Broke GrTessellatingPathRenderer's tessellator out into a separate file.

src/gpu/GrTessellator.h

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrTessellator_DEFINED
+#define GrTessellator_DEFINED
+
+#include "SkChunkAlloc.h"
+#include "GrPathRenderer.h"
+
+/**
+ * Provides utility functions for converting paths to a collection of triangles.
+ */
+
+#define TESSELLATOR_LOGGING_ENABLED 0
+#define TESSELLATOR_WIREFRAME 0
+

[bsalomon, 2016/01/04 21:45:21]

Maybe we should put all these structs and functions inside a namespace?
GrPathTessellator?

[Stephen White, 2016/01/04 22:51:19]

Maybe GrTessellator, to match the .h?

Agreed that the current names are too generic to live in the global namespace. 
Whatever we do, we should probably do it to TessellatorVertex (below) too.
(GrTessellator::Vertex?)

+struct Poly;
+struct Edge;
+
+/**
+ * Vertices are used in three ways: first, the path contours are converted into a circularly-linked 
+ * list of vertices for each contour. After edge construction, the same vertices are re-ordered by 
+ * the merge sort according to the sweep_lt comparator (usually, increasing in Y) using the same 
+ * fPrev/fNext pointers that were used for the contours, to avoid reallocation. Finally, 
+ * MonotonePolys are built containing a circularly-linked list of vertices. Currently, those 
+ * Vertices are newly-allocated for the MonotonePolys, since an individual TessellatorVertex from 
+ * the path mesh may belong to multiple MonotonePolys, so the original vertices cannot be re-used.
+ */
+struct TessellatorVertex {

[bsalomon, 2016/01/04 21:45:21]

Does this get used by any client of tessellator? I don't see it in the sig of
the two functions at the bottom.

[Stephen White, 2016/01/04 22:51:19]

+1. IWBN to keep this in the .cpp if not necessary to expose.

+  TessellatorVertex(const SkPoint& point)
+    : fPoint(point), fPrev(nullptr), fNext(nullptr)
+    , fFirstEdgeAbove(nullptr), fLastEdgeAbove(nullptr)
+    , fFirstEdgeBelow(nullptr), fLastEdgeBelow(nullptr)
+    , fProcessed(false)
+#if TESSELLATOR_LOGGING_ENABLED
+    , fID (-1.0f)
+#endif
+    {}
+    SkPoint fPoint;           // Vertex position
+    TessellatorVertex* fPrev; // Linked list of contours, then Y-sorted vertices.

[Stephen White, 2016/01/04 22:51:19]

Nit: spacing of these is weird now.

+    TessellatorVertex* fNext; // "
+    Edge*   fFirstEdgeAbove;  // Linked list of edges above this vertex.
+    Edge*   fLastEdgeAbove;   // "
+    Edge*   fFirstEdgeBelow;  // Linked list of edges below this vertex.
+    Edge*   fLastEdgeBelow;   // "
+    bool    fProcessed;       // Has this vertex been seen in simplify()?
+#if TESSELLATOR_LOGGING_ENABLED
+    float   fID;              // Identifier used for logging.
+#endif
+};
+
+struct EdgeList {
+    EdgeList() : fHead(nullptr), fTail(nullptr) {}
+    Edge* fHead;
+    Edge* fTail;
+};
+
+struct Edge {
+    Edge(TessellatorVertex* top, TessellatorVertex* bottom, int winding)
+        : fTop(top)
+        , fBottom(bottom)
+        , fWinding(winding)
+        , fLeft(nullptr)
+        , fRight(nullptr)
+        , fPrevEdgeAbove(nullptr)
+        , fNextEdgeAbove(nullptr)
+        , fPrevEdgeBelow(nullptr)
+        , fNextEdgeBelow(nullptr)
+        , fLeftPoly(nullptr)
+        , fRightPoly(nullptr) {
+            recompute();
+        }
+    TessellatorVertex* fTop;    // The top vertex in vertex-sort-order (sweep_lt).

[Stephen White, 2016/01/04 22:51:19]

Nit: spacing of these is weird now.

+    TessellatorVertex* fBottom; // The bottom vertex in vertex-sort-order.
+    int    fWinding;            // 1 == edge goes downward; -1 = edge goes upward.
+    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".
+    Edge*  fNextEdgeAbove;      // "
+    Edge*  fPrevEdgeBelow;      // The linked list of edges in the top Vertex's "edges below".
+    Edge*  fNextEdgeBelow;      // "
+    Poly*  fLeftPoly;           // The Poly to the left of this edge, if any.
+    Poly*  fRightPoly;          // The Poly to the right of this edge, if any.
+    double fDX;                 // The line equation for this edge, in implicit form.
+    double fDY;                 // fDY * x + fDX * y + fC = 0, for point (x, y) on the line.
+    double fC;
+    double dist(const SkPoint& p) const;
+    bool isRightOf(TessellatorVertex* v) const;
+    bool isLeftOf(TessellatorVertex* v) const;
+    void recompute();
+    bool intersect(const Edge& other, SkPoint* p);
+    bool isActive(EdgeList* activeEdges) const;
+};
+
+struct WindingVertex {
+    SkPoint fPos;
+    int fWinding;
+};
+
+Poly* path_to_polys(const SkPath& path, SkScalar tolerance, const SkRect& clipBounds, 

[bsalomon, 2016/01/04 21:45:21]

Does this need to be exposed? It looks like Poly is not exposed so the only
thing that could be done with the returned value is to pass it to one of the
following functions. Would a caller reuse the same returned Poly* multiple
times? Wondering if we could just have PathToTriangles and PathToVertices.

[Stephen White, 2016/01/04 22:51:19]

Maybe they should be in the GrTessellator namespace too?

e.g., GrTessellator::PathToVertices()? Then it would be a little 
clearer that the paths were being tessellated.

+                    bool* isLinear);
+
+// creates an array of (point, winding) vertices and sets the 'verts' out parameter to point to it. 
+// CALLER IS RESPONSIBLE for deleting this buffer to avoid a memory leak!
+int polys_to_vertices(Poly* polys, SkPath::FillType fillType, bool isLinear,

[bsalomon, 2016/01/04 21:45:21]

Is this (and polys_to_triangles) destructive to polys?

+        WindingVertex** verts);
+
+int polys_to_triangles(Poly* polys, SkPath::FillType fillType, bool isLinear,
+        GrResourceProvider* resourceProvider, SkAutoTUnref<GrVertexBuffer>& vertexBuffer, 
+        bool canMapVB);
+
+#endif