Quality and performance fixes for AA tessellating path renderer.

Use quads rather than triangles for the edge geometry. This allows
us to perform a simpler edge categorization (see below). It also
improves performance by reducing the number of edges processed during
the simplify and tessellate steps.

Label AA edges as three types: inner, outer, and connector. This
results in correct alpha values for intersected edges, even when
the top or bottom vertex has been merged with a vertex on edges
of different types.

Changed the "collinear edges" sample from the concavepaths GM for a
"fast-foward" shape, which more clearly shows the problem being fixed
here. (The collinearity from the "collinear edges" was actually being
removed earlier up the stack, causing the path to become convex and
not exercise the concave path renderers anyway.)

NOTE: this will cause changes in the "concavepaths" GM results, and
minor pixel diffs in a number of other tests.

Change-Id: I6c2b0cdb35cda42b01cf1100621271fef5be35b0
Reviewed-on: https://skia-review.googlesource.com/6430
Reviewed-by: Stephan White <senorblanco@chromium.org>
Commit-Queue: Stephan White <senorblanco@chromium.org>

1 files changed, 43 insertions, 27 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index e75e1bbd9f..16f629ef64 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -309,10 +309,12 @@ struct Line {
  */
 
 struct Edge {
-    Edge(Vertex* top, Vertex* bottom, int winding)
+    enum class Type { kInner, kOuter, kConnector };
+    Edge(Vertex* top, Vertex* bottom, int winding, Type type)
         : fWinding(winding)
         , fTop(top)
         , fBottom(bottom)
+        , fType(type)
         , fLeft(nullptr)
         , fRight(nullptr)
         , fPrevEdgeAbove(nullptr)
@@ -332,6 +334,7 @@ struct Edge {
     int      fWinding;          // 1 == edge goes downward; -1 = edge goes upward.
     Vertex*  fTop;              // The top vertex in vertex-sort-order (sweep_lt).
     Vertex*  fBottom;           // The bottom vertex in vertex-sort-order.
+    Type     fType;
     Edge*    fLeft;             // The linked list of edges in the active edge list.
     Edge*    fRight;            // "
     Edge*    fPrevEdgeAbove;    // The linked list of edges in the bottom Vertex's "edges above".
@@ -531,7 +534,8 @@ struct Poly {
             fTail->addEdge(e);
             fCount++;
         } else {
-            e = ALLOC_NEW(Edge, (fTail->fLastEdge->fBottom, e->fBottom, 1), alloc);
+            e = ALLOC_NEW(Edge, (fTail->fLastEdge->fBottom, e->fBottom, 1, Edge::Type::kInner),
+                          alloc);
             fTail->addEdge(e);
             fCount++;
             if (partner) {
@@ -767,12 +771,11 @@ inline bool apply_fill_type(SkPath::FillType fillType, Poly* poly) {
     }
 }
 
-Edge* new_edge(Vertex* prev, Vertex* next, SkChunkAlloc& alloc, Comparator& c,
-               int winding_scale = 1) {
-    int winding = c.sweep_lt(prev->fPoint, next->fPoint) ? winding_scale : -winding_scale;
+Edge* new_edge(Vertex* prev, Vertex* next, SkChunkAlloc& alloc, Comparator& c, Edge::Type type) {
+    int winding = c.sweep_lt(prev->fPoint, next->fPoint) ? 1 : -1;
     Vertex* top = winding < 0 ? next : prev;
     Vertex* bottom = winding < 0 ? prev : next;
-    return ALLOC_NEW(Edge, (top, bottom, winding), alloc);
+    return ALLOC_NEW(Edge, (top, bottom, winding, type), alloc);
 }
 
 void remove_edge(Edge* edge, EdgeList* edges) {
@@ -825,7 +828,10 @@ void find_enclosing_edges(Edge* edge, EdgeList* edges, Comparator& c, Edge** lef
 }
 
 void fix_active_state(Edge* edge, EdgeList* activeEdges, Comparator& c) {
-    if (activeEdges && activeEdges->contains(edge)) {
+    if (!activeEdges) {
+        return;
+    }
+    if (activeEdges->contains(edge)) {
         if (edge->fBottom->fProcessed || !edge->fTop->fProcessed) {
             remove_edge(edge, activeEdges);
         }
@@ -1021,7 +1027,7 @@ void split_edge(Edge* edge, Vertex* v, EdgeList* activeEdges, Comparator& c, SkC
     } else if (c.sweep_gt(v->fPoint, edge->fBottom->fPoint)) {
         set_bottom(edge, v, activeEdges, c);
     } else {
-        Edge* newEdge = ALLOC_NEW(Edge, (v, edge->fBottom, edge->fWinding), alloc);
+        Edge* newEdge = ALLOC_NEW(Edge, (v, edge->fBottom, edge->fWinding, edge->fType), alloc);
         insert_edge_below(newEdge, v, c);
         insert_edge_above(newEdge, edge->fBottom, c);
         set_bottom(edge, v, activeEdges, c);
@@ -1031,9 +1037,8 @@ void split_edge(Edge* edge, Vertex* v, EdgeList* activeEdges, Comparator& c, SkC
     }
 }
 
-Edge* connect(Vertex* prev, Vertex* next, SkChunkAlloc& alloc, Comparator c,
-              int winding_scale = 1) {
-    Edge* edge = new_edge(prev, next, alloc, c, winding_scale);
+Edge* connect(Vertex* prev, Vertex* next, SkChunkAlloc& alloc, Comparator c, Edge::Type type) {
+    Edge* edge = new_edge(prev, next, alloc, c, type);
     if (edge->fWinding > 0) {
         insert_edge_below(edge, prev, c);
         insert_edge_above(edge, next, c);
@@ -1063,8 +1068,14 @@ void merge_vertices(Vertex* src, Vertex* dst, Vertex** head, Comparator& c, SkCh
 }
 
 uint8_t max_edge_alpha(Edge* a, Edge* b) {
-    return SkTMax(SkTMax(a->fTop->fAlpha, a->fBottom->fAlpha),
-                  SkTMax(b->fTop->fAlpha, b->fBottom->fAlpha));
+    if (a->fType == Edge::Type::kInner && b->fType == Edge::Type::kInner) {
+        return 255;
+    } else if (a->fType == Edge::Type::kOuter && b->fType == Edge::Type::kOuter) {
+        return 0;
+    } else {
+        return SkTMax(SkTMax(a->fTop->fAlpha, a->fBottom->fAlpha),
+                      SkTMax(b->fTop->fAlpha, b->fBottom->fAlpha));
+    }
 }
 
 Vertex* check_for_intersection(Edge* edge, Edge* other, EdgeList* activeEdges, Comparator& c,
@@ -1169,7 +1180,7 @@ Vertex* build_edges(Vertex** contours, int contourCnt, Comparator& c, SkChunkAll
     for (int i = 0; i < contourCnt; ++i) {
         for (Vertex* v = contours[i]; v != nullptr;) {
             Vertex* vNext = v->fNext;
-            connect(v->fPrev, v, alloc, c);
+            connect(v->fPrev, v, alloc, c, Edge::Type::kInner);
             if (prev) {
                 prev->fNext = v;
                 v->fPrev = prev;
@@ -1295,8 +1306,8 @@ void simplify(Vertex* vertices, Comparator& c, SkChunkAlloc& alloc) {
             }
         } while (restartChecks);
         if (v->fAlpha == 0) {
-            if ((leftEnclosingEdge && leftEnclosingEdge->fWinding < 0) &&
-                (rightEnclosingEdge && rightEnclosingEdge->fWinding > 0)) {
+            if ((leftEnclosingEdge && leftEnclosingEdge->fWinding > 0) &&
+                (rightEnclosingEdge && rightEnclosingEdge->fWinding < 0)) {
                 v->fAlpha = max_edge_alpha(leftEnclosingEdge, rightEnclosingEdge);
             }
         }
@@ -1391,7 +1402,8 @@ Poly* tessellate(Vertex* vertices, SkChunkAlloc& alloc) {
                             rightEnclosingEdge->fLeftPoly = rightPoly;
                         }
                     }
-                    Edge* join = ALLOC_NEW(Edge, (leftPoly->lastVertex(), v, 1), alloc);
+                    Edge* join = ALLOC_NEW(Edge,
+                        (leftPoly->lastVertex(), v, 1, Edge::Type::kInner), alloc);
                     leftPoly = leftPoly->addEdge(join, Poly::kRight_Side, alloc);
                     rightPoly = rightPoly->addEdge(join, Poly::kLeft_Side, alloc);
                 }
@@ -1469,7 +1481,7 @@ void simplify_boundary(EdgeList* boundary, Comparator& c, SkChunkAlloc& alloc) {
         get_edge_normal(e, &normal);
         float denom = 0.25f * static_cast<float>(e->fLine.magSq());
         if (prevNormal.dot(normal) < 0.0 && (dist * dist) <= denom) {
-            Edge* join = new_edge(prev, next, alloc, c);
+            Edge* join = new_edge(prev, next, alloc, c, Edge::Type::kInner);
             insert_edge(join, e, boundary);
             remove_edge(prevEdge, boundary);
             remove_edge(e, boundary);
@@ -1517,8 +1529,8 @@ void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, Sk
             Vertex* innerVertex = ALLOC_NEW(Vertex, (innerPoint, 255), alloc);
             Vertex* outerVertex = ALLOC_NEW(Vertex, (outerPoint, 0), alloc);
             if (innerVertices.fTail && outerVertices.fTail) {
-                Edge innerEdge(innerVertices.fTail, innerVertex, 1);
-                Edge outerEdge(outerVertices.fTail, outerVertex, 1);
+                Edge innerEdge(innerVertices.fTail, innerVertex, 1, Edge::Type::kInner);
+                Edge outerEdge(outerVertices.fTail, outerVertex, 1, Edge::Type::kInner);
                 SkVector innerNormal;
                 get_edge_normal(&innerEdge, &innerNormal);
                 SkVector outerNormal;
@@ -1560,10 +1572,9 @@ void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, Sk
         return;
     }
     do {
-        connect(outerVertex->fNext, outerVertex, alloc, c);
-        connect(innerVertex->fNext, innerVertex, alloc, c, 2);
-        connect(innerVertex, outerVertex->fNext, alloc, c, 2);
-        connect(outerVertex, innerVertex, alloc, c, 2);
+        connect(outerVertex->fPrev, outerVertex, alloc, c, Edge::Type::kOuter);
+        connect(innerVertex->fPrev, innerVertex, alloc, c, Edge::Type::kInner);
+        connect(outerVertex, innerVertex, alloc, c, Edge::Type::kConnector)->fWinding = 0;
         Vertex* innerNext = innerVertex->fNext;
         Vertex* outerNext = outerVertex->fNext;
         mesh->append(innerVertex);
@@ -1637,9 +1648,9 @@ Vertex* contours_to_mesh(Vertex** contours, int contourCnt, bool antialias,
     return build_edges(contours, contourCnt, c, alloc);
 }
 
-Poly* mesh_to_polys(Vertex** vertices, Comparator& c, SkChunkAlloc& alloc) {
+void sort_and_simplify(Vertex** vertices, Comparator& c, SkChunkAlloc& alloc) {
     if (!vertices || !*vertices) {
-        return nullptr;
+        return;
     }
 
     // Sort vertices in Y (secondarily in X).
@@ -1652,6 +1663,10 @@ Poly* mesh_to_polys(Vertex** vertices, Comparator& c, SkChunkAlloc& alloc) {
     }
 #endif
     simplify(*vertices, c, alloc);
+}
+
+Poly* mesh_to_polys(Vertex** vertices, Comparator& c, SkChunkAlloc& alloc) {
+    sort_and_simplify(vertices, c, alloc);
     return tessellate(*vertices, alloc);
 }
 
@@ -1677,7 +1692,8 @@ Poly* contours_to_polys(Vertex** contours, int contourCnt, SkPath::FillType fill
                 boundary_to_aa_mesh(boundary, &aaMesh, c, alloc);
             }
         }
-        return mesh_to_polys(&aaMesh.fHead, c, alloc);
+        sort_and_simplify(&aaMesh.fHead, c, alloc);
+        return tessellate(aaMesh.fHead, alloc);
     }
     return polys;
 }