diff --git a/libs/hwui/AmbientShadow.cpp b/libs/hwui/AmbientShadow.cpp
index 904ec8c..c1af5f5 100644
--- a/libs/hwui/AmbientShadow.cpp
+++ b/libs/hwui/AmbientShadow.cpp
@@ -147,6 +147,8 @@
 
 /**
  * Generate an array of rays' direction vectors.
+ * To make sure the vertices generated are clockwise, the directions are from PI
+ * to -PI.
  *
  * @param rays The number of rays shooting out from the centroid.
  * @param vertices Vertices of the polygon.
@@ -160,8 +162,8 @@
     if (vertexCount * 2 > rays) {
         float deltaAngle = 2 * M_PI / rays;
         for (int i = 0; i < rays; i++) {
-            dir[i].x = sinf(deltaAngle * i);
-            dir[i].y = cosf(deltaAngle * i);
+            dir[i].x = cosf(M_PI - deltaAngle * i);
+            dir[i].y = sinf(M_PI - deltaAngle * i);
         }
         return;
     }
@@ -178,50 +180,52 @@
     // Since the incoming polygon is clockwise, we can find the dip to identify
     // the minimal theta.
     float polyThetas[vertexCount];
-    int minimalPolyThetaIndex = 0;
+    int maxPolyThetaIndex = 0;
     for (int i = 0; i < vertexCount; i++) {
         polyThetas[i] = atan2(vertices[i].y - centroid3d.y,
                 vertices[i].x - centroid3d.x);
-        if (i > 0 && polyThetas[i] < polyThetas[i - 1]) {
-            minimalPolyThetaIndex = i;
+        if (i > 0 && polyThetas[i] > polyThetas[i - 1]) {
+            maxPolyThetaIndex = i;
         }
     }
 
-    int polyThetaIndex = minimalPolyThetaIndex;
-    float polyTheta = polyThetas[minimalPolyThetaIndex];
+    // Both poly's thetas and uniform thetas are in decrease order(clockwise)
+    // from PI to -PI.
+    int polyThetaIndex = maxPolyThetaIndex;
+    float polyTheta = polyThetas[maxPolyThetaIndex];
     int uniformThetaIndex = 0;
-    float uniformTheta = - M_PI;
+    float uniformTheta = M_PI;
     for (int i = 0; i < rays; i++) {
         // Compare both thetas and pick the smaller one and move on.
         bool hasThetaCollision = abs(polyTheta - uniformTheta) < MINIMAL_DELTA_THETA;
-        if (polyTheta < uniformTheta || hasThetaCollision) {
+        if (polyTheta > uniformTheta || hasThetaCollision) {
             if (hasThetaCollision) {
                 // Shift the uniformTheta to middle way between current polyTheta
                 // and next uniform theta. The next uniform theta can wrap around
                 // to exactly PI safely here.
                 // Note that neither polyTheta nor uniformTheta can be FLT_MAX
                 // due to the hasThetaCollision is true.
-                uniformTheta = (polyTheta +  deltaAngle * (uniformThetaIndex + 1) - M_PI) / 2;
+                uniformTheta = (polyTheta +  M_PI - deltaAngle * (uniformThetaIndex + 1)) / 2;
 #if DEBUG_SHADOW
                 ALOGD("Shifted uniformTheta to %f", uniformTheta);
 #endif
             }
             rayThetas[i] = polyTheta;
             polyThetaIndex = (polyThetaIndex + 1) % vertexCount;
-            if (polyThetaIndex != minimalPolyThetaIndex) {
+            if (polyThetaIndex != maxPolyThetaIndex) {
                 polyTheta = polyThetas[polyThetaIndex];
             } else {
                 // out of poly points.
-                polyTheta = FLT_MAX;
+                polyTheta = - FLT_MAX;
             }
         } else {
             rayThetas[i] = uniformTheta;
             uniformThetaIndex++;
             if (uniformThetaIndex < uniformRayCount) {
-                uniformTheta = deltaAngle * uniformThetaIndex - M_PI;
+                uniformTheta = M_PI - deltaAngle * uniformThetaIndex;
             } else {
                 // out of uniform points.
-                uniformTheta = FLT_MAX;
+                uniformTheta = - FLT_MAX;
             }
         }
     }
@@ -232,8 +236,8 @@
 #endif
         // TODO: Fix the intersection precision problem and remvoe the delta added
         // here.
-        dir[i].x = sinf(rayThetas[i] + MINIMAL_DELTA_THETA);
-        dir[i].y = cosf(rayThetas[i] + MINIMAL_DELTA_THETA);
+        dir[i].x = cosf(rayThetas[i] + MINIMAL_DELTA_THETA);
+        dir[i].y = sinf(rayThetas[i] + MINIMAL_DELTA_THETA);
     }
 }
 
@@ -308,13 +312,12 @@
     Vector2 p1 = dir[preIndex] * rayDist[preIndex];
     Vector2 p2 = dir[postIndex] * rayDist[postIndex];
 
-    // Now the V (deltaX, deltaY) is the vector going CW around the poly.
+    // Now the rays are going CW around the poly.
     Vector2 delta = p2 - p1;
     if (delta.length() != 0) {
         delta.normalize();
-        // Calculate the normal , which is CCW 90 rotate to the V.
-        // 90 degrees CCW about z-axis: (x, y, z) -> (-y, x, z)
-        normal.x = -delta.y;
+        // Calculate the normal , which is CCW 90 rotate to the delta.
+        normal.x = - delta.y;
         normal.y = delta.x;
     }
 }
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index f37487f..958cd32 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -3198,6 +3198,10 @@
     const float casterRefinementThresholdSquared = 20.0f; // TODO: experiment with this value
     PathTessellator::approximatePathOutlineVertices(*casterPerimeter,
             casterRefinementThresholdSquared, casterVertices2d);
+    if (!ShadowTessellator::isClockwisePath(*casterPerimeter)) {
+        ShadowTessellator::reverseVertexArray(casterVertices2d.editArray(),
+                casterVertices2d.size());
+    }
 
     if (casterVertices2d.size() == 0) {
         // empty caster polygon computed from path
diff --git a/libs/hwui/ShadowTessellator.cpp b/libs/hwui/ShadowTessellator.cpp
index 4d0edfb..ee60a63 100644
--- a/libs/hwui/ShadowTessellator.cpp
+++ b/libs/hwui/ShadowTessellator.cpp
@@ -169,5 +169,67 @@
     return centroid;
 }
 
+/**
+ * Test whether the polygon is order in clockwise.
+ *
+ * @param polygon the polygon as a Vector2 array
+ * @param len the number of points of the polygon
+ */
+bool ShadowTessellator::isClockwise(const Vector2* polygon, int len) {
+    double sum = 0;
+    double p1x = polygon[len - 1].x;
+    double p1y = polygon[len - 1].y;
+    for (int i = 0; i < len; i++) {
+
+        double p2x = polygon[i].x;
+        double p2y = polygon[i].y;
+        sum += p1x * p2y - p2x * p1y;
+        p1x = p2x;
+        p1y = p2y;
+    }
+    return sum < 0;
+}
+
+bool ShadowTessellator::isClockwisePath(const SkPath& path) {
+    SkPath::Iter iter(path, false);
+    SkPoint pts[4];
+    SkPath::Verb v;
+
+    Vector<Vector2> arrayForDirection;
+    while (SkPath::kDone_Verb != (v = iter.next(pts))) {
+            switch (v) {
+            case SkPath::kMove_Verb:
+                arrayForDirection.add(Vector2(pts[0].x(), pts[0].y()));
+                break;
+            case SkPath::kLine_Verb:
+                arrayForDirection.add(Vector2(pts[1].x(), pts[1].y()));
+                break;
+            case SkPath::kQuad_Verb:
+                arrayForDirection.add(Vector2(pts[1].x(), pts[1].y()));
+                arrayForDirection.add(Vector2(pts[2].x(), pts[2].y()));
+                break;
+            case SkPath::kCubic_Verb:
+                arrayForDirection.add(Vector2(pts[1].x(), pts[1].y()));
+                arrayForDirection.add(Vector2(pts[2].x(), pts[2].y()));
+                arrayForDirection.add(Vector2(pts[3].x(), pts[3].y()));
+                break;
+            default:
+                break;
+            }
+    }
+
+    return isClockwise(arrayForDirection.array(), arrayForDirection.size());
+}
+
+void ShadowTessellator::reverseVertexArray(Vertex* polygon, int len) {
+    int n = len / 2;
+    for (int i = 0; i < n; i++) {
+        Vertex tmp = polygon[i];
+        int k = len - 1 - i;
+        polygon[i] = polygon[k];
+        polygon[k] = tmp;
+    }
+}
+
 }; // namespace uirenderer
 }; // namespace android
diff --git a/libs/hwui/ShadowTessellator.h b/libs/hwui/ShadowTessellator.h
index 05370dd..64e69bc 100644
--- a/libs/hwui/ShadowTessellator.h
+++ b/libs/hwui/ShadowTessellator.h
@@ -80,6 +80,27 @@
     static void generateShadowIndices(uint16_t*  shadowIndices);
 
     static Vector2 centroid2d(const Vector2* poly, int polyLength);
+
+    static bool isClockwise(const Vector2* polygon, int len);
+
+    /**
+     * Determine whether the path is clockwise, using the control points.
+     *
+     * TODO: Given the skia is using inverted Y coordinate, shadow system needs
+     * to convert to the same coordinate to avoid the extra reverse.
+     *
+     * @param path The path to be examined.
+     */
+    static bool isClockwisePath(const SkPath &path);
+
+    /**
+     * Reverse the vertex array.
+     *
+     * @param polygon The vertex array to be reversed.
+     * @param len The length of the vertex array.
+     */
+    static void reverseVertexArray(Vertex* polygon, int len);
+
 }; // ShadowTessellator
 
 }; // namespace uirenderer
diff --git a/libs/hwui/SpotShadow.cpp b/libs/hwui/SpotShadow.cpp
index 5fa0ba5..3ebe7b4 100644
--- a/libs/hwui/SpotShadow.cpp
+++ b/libs/hwui/SpotShadow.cpp
@@ -174,10 +174,10 @@
 int SpotShadow::intersection(const Vector2* poly1, int poly1Length,
         Vector2* poly2, int poly2Length) {
 #if DEBUG_SHADOW
-    if (!isClockwise(poly1, poly1Length)) {
+    if (!ShadowTessellator::isClockwise(poly1, poly1Length)) {
         ALOGW("Poly1 is not clockwise! Intersection is wrong!");
     }
-    if (!isClockwise(poly2, poly2Length)) {
+    if (!ShadowTessellator::isClockwise(poly2, poly2Length)) {
         ALOGW("Poly2 is not clockwise! Intersection is wrong!");
     }
 #endif
@@ -407,33 +407,12 @@
     if (polygon == 0  || len == 0) {
         return;
     }
-    if (!isClockwise(polygon, len)) {
+    if (!ShadowTessellator::isClockwise(polygon, len)) {
         reverse(polygon, len);
     }
 }
 
 /**
- * Test whether the polygon is order in clockwise.
- *
- * @param polygon the polygon as a Vector2 array
- * @param len the number of points of the polygon
- */
-bool SpotShadow::isClockwise(const Vector2* polygon, int len) {
-    double sum = 0;
-    double p1x = polygon[len - 1].x;
-    double p1y = polygon[len - 1].y;
-    for (int i = 0; i < len; i++) {
-
-        double p2x = polygon[i].x;
-        double p2y = polygon[i].y;
-        sum += p1x * p2y - p2x * p1y;
-        p1x = p2x;
-        p1y = p2y;
-    }
-    return sum < 0;
-}
-
-/**
  * Reverse the polygon
  *
  * @param polygon the polygon as a Vector2 array
diff --git a/libs/hwui/SpotShadow.h b/libs/hwui/SpotShadow.h
index 599d37e..fb3e6d5 100644
--- a/libs/hwui/SpotShadow.h
+++ b/libs/hwui/SpotShadow.h
@@ -56,7 +56,6 @@
 
     static bool testPointInsidePolygon(const Vector2 testPoint, const Vector2* poly, int len);
     static void makeClockwise(Vector2* polygon, int len);
-    static bool isClockwise(const Vector2* polygon, int len);
     static void reverse(Vector2* polygon, int len);
     static inline bool lineIntersection(double x1, double y1, double x2, double y2,
             double x3, double y3, double x4, double y4, Vector2& ret);