GrTessellator (AA): implement fast path for non-intersecting geometry.

In the common case, there are no intersections in the inner or outer
meshes generated for edge-AA. In that case, we don't have to build
connector edges, and we don't need to run the full simplify and
tessellate path on the full combined mesh. In order to maintain the
correspondence between inner and outer meshes, we can keep partner
pointers between inner and outer vertices instead.

So the new flow is:

- stroke the original boundaries to generate inner & outer meshes
- assign partner pointers to join inner & outer vertices
- build Edges only for Inner and Outer contours
- sort the two meshes independently
- do a complexity check on both meshes (simplified Bentley-Ottmann that
  just aborts on the first found intersection)
- if neither mesh is complex, use the fast path:
  - tessellate only the inner mesh
  - return the outer mesh, and use the partner pointers to generate
    the outer geometry triangles
- otherwise, use the complex path (as before):
  - connect the inner & outer partners with Connector Edges
  - merge the inner & outer meshes via sorted_merge()
  - simplify and tessellate the resulting complete mesh

On a 2012 Retina MBP (Intel), this yields:
Canvas Arcs +6%
Stroke Shapes +6%
Fill Shapes +15%

On a Z620 Ubuntu w/NVidia GTX 650:
Canvas Arcs: +5.0%
Stroke Shapes: +1.8%
Fill Shapes: +17.6%

Other changes:

- implemented VertexList::append(VertexList), for use by sorted_merge()
- renamed boundary_to_aa_mesh() to stroke_boundary(), and made it append
  inner & outer contours to inner & outer meshes
- the connect() loop at the bottom of stroke_boundary() now uses open
  VertexLists, since it can then append them easily to the inner & outer meshes
- sort_and_simplify() changed to sort_mesh(), with merging and simplification
  done explicitly by the callers
- sorted_merge() factored out of merge_sort(), for use when zipping together
  the inner and outer meshes

Change-Id: Ib00f9f12a375412eff35dd2bb78ccd787d9c37ce
Reviewed-on: https://skia-review.googlesource.com/9600
Commit-Queue: Stephen White <senorblanco@chromium.org>
Reviewed-by: Brian Salomon <bsalomon@google.com>

1 files changed, 188 insertions, 55 deletions

diff --git a/src/gpu/GrTessellator.cpp b/src/gpu/GrTessellator.cpp
index 7ca1f4ba0b..d7dd35716e 100644
--- a/src/gpu/GrTessellator.cpp
+++ b/src/gpu/GrTessellator.cpp
@@ -30,16 +30,16 @@
  *
  * Run steps 1-5 above to produce polygons.
  * 5b) Apply fill rules to extract boundary contours from the polygons (extract_boundaries()).
- * 5c) Simplify boundaries to remove "pointy" vertices which cause inversions (simplify_boundary()).
+ * 5c) Simplify boundaries to remove "pointy" vertices that cause inversions (simplify_boundary()).
  * 5d) Displace edges by half a pixel inward and outward along their normals. Intersect to find
  *     new vertices, and set zero alpha on the exterior and one alpha on the interior. Build a new
- *     antialiased mesh from those vertices (boundary_to_aa_mesh()).
+ *     antialiased mesh from those vertices (stroke_boundary()).
  * Run steps 3-6 above on the new mesh, and produce antialiased triangles.
  *
  * The vertex sorting in step (3) is a merge sort, since it plays well with the linked list
  * of vertices (and the necessity of inserting new vertices on intersection).
  *
- * Stages (4) and (5) use an active edge list, which a list of all edges for which the
+ * Stages (4) and (5) use an active edge list -- a list of all edges for which the
  * sweep line has crossed the top vertex, but not the bottom vertex.  It's sorted
  * left-to-right based on the point where both edges are active (when both top vertices
  * have been seen, so the "lower" top vertex of the two). If the top vertices are equal
@@ -145,6 +145,7 @@ struct Vertex {
     : fPoint(point), fPrev(nullptr), fNext(nullptr)
     , fFirstEdgeAbove(nullptr), fLastEdgeAbove(nullptr)
     , fFirstEdgeBelow(nullptr), fLastEdgeBelow(nullptr)
+    , fPartner(nullptr)
     , fProcessed(false)
     , fAlpha(alpha)
 #if LOGGING_ENABLED
@@ -158,6 +159,7 @@ struct Vertex {
     Edge*   fLastEdgeAbove;   // "
     Edge*   fFirstEdgeBelow;  // Linked list of edges below this vertex.
     Edge*   fLastEdgeBelow;   // "
+    Vertex* fPartner;         // Corresponding inner or outer vertex (for AA).
     bool    fProcessed;       // Has this vertex been seen in simplify()?
     uint8_t fAlpha;
 #if LOGGING_ENABLED
@@ -242,6 +244,18 @@ struct VertexList {
     void append(Vertex* v) {
         insert(v, fTail, nullptr);
     }
+    void append(const VertexList& list) {
+        if (!list.fHead) {
+            return;
+        }
+        if (fTail) {
+            fTail->fNext = list.fHead;
+            list.fHead->fPrev = fTail;
+        } else {
+            fHead = list.fHead;
+        }
+        fTail = list.fTail;
+    }
     void prepend(Vertex* v) {
         insert(v, nullptr, fHead);
     }
@@ -297,7 +311,7 @@ struct Line {
  * An Edge joins a top Vertex to a bottom Vertex. Edge ordering for the list of "edges above" and
  * "edge below" a vertex as well as for the active edge list is handled by isLeftOf()/isRightOf().
  * Note that an Edge will give occasionally dist() != 0 for its own endpoints (because floating
- * point). For speed, that case is only tested by the callers which require it (e.g.,
+ * point). For speed, that case is only tested by the callers that require it (e.g.,
  * cleanup_active_edges()). Edges also handle checking for intersection with other edges.
  * Currently, this converts the edges to the parametric form, in order to avoid doing a division
  * until an intersection has been confirmed. This is slightly slower in the "found" case, but
@@ -419,6 +433,11 @@ struct EdgeList {
     void remove(Edge* edge) {
         list_remove<Edge, &Edge::fLeft, &Edge::fRight>(edge, &fHead, &fTail);
     }
+    void removeAll() {
+        while (fHead) {
+            this->remove(fHead);
+        }
+    }
     void close() {
         if (fHead && fTail) {
             fTail->fRight = fHead;
@@ -1023,6 +1042,9 @@ void merge_vertices(Vertex* src, Vertex* dst, VertexList* mesh, Comparator& c,
     LOG("found coincident verts at %g, %g; merging %g into %g\n", src->fPoint.fX, src->fPoint.fY,
         src->fID, dst->fID);
     dst->fAlpha = SkTMax(src->fAlpha, dst->fAlpha);
+    if (src->fPartner) {
+        src->fPartner->fPartner = dst;
+    }
     for (Edge* edge = src->fFirstEdgeAbove; edge;) {
         Edge* next = edge->fNextEdgeAbove;
         set_bottom(edge, dst, nullptr, c);
@@ -1127,6 +1149,9 @@ void sanitize_contours(VertexList* contours, int contourCnt, bool approximate) {
 }
 
 void merge_coincident_vertices(VertexList* mesh, Comparator& c, SkArenaAlloc& alloc) {
+    if (!mesh->fHead) {
+        return;
+    }
     for (Vertex* v = mesh->fHead->fNext; v != nullptr; v = v->fNext) {
         if (c.sweep_lt(v->fPoint, v->fPrev->fPoint)) {
             v->fPoint = v->fPrev->fPoint;
@@ -1153,6 +1178,44 @@ void build_edges(VertexList* contours, int contourCnt, VertexList* mesh, Compara
     }
 }
 
+void connect_partners(VertexList* outerVertices, Comparator& c, SkArenaAlloc& alloc) {
+    for (Vertex* outer = outerVertices->fHead; outer; outer = outer->fNext) {
+        if (Vertex* inner = outer->fPartner) {
+            // Connector edges get zero winding, since they're only structural (i.e., to ensure
+            // no 0-0-0 alpha triangles are produced), and shouldn't affect the poly winding number.
+            connect(outer, inner, Edge::Type::kConnector, c, alloc, 0);
+            inner->fPartner = outer->fPartner = nullptr;
+        }
+    }
+}
+
+template <CompareFunc sweep_lt>
+void sorted_merge(VertexList* front, VertexList* back, VertexList* result) {
+    Vertex* a = front->fHead;
+    Vertex* b = back->fHead;
+    while (a && b) {
+        if (sweep_lt(a->fPoint, b->fPoint)) {
+            front->remove(a);
+            result->append(a);
+            a = front->fHead;
+        } else {
+            back->remove(b);
+            result->append(b);
+            b = back->fHead;
+        }
+    }
+    result->append(*front);
+    result->append(*back);
+}
+
+void sorted_merge(VertexList* front, VertexList* back, VertexList* result, Comparator& c) {
+    if (c.fDirection == Comparator::Direction::kHorizontal) {
+        sorted_merge<sweep_lt_horiz>(front, back, result);
+    } else {
+        sorted_merge<sweep_lt_vert>(front, back, result);
+    }
+}
+
 // Stage 3: sort the vertices by increasing sweep direction.
 
 template <CompareFunc sweep_lt>
@@ -1180,25 +1243,7 @@ void merge_sort(VertexList* vertices) {
     merge_sort<sweep_lt>(&back);
 
     vertices->fHead = vertices->fTail = nullptr;
-    Vertex* a = front.fHead;
-    Vertex* b = back.fHead;
-    while (a && b) {
-        if (sweep_lt(a->fPoint, b->fPoint)) {
-            Vertex* next = a->fNext;
-            vertices->append(a);
-            a = next;
-        } else {
-            Vertex* next = b->fNext;
-            vertices->append(b);
-            b = next;
-        }
-    }
-    if (a) {
-        vertices->insert(a, vertices->fTail, a->fNext);
-    }
-    if (b) {
-        vertices->insert(b, vertices->fTail, b->fNext);
-    }
+    sorted_merge<sweep_lt>(&front, &back, vertices);
 }
 
 // Stage 4: Simplify the mesh by inserting new vertices at intersecting edges.
@@ -1259,6 +1304,48 @@ void simplify(const VertexList& vertices, Comparator& c, SkArenaAlloc& alloc) {
     }
 }
 
+// This is a stripped-down version of simplify() (the Bentley-Ottmann algorithm) that
+// early-returns true on the first found intersection, false if none.
+bool is_complex(const VertexList& vertices) {
+    LOG("testing polygon complexity\n");
+    EdgeList activeEdges;
+    for (Vertex* v = vertices.fHead; v != nullptr; v = v->fNext) {
+        if (!v->fFirstEdgeAbove && !v->fFirstEdgeBelow) {
+            continue;
+        }
+        Edge* leftEnclosingEdge;
+        Edge* rightEnclosingEdge;
+        find_enclosing_edges(v, &activeEdges, &leftEnclosingEdge, &rightEnclosingEdge);
+        SkPoint dummy;
+        if (v->fFirstEdgeBelow) {
+            for (Edge* edge = v->fFirstEdgeBelow; edge; edge = edge->fNextEdgeBelow) {
+                if (edge && leftEnclosingEdge && edge->intersect(*leftEnclosingEdge, &dummy)) {
+                    activeEdges.removeAll();
+                    return true;
+                }
+                if (edge && rightEnclosingEdge && edge->intersect(*rightEnclosingEdge, &dummy)) {
+                    activeEdges.removeAll();
+                    return true;
+                }
+            }
+        } else if (leftEnclosingEdge && rightEnclosingEdge &&
+                   leftEnclosingEdge->intersect(*rightEnclosingEdge, &dummy)) {
+            activeEdges.removeAll();
+            return true;
+        }
+        for (Edge* e = v->fFirstEdgeAbove; e; e = e->fNextEdgeAbove) {
+            remove_edge(e, &activeEdges);
+        }
+        Edge* leftEdge = leftEnclosingEdge;
+        for (Edge* e = v->fFirstEdgeBelow; e; e = e->fNextEdgeBelow) {
+            insert_edge(e, leftEdge, &activeEdges);
+            leftEdge = e;
+        }
+    }
+    activeEdges.removeAll();
+    return false;
+}
+
 // Stage 5: Tessellate the simplified mesh into monotone polygons.
 
 Poly* tessellate(const VertexList& vertices, SkArenaAlloc& alloc) {
@@ -1463,7 +1550,8 @@ void fix_inversions(Vertex* prev, Vertex* next, Edge* prevBisector, Edge* nextBi
 // find new vertices, and set zero alpha on the exterior and one alpha on the interior. Build a
 // new antialiased mesh from those vertices.
 
-void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, SkArenaAlloc& alloc) {
+void stroke_boundary(EdgeList* boundary, VertexList* innerMesh, VertexList* outerMesh,
+                     Comparator& c, SkArenaAlloc& alloc) {
     // A boundary with fewer than 3 edges is degenerate.
     if (!boundary->fHead || !boundary->fHead->fRight || !boundary->fHead->fRight->fRight) {
         return;
@@ -1492,6 +1580,8 @@ void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, Sk
             Edge* bisector = new_edge(outerVertex, innerVertex, Edge::Type::kConnector, c, alloc);
             fix_inversions(innerVertices.fTail, innerVertex, prevBisector, bisector, prevEdge, c);
             fix_inversions(outerVertices.fTail, outerVertex, prevBisector, bisector, prevEdge, c);
+            innerVertex->fPartner = outerVertex;
+            outerVertex->fPartner = innerVertex;
             innerVertices.append(innerVertex);
             outerVertices.append(outerVertex);
             prevBisector = bisector;
@@ -1500,8 +1590,6 @@ void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, Sk
         prevOuter = outer;
         prevEdge = e;
     }
-    innerVertices.close();
-    outerVertices.close();
 
     Vertex* innerVertex = innerVertices.fHead;
     Vertex* outerVertex = outerVertices.fHead;
@@ -1512,22 +1600,21 @@ void boundary_to_aa_mesh(EdgeList* boundary, VertexList* mesh, Comparator& c, Sk
                               alloc);
     fix_inversions(innerVertices.fTail, innerVertices.fHead, prevBisector, bisector, prevEdge, c);
     fix_inversions(outerVertices.fTail, outerVertices.fHead, prevBisector, bisector, prevEdge, c);
-    do {
+    Vertex* prevInnerVertex = innerVertices.fTail;
+    Vertex* prevOuterVertex = outerVertices.fTail;
+    while (innerVertex && outerVertex) {
         // Connect vertices into a quad mesh. Outer edges get default (1) winding.
         // Inner edges get -2 winding. This ensures that the interior is always filled
         // (-1 winding number for normal cases, 3 for thin features where the interior inverts).
-        // Connector edges get zero winding, since they're only structural (i.e., to ensure
-        // no 0-0-0 alpha triangles are produced), and shouldn't affect the poly winding number.
-        connect(outerVertex->fPrev, outerVertex, Edge::Type::kOuter, c, alloc);
-        connect(innerVertex->fPrev, innerVertex, Edge::Type::kInner, c, alloc, -2);
-        connect(outerVertex, innerVertex, Edge::Type::kConnector, c, alloc, 0);
-        Vertex* innerNext = innerVertex->fNext;
-        Vertex* outerNext = outerVertex->fNext;
-        mesh->append(innerVertex);
-        mesh->append(outerVertex);
-        innerVertex = innerNext;
-        outerVertex = outerNext;
-    } while (innerVertex != innerVertices.fHead && outerVertex != outerVertices.fHead);
+        connect(prevOuterVertex, outerVertex, Edge::Type::kOuter, c, alloc);
+        connect(prevInnerVertex, innerVertex, Edge::Type::kInner, c, alloc, -2);
+        prevInnerVertex = innerVertex;
+        prevOuterVertex = outerVertex;
+        innerVertex = innerVertex->fNext;
+        outerVertex = outerVertex->fNext;
+    }
+    innerMesh->append(innerVertices);
+    outerMesh->append(outerVertices);
 }
 
 void extract_boundary(EdgeList* boundary, Edge* e, SkPath::FillType fillType, SkArenaAlloc& alloc) {
@@ -1562,7 +1649,8 @@ void extract_boundary(EdgeList* boundary, Edge* e, SkPath::FillType fillType, Sk
 
 // Stage 5b: Extract boundaries from mesh, simplify and stroke them into a new mesh.
 
-void extract_boundaries(const VertexList& inMesh, VertexList* outMesh, SkPath::FillType fillType,
+void extract_boundaries(const VertexList& inMesh, VertexList* innerVertices,
+                        VertexList* outerVertices, SkPath::FillType fillType,
                         Comparator& c, SkArenaAlloc& alloc) {
     remove_non_boundary_edges(inMesh, fillType, alloc);
     for (Vertex* v = inMesh.fHead; v; v = v->fNext) {
@@ -1570,12 +1658,12 @@ void extract_boundaries(const VertexList& inMesh, VertexList* outMesh, SkPath::F
             EdgeList boundary;
             extract_boundary(&boundary, v->fFirstEdgeBelow, fillType, alloc);
             simplify_boundary(&boundary, c, alloc);
-            boundary_to_aa_mesh(&boundary, outMesh, c, alloc);
+            stroke_boundary(&boundary, innerVertices, outerVertices, c, alloc);
         }
     }
 }
 
-// This is a driver function which calls stages 2-5 in turn.
+// This is a driver function that calls stages 2-5 in turn.
 
 void contours_to_mesh(VertexList* contours, int contourCnt, bool antialias,
                       VertexList* mesh, Comparator& c, SkArenaAlloc& alloc) {
@@ -1593,7 +1681,7 @@ void contours_to_mesh(VertexList* contours, int contourCnt, bool antialias,
     build_edges(contours, contourCnt, mesh, c, alloc);
 }
 
-void sort_and_simplify(VertexList* vertices, Comparator& c, SkArenaAlloc& alloc) {
+void sort_mesh(VertexList* vertices, Comparator& c, SkArenaAlloc& alloc) {
     if (!vertices || !vertices->fHead) {
         return;
     }
@@ -1604,29 +1692,43 @@ void sort_and_simplify(VertexList* vertices, Comparator& c, SkArenaAlloc& alloc)
     } else {
         merge_sort<sweep_lt_vert>(vertices);
     }
-    merge_coincident_vertices(vertices, c, alloc);
 #if LOGGING_ENABLED
     for (Vertex* v = vertices->fHead; v != nullptr; v = v->fNext) {
         static float gID = 0.0f;
         v->fID = gID++;
     }
 #endif
-    simplify(*vertices, c, alloc);
 }
 
 Poly* contours_to_polys(VertexList* contours, int contourCnt, SkPath::FillType fillType,
-                        const SkRect& pathBounds, bool antialias,
+                        const SkRect& pathBounds, bool antialias, VertexList* outerMesh,
                         SkArenaAlloc& alloc) {
     Comparator c(pathBounds.width() > pathBounds.height() ? Comparator::Direction::kHorizontal
                                                           : Comparator::Direction::kVertical);
     VertexList mesh;
     contours_to_mesh(contours, contourCnt, antialias, &mesh, c, alloc);
-    sort_and_simplify(&mesh, c, alloc);
+    sort_mesh(&mesh, c, alloc);
+    merge_coincident_vertices(&mesh, c, alloc);
+    simplify(mesh, c, alloc);
     if (antialias) {
-        VertexList aaMesh;
-        extract_boundaries(mesh, &aaMesh, fillType, c, alloc);
-        sort_and_simplify(&aaMesh, c, alloc);
-        return tessellate(aaMesh, alloc);
+        VertexList innerMesh;
+        extract_boundaries(mesh, &innerMesh, outerMesh, fillType, c, alloc);
+        sort_mesh(&innerMesh, c, alloc);
+        sort_mesh(outerMesh, c, alloc);
+        if (is_complex(innerMesh) || is_complex(*outerMesh)) {
+            LOG("found complex mesh; taking slow path\n");
+            VertexList aaMesh;
+            connect_partners(outerMesh, c, alloc);
+            sorted_merge(&innerMesh, outerMesh, &aaMesh, c);
+            merge_coincident_vertices(&aaMesh, c, alloc);
+            simplify(aaMesh, c, alloc);
+            outerMesh->fHead = outerMesh->fTail = nullptr;
+            return tessellate(aaMesh, alloc);
+        } else {
+            LOG("no complex polygons; taking fast path\n");
+            merge_coincident_vertices(&innerMesh, c, alloc);
+            return tessellate(innerMesh, alloc);
+        }
     } else {
         return tessellate(mesh, alloc);
     }
@@ -1644,7 +1746,8 @@ void* polys_to_triangles(Poly* polys, SkPath::FillType fillType, const AAParams*
 }
 
 Poly* path_to_polys(const SkPath& path, SkScalar tolerance, const SkRect& clipBounds,
-                    int contourCnt, SkArenaAlloc& alloc, bool antialias, bool* isLinear) {
+                    int contourCnt, SkArenaAlloc& alloc, bool antialias, bool* isLinear,
+                    VertexList* outerMesh) {
     SkPath::FillType fillType = path.getFillType();
     if (SkPath::IsInverseFillType(fillType)) {
         contourCnt++;
@@ -1653,7 +1756,7 @@ Poly* path_to_polys(const SkPath& path, SkScalar tolerance, const SkRect& clipBo
 
     path_to_contours(path, tolerance, clipBounds, contours.get(), alloc, isLinear);
     return contours_to_polys(contours.get(), contourCnt, path.getFillType(), path.getBounds(),
-                             antialias, alloc);
+                             antialias, outerMesh, alloc);
 }
 
 int get_contour_count(const SkPath& path, SkScalar tolerance) {
@@ -1679,6 +1782,30 @@ int count_points(Poly* polys, SkPath::FillType fillType) {
     return count;
 }
 
+int count_outer_mesh_points(const VertexList& outerMesh) {
+    int count = 0;
+    for (Vertex* v = outerMesh.fHead; v; v = v->fNext) {
+        for (Edge* e = v->fFirstEdgeBelow; e; e = e->fNextEdgeBelow) {
+            count += TESSELLATOR_WIREFRAME ? 12 : 6;
+        }
+    }
+    return count;
+}
+
+void* outer_mesh_to_triangles(const VertexList& outerMesh, const AAParams* aaParams, void* data) {
+    for (Vertex* v = outerMesh.fHead; v; v = v->fNext) {
+        for (Edge* e = v->fFirstEdgeBelow; e; e = e->fNextEdgeBelow) {
+            Vertex* v0 = e->fTop;
+            Vertex* v1 = e->fBottom;
+            Vertex* v2 = e->fBottom->fPartner;
+            Vertex* v3 = e->fTop->fPartner;
+            data = emit_triangle(v0, v1, v2, aaParams, data);
+            data = emit_triangle(v0, v2, v3, aaParams, data);
+        }
+    }
+    return data;
+}
+
 } // namespace
 
 namespace GrTessellator {
@@ -1694,13 +1821,17 @@ int PathToTriangles(const SkPath& path, SkScalar tolerance, const SkRect& clipBo
         return 0;
     }
     SkArenaAlloc alloc(kArenaChunkSize);
+    VertexList outerMesh;
     Poly* polys = path_to_polys(path, tolerance, clipBounds, contourCnt, alloc, antialias,
-                                isLinear);
+                                isLinear, &outerMesh);
     SkPath::FillType fillType = antialias ? SkPath::kWinding_FillType : path.getFillType();
     int count = count_points(polys, fillType);
     if (0 == count) {
         return 0;
     }
+    if (antialias) {
+        count += count_outer_mesh_points(outerMesh);
+    }
 
     void* verts = vertexAllocator->lock(count);
     if (!verts) {
@@ -1714,6 +1845,7 @@ int PathToTriangles(const SkPath& path, SkScalar tolerance, const SkRect& clipBo
     aaParams.fColor = color;
 
     void* end = polys_to_triangles(polys, fillType, antialias ? &aaParams : nullptr, verts);
+    end = outer_mesh_to_triangles(outerMesh, &aaParams, end);
     int actualCount = static_cast<int>((static_cast<uint8_t*>(end) - static_cast<uint8_t*>(verts))
                                        / vertexAllocator->stride());
     SkASSERT(actualCount <= count);
@@ -1729,7 +1861,8 @@ int PathToVertices(const SkPath& path, SkScalar tolerance, const SkRect& clipBou
     }
     SkArenaAlloc alloc(kArenaChunkSize);
     bool isLinear;
-    Poly* polys = path_to_polys(path, tolerance, clipBounds, contourCnt, alloc, false, &isLinear);
+    Poly* polys = path_to_polys(path, tolerance, clipBounds, contourCnt, alloc, false, &isLinear,
+                                nullptr);
     SkPath::FillType fillType = path.getFillType();
     int count = count_points(polys, fillType);
     if (0 == count) {