Add GrAAConvexTessellator class

src/gpu/GrAAConvexTessellator.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 GrAAConvexTessellator_DEFINED
+#define GrAAConvexTessellator_DEFINED
+
+#include "SkColor.h"
+#include "SkPoint.h"
+#include "SkScalar.h"
+#include "SkTDArray.h"
+
+class SkCanvas;
+class SkMatrix;
+class SkPath;
+
+//#define GR_AA_CONVEX_TESSELLATOR_VIZ 1
+
+class GrAAConvexTessellator;
+
+// The AAConvexTessellator holds the global pool of points and the triangulation
+// that connects them. It also drives the tessellation process.
+// The outward facing normals of the original polygon are stored (in 'fNorms') to service
+// computeDepthFromEdge requests.
+class GrAAConvexTessellator {
+public:
+    GrAAConvexTessellator(SkScalar targetDepth = 0.5f)
+        : fSide(SkPoint::kOn_Side)
+        , fTargetDepth(targetDepth) {
+    }
+
+    void setTargetDepth(SkScalar targetDepth) { fTargetDepth = targetDepth; }
+    SkScalar targetDepth() const { return fTargetDepth; }
+
+    SkPoint::Side side() const { return fSide; }
+
+    bool tessellate(const SkMatrix& m, const SkPath& path);
+
+    // The next five should only be called after tessellate to extract the result
+    int numPts() const { return fPts.count(); }
+    int numIndices() const { return fIndices.count(); }
+
+    const SkPoint& lastPoint() const { return fPts.top(); }
+    const SkPoint& point(int index) const { return fPts[index]; }
+    int index(int index) const { return fIndices[index]; }
+    SkScalar depth(int index) const {return fDepths[index]; }
+
+#if GR_AA_CONVEX_TESSELLATOR_VIZ
+    void draw(SkCanvas* canvas) const;
+#endif
+
+    // The tessellator can be reused for multiple paths by rewinding in between
+    void rewind();
+
+private:
+    // CandidateVerts holds the vertices for the next ring while they are 
+    // being generated. Its main function is to de-dup the points.
+    class CandidateVerts {
+    public:
+        void setReserve(int numPts) { fPts.setReserve(numPts); }
+        void rewind() { fPts.rewind(); }
+
+        int numPts() const { return fPts.count(); }
+
+        const SkPoint& lastPoint() const { return fPts.top().fPt; }
+        const SkPoint& firstPoint() const { return fPts[0].fPt; }
+        const SkPoint& point(int index) const { return fPts[index].fPt; }
+
+        int originatingIdx(int index) const { return fPts[index].fOriginatingIdx; }
+        int origEdge(int index) const { return fPts[index].fOrigEdgeId; }
+        bool needsToBeNew(int index) const { return fPts[index].fNeedsToBeNew; }
+
+        int addNewPt(const SkPoint& newPt, int originatingIdx, int origEdge, bool needsToBeNew) {
+            struct PointData* pt = fPts.push();
+            pt->fPt = newPt;
+            pt->fOrigEdgeId = origEdge;
+            pt->fOriginatingIdx = originatingIdx;
+            pt->fNeedsToBeNew = needsToBeNew;
+            return fPts.count() - 1;
+        }
+
+        int fuseWithPrior(int origEdgeId) {
+            fPts.top().fOrigEdgeId = origEdgeId;
+            fPts.top().fOriginatingIdx = -1;
+            fPts.top().fNeedsToBeNew = true;
+            return fPts.count() - 1;
+        }
+
+        int fuseWithNext() {
+            fPts[0].fOriginatingIdx = -1;
+            fPts[0].fNeedsToBeNew = true;
+            return 0;
+        }
+
+        int fuseWithBoth() {
+            if (fPts.count() > 1) {
+                fPts.pop();
+            }
+
+            fPts[0].fOriginatingIdx = -1;
+            fPts[0].fNeedsToBeNew = true;
+            return 0;
+        }
+
+    private:
+        struct PointData {
+            SkPoint fPt;
+            int     fOriginatingIdx;
+            int     fOrigEdgeId;
+            bool    fNeedsToBeNew;
+        };
+
+        SkTDArray<struct PointData> fPts;
+    };
+
+    // The Ring holds a set of indices into the global pool that together define
+    // a single polygon inset.
+    class Ring {
+    public:
+        void setReserve(int numPts) { fPts.setReserve(numPts); }
+        void rewind() { fPts.rewind(); }
+
+        int numPts() const { return fPts.count(); }
+
+        void addIdx(int index, int origEdgeId) {
+            struct PointData* pt = fPts.push();
+            pt->fIndex = index;
+            pt->fOrigEdgeId = origEdgeId;
+        }
+
+        // init should be called after all the indices have been added (via addIdx)
+        void init(const GrAAConvexTessellator& tess);
+        void init(const SkTDArray<SkVector>& norms, const SkTDArray<SkVector>& bisectors);
+
+        const SkPoint& norm(int index) const { return fPts[index].fNorm; }
+        const SkPoint& bisector(int index) const { return fPts[index].fBisector; }
+        int index(int index) const { return fPts[index].fIndex; }
+        int origEdgeID(int index) const { return fPts[index].fOrigEdgeId; }
+
+    #if GR_AA_CONVEX_TESSELLATOR_VIZ
+        void draw(SkCanvas* canvas, const GrAAConvexTessellator& tess) const;
+    #endif
+
+    private:
+        void computeNormals(const GrAAConvexTessellator& result);
+        void computeBisectors();
+
+        SkDEBUGCODE(bool isConvex(const GrAAConvexTessellator& tess) const;)
+
+        struct PointData {
+            SkPoint fNorm;
+            SkPoint fBisector;
+            int     fIndex;
+            int     fOrigEdgeId;
+        };
+
+        SkTDArray<PointData> fPts;
+    };
+
+    bool movable(int index) const { return fMovable[index]; }
+
+    // Movable points are those that can be slid along their bisector.
+    // Basically, a point is immovable if it is part of the original
+    // polygon or it results from the fusing of two bisectors.
+    int addPt(const SkPoint& pt, SkScalar depth, bool movable);
+    void popLastPt();
+    void popFirstPtShuffle();
+
+    void updatePt(int index, const SkPoint& pt, SkScalar depth);
+
+    void addTri(int i0, int i1, int i2);
+
+    void reservePts(int count) {
+        fPts.setReserve(count);
+        fDepths.setReserve(count);  
+        fMovable.setReserve(count);
+    }
+
+    SkScalar computeDepthFromEdge(int edgeIdx, const SkPoint& p) const;
+
+    bool computePtAlongBisector(int startIdx, const SkPoint& bisector,
+                                int edgeIdx, SkScalar desiredDepth,
+                                SkPoint* result) const;
+
+    void terminate(const Ring& lastRing);
+
+    // return false on failure/degenerate path
+    bool extractFromPath(const SkMatrix& m, const SkPath& path);
+    void computeBisectors();
+
+    void fanRing(const Ring& ring);
+    void createOuterRing();
+
+    Ring* getNextRing(Ring* lastRing);
+
+    bool createInsetRing(const Ring& lastRing, Ring* nextRing);
+
+    void validate() const;
+
+
+#ifdef SK_DEBUG
+    SkScalar computeRealDepth(const SkPoint& p) const;
+    void checkAllDepths() const;
+#endif
+
+    // fPts, fWeights & fMovable should always have the same # of elements
+    SkTDArray<SkPoint>  fPts;
+    SkTDArray<SkScalar> fDepths;
+    // movable points are those that can be slid further along their bisector
+    SkTDArray<bool>     fMovable;
+
+    // The outward facing normals for the original polygon
+    SkTDArray<SkVector> fNorms;
+    // The inward facing bisector at each point in the original polygon. Only
+    // needed for exterior ring creation and then handed off to the initial ring.
+    SkTDArray<SkVector> fBisectors;
+    SkPoint::Side       fSide;    // winding of the original polygon
+
+    // The triangulation of the points
+    SkTDArray<int>      fIndices;
+
+    Ring                fInitialRing;
+#if GR_AA_CONVEX_TESSELLATOR_VIZ
+    // When visualizing save all the rings
+    SkTDArray<Ring*>    fRings;
+#else
+    Ring                fRings[2];
+#endif
+    CandidateVerts      fCandidateVerts;
+
+    SkScalar            fTargetDepth;
+
+    // If some goes wrong with the inset computation the tessellator will 
+    // truncate the creation of the inset polygon. In this case the depth
+    // check will complain.
+    SkDEBUGCODE(bool fShouldCheckDepths;)
+};
+
+
+#endif
+