From afd25f703d9bbc9cd80b03b63b30abd14db4911d Mon Sep 17 00:00:00 2001
From: caryclark <caryclark@google.com>
Date: Sat, 30 Jan 2016 14:07:20 -0800
Subject: [PATCH] combine vertical overlapping edges

Paths outside clips, and sometimes paths inside clips, devolve
to multiple adjacent or overlapping vertical edges. Combine
these edges when possible to reduce the overall edge count.

R=reed@google.com
BUG=573166
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1654433002

Review URL: https://codereview.chromium.org/1654433002
---
 src/core/SkEdgeBuilder.cpp | 78 +++++++++++++++++++++++++++++++++++++-
 src/core/SkEdgeBuilder.h   |  9 +++++
 2 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/src/core/SkEdgeBuilder.cpp b/src/core/SkEdgeBuilder.cpp
index 92c8330c16..dc390389c0 100644
--- a/src/core/SkEdgeBuilder.cpp
+++ b/src/core/SkEdgeBuilder.cpp
@@ -22,11 +22,70 @@ SkEdgeBuilder::SkEdgeBuilder() : fAlloc(16*1024) {
     fEdgeList = nullptr;
 }
 
+SkEdgeBuilder::Combine SkEdgeBuilder::CombineVertical(const SkEdge* edge, SkEdge* last) {
+    if (last->fCurveCount || last->fDX || edge->fX != last->fX) {
+        return kNo_Combine;
+    }
+    if (edge->fWinding == last->fWinding) {
+        if (edge->fLastY + 1 == last->fFirstY) {
+            last->fFirstY = edge->fFirstY;
+            return kPartial_Combine;
+        }
+        if (edge->fFirstY == last->fLastY + 1) {
+            last->fLastY = edge->fLastY;
+            return kPartial_Combine;
+        }
+        return kNo_Combine;
+    }
+    if (edge->fFirstY == last->fFirstY) {
+        if (edge->fLastY == last->fLastY) {
+            return kTotal_Combine;
+        }
+        if (edge->fLastY < last->fLastY) {
+            last->fFirstY = edge->fLastY + 1;
+            return kPartial_Combine;
+        }
+        last->fFirstY = last->fLastY + 1;
+        last->fLastY = edge->fLastY;
+        last->fWinding = edge->fWinding;
+        return kPartial_Combine;
+    }
+    if (edge->fLastY == last->fLastY) {
+        if (edge->fFirstY > last->fFirstY) {
+            last->fLastY = edge->fFirstY - 1;
+            return kPartial_Combine;
+        }
+        last->fLastY = last->fFirstY - 1;
+        last->fFirstY = edge->fFirstY;
+        last->fWinding = edge->fWinding;
+        return kPartial_Combine;
+    }
+    return kNo_Combine;
+}
+
+static bool vertical_line(const SkEdge* edge) {
+#ifdef SK_SUPPORT_LEGACY_VERTICAL_EDGE  // this disables combining vertical overlapping edges
+    return false;
+#endif
+    return !edge->fDX && !edge->fCurveCount;
+}
+
 void SkEdgeBuilder::addLine(const SkPoint pts[]) {
     SkEdge* edge = typedAllocThrow<SkEdge>(fAlloc);
     if (edge->setLine(pts[0], pts[1], fShiftUp)) {
+        if (vertical_line(edge) && fList.count()) {
+            Combine combine = CombineVertical(edge, *(fList.end() - 1));
+            if (kNo_Combine != combine) {
+                if (kTotal_Combine == combine) {
+                    fList.pop();
+                }
+                goto unallocate_edge;
+            }
+        }
         fList.push(edge);
     } else {
+unallocate_edge:
+        ;
         // TODO: unallocate edge from storage...
     }
 }
@@ -79,6 +138,11 @@ static void setShiftedClip(SkRect* dst, const SkIRect& src, int shift) {
              SkIntToScalar(src.fBottom >> shift));
 }
 
+SkEdgeBuilder::Combine SkEdgeBuilder::checkVertical(const SkEdge* edge, SkEdge** edgePtr) {
+    return !vertical_line(edge) || edgePtr <= fEdgeList ? kNo_Combine :
+            CombineVertical(edge, edgePtr[-1]);
+}
+
 int SkEdgeBuilder::buildPoly(const SkPath& path, const SkIRect* iclip, int shiftUp,
                              bool canCullToTheRight) {
     SkPath::Iter    iter(path, true);
@@ -119,7 +183,12 @@ int SkEdgeBuilder::buildPoly(const SkPath& path, const SkIRect* iclip, int shift
                     SkASSERT(lineCount <= SkLineClipper::kMaxClippedLineSegments);
                     for (int i = 0; i < lineCount; i++) {
                         if (edge->setLine(lines[i], lines[i + 1], shiftUp)) {
-                            *edgePtr++ = edge++;
+                            Combine combine = checkVertical(edge, edgePtr);
+                            if (kNo_Combine == combine) {
+                                *edgePtr++ = edge++;
+                            } else if (kTotal_Combine == combine) {
+                                --edgePtr;
+                            }
                         }
                     }
                     break;
@@ -139,7 +208,12 @@ int SkEdgeBuilder::buildPoly(const SkPath& path, const SkIRect* iclip, int shift
                     break;
                 case SkPath::kLine_Verb:
                     if (edge->setLine(pts[0], pts[1], shiftUp)) {
-                        *edgePtr++ = edge++;
+                        Combine combine = checkVertical(edge, edgePtr);
+                        if (kNo_Combine == combine) {
+                            *edgePtr++ = edge++;
+                        } else if (kTotal_Combine == combine) {
+                            --edgePtr;
+                        }
                     }
                     break;
                 default:
diff --git a/src/core/SkEdgeBuilder.h b/src/core/SkEdgeBuilder.h
index 625465b8a6..047460d4fe 100644
--- a/src/core/SkEdgeBuilder.h
+++ b/src/core/SkEdgeBuilder.h
@@ -27,6 +27,15 @@ public:
     SkEdge** edgeList() { return fEdgeList; }
 
 private:
+    enum Combine {
+        kNo_Combine,
+        kPartial_Combine,
+        kTotal_Combine
+    };
+
+    static Combine CombineVertical(const SkEdge* edge, SkEdge* last);
+    Combine checkVertical(const SkEdge* edge, SkEdge** edgePtr);
+
     SkChunkAlloc        fAlloc;
     SkTDArray<SkEdge*>  fList;