diff --git a/libs/hwui/Android.mk b/libs/hwui/Android.mk
index 4f0d15a..0fd01d4 100644
--- a/libs/hwui/Android.mk
+++ b/libs/hwui/Android.mk
@@ -42,6 +42,7 @@
 		SkiaColorFilter.cpp \
 		SkiaShader.cpp \
 		Snapshot.cpp \
+		SpotShadow.cpp \
 		StatefulBaseRenderer.cpp \
 		Stencil.cpp \
 		Texture.cpp \
diff --git a/libs/hwui/OpenGLRenderer.cpp b/libs/hwui/OpenGLRenderer.cpp
index 22cd2d4..4f6da2b 100644
--- a/libs/hwui/OpenGLRenderer.cpp
+++ b/libs/hwui/OpenGLRenderer.cpp
@@ -3194,10 +3194,18 @@
     paint.setColor(mCaches.propertyShadowStrength << 24);
     paint.setAntiAlias(true); // want to use AlphaVertex
 
-    VertexBuffer shadowVertexBuffer;
+    VertexBuffer ambientShadowVertexBuffer;
     ShadowTessellator::tessellateAmbientShadow(width, height, casterTransform,
-            shadowVertexBuffer);
-    return drawVertexBuffer(shadowVertexBuffer, &paint);
+            ambientShadowVertexBuffer);
+    drawVertexBuffer(ambientShadowVertexBuffer, &paint);
+
+    VertexBuffer spotShadowVertexBuffer;
+    ShadowTessellator::tessellateSpotShadow(width, height,
+            getWidth(), getHeight(), casterTransform,
+            spotShadowVertexBuffer);
+    drawVertexBuffer(spotShadowVertexBuffer, &paint);
+
+    return DrawGlInfo::kStatusDrew;
 }
 
 status_t OpenGLRenderer::drawColorRects(const float* rects, int count, int color,
diff --git a/libs/hwui/ShadowTessellator.cpp b/libs/hwui/ShadowTessellator.cpp
index 49a3d2c..6385ef7 100644
--- a/libs/hwui/ShadowTessellator.cpp
+++ b/libs/hwui/ShadowTessellator.cpp
@@ -21,14 +21,30 @@
 
 #include "AmbientShadow.h"
 #include "ShadowTessellator.h"
+#include "SpotShadow.h"
 
 namespace android {
 namespace uirenderer {
 
+template<typename T>
+static inline T max(T a, T b) {
+    return a > b ? a : b;
+}
+
 // TODO: Support path as the input of the polygon instead of the rect's width
-// and height.
-void ShadowTessellator::tessellateAmbientShadow(float width, float height,
-        const mat4& casterTransform, VertexBuffer& shadowVertexBuffer) {
+// and height. And the z values need to be computed according to the
+// transformation for each vertex.
+/**
+ * Generate the polygon for the caster.
+ *
+ * @param width the width of the caster
+ * @param height the height of the caster
+ * @param casterTransform transformation info of the caster
+ * @param polygon return the caster's polygon
+ *
+ */
+void ShadowTessellator::generateCasterPolygon(float width, float height,
+        const mat4& casterTransform, int vertexCount, Vector3* polygon) {
 
     Vector3 pivot(width / 2, height / 2, 0.0f);
     casterTransform.mapPoint3d(pivot);
@@ -39,10 +55,6 @@
             pivot.x + width * zScaleFactor, pivot.y + height * zScaleFactor);
 
     // Generate the caster's polygon from the rect.
-    // TODO: support arbitrary polygon, and the z value need to be computed
-    // according to the transformation for each vertex.
-    const int vertexCount = 4;
-    Vector3 polygon[vertexCount];
     polygon[0].x = blockRect.left;
     polygon[0].y = blockRect.top;
     polygon[0].z = pivot.z;
@@ -55,19 +67,51 @@
     polygon[3].x = blockRect.left;
     polygon[3].y = blockRect.bottom;
     polygon[3].z = pivot.z;
+}
+
+void ShadowTessellator::tessellateAmbientShadow(float width, float height,
+        const mat4& casterTransform, VertexBuffer& shadowVertexBuffer) {
+
+    const int vertexCount = 4;
+    Vector3 polygon[vertexCount];
+    generateCasterPolygon(width, height, casterTransform, vertexCount, polygon);
 
     // A bunch of parameters to tweak the shadow.
     // TODO: Allow some of these changable by debug settings or APIs.
-    const int rays = 120;
+    const int rays = 128;
     const int layers = 2;
     const float strength = 0.5;
-    const float heightFactor = 120;
-    const float geomFactor = 60;
+    const float heightFactor = 128;
+    const float geomFactor = 64;
 
     AmbientShadow::createAmbientShadow(polygon, vertexCount, rays, layers, strength,
             heightFactor, geomFactor, shadowVertexBuffer);
 
 }
 
+void ShadowTessellator::tessellateSpotShadow(float width, float height,
+        int screenWidth, int screenHeight,
+        const mat4& casterTransform, VertexBuffer& shadowVertexBuffer) {
+    const int vertexCount = 4;
+    Vector3 polygon[vertexCount];
+    generateCasterPolygon(width, height, casterTransform, vertexCount, polygon);
+
+    // A bunch of parameters to tweak the shadow.
+    // TODO: Allow some of these changable by debug settings or APIs.
+    const int rays = 256;
+    const int layers = 2;
+    const float strength = 0.5;
+    int maximal = max(screenWidth, screenHeight);
+    Vector3 lightCenter(screenWidth / 2, 0, maximal);
+#if DEBUG_SHADOW
+    ALOGD("light center %f %f %f", lightCenter.x, lightCenter.y, lightCenter.z);
+#endif
+    const float lightSize = maximal / 8;
+    const int lightVertexCount = 16;
+
+    SpotShadow::createSpotShadow(polygon, vertexCount, lightCenter, lightSize,
+            lightVertexCount, rays, layers, strength, shadowVertexBuffer);
+
+}
 }; // namespace uirenderer
 }; // namespace android
diff --git a/libs/hwui/ShadowTessellator.h b/libs/hwui/ShadowTessellator.h
index 05cb00c..fff00b1 100644
--- a/libs/hwui/ShadowTessellator.h
+++ b/libs/hwui/ShadowTessellator.h
@@ -29,6 +29,14 @@
     static void tessellateAmbientShadow(float width, float height,
             const mat4& casterTransform, VertexBuffer& shadowVertexBuffer);
 
+    static void tessellateSpotShadow(float width, float height,
+            int screenWidth, int screenHeight,
+            const mat4& casterTransform, VertexBuffer& shadowVertexBuffer);
+
+private:
+    static void generateCasterPolygon(float width, float height,
+            const mat4& casterTransform, int vertexCount, Vector3* polygon);
+
 }; // ShadowTessellator
 
 }; // namespace uirenderer
diff --git a/libs/hwui/SpotShadow.cpp b/libs/hwui/SpotShadow.cpp
new file mode 100644
index 0000000..5d489a7
--- /dev/null
+++ b/libs/hwui/SpotShadow.cpp
@@ -0,0 +1,839 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "OpenGLRenderer"
+
+#define SHADOW_SHRINK_SCALE 0.1f
+
+#include <math.h>
+#include <utils/Log.h>
+
+#include "SpotShadow.h"
+#include "Vertex.h"
+
+namespace android {
+namespace uirenderer {
+
+/**
+ * Calculate the intersection of a ray with a polygon.
+ * It assumes the ray originates inside the polygon.
+ *
+ * @param poly The polygon, which is represented in a Vector2 array.
+ * @param polyLength The length of caster's polygon in terms of number of
+ *                   vertices.
+ * @param point the start of the ray
+ * @param dx the x vector of the ray
+ * @param dy the y vector of the ray
+ * @return the distance along the ray if it intersects with the polygon FP_NAN if otherwise
+ */
+float SpotShadow::rayIntersectPoly(const Vector2* poly, int polyLength,
+        const Vector2& point, float dx, float dy) {
+    double px = point.x;
+    double py = point.y;
+    int p1 = polyLength - 1;
+    for (int p2 = 0; p2 < polyLength; p2++) {
+        double p1x = poly[p1].x;
+        double p1y = poly[p1].y;
+        double p2x = poly[p2].x;
+        double p2y = poly[p2].y;
+        // The math below is derived from solving this formula, basically the
+        // intersection point should stay on both the ray and the edge of (p1, p2).
+        // solve([p1x+t*(p2x-p1x)=dx*t2+px,p1y+t*(p2y-p1y)=dy*t2+py],[t,t2]);
+        double div = (dx * (p1y - p2y) + dy * p2x - dy * p1x);
+        if (div != 0) {
+            double t = (dx * (p1y - py) + dy * px - dy * p1x) / (div);
+            if (t >= 0 && t <= 1) {
+                double t2 = (p1x * (py - p2y) + p2x * (p1y - py) +
+                        px * (p2y - p1y)) / div;
+                if (t2 > 0) {
+                    return (float)t2;
+                }
+            }
+        }
+        p1 = p2;
+    }
+    return FP_NAN;
+}
+
+/**
+ * Calculate the centroid of a 2d polygon.
+ *
+ * @param poly The polygon, which is represented in a Vector2 array.
+ * @param polyLength The length of the polygon in terms of number of vertices.
+ * @return the centroid of the polygon.
+ */
+Vector2 SpotShadow::centroid2d(const Vector2* poly, int polyLength) {
+    double sumx = 0;
+    double sumy = 0;
+    int p1 = polyLength - 1;
+    double area = 0;
+    for (int p2 = 0; p2 < polyLength; p2++) {
+        double x1 = poly[p1].x;
+        double y1 = poly[p1].y;
+        double x2 = poly[p2].x;
+        double y2 = poly[p2].y;
+        double a = (x1 * y2 - x2 * y1);
+        sumx += (x1 + x2) * a;
+        sumy += (y1 + y2) * a;
+        area += a;
+        p1 = p2;
+    }
+
+    double centroidx = sumx / (3 * area);
+    double centroidy = sumy / (3 * area);
+    return Vector2((float)centroidx, (float)centroidy);
+}
+
+/**
+ * Sort points by their X coordinates
+ *
+ * @param points the points as a Vector2 array.
+ * @param pointsLength the number of vertices of the polygon.
+ */
+void SpotShadow::xsort(Vector2* points, int pointsLength) {
+    quicksortX(points, 0, pointsLength - 1);
+}
+
+/**
+ * compute the convex hull of a collection of Points
+ *
+ * @param points the points as a Vector2 array.
+ * @param pointsLength the number of vertices of the polygon.
+ * @param retPoly pre allocated array of floats to put the vertices
+ * @return the number of points in the polygon 0 if no intersection
+ */
+int SpotShadow::hull(Vector2* points, int pointsLength, Vector2* retPoly) {
+    xsort(points, pointsLength);
+    int n = pointsLength;
+    Vector2 lUpper[n];
+    lUpper[0] = points[0];
+    lUpper[1] = points[1];
+
+    int lUpperSize = 2;
+
+    for (int i = 2; i < n; i++) {
+        lUpper[lUpperSize] = points[i];
+        lUpperSize++;
+
+        while (lUpperSize > 2 && !rightTurn(
+                (double)lUpper[lUpperSize - 3].x, (double)lUpper[lUpperSize - 3].y,
+                (double)lUpper[lUpperSize - 2].x, (double)lUpper[lUpperSize - 2].y,
+                (double)lUpper[lUpperSize - 1].x, (double)lUpper[lUpperSize - 1].y)) {
+            // Remove the middle point of the three last
+            lUpper[lUpperSize - 2].x = lUpper[lUpperSize - 1].x;
+            lUpper[lUpperSize - 2].y = lUpper[lUpperSize - 1].y;
+            lUpperSize--;
+        }
+    }
+
+    Vector2 lLower[n];
+    lLower[0] = points[n - 1];
+    lLower[1] = points[n - 2];
+
+    int lLowerSize = 2;
+
+    for (int i = n - 3; i >= 0; i--) {
+        lLower[lLowerSize] = points[i];
+        lLowerSize++;
+
+        while (lLowerSize > 2 && !rightTurn(
+                (double)lLower[lLowerSize - 3].x, (double)lLower[lLowerSize - 3].y,
+                (double)lLower[lLowerSize - 2].x, (double)lLower[lLowerSize - 2].y,
+                (double)lLower[lLowerSize - 1].x, (double)lLower[lLowerSize - 1].y)) {
+            // Remove the middle point of the three last
+            lLower[lLowerSize - 2] = lLower[lLowerSize - 1];
+            lLowerSize--;
+        }
+    }
+    int count = 0;
+
+    for (int i = 0; i < lUpperSize; i++) {
+        retPoly[count] = lUpper[i];
+        count++;
+    }
+
+    for (int i = 1; i < lLowerSize - 1; i++) {
+        retPoly[count] = lLower[i];
+        count++;
+    }
+    // TODO: Add test harness which verify that all the points are inside the hull.
+    return count;
+}
+
+/**
+ * Test whether the 3 points form a right hand turn
+ *
+ * @param ax the x coordinate of point a
+ * @param ay the y coordinate of point a
+ * @param bx the x coordinate of point b
+ * @param by the y coordinate of point b
+ * @param cx the x coordinate of point c
+ * @param cy the y coordinate of point c
+ * @return true if a right hand turn
+ */
+bool SpotShadow::rightTurn(double ax, double ay, double bx, double by,
+        double cx, double cy) {
+    return (bx - ax) * (cy - ay) - (by - ay) * (cx - ax) > EPSILON;
+}
+
+/**
+ * Calculates the intersection of poly1 with poly2 and put in poly2.
+ *
+ *
+ * @param poly1 The 1st polygon, as a Vector2 array.
+ * @param poly1Length The number of vertices of 1st polygon.
+ * @param poly2 The 2nd and output polygon, as a Vector2 array.
+ * @param poly2Length The number of vertices of 2nd polygon.
+ * @return number of vertices in output polygon as poly2.
+ */
+int SpotShadow::intersection(Vector2* poly1, int poly1Length,
+        Vector2* poly2, int poly2Length) {
+    makeClockwise(poly1, poly1Length);
+    makeClockwise(poly2, poly2Length);
+    Vector2 poly[poly1Length * poly2Length + 2];
+    int count = 0;
+    int pcount = 0;
+
+    // If one vertex from one polygon sits inside another polygon, add it and
+    // count them.
+    for (int i = 0; i < poly1Length; i++) {
+        if (testPointInsidePolygon(poly1[i], poly2, poly2Length)) {
+            poly[count] = poly1[i];
+            count++;
+            pcount++;
+
+        }
+    }
+
+    int insidePoly2 = pcount;
+    for (int i = 0; i < poly2Length; i++) {
+        if (testPointInsidePolygon(poly2[i], poly1, poly1Length)) {
+            poly[count] = poly2[i];
+            count++;
+        }
+    }
+
+    int insidePoly1 = count - insidePoly2;
+    // If all vertices from poly1 are inside poly2, then just return poly1.
+    if (insidePoly2 == poly1Length) {
+        memcpy(poly2, poly1, poly1Length * sizeof(Vector2));
+        return poly1Length;
+    }
+
+    // If all vertices from poly2 are inside poly1, then just return poly2.
+    if (insidePoly1 == poly2Length) {
+        return poly2Length;
+    }
+
+    // Since neither polygon fully contain the other one, we need to add all the
+    // intersection points.
+    Vector2 intersection;
+    for (int i = 0; i < poly2Length; i++) {
+        for (int j = 0; j < poly1Length; j++) {
+            int poly2LineStart = i;
+            int poly2LineEnd = ((i + 1) % poly2Length);
+            int poly1LineStart = j;
+            int poly1LineEnd = ((j + 1) % poly1Length);
+            bool found = lineIntersection(
+                    poly2[poly2LineStart].x, poly2[poly2LineStart].y,
+                    poly2[poly2LineEnd].x, poly2[poly2LineEnd].y,
+                    poly1[poly1LineStart].x, poly1[poly1LineStart].y,
+                    poly1[poly1LineEnd].x, poly1[poly1LineEnd].y,
+                    intersection);
+            if (found) {
+                poly[count].x = intersection.x;
+                poly[count].y = intersection.y;
+                count++;
+            } else {
+                Vector2 delta = poly2[i] - poly1[j];
+                if (delta.lengthSquared() < 0.01) {
+                    poly[count] = poly2[i];
+                    count++;
+                }
+            }
+        }
+    }
+
+    if (count == 0) {
+        return 0;
+    }
+
+    // Sort the result polygon around the center.
+    Vector2 center(0.0f, 0.0f);
+    for (int i = 0; i < count; i++) {
+        center += poly[i];
+    }
+    center /= count;
+    sort(poly, count, center);
+
+    // TODO: Verify the intersection works correctly, like any random point
+    // inside both poly1 and poly2 should be inside the intersection, and the
+    // result intersection polygon is convex.
+
+    // Merge the vertices if they are too close.
+    poly2[0] = poly[0];
+    int resultLength = 1;
+    for (int i = 1; i < count; i++) {
+        Vector2 delta = poly[i] - poly[i - 1];
+        if (delta.lengthSquared() >= 0.01) {
+            poly2[resultLength] = poly[i];
+            resultLength++;
+        }
+    }
+
+    return resultLength;
+}
+
+/**
+ * Sort points about a center point
+ *
+ * @param poly The in and out polyogon as a Vector2 array.
+ * @param polyLength The number of vertices of the polygon.
+ * @param center the center ctr[0] = x , ctr[1] = y to sort around.
+ */
+void SpotShadow::sort(Vector2* poly, int polyLength, const Vector2& center) {
+    quicksortCirc(poly, 0, polyLength - 1, center);
+}
+
+/**
+ * Calculate the angle between and x and a y coordinate
+ */
+float SpotShadow::angle(const Vector2& point, const Vector2& center) {
+    return -(float)atan2(point.x - center.x, point.y - center.y);
+}
+
+/**
+ * Swap points pointed to by i and j
+ */
+void SpotShadow::swap(Vector2* points, int i, int j) {
+    Vector2 temp = points[i];
+    points[i] = points[j];
+    points[j] = temp;
+}
+
+/**
+ * quick sort implementation about the center.
+ */
+void SpotShadow::quicksortCirc(Vector2* points, int low, int high,
+        const Vector2& center) {
+    int i = low, j = high;
+    int p = low + (high - low) / 2;
+    float pivot = angle(points[p], center);
+    while (i <= j) {
+        while (angle(points[i], center) < pivot) {
+            i++;
+        }
+        while (angle(points[j], center) > pivot) {
+            j--;
+        }
+
+        if (i <= j) {
+            swap(points, i, j);
+            i++;
+            j--;
+        }
+    }
+    if (low < j) quicksortCirc(points, low, j, center);
+    if (i < high) quicksortCirc(points, i, high, center);
+}
+
+/**
+ * Sort points by x axis
+ *
+ * @param points points to sort
+ * @param low start index
+ * @param high end index
+ */
+void SpotShadow::quicksortX(Vector2* points, int low, int high) {
+    int i = low, j = high;
+    int p = low + (high - low) / 2;
+    float pivot = points[p].x;
+    while (i <= j) {
+        while (points[i].x < pivot) {
+            i++;
+        }
+        while (points[j].x > pivot) {
+            j--;
+        }
+
+        if (i <= j) {
+            swap(points, i, j);
+            i++;
+            j--;
+        }
+    }
+    if (low < j) quicksortX(points, low, j);
+    if (i < high) quicksortX(points, i, high);
+}
+
+/**
+ * Test whether a point is inside the polygon.
+ *
+ * @param testPoint the point to test
+ * @param poly the polygon
+ * @return true if the testPoint is inside the poly.
+ */
+bool SpotShadow::testPointInsidePolygon(const Vector2 testPoint,
+        const Vector2* poly, int len) {
+    bool c = false;
+    double testx = testPoint.x;
+    double testy = testPoint.y;
+    for (int i = 0, j = len - 1; i < len; j = i++) {
+        double startX = poly[j].x;
+        double startY = poly[j].y;
+        double endX = poly[i].x;
+        double endY = poly[i].y;
+
+        if (((endY > testy) != (startY > testy)) &&
+            (testx < (startX - endX) * (testy - endY)
+             / (startY - endY) + endX)) {
+            c = !c;
+        }
+    }
+    return c;
+}
+
+/**
+ * Make the polygon turn clockwise.
+ *
+ * @param polygon the polygon as a Vector2 array.
+ * @param len the number of points of the polygon
+ */
+void SpotShadow::makeClockwise(Vector2* polygon, int len) {
+    if (polygon == 0  || len == 0) {
+        return;
+    }
+    if (!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(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
+ * @param len the number of points of the polygon
+ */
+void SpotShadow::reverse(Vector2* polygon, int len) {
+    int n = len / 2;
+    for (int i = 0; i < n; i++) {
+        Vector2 tmp = polygon[i];
+        int k = len - 1 - i;
+        polygon[i] = polygon[k];
+        polygon[k] = tmp;
+    }
+}
+
+/**
+ * Intersects two lines in parametric form. This function is called in a tight
+ * loop, and we need double precision to get things right.
+ *
+ * @param x1 the x coordinate point 1 of line 1
+ * @param y1 the y coordinate point 1 of line 1
+ * @param x2 the x coordinate point 2 of line 1
+ * @param y2 the y coordinate point 2 of line 1
+ * @param x3 the x coordinate point 1 of line 2
+ * @param y3 the y coordinate point 1 of line 2
+ * @param x4 the x coordinate point 2 of line 2
+ * @param y4 the y coordinate point 2 of line 2
+ * @param ret the x,y location of the intersection
+ * @return true if it found an intersection
+ */
+inline bool SpotShadow::lineIntersection(double x1, double y1, double x2, double y2,
+        double x3, double y3, double x4, double y4, Vector2& ret) {
+    double d = (x1 - x2) * (y3 - y4) - (y1 - y2) * (x3 - x4);
+    if (d == 0.0) return false;
+
+    double dx = (x1 * y2 - y1 * x2);
+    double dy = (x3 * y4 - y3 * x4);
+    double x = (dx * (x3 - x4) - (x1 - x2) * dy) / d;
+    double y = (dx * (y3 - y4) - (y1 - y2) * dy) / d;
+
+    // The intersection should be in the middle of the point 1 and point 2,
+    // likewise point 3 and point 4.
+    if (((x - x1) * (x - x2) > EPSILON)
+        || ((x - x3) * (x - x4) > EPSILON)
+        || ((y - y1) * (y - y2) > EPSILON)
+        || ((y - y3) * (y - y4) > EPSILON)) {
+        // Not interesected
+        return false;
+    }
+    ret.x = x;
+    ret.y = y;
+    return true;
+
+}
+
+/**
+ * Compute a horizontal circular polygon about point (x , y , height) of radius
+ * (size)
+ *
+ * @param points number of the points of the output polygon.
+ * @param lightCenter the center of the light.
+ * @param size the light size.
+ * @param ret result polygon.
+ */
+void SpotShadow::computeLightPolygon(int points, const Vector3& lightCenter,
+        float size, Vector3* ret) {
+    // TODO: Caching all the sin / cos values and store them in a look up table.
+    for (int i = 0; i < points; i++) {
+        double angle = 2 * i * M_PI / points;
+        ret[i].x = sinf(angle) * size + lightCenter.x;
+        ret[i].y = cosf(angle) * size + lightCenter.y;
+        ret[i].z = lightCenter.z;
+    }
+}
+
+/**
+* Generate the shadow from a spot light.
+*
+* @param poly x,y,z vertexes of a convex polygon that occludes the light source
+* @param polyLength number of vertexes of the occluding polygon
+* @param lightCenter the center of the light
+* @param lightSize the radius of the light source
+* @param lightVertexCount the vertex counter for the light polygon
+* @param rays the number of vertexes to create along the edges of the shadow
+* @param layers the number of layers of triangles strips to create
+* @param strength the "darkness" of the shadow
+* @param shadowTriangleStrip return an (x,y,alpha) triangle strip representing the shadow. Return
+*                            empty strip if error.
+*
+*/
+void SpotShadow::createSpotShadow(const Vector3* poly, int polyLength,
+        const Vector3& lightCenter, float lightSize, int lightVertexCount,
+        int rays, int layers, float strength, VertexBuffer& retStrips) {
+    Vector3 light[lightVertexCount * 3];
+    computeLightPolygon(lightVertexCount, lightCenter, lightSize, light);
+    computeSpotShadow(light, lightVertexCount, lightCenter,
+            poly, polyLength, rays, layers, strength, retStrips);
+}
+
+/**
+ * Generate the shadow spot light of shape lightPoly and a object poly
+ *
+ * @param lightPoly x,y,z vertex of a convex polygon that is the light source
+ * @param lightPolyLength number of vertexes of the light source polygon
+ * @param poly x,y,z vertexes of a convex polygon that occludes the light source
+ * @param polyLength number of vertexes of the occluding polygon
+ * @param rays the number of vertexes to create along the edges of the shadow
+ * @param layers the number of layers of triangles strips to create
+ * @param strength the "darkness" of the shadow
+ * @param shadowTriangleStrip return an (x,y,alpha) triangle strip representing the shadow. Return
+ *                            empty strip if error.
+ */
+void SpotShadow::computeSpotShadow(const Vector3* lightPoly, int lightPolyLength,
+        const Vector3& lightCenter, const Vector3* poly, int polyLength,
+        int rays, int layers, float strength, VertexBuffer& shadowTriangleStrip) {
+    // Point clouds for all the shadowed vertices
+    Vector2 shadowRegion[lightPolyLength * polyLength];
+    // Shadow polygon from one point light.
+    Vector2 outline[polyLength];
+    Vector2 umbraMem[polyLength * lightPolyLength];
+    Vector2* umbra = umbraMem;
+
+    int umbraLength = 0;
+
+    // Validate input, receiver is always at z = 0 plane.
+    bool inputPolyPositionValid = true;
+    for (int i = 0; i < polyLength; i++) {
+        if (poly[i].z <= 0.00001) {
+            inputPolyPositionValid = false;
+            ALOGE("polygon below the surface");
+            break;
+        }
+        if (poly[i].z >= lightPoly[0].z) {
+            inputPolyPositionValid = false;
+            ALOGE("polygon above the light");
+            break;
+        }
+    }
+
+    // If the caster's position is invalid, don't draw anything.
+    if (!inputPolyPositionValid) {
+        return;
+    }
+
+    // Calculate the umbra polygon based on intersections of all outlines
+    int k = 0;
+    for (int j = 0; j < lightPolyLength; j++) {
+        int m = 0;
+        for (int i = 0; i < polyLength; i++) {
+            float t = lightPoly[j].z - poly[i].z;
+            if (t == 0) {
+                return;
+            }
+            t = lightPoly[j].z / t;
+            float x = lightPoly[j].x - t * (lightPoly[j].x - poly[i].x);
+            float y = lightPoly[j].y - t * (lightPoly[j].y - poly[i].y);
+
+            Vector2 newPoint = Vector2(x, y);
+            shadowRegion[k] = newPoint;
+            outline[m] = newPoint;
+
+            k++;
+            m++;
+        }
+
+        // For the first light polygon's vertex, use the outline as the umbra.
+        // Later on, use the intersection of the outline and existing umbra.
+        if (umbraLength == 0) {
+            for (int i = 0; i < polyLength; i++) {
+                umbra[i] = outline[i];
+            }
+            umbraLength = polyLength;
+        } else {
+            int col = ((j * 255) / lightPolyLength);
+            umbraLength = intersection(outline, polyLength, umbra, umbraLength);
+            if (umbraLength == 0) {
+                break;
+            }
+        }
+    }
+
+    // Generate the penumbra area using the hull of all shadow regions.
+    int shadowRegionLength = k;
+    Vector2 penumbra[k];
+    int penumbraLength = hull(shadowRegion, shadowRegionLength, penumbra);
+
+    // no real umbra make a fake one
+    if (umbraLength < 3) {
+        // The shadow from the centroid of the light polygon.
+        Vector2 centShadow[polyLength];
+
+        for (int i = 0; i < polyLength; i++) {
+            float t = lightCenter.z - poly[i].z;
+            if (t == 0) {
+                return;
+            }
+            t = lightCenter.z / t;
+            float x = lightCenter.x - t * (lightCenter.x - poly[i].x);
+            float y = lightCenter.y - t * (lightCenter.y - poly[i].y);
+
+            centShadow[i].x = x;
+            centShadow[i].y = y;
+        }
+
+        // Shrink the centroid's shadow by 10%.
+        // TODO: Study the magic number of 10%.
+        Vector2 shadowCentroid = centroid2d(centShadow, polyLength);
+        for (int i = 0; i < polyLength; i++) {
+            centShadow[i] = shadowCentroid * (1.0f - SHADOW_SHRINK_SCALE) +
+                    centShadow[i] * SHADOW_SHRINK_SCALE;
+        }
+#if DEBUG_SHADOW
+        ALOGD("No real umbra make a fake one, centroid2d =  %f , %f",
+                shadowCentroid.x, shadowCentroid.y);
+#endif
+        // Set the fake umbra, whose size is the same as the original polygon.
+        umbra = centShadow;
+        umbraLength = polyLength;
+    }
+
+    generateTriangleStrip(penumbra, penumbraLength, umbra, umbraLength,
+            rays, layers, strength, shadowTriangleStrip);
+}
+
+/**
+ * Generate a triangle strip given two convex polygons
+ *
+ * @param penumbra The outer polygon x,y vertexes
+ * @param penumbraLength The number of vertexes in the outer polygon
+ * @param umbra The inner outer polygon x,y vertexes
+ * @param umbraLength The number of vertexes in the inner polygon
+ * @param rays The number of points along the polygons to create
+ * @param layers The number of layers of triangle strips between the umbra and penumbra
+ * @param strength The max alpha of the umbra
+ * @param shadowTriangleStrip return an (x,y,alpha) triangle strip representing the shadow. Return
+ *                            empty strip if error.
+**/
+void SpotShadow::generateTriangleStrip(const Vector2* penumbra, int penumbraLength,
+        const Vector2* umbra, int umbraLength, int rays, int layers,
+        float strength, VertexBuffer& shadowTriangleStrip) {
+
+    int rings = layers + 1;
+    int size = rays * rings;
+
+    float step = M_PI * 2 / rays;
+    // Centroid of the umbra.
+    Vector2 centroid = centroid2d(umbra, umbraLength);
+#if DEBUG_SHADOW
+    ALOGD("centroid2d =  %f , %f", centroid.x, centroid.y);
+#endif
+    // Intersection to the penumbra.
+    float penumbraDistPerRay[rays];
+    // Intersection to the umbra.
+    float umbraDistPerRay[rays];
+
+    for (int i = 0; i < rays; i++) {
+        // TODO: Setup a lookup table for all the sin/cos.
+        float dx = sinf(step * i);
+        float dy = cosf(step * i);
+        umbraDistPerRay[i] = rayIntersectPoly(umbra, umbraLength, centroid,
+                dx, dy);
+        if (isnan(umbraDistPerRay[i])) {
+            ALOGE("rayIntersectPoly returns NAN");
+            return;
+        }
+        penumbraDistPerRay[i] = rayIntersectPoly(penumbra, penumbraLength,
+                centroid, dx, dy);
+        if (isnan(umbraDistPerRay[i])) {
+            ALOGE("rayIntersectPoly returns NAN");
+            return;
+        }
+    }
+
+    int stripSize = getStripSize(rays, layers);
+    AlphaVertex* shadowVertices = shadowTriangleStrip.alloc<AlphaVertex>(stripSize);
+    int currentIndex = 0;
+    // Calculate the vertex values in the penumbra area.
+    for (int r = 0; r < layers; r++) {
+        int firstInEachLayer = currentIndex;
+        for (int i = 0; i < rays; i++) {
+            float dx = sinf(step * i);
+            float dy = cosf(step * i);
+
+            for (int j = r; j < (r + 2); j++) {
+                float layerRatio = j / (float)(rings - 1);
+                float deltaDist = layerRatio * (umbraDistPerRay[i] - penumbraDistPerRay[i]);
+                float currentDist = penumbraDistPerRay[i] + deltaDist;
+                float op = calculateOpacity(layerRatio, deltaDist);
+                AlphaVertex::set(&shadowVertices[currentIndex],
+                        dx * currentDist + centroid.x,
+                        dy * currentDist + centroid.y,
+                        layerRatio * op * strength);
+                currentIndex++;
+            }
+        }
+
+        // Duplicate the vertices from one layer to another one to make triangle
+        // strip.
+        shadowVertices[currentIndex++] = shadowVertices[firstInEachLayer];
+        firstInEachLayer++;
+        shadowVertices[currentIndex++] = shadowVertices[firstInEachLayer];
+    }
+
+    int lastInPenumbra = currentIndex - 1;
+    shadowVertices[currentIndex++] = shadowVertices[lastInPenumbra];
+
+    // Preallocate the vertices (index as [firstInUmbra - 1]) for jumping from
+    // the penumbra to umbra.
+    currentIndex++;
+    int firstInUmbra = currentIndex;
+
+    // traverse the umbra area in a zig zag pattern for strips.
+    for (int k = 0; k < rays; k++) {
+        int i = k / 2;
+        if ((k & 1) == 1) {
+            i = rays - i - 1;
+        }
+        float dx = sinf(step * i);
+        float dy = cosf(step * i);
+
+        float ratio = 1.0;
+        float deltaDist = ratio * (umbraDistPerRay[i] - penumbraDistPerRay[i]);
+        float currentDist = penumbraDistPerRay[i] + deltaDist;
+        float op = calculateOpacity(ratio, deltaDist);
+        AlphaVertex::set(&shadowVertices[currentIndex],
+                dx * currentDist + centroid.x, dy * currentDist + centroid.y,
+                ratio * op * strength);
+        currentIndex++;
+
+    }
+
+    // Back fill the one vertex for jumping from penumbra to umbra.
+    shadowVertices[firstInUmbra - 1] = shadowVertices[firstInUmbra];
+
+#if DEBUG_SHADOW
+    for (int i = 0; i < currentIndex; i++) {
+        ALOGD("shadow value: i %d, (x:%f, y:%f, a:%f)", i, shadowVertices[i].x,
+                shadowVertices[i].y, shadowVertices[i].alpha);
+    }
+#endif
+}
+
+/**
+ * This is only for experimental purpose.
+ * After intersections are calculated, we could smooth the polygon if needed.
+ * So far, we don't think it is more appealing yet.
+ *
+ * @param level The level of smoothness.
+ * @param rays The total number of rays.
+ * @param rayDist (In and Out) The distance for each ray.
+ *
+ */
+void SpotShadow::smoothPolygon(int level, int rays, float* rayDist) {
+    for (int k = 0; k < level; k++) {
+        for (int i = 0; i < rays; i++) {
+            float p1 = rayDist[(rays - 1 + i) % rays];
+            float p2 = rayDist[i];
+            float p3 = rayDist[(i + 1) % rays];
+            rayDist[i] = (p1 + p2 * 2 + p3) / 4;
+        }
+    }
+}
+
+/**
+ * Calculate the opacity according to the distance and falloff ratio.
+ *
+ * @param distRatio The distance ratio of current sample between umbra and
+ *                  penumbra area.
+ * @param deltaDist The distance between current sample to the penumbra area.
+ * @return The opacity according to the distance between umbra and penumbra.
+ */
+float SpotShadow::calculateOpacity(float distRatio, float deltaDist) {
+    // TODO: Experiment on the opacity calculation.
+    float falloffRatio = 1 + deltaDist * deltaDist;
+    return (distRatio + 1 - 1 / falloffRatio) / 2;
+}
+
+/**
+ * Calculate the number of vertex we will create given a number of rays and layers
+ *
+ * @param rays number of points around the polygons you want
+ * @param layers number of layers of triangle strips you need
+ * @return number of vertex (multiply by 3 for number of floats)
+ */
+int SpotShadow::getStripSize(int rays, int layers) {
+    return  (2 + rays + ((layers) * 2 * (rays + 1)));
+}
+
+}; // namespace uirenderer
+}; // namespace android
+
+
+
+
diff --git a/libs/hwui/SpotShadow.h b/libs/hwui/SpotShadow.h
new file mode 100644
index 0000000..d8db43bf
--- /dev/null
+++ b/libs/hwui/SpotShadow.h
@@ -0,0 +1,77 @@
+/*
+ * Copyright (C) 2014 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef ANDROID_HWUI_SPOT_SHADOW_H
+#define ANDROID_HWUI_SPOT_SHADOW_H
+
+#include "Debug.h"
+#include "Vector.h"
+#include "VertexBuffer.h"
+
+namespace android {
+namespace uirenderer {
+
+class SpotShadow {
+public:
+    static void createSpotShadow(const Vector3* poly, int polyLength,
+            const Vector3& lightCenter, float lightSize, int lightVertexCount,
+            int rays, int layers, float strength, VertexBuffer& retStrips);
+
+private:
+    static void computeSpotShadow(const Vector3* lightPoly, int lightPolyLength,
+            const Vector3& lightCenter, const Vector3* poly, int polyLength,
+            int rays, int layers, float strength, VertexBuffer& retstrips);
+
+    static void computeLightPolygon(int points, const Vector3& lightCenter,
+            float size, Vector3* ret);
+
+    static int  getStripSize(int rays, int layers);
+    static void smoothPolygon(int level, int rays, float* rayDist);
+    static float calculateOpacity(float jf, float deltaDist);
+    static float rayIntersectPoly(const Vector2* poly, int polyLength,
+            const Vector2& point, float dx, float dy);
+
+    static Vector2 centroid2d(const Vector2* poly, int polyLength);
+
+    static void xsort(Vector2* points, int pointsLength);
+    static int hull(Vector2* points, int pointsLength, Vector2* retPoly);
+    static bool rightTurn(double ax, double ay, double bx, double by, double cx, double cy);
+    static int intersection(Vector2* poly1, int poly1length, Vector2* poly2, int poly2length);
+    static void sort(Vector2* poly, int polyLength, const Vector2& center);
+
+    static float angle(const Vector2& point, const Vector2& center);
+    static void swap(Vector2* points, int i, int j);
+    static void quicksortCirc(Vector2* points, int low, int high, const Vector2& center);
+    static void quicksortX(Vector2* points, int low, int high);
+
+    static bool testPointInsidePolygon(const Vector2 testPoint, const Vector2* poly, int len);
+    static void makeClockwise(Vector2* polygon, int len);
+    static bool isClockwise(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);
+
+    static void generateTriangleStrip(const Vector2* penumbra, int penumbraLength,
+            const Vector2* umbra, int umbraLength, int rays, int layers,
+            float strength, VertexBuffer& retstrips);
+
+    static const double EPSILON = 1e-7;
+}; // SpotShadow
+
+}; // namespace uirenderer
+}; // namespace android
+
+#endif // ANDROID_HWUI_SPOT_SHADOW_H
diff --git a/libs/hwui/Vector.h b/libs/hwui/Vector.h
index 5110272..15b9d6b 100644
--- a/libs/hwui/Vector.h
+++ b/libs/hwui/Vector.h
@@ -36,6 +36,10 @@
         x(px), y(py) {
     }
 
+    float lengthSquared() const {
+        return x * x + y * y;
+    }
+
     float length() const {
         return sqrt(x * x + y * y);
     }