Add some new PolyUtils tests.

Also:
* clean up PolyUtils checks to be correct and consistent.
* fix some bugs discovered by the unit tests.

Bug: skia:
Change-Id: I1a8e07d13cb44fecc67344154dc1002f3f910f5d
Reviewed-on: https://skia-review.googlesource.com/138592
Reviewed-by: Robert Phillips <robertphillips@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>

7 files changed, 421 insertions, 141 deletions

diff --git a/gn/tests.gni b/gn/tests.gni
index 2068ae527c..7ffbb0b00f 100644
--- a/gn/tests.gni
+++ b/gn/tests.gni
@@ -173,6 +173,7 @@ tests_sources = [
   "$_tests/PixelRefTest.cpp",
   "$_tests/Point3Test.cpp",
   "$_tests/PointTest.cpp",
+  "$_tests/PolyUtilsTest.cpp",
   "$_tests/PremulAlphaRoundTripTest.cpp",
   "$_tests/PrimitiveProcessorTest.cpp",
   "$_tests/ProcessorTest.cpp",
diff --git a/src/utils/SkPolyUtils.cpp b/src/utils/SkPolyUtils.cpp
index ea9d649a5c..e323f21762 100755
--- a/src/utils/SkPolyUtils.cpp
+++ b/src/utils/SkPolyUtils.cpp
@@ -35,13 +35,20 @@ static int compute_side(const SkPoint& s0, const SkPoint& s1, const SkPoint& p)
     return 0;
 }
 
-// returns 1 for ccw, -1 for cw and 0 if degenerate
-static int get_winding(const SkPoint* polygonVerts, int polygonSize) {
+// Returns 1 for cw, -1 for ccw and 0 if zero signed area (either degenerate or self-intersecting)
+int SkGetPolygonWinding(const SkPoint* polygonVerts, int polygonSize) {
+    if (polygonSize < 3) {
+        return 0;
+    }
+
     // compute area and use sign to determine winding
     SkScalar quadArea = 0;
-    for (int curr = 0; curr < polygonSize; ++curr) {
+    SkVector v0 = polygonVerts[1] - polygonVerts[0];
+    for (int curr = 1; curr < polygonSize - 1; ++curr) {
         int next = (curr + 1) % polygonSize;
-        quadArea += polygonVerts[curr].cross(polygonVerts[next]);
+        SkVector v1 = polygonVerts[next] - polygonVerts[0];
+        quadArea += v0.cross(v1);
+        v0 = v1;
     }
     if (SkScalarNearlyZero(quadArea)) {
         return 0;
@@ -111,6 +118,15 @@ bool SkOffsetSegment(const SkPoint& p0, const SkPoint& p1, SkScalar d0, SkScalar
     return true;
 }
 
+// compute fraction of d along v
+static inline SkScalar compute_param(const SkVector& v, const SkVector& d) {
+    if (SkScalarNearlyZero(v.fX)) {
+        return d.fY / v.fY;
+    } else {
+        return d.fX / v.fX;
+    }
+}
+
 // Compute the intersection 'p' between segments s0 and s1, if any.
 // 's' is the parametric value for the intersection along 's0' & 't' is the same for 's1'.
 // Returns false if there is no intersection.
@@ -132,36 +148,60 @@ static bool compute_intersection(const OffsetSegment& s0, const OffsetSegment& s
 
     SkVector v0 = s0.fP1 - s0.fP0;
     SkVector v1 = s1.fP1 - s1.fP0;
-    // We should have culled coincident points before this
-    SkASSERT(!SkPointPriv::EqualsWithinTolerance(s0.fP0, s0.fP1));
-    SkASSERT(!SkPointPriv::EqualsWithinTolerance(s1.fP0, s1.fP1));
-
     SkVector d = s1.fP0 - s0.fP0;
     SkScalar perpDot = v0.cross(v1);
     SkScalar localS, localT;
     if (SkScalarNearlyZero(perpDot)) {
         // segments are parallel, but not collinear
-        if (!SkScalarNearlyZero(d.dot(d), SK_ScalarNearlyZero*SK_ScalarNearlyZero)) {
+        if (!SkScalarNearlyZero(d.cross(v0)) || !SkScalarNearlyZero(d.cross(v1))) {
             return false;
         }
 
-        // project segment1's endpoints onto segment0
-        localS = d.fX / v0.fX;
-        localT = 0;
-        if (localS < 0 || localS > SK_Scalar1) {
-            // the first endpoint doesn't lie on segment0, try the other one
-            SkScalar oldLocalS = localS;
-            localS = (s1.fP1.fX - s0.fP0.fX) / v0.fX;
-            localT = SK_Scalar1;
+        // Check for degenerate segments
+        if (!SkPointPriv::CanNormalize(v0.fX, v0.fY)) {
+            // Both are degenerate
+            if (!SkPointPriv::CanNormalize(v1.fX, v1.fY)) {
+                // Check if they're the same point
+                if (!SkPointPriv::CanNormalize(d.fX, d.fY)) {
+                    *p = s0.fP0;
+                    *s = 0;
+                    *t = 0;
+                    return true;
+                } else {
+                    return false;
+                }
+            }
+            // Otherwise project onto segment1
+            localT = compute_param(v1, -d);
+            if (localT < 0 || localT > SK_Scalar1) {
+                return false;
+            }
+            localS = 0;
+        } else {
+            // Project segment1's endpoints onto segment0
+            localS = compute_param(v0, d);
+            localT = 0;
             if (localS < 0 || localS > SK_Scalar1) {
-                // it's possible that segment1's interval surrounds segment0
-                // this is false if the params have the same signs, and in that case no collision
-                if (localS*oldLocalS > 0) {
+                // The first endpoint doesn't lie on segment0
+                // If segment1 is degenerate, then there's no collision
+                if (!SkPointPriv::CanNormalize(v1.fX, v1.fY)) {
                     return false;
                 }
-                // otherwise project segment0's endpoint onto segment1 instead
-                localS = 0;
-                localT = -d.fX / v1.fX;
+
+                // Otherwise try the other one
+                SkScalar oldLocalS = localS;
+                localS = compute_param(v0, s1.fP1 - s0.fP0);
+                localT = SK_Scalar1;
+                if (localS < 0 || localS > SK_Scalar1) {
+                    // it's possible that segment1's interval surrounds segment0
+                    // this is false if params have the same signs, and in that case no collision
+                    if (localS*oldLocalS > 0) {
+                        return false;
+                    }
+                    // otherwise project segment0's endpoint onto segment1 instead
+                    localS = 0;
+                    localT = compute_param(v1, -d);
+                }
             }
         }
     } else {
@@ -175,8 +215,7 @@ static bool compute_intersection(const OffsetSegment& s0, const OffsetSegment& s
         }
     }
 
-    v0 *= localS;
-    *p = s0.fP0 + v0;
+    *p = s0.fP0 + v0*localS;
     *s = localS;
     *t = localT;
 
@@ -207,25 +246,49 @@ static SkScalar compute_crossing_distance(const OffsetSegment& s0, const OffsetS
     return localS;
 }
 
-static bool is_convex(const SkTDArray<SkPoint>& poly) {
-    if (poly.count() <= 3) {
-        return true;
+bool SkIsConvexPolygon(const SkPoint* polygonVerts, int polygonSize) {
+    if (polygonSize < 3) {
+        return false;
     }
 
-    SkVector v0 = poly[0] - poly[poly.count() - 1];
-    SkVector v1 = poly[1] - poly[poly.count() - 1];
-    SkScalar winding = v0.cross(v1);
-
-    for (int i = 0; i < poly.count() - 1; ++i) {
-        int j = i + 1;
-        int k = (i + 2) % poly.count();
+    SkScalar lastArea = 0;
+    SkScalar lastPerpDot = 0;
 
-        SkVector v0 = poly[j] - poly[i];
-        SkVector v1 = poly[k] - poly[i];
+    int prevIndex = polygonSize - 1;
+    int currIndex = 0;
+    int nextIndex = 1;
+    SkPoint origin = polygonVerts[0];
+    SkVector v0 = polygonVerts[currIndex] - polygonVerts[prevIndex];
+    SkVector v1 = polygonVerts[nextIndex] - polygonVerts[currIndex];
+    SkVector w0 = polygonVerts[currIndex] - origin;
+    SkVector w1 = polygonVerts[nextIndex] - origin;
+    for (int i = 0; i < polygonSize; ++i) {
+        // Check that winding direction is always the same (otherwise we have a reflex vertex)
         SkScalar perpDot = v0.cross(v1);
-        if (winding*perpDot < 0) {
+        if (lastPerpDot*perpDot < 0) {
             return false;
         }
+        if (0 != perpDot) {
+            lastPerpDot = perpDot;
+        }
+
+        // If the signed area ever flips it's concave
+        // TODO: see if we can verify convexity only with signed area
+        SkScalar quadArea = w0.cross(w1);
+        if (quadArea*lastArea < 0) {
+            return false;
+        }
+        if (0 != quadArea) {
+            lastArea = quadArea;
+        }
+
+        prevIndex = currIndex;
+        currIndex = nextIndex;
+        nextIndex = (currIndex + 1) % polygonSize;
+        v0 = v1;
+        v1 = polygonVerts[nextIndex] - polygonVerts[currIndex];
+        w0 = w1;
+        w1 = polygonVerts[nextIndex] - origin;
     }
 
     return true;
@@ -281,7 +344,7 @@ bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize
     }
 
     // get winding direction
-    int winding = get_winding(inputPolygonVerts, inputPolygonSize);
+    int winding = SkGetPolygonWinding(inputPolygonVerts, inputPolygonSize);
     if (0 == winding) {
         return false;
     }
@@ -395,7 +458,7 @@ bool SkInsetConvexPolygon(const SkPoint* inputPolygonVerts, int inputPolygonSize
         insetPolygon->pop();
     }
 
-    return (insetPolygon->count() >= 3 && is_convex(*insetPolygon));
+    return SkIsConvexPolygon(insetPolygon->begin(), insetPolygon->count());
 }
 
 ///////////////////////////////////////////////////////////////////////////////////////////
@@ -416,6 +479,8 @@ void SkComputeRadialSteps(const SkVector& v1, const SkVector& v2, SkScalar r,
     *n = steps;
 }
 
+///////////////////////////////////////////////////////////////////////////////////////////
+
 // tolerant less-than comparison
 static inline bool nearly_lt(SkScalar a, SkScalar b, SkScalar tolerance = SK_ScalarNearlyZero) {
     return a < b - tolerance;
@@ -626,7 +691,7 @@ bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSiz
     }
 
     // get winding direction
-    int winding = get_winding(inputPolygonVerts, inputPolygonSize);
+    int winding = SkGetPolygonWinding(inputPolygonVerts, inputPolygonSize);
     if (0 == winding) {
         return false;
     }
@@ -787,7 +852,7 @@ bool SkOffsetSimplePolygon(const SkPoint* inputPolygonVerts, int inputPolygonSiz
     }
 
     // check winding of offset polygon (it should be same as the original polygon)
-    SkScalar offsetWinding = get_winding(offsetPolygon->begin(), offsetPolygon->count());
+    SkScalar offsetWinding = SkGetPolygonWinding(offsetPolygon->begin(), offsetPolygon->count());
 
     return (winding*offsetWinding > 0 &&
             SkIsSimplePolygon(offsetPolygon->begin(), offsetPolygon->count()));
@@ -891,7 +956,7 @@ bool SkTriangulateSimplePolygon(const SkPoint* polygonVerts, uint16_t* indexMap,
     // get winding direction
     // TODO: we do this for all the polygon routines -- might be better to have the client
     // compute it and pass it in
-    int winding = get_winding(polygonVerts, polygonSize);
+    int winding = SkGetPolygonWinding(polygonVerts, polygonSize);
     if (0 == winding) {
         return false;
     }
diff --git a/src/utils/SkPolyUtils.h b/src/utils/SkPolyUtils.h
index ab5ebb8d40..9c25a078ff 100755
--- a/src/utils/SkPolyUtils.h
+++ b/src/utils/SkPolyUtils.h
@@ -118,7 +118,28 @@ void SkComputeRadialSteps(const SkVector& offset0, const SkVector& offset1, SkSc
                           SkScalar* rotSin, SkScalar* rotCos, int* n);
 
 /**
+ * Determine winding direction for a polygon.
+ * The input polygon must be simple or the result will be meaningless.
+ *
+ * @param polygonVerts  Array of points representing the vertices of the polygon.
+ * @param polygonSize  Number of vertices in the polygon.
+ * @return 1 for cw, -1 for ccw, and 0 if zero signed area (either degenerate or self-intersecting).
+ *         The y-axis is assumed to be pointing down.
+ */
+int SkGetPolygonWinding(const SkPoint* polygonVerts, int polygonSize);
+
+/**
+ * Determine whether a polygon is convex or not.
+ *
+ * @param polygonVerts  Array of points representing the vertices of the polygon.
+ * @param polygonSize  Number of vertices in the polygon.
+ * @return true if the polygon is convex, false otherwise.
+ */
+bool SkIsConvexPolygon(const SkPoint* polygonVerts, int polygonSize);
+
+/**
  * Determine whether a polygon is simple (i.e., not self-intersecting) or not.
+ * The input polygon must have no coincident vertices or the test will fail.
  *
  * @param polygonVerts  Array of points representing the vertices of the polygon.
  * @param polygonSize  Number of vertices in the polygon.
diff --git a/src/utils/SkShadowTessellator.cpp b/src/utils/SkShadowTessellator.cpp
index 3d84e8fdad..873e6d2687 100755
--- a/src/utils/SkShadowTessellator.cpp
+++ b/src/utils/SkShadowTessellator.cpp
@@ -92,7 +92,6 @@ protected:
     SkPoint             fCentroid;
     SkScalar            fArea;
     SkScalar            fLastArea;
-    int                 fAreaSignFlips;
     SkScalar            fLastCross;
 
     int                 fFirstVertexIndex;
@@ -137,18 +136,16 @@ static bool duplicate_pt(const SkPoint& p0, const SkPoint& p1) {
 
 static SkScalar perp_dot(const SkPoint& p0, const SkPoint& p1, const SkPoint& p2) {
     SkVector v0 = p1 - p0;
-    SkVector v1 = p2 - p0;
+    SkVector v1 = p2 - p1;
     return v0.cross(v1);
 }
 
-
 SkBaseShadowTessellator::SkBaseShadowTessellator(const SkPoint3& zPlaneParams, bool transparent)
         : fZPlaneParams(zPlaneParams)
         , fZOffset(0)
         , fCentroid({0, 0})
         , fArea(0)
         , fLastArea(0)
-        , fAreaSignFlips(0)
         , fLastCross(0)
         , fFirstVertexIndex(-1)
         , fSucceeded(false)
@@ -189,15 +186,20 @@ bool SkBaseShadowTessellator::accumulateCentroid(const SkPoint& curr, const SkPo
         return false;
     }
 
-    SkScalar quadArea = curr.cross(next);
-    fCentroid.fX += (curr.fX + next.fX) * quadArea;
-    fCentroid.fY += (curr.fY + next.fY) * quadArea;
+    SkASSERT(fPathPolygon.count() > 0);
+    SkVector v0 = curr - fPathPolygon[0];
+    SkVector v1 = next - fPathPolygon[0];
+    SkScalar quadArea = v0.cross(v1);
+    fCentroid.fX += (v0.fX + v1.fX) * quadArea;
+    fCentroid.fY += (v0.fY + v1.fY) * quadArea;
     fArea += quadArea;
     // convexity check
     if (quadArea*fLastArea < 0) {
-        ++fAreaSignFlips;
+        fIsConvex = false;
+    }
+    if (0 != quadArea) {
+        fLastArea = quadArea;
     }
-    fLastArea = quadArea;
 
     return true;
 }
@@ -215,7 +217,9 @@ bool SkBaseShadowTessellator::checkConvexity(const SkPoint& p0,
     if (fLastCross*cross < 0) {
         fIsConvex = false;
     }
-    fLastCross = cross;
+    if (0 != cross) {
+        fLastCross = cross;
+    }
 
     return true;
 }
@@ -229,6 +233,9 @@ void SkBaseShadowTessellator::finishPathPolygon() {
     }
 
     if (fPathPolygon.count() > 2) {
+        // do this before the final convexity check, so we use the correct fPathPolygon[0]
+        fCentroid *= sk_ieee_float_divide(1, 3 * fArea);
+        fCentroid += fPathPolygon[0];
         if (!checkConvexity(fPathPolygon[fPathPolygon.count() - 2],
                             fPathPolygon[fPathPolygon.count() - 1],
                             fPathPolygon[0])) {
@@ -238,14 +245,6 @@ void SkBaseShadowTessellator::finishPathPolygon() {
         }
     }
 
-    fCentroid *= sk_ieee_float_divide(1, 3 * fArea);
-    // It's possible to have a concave path that self-intersects but also passes the
-    // cross-product check (e.g., a star). In that case, the signed area will change signs more
-    // than twice, so we check for that here.
-    if (fAreaSignFlips > 2) {
-        fIsConvex = false;
-    }
-
     // if area is positive, winding is ccw
     fDirection = fArea > 0 ? -1 : 1;
 }
diff --git a/tests/InsetConvexPolyTest.cpp b/tests/InsetConvexPolyTest.cpp
index 022060c0f4..facabb76fa 100644
--- a/tests/InsetConvexPolyTest.cpp
+++ b/tests/InsetConvexPolyTest.cpp
@@ -7,30 +7,6 @@
 #include "Test.h"
 #include "SkPolyUtils.h"
 
-static bool is_convex(const SkTDArray<SkPoint>& poly) {
-    if (poly.count() < 3) {
-        return false;
-    }
-
-    SkVector v0 = poly[0] - poly[poly.count() - 1];
-    SkVector v1 = poly[1] - poly[poly.count() - 1];
-    SkScalar winding = v0.cross(v1);
-
-    for (int i = 0; i < poly.count()-1; ++i) {
-        int j = i + 1;
-        int k = (i + 2) % poly.count();
-
-        SkVector v0 = poly[j] - poly[i];
-        SkVector v1 = poly[k] - poly[i];
-        SkScalar perpDot = v0.cross(v1);
-        if (winding*perpDot < 0) {
-            return false;
-        }
-    }
-
-    return true;
-}
-
 DEF_TEST(InsetConvexPoly, reporter) {
     SkTDArray<SkPoint> rrectPoly;
 
@@ -55,18 +31,18 @@ DEF_TEST(InsetConvexPoly, reporter) {
     *rrectPoly.push() = SkPoint::Make(-100 - 4.330127f, 50 + 2.5f);
     *rrectPoly.push() = SkPoint::Make(-100 - 3.535534f, 50 + 3.535534f);
     *rrectPoly.push() = SkPoint::Make(-100 - 2.5f, 50 + 4.330127f);
-    REPORTER_ASSERT(reporter, is_convex(rrectPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(rrectPoly.begin(), rrectPoly.count()));
 
     // inset a little
     SkTDArray<SkPoint> insetPoly;
-    bool result = SkInsetConvexPolygon(&rrectPoly[0], rrectPoly.count(), 3, &insetPoly);
+    bool result = SkInsetConvexPolygon(rrectPoly.begin(), rrectPoly.count(), 3, &insetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(insetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(insetPoly.begin(), insetPoly.count()));
 
     // inset to rect
-    result = SkInsetConvexPolygon(&rrectPoly[0], rrectPoly.count(), 10, &insetPoly);
+    result = SkInsetConvexPolygon(rrectPoly.begin(), rrectPoly.count(), 10, &insetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(insetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(insetPoly.begin(), insetPoly.count()));
     REPORTER_ASSERT(reporter, insetPoly.count() == 4);
     if (insetPoly.count() == 4) {
         REPORTER_ASSERT(reporter, insetPoly[0].equals(-95, 45));
@@ -77,9 +53,9 @@ DEF_TEST(InsetConvexPoly, reporter) {
 
     // just to full inset
     // fails, but outputs a line segment
-    result = SkInsetConvexPolygon(&rrectPoly[0], rrectPoly.count(), 55, &insetPoly);
+    result = SkInsetConvexPolygon(rrectPoly.begin(), rrectPoly.count(), 55, &insetPoly);
     REPORTER_ASSERT(reporter, !result);
-    REPORTER_ASSERT(reporter, !is_convex(insetPoly));
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(insetPoly.begin(), insetPoly.count()));
     REPORTER_ASSERT(reporter, insetPoly.count() == 2);
     if (insetPoly.count() == 2) {
         REPORTER_ASSERT(reporter, insetPoly[0].equals(-50, 0));
@@ -87,7 +63,7 @@ DEF_TEST(InsetConvexPoly, reporter) {
     }
 
     // past full inset
-    result = SkInsetConvexPolygon(&rrectPoly[0], rrectPoly.count(), 75, &insetPoly);
+    result = SkInsetConvexPolygon(rrectPoly.begin(), rrectPoly.count(), 75, &insetPoly);
     REPORTER_ASSERT(reporter, !result);
     REPORTER_ASSERT(reporter, insetPoly.count() == 0);
 
@@ -120,10 +96,11 @@ DEF_TEST(InsetConvexPoly, reporter) {
     *clippedRRectPoly.push() = SkPoint::Make(381.195313f, 432.207275f);
     *clippedRRectPoly.push() = SkPoint::Make(377.312134f, 432.947998f);
     *clippedRRectPoly.push() = SkPoint::Make(342.289948f, 432.947998f);
-    REPORTER_ASSERT(reporter, is_convex(clippedRRectPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(clippedRRectPoly.begin(),
+                                                clippedRRectPoly.count()));
 
-    result = SkInsetConvexPolygon(&clippedRRectPoly[0], clippedRRectPoly.count(), 32.3699417f,
+    result = SkInsetConvexPolygon(clippedRRectPoly.begin(), clippedRRectPoly.count(), 32.3699417f,
                                   &insetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(insetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(insetPoly.begin(), insetPoly.count()));
 }
diff --git a/tests/OffsetSimplePolyTest.cpp b/tests/OffsetSimplePolyTest.cpp
index 547dc9e529..0f4f18f2ad 100644
--- a/tests/OffsetSimplePolyTest.cpp
+++ b/tests/OffsetSimplePolyTest.cpp
@@ -7,30 +7,6 @@
 #include "Test.h"
 #include "SkPolyUtils.h"
 
-static bool is_convex(const SkTDArray<SkPoint>& poly) {
-    if (poly.count() < 3) {
-        return false;
-    }
-
-    SkVector v0 = poly[0] - poly[poly.count() - 1];
-    SkVector v1 = poly[1] - poly[poly.count() - 1];
-    SkScalar winding = v0.cross(v1);
-
-    for (int i = 0; i < poly.count()-1; ++i) {
-        int j = i + 1;
-        int k = (i + 2) % poly.count();
-
-        SkVector v0 = poly[j] - poly[i];
-        SkVector v1 = poly[k] - poly[i];
-        SkScalar perpDot = v0.cross(v1);
-        if (winding*perpDot < 0) {
-            return false;
-        }
-    }
-
-    return true;
-}
-
 DEF_TEST(OffsetSimplePoly, reporter) {
     SkTDArray<SkPoint> rrectPoly;
 
@@ -58,18 +34,18 @@ DEF_TEST(OffsetSimplePoly, reporter) {
     *rrectPoly.push() = SkPoint::Make(-100 - 4.330127f, 50 + 2.5f);
     *rrectPoly.push() = SkPoint::Make(-100 - 3.535534f, 50 + 3.535534f);
     *rrectPoly.push() = SkPoint::Make(-100 - 2.5f, 50 + 4.330127f);
-    REPORTER_ASSERT(reporter, is_convex(rrectPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(rrectPoly.begin(), rrectPoly.count()));
 
     // inset a little
     SkTDArray<SkPoint> offsetPoly;
-    bool result = SkOffsetSimplePolygon(&rrectPoly[0], rrectPoly.count(), 3, &offsetPoly);
+    bool result = SkOffsetSimplePolygon(rrectPoly.begin(), rrectPoly.count(), 3, &offsetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(offsetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(offsetPoly.begin(), offsetPoly.count()));
 
     // inset to rect
-    result = SkOffsetSimplePolygon(&rrectPoly[0], rrectPoly.count(), 10, &offsetPoly);
+    result = SkOffsetSimplePolygon(rrectPoly.begin(), rrectPoly.count(), 10, &offsetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(offsetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(offsetPoly.begin(), offsetPoly.count()));
     REPORTER_ASSERT(reporter, offsetPoly.count() == 4);
     if (offsetPoly.count() == 4) {
         REPORTER_ASSERT(reporter, offsetPoly[0].equals(-95, 45));
@@ -80,9 +56,9 @@ DEF_TEST(OffsetSimplePoly, reporter) {
 
     // just to full inset
     // fails, but outputs a line segment
-    result = SkOffsetSimplePolygon(&rrectPoly[0], rrectPoly.count(), 55, &offsetPoly);
+    result = SkOffsetSimplePolygon(rrectPoly.begin(), rrectPoly.count(), 55, &offsetPoly);
     REPORTER_ASSERT(reporter, !result);
-    REPORTER_ASSERT(reporter, !is_convex(offsetPoly));
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(offsetPoly.begin(), offsetPoly.count()));
     REPORTER_ASSERT(reporter, offsetPoly.count() == 2);
     if (offsetPoly.count() == 2) {
         REPORTER_ASSERT(reporter, offsetPoly[0].equals(-50, 0));
@@ -90,7 +66,7 @@ DEF_TEST(OffsetSimplePoly, reporter) {
     }
 
     // past full inset
-    result = SkOffsetSimplePolygon(&rrectPoly[0], rrectPoly.count(), 75, &offsetPoly);
+    result = SkOffsetSimplePolygon(rrectPoly.begin(), rrectPoly.count(), 75, &offsetPoly);
     REPORTER_ASSERT(reporter, !result);
 
     // troublesome case
@@ -122,12 +98,13 @@ DEF_TEST(OffsetSimplePoly, reporter) {
     *clippedRRectPoly.push() = SkPoint::Make(381.195313f, 432.207275f);
     *clippedRRectPoly.push() = SkPoint::Make(377.312134f, 432.947998f);
     *clippedRRectPoly.push() = SkPoint::Make(342.289948f, 432.947998f);
-    REPORTER_ASSERT(reporter, is_convex(clippedRRectPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(clippedRRectPoly.begin(),
+                                                clippedRRectPoly.count()));
 
-    result = SkOffsetSimplePolygon(&clippedRRectPoly[0], clippedRRectPoly.count(), 32.3699417f,
+    result = SkOffsetSimplePolygon(clippedRRectPoly.begin(), clippedRRectPoly.count(), 32.3699417f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
-    REPORTER_ASSERT(reporter, is_convex(offsetPoly));
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(offsetPoly.begin(), offsetPoly.count()));
 
     ////////////////////////////////////////////////////////////////////////////////
     // Concave tests
@@ -145,46 +122,54 @@ DEF_TEST(OffsetSimplePoly, reporter) {
     *starPoly.push() = SkPoint::Make(-28.86f, 0.0f);
     *starPoly.push() = SkPoint::Make(-43.30f, -25.0f);
     *starPoly.push() = SkPoint::Make(-14.43f, -25.0f);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(starPoly.begin(), starPoly.count()));
 
     // try a variety of distances
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), 0.1f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), 0.1f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), 5.665f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), 5.665f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), 28,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), 28,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
     // down to a point
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), 28.866f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), 28.866f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, !result);
 
     // and past
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), 50.5f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), 50.5f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, !result);
 
     // and now out
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), -0.1f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), -0.1f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), -5.6665f,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), -5.6665f,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), -50,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), -50,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
-    result = SkOffsetSimplePolygon(&starPoly[0], starPoly.count(), -100,
+    result = SkOffsetSimplePolygon(starPoly.begin(), starPoly.count(), -100,
                                    &offsetPoly);
     REPORTER_ASSERT(reporter, result);
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(offsetPoly.begin(), offsetPoly.count()));
 
     SkTDArray<SkPoint> intersectingPoly;
     *intersectingPoly.push() = SkPoint::Make(0.0f, -50.0f);
@@ -201,6 +186,6 @@ DEF_TEST(OffsetSimplePoly, reporter) {
     *intersectingPoly.push() = SkPoint::Make(-14.43f, -25.0f);
 
     // SkOffsetSimplePolygon now assumes that the input is simple, so we'll just check for that
-    result = SkIsSimplePolygon(&intersectingPoly[0], intersectingPoly.count());
+    result = SkIsSimplePolygon(intersectingPoly.begin(), intersectingPoly.count());
     REPORTER_ASSERT(reporter, !result);
 }
diff --git a/tests/PolyUtilsTest.cpp b/tests/PolyUtilsTest.cpp
new file mode 100644
index 0000000000..bc5a1a4858
--- /dev/null
+++ b/tests/PolyUtilsTest.cpp
@@ -0,0 +1,232 @@
+/*
+ * Copyright 2018 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+#include "Test.h"
+#include "SkPolyUtils.h"
+
+DEF_TEST(PolyUtils, reporter) {
+
+    SkTDArray<SkPoint> poly;
+    // init simple index map
+    uint16_t indexMap[256];
+    for (int i = 0; i < 256; ++i) {
+        indexMap[i] = i;
+    }
+    SkTDArray<uint16_t> triangleIndices;
+
+    // skinny triangle
+    *poly.push() = SkPoint::Make(-100, 55);
+    *poly.push() = SkPoint::Make(100, 55);
+    *poly.push() = SkPoint::Make(102.5f, 54.330127f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) < 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // switch winding
+    poly[2].set(102.5f, 55.330127f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) > 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // make degenerate
+    poly[2].set(100 + 2.5f, 55);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) == 0);
+    // TODO: should these fail?
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, !SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                          &triangleIndices));
+
+    // giant triangle
+    poly[0].set(-1.0e+37f, 1.0e+37f);
+    poly[1].set(1.0e+37f, 1.0e+37f);
+    poly[2].set(-1.0e+37f, -1.0e+37f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) < 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // teeny triangle
+    poly[0].set(-1.0e-38f, 1.0e-38f);
+    poly[1].set(-1.0e-38f, -1.0e-38f);
+    poly[2].set(1.0e-38f, 1.0e-38f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) == 0);
+    // TODO: should these fail?
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, !SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                          &triangleIndices));
+
+    // triangle way off in space (relative to size so we don't completely obliterate values)
+    poly[0].set(-100 + 1.0e+9f, 55 - 1.0e+9f);
+    poly[1].set(100 + 1.0e+9f, 55 - 1.0e+9f);
+    poly[2].set(150 + 1.0e+9f, 100 - 1.0e+9f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) > 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    ///////////////////////////////////////////////////////////////////////
+    // round rect
+    poly.reset();
+    *poly.push() = SkPoint::Make(-100, 55);
+    *poly.push() = SkPoint::Make(100, 55);
+    *poly.push() = SkPoint::Make(100 + 2.5f, 50 + 4.330127f);
+    *poly.push() = SkPoint::Make(100 + 3.535534f, 50 + 3.535534f);
+    *poly.push() = SkPoint::Make(100 + 4.330127f, 50 + 2.5f);
+    *poly.push() = SkPoint::Make(105, 50);
+    *poly.push() = SkPoint::Make(105, -50);
+    *poly.push() = SkPoint::Make(100 + 4.330127f, -50 - 2.5f);
+    *poly.push() = SkPoint::Make(100 + 3.535534f, -50 - 3.535534f);
+    *poly.push() = SkPoint::Make(100 + 2.5f, -50 - 4.330127f);
+    *poly.push() = SkPoint::Make(100, -55);
+    *poly.push() = SkPoint::Make(-100, -55);
+    *poly.push() = SkPoint::Make(-100 - 2.5f, -50 - 4.330127f);
+    *poly.push() = SkPoint::Make(-100 - 3.535534f, -50 - 3.535534f);
+    *poly.push() = SkPoint::Make(-100 - 4.330127f, -50 - 2.5f);
+    *poly.push() = SkPoint::Make(-105, -50);
+    *poly.push() = SkPoint::Make(-105, 50);
+    *poly.push() = SkPoint::Make(-100 - 4.330127f, 50 + 2.5f);
+    *poly.push() = SkPoint::Make(-100 - 3.535534f, 50 + 3.535534f);
+    *poly.push() = SkPoint::Make(-100 - 2.5f, 50 + 4.330127f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) < 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // translate far enough to obliterate some low bits
+    for (int i = 0; i < poly.count(); ++i) {
+        poly[i].offset(1.0e+7f, 1.0e+7f);
+    }
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) < 0);
+    // Due to floating point error it's no longer convex
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                          &triangleIndices));
+
+    // translate a little farther to create some coincident vertices
+    for (int i = 0; i < poly.count(); ++i) {
+        poly[i].offset(4.0e+7f, 4.0e+7f);
+    }
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) < 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    // These can't handle coincident vertices
+    REPORTER_ASSERT(reporter, !SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, !SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                          &triangleIndices));
+
+    // troublesome case -- clipped roundrect
+    poly.reset();
+    *poly.push() = SkPoint::Make(335.928101f, 428.219055f);
+    *poly.push() = SkPoint::Make(330.414459f, 423.034912f);
+    *poly.push() = SkPoint::Make(325.749084f, 417.395508f);
+    *poly.push() = SkPoint::Make(321.931946f, 411.300842f);
+    *poly.push() = SkPoint::Make(318.963074f, 404.750977f);
+    *poly.push() = SkPoint::Make(316.842468f, 397.745850f);
+    *poly.push() = SkPoint::Make(315.570068f, 390.285522f);
+    *poly.push() = SkPoint::Make(315.145966f, 382.369965f);
+    *poly.push() = SkPoint::Make(315.570068f, 374.454346f);
+    *poly.push() = SkPoint::Make(316.842468f, 366.994019f);
+    *poly.push() = SkPoint::Make(318.963074f, 359.988892f);
+    *poly.push() = SkPoint::Make(321.931946f, 353.439056f);
+    *poly.push() = SkPoint::Make(325.749084f, 347.344421f);
+    *poly.push() = SkPoint::Make(330.414459f, 341.705017f);
+    *poly.push() = SkPoint::Make(335.928101f, 336.520813f);
+    *poly.push() = SkPoint::Make(342.289948f, 331.791901f);
+    *poly.push() = SkPoint::Make(377.312134f, 331.791901f);
+    *poly.push() = SkPoint::Make(381.195313f, 332.532593f);
+    *poly.push() = SkPoint::Make(384.464935f, 334.754700f);
+    *poly.push() = SkPoint::Make(386.687042f, 338.024292f);
+    *poly.push() = SkPoint::Make(387.427765f, 341.907532f);
+    *poly.push() = SkPoint::Make(387.427765f, 422.832367f);
+    *poly.push() = SkPoint::Make(386.687042f, 426.715576f);
+    *poly.push() = SkPoint::Make(384.464935f, 429.985168f);
+    *poly.push() = SkPoint::Make(381.195313f, 432.207275f);
+    *poly.push() = SkPoint::Make(377.312134f, 432.947998f);
+    *poly.push() = SkPoint::Make(342.289948f, 432.947998f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) > 0);
+    REPORTER_ASSERT(reporter, SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // a star is born
+    poly.reset();
+    *poly.push() = SkPoint::Make(0.0f, -50.0f);
+    *poly.push() = SkPoint::Make(14.43f, -25.0f);
+    *poly.push() = SkPoint::Make(43.30f, -25.0f);
+    *poly.push() = SkPoint::Make(28.86f, 0.0f);
+    *poly.push() = SkPoint::Make(43.30f, 25.0f);
+    *poly.push() = SkPoint::Make(14.43f, 25.0f);
+    *poly.push() = SkPoint::Make(0.0f, 50.0f);
+    *poly.push() = SkPoint::Make(-14.43f, 25.0f);
+    *poly.push() = SkPoint::Make(-43.30f, 25.0f);
+    *poly.push() = SkPoint::Make(-28.86f, 0.0f);
+    *poly.push() = SkPoint::Make(-43.30f, -25.0f);
+    *poly.push() = SkPoint::Make(-14.43f, -25.0f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) > 0);
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // self-intersecting polygon
+    poly.reset();
+    *poly.push() = SkPoint::Make(0.0f, -50.0f);
+    *poly.push() = SkPoint::Make(14.43f, -25.0f);
+    *poly.push() = SkPoint::Make(43.30f, -25.0f);
+    *poly.push() = SkPoint::Make(-28.86f, 0.0f);
+    *poly.push() = SkPoint::Make(43.30f, 25.0f);
+    *poly.push() = SkPoint::Make(14.43f, 25.0f);
+    *poly.push() = SkPoint::Make(0.0f, 50.0f);
+    *poly.push() = SkPoint::Make(-14.43f, 25.0f);
+    *poly.push() = SkPoint::Make(-43.30f, 25.0f);
+    *poly.push() = SkPoint::Make(28.86f, 0.0f);
+    *poly.push() = SkPoint::Make(-43.30f, -25.0f);
+    *poly.push() = SkPoint::Make(-14.43f, -25.0f);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) > 0);
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, !SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    // running this just to make sure it doesn't crash
+    // the fact that it succeeds doesn't mean anything since the input is not simple
+    REPORTER_ASSERT(reporter, SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                         &triangleIndices));
+
+    // self-intersecting polygon with coincident point
+    poly.reset();
+    *poly.push() = SkPoint::Make(0.0f, 0.0f);
+    *poly.push() = SkPoint::Make(-50, -50);
+    *poly.push() = SkPoint::Make(50, -50);
+    *poly.push() = SkPoint::Make(0.00000001f, -0.00000001f);
+    *poly.push() = SkPoint::Make(-50, 50);
+    *poly.push() = SkPoint::Make(50, 50);
+    REPORTER_ASSERT(reporter, SkGetPolygonWinding(poly.begin(), poly.count()) == 0);
+    REPORTER_ASSERT(reporter, !SkIsConvexPolygon(poly.begin(), poly.count()));
+    REPORTER_ASSERT(reporter, !SkIsSimplePolygon(poly.begin(), poly.count()));
+    triangleIndices.reset();
+    // running this just to make sure it doesn't crash
+    REPORTER_ASSERT(reporter, !SkTriangulateSimplePolygon(poly.begin(), indexMap, poly.count(),
+                                                          &triangleIndices));
+}