 1 and 0 to be valid
-                    if ((lrOOrder ^ trOOrder) == 1) {
-                        return trOOrder;
-                    }
-                } else if (lrShare) {
+                if (lrShare) {
                     int ltOOrder = lh->allOnOriginalSide(this);
-                    int trOOrder = rh->allOnOriginalSide(this);
-                    if ((ltOOrder ^ trOOrder) == 1) {
+                    int rtOOrder = rh->allOnOriginalSide(this);
+                    if ((rtOOrder ^ ltOOrder) == 1) {
                         return ltOOrder;
                     }
+                } else if (trShare) {
+                    int tlOOrder = this->allOnOriginalSide(lh);
+                    int rlOOrder = rh->allOnOriginalSide(lh);
+                    if ((tlOOrder ^ rlOOrder) == 1) {
+                        return rlOOrder;
+                    }
                 } else {
-                    SkASSERT(trShare);
-                    int ltOOrder = this->allOnOriginalSide(lh);
-                    int lrOOrder = rh->allOnOriginalSide(lh);
-                    if ((ltOOrder ^ lrOOrder) == 1) {
-                        return lrOOrder;
+                    SkASSERT(ltShare);
+                    int trOOrder = rh->allOnOriginalSide(this);
+                    int lrOOrder = lh->allOnOriginalSide(rh);
+                    // result must be 0 and 1 or 1 and 0 to be valid
+                    if ((lrOOrder ^ trOOrder) == 1) {
+                        return trOOrder;
                     }
                 }
             }