Combine analytic edges with tolerance

src/core/SkEdgeBuilder.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkEdgeBuilder.h"
 #include "SkPath.h"
 #include "SkEdge.h"
 #include "SkAnalyticEdge.h"
@@ skipping 45 matching lines @@
             return kPartial_Combine;
         }
         last->fLastY = last->fFirstY - 1;
         last->fFirstY = edge->fFirstY;
         last->fWinding = edge->fWinding;
         return kPartial_Combine;
     }
     return kNo_Combine;
 }
 
+static inline bool approximatelyEqual(SkFixed a, SkFixed b) {
+    return SkAbs32(a - b) < 0x100;
+}
+
 SkEdgeBuilder::Combine SkEdgeBuilder::CombineVertical(
         const SkAnalyticEdge* edge, SkAnalyticEdge* last) {
     SkASSERT(fAnalyticAA);
     if (last->fCurveCount || last->fDX || edge->fX != last->fX) {
         return kNo_Combine;
     }
     if (edge->fWinding == last->fWinding) {
         if (edge->fLowerY == last->fUpperY) {
             last->fUpperY = edge->fUpperY;
             last->fY = last->fUpperY;
             return kPartial_Combine;
         }
-        if (edge->fUpperY == last->fLowerY) {
+        if (approximatelyEqual(edge->fUpperY, last->fLowerY)) {
             last->fLowerY = edge->fLowerY;
             return kPartial_Combine;
         }
         return kNo_Combine;
     }
-    if (edge->fUpperY == last->fUpperY) {
-        if (edge->fLowerY == last->fLowerY) {
+    if (approximatelyEqual(edge->fUpperY, last->fUpperY)) {
+        if (approximatelyEqual(edge->fLowerY, last->fLowerY)) {
             return kTotal_Combine;
         }
         if (edge->fLowerY < last->fLowerY) {
             last->fUpperY = edge->fLowerY;
             last->fY = last->fUpperY;
             return kPartial_Combine;
         }
         last->fUpperY = last->fLowerY;
         last->fY = last->fUpperY;
         last->fLowerY = edge->fLowerY;
         last->fWinding = edge->fWinding;
         return kPartial_Combine;
     }
-    if (edge->fLowerY == last->fLowerY) {
+    if (approximatelyEqual(edge->fLowerY, last->fLowerY)) {
         if (edge->fUpperY > last->fUpperY) {
             last->fLowerY = edge->fUpperY;
             return kPartial_Combine;
         }
         last->fLowerY = last->fUpperY;
         last->fUpperY = edge->fUpperY;
         last->fY = last->fUpperY;
         last->fWinding = edge->fWinding;
         return kPartial_Combine;
     }
@@ skipping 329 matching lines @@
                 }
                 default:
                     SkDEBUGFAIL("unexpected verb");
                     break;
             }
         }
     }
     fEdgeList = fList.begin();
     return fList.count();
 }