Path ops formerly found the topmost unprocessed edge and determined its angle sort order to initialize the winding. This never worked correctly with cubics and was flaky with paths consisting mostly of vertical edges.

This replacement shoots axis-aligned rays through all intersecting edges to find the outermost one either horizontally or vertically. The resulting code is smaller and twice as fast.

To support this, most of the horizontal / vertical intersection code was rewritten and standardized, and old code supporting the top-directed winding was deleted.

Contours were pointed to by an SkTDArray. Instead, put them in a linked list, and designate the list head with its own class to ensure that methods that take lists of contours start at the top. This change removed a large percentage of memory allocations used by path ops.

TBR=reed@google.com
BUG=skia:3588

Review URL: https://codereview.chromium.org/1111333002

1 files changed, 17 insertions, 53 deletions

diff --git a/src/pathops/SkPathOpsSimplify.cpp b/src/pathops/SkPathOpsSimplify.cpp
index 14c6837c1b..d37998b448 100644
--- a/src/pathops/SkPathOpsSimplify.cpp
+++ b/src/pathops/SkPathOpsSimplify.cpp
@@ -10,41 +10,17 @@
 #include "SkPathOpsCommon.h"
 #include "SkPathWriter.h"
 
-static bool bridgeWinding(SkTDArray<SkOpContour* >& contourList, SkPathWriter* simple,
+static bool bridgeWinding(SkOpContourHead* contourList, SkPathWriter* simple,
         SkChunkAlloc* allocator) {
-    bool firstContour = true;
     bool unsortable = false;
-    bool topUnsortable = false;
-    bool firstPass = true;
-    SkDPoint lastTopLeft;
-    SkDPoint topLeft = {SK_ScalarMin, SK_ScalarMin};
     do {
-        SkOpSpanBase* start = NULL;
-        SkOpSpanBase* end = NULL;
-        bool topDone;
-        bool onlyVertical = false;
-        lastTopLeft = topLeft;
-        SkOpSegment* current = FindSortableTop(contourList, firstPass, SkOpAngle::kUnaryWinding,
-                &firstContour, &start, &end, &topLeft, &topUnsortable, &topDone, &onlyVertical,
-                allocator);
-        if (!current) {
-            if ((!topUnsortable || firstPass) && !topDone) {
-                SkASSERT(topLeft.fX != SK_ScalarMin && topLeft.fY != SK_ScalarMin);
-                if (lastTopLeft.fX == SK_ScalarMin && lastTopLeft.fY == SK_ScalarMin) {
-                    if (firstPass) {
-                        firstPass = false;
-                    } else {
-                        break;
-                    }
-                }
-                topLeft.fX = topLeft.fY = SK_ScalarMin;
-                continue;
-            }
-            break;
-        } else if (onlyVertical) {
+        SkOpSpan* span = FindSortableTop(contourList);
+        if (!span) {
             break;
         }
-        firstPass = !topUnsortable || lastTopLeft != topLeft;
+        SkOpSegment* current = span->segment();
+        SkOpSpanBase* start = span->next();
+        SkOpSpanBase* end = span;
         SkTDArray<SkOpSpanBase*> chase;
         do {
             if (current->activeWinding(start, end)) {
@@ -93,7 +69,6 @@ static bool bridgeWinding(SkTDArray<SkOpContour* >& contourList, SkPathWriter* s
                 if (last && !last->chased()) {
                     last->setChased(true);
                     SkASSERT(!SkPathOpsDebug::ChaseContains(chase, last));
-                    // assert that last isn't already in array
                     *chase.append() = last;
 #if DEBUG_WINDING
                     SkDebugf("%s chase.append id=%d", __FUNCTION__, last->segment()->debugID());
@@ -117,7 +92,7 @@ static bool bridgeWinding(SkTDArray<SkOpContour* >& contourList, SkPathWriter* s
 }
 
 // returns true if all edges were processed
-static bool bridgeXor(SkTDArray<SkOpContour* >& contourList, SkPathWriter* simple,
+static bool bridgeXor(SkOpContourHead* contourList, SkPathWriter* simple,
         SkChunkAlloc* allocator) {
     SkOpSegment* current;
     SkOpSpanBase* start;
@@ -191,8 +166,9 @@ bool Simplify(const SkPath& path, SkPath* result) {
     // turn path into list of segments
     SkOpCoincidence coincidence;
     SkOpContour contour;
-    SkOpGlobalState globalState(&coincidence  SkDEBUGPARAMS(&contour));
-#if DEBUG_SORT || DEBUG_SWAP_TOP
+    SkOpContourHead* contourList = static_cast<SkOpContourHead*>(&contour);
+    SkOpGlobalState globalState(&coincidence, contourList);
+#if DEBUG_SORT
     SkPathOpsDebug::gSortCount = SkPathOpsDebug::gSortCountDefault;
 #endif
     SkOpEdgeBuilder builder(path, &contour, &allocator, &globalState);
@@ -202,34 +178,22 @@ bool Simplify(const SkPath& path, SkPath* result) {
 #if DEBUG_DUMP_SEGMENTS
     contour.dumpSegments((SkPathOp) -1);
 #endif
-    SkTDArray<SkOpContour* > contourList;
-    MakeContourList(&contour, contourList, false, false);
-    SkOpContour** currentPtr = contourList.begin();
-    if (!currentPtr) {
+    if (!SortContourList(&contourList, false, false)) {
         result->reset();
         result->setFillType(fillType);
         return true;
     }
-    if ((*currentPtr)->count() == 0) {
-        SkASSERT((*currentPtr)->next() == NULL);
-        result->reset();
-        result->setFillType(fillType);
-        return true;
-    }
-    SkOpContour** listEnd2 = contourList.end();
     // find all intersections between segments
+    SkOpContour* current = contourList;
     do {
-        SkOpContour** nextPtr = currentPtr;
-        SkOpContour* current = *currentPtr++;
-        SkOpContour* next;
-        do {
-            next = *nextPtr++;
-        } while (AddIntersectTs(current, next, &coincidence, &allocator) && nextPtr != listEnd2);
-    } while (currentPtr != listEnd2);
+        SkOpContour* next = current;
+        while (AddIntersectTs(current, next, &coincidence, &allocator)
+                && (next = next->next()));
+    } while ((current = current->next()));
 #if DEBUG_VALIDATE
     globalState.setPhase(SkOpGlobalState::kWalking);
 #endif
-    if (!HandleCoincidence(&contourList, &coincidence, &allocator, &globalState)) {
+    if (!HandleCoincidence(contourList, &coincidence, &allocator)) {
         return false;
     }
     // construct closed contours