diff --git a/java/src/com/android/inputmethod/keyboard/internal/GesturePreviewTrail.java b/java/src/com/android/inputmethod/keyboard/internal/GesturePreviewTrail.java
index b047fe0..e3e6d39 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GesturePreviewTrail.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GesturePreviewTrail.java
@@ -44,6 +44,7 @@
     // The wall time of the zero value in {@link #mEventTimes}
     private long mCurrentTimeBase;
     private int mTrailStartIndex;
+    private int mLastInterpolatedDrawIndex;
 
     static final class Params {
         public final int mTrailColor;
@@ -96,6 +97,17 @@
         }
         final int[] eventTimes = mEventTimes.getPrimitiveArray();
         final int strokeId = stroke.getGestureStrokeId();
+        // Because interpolation algorithm in {@link GestureStrokeWithPreviewPoints} can't determine
+        // the interpolated points in the last segment of gesture stroke, it may need recalculation
+        // of interpolation when new segments are added to the stroke.
+        // {@link #mLastInterpolatedDrawIndex} holds the start index of the last segment. It may
+        // be updated by the interpolation
+        // {@link GestureStrokeWithPreviewPoints#interpolatePreviewStroke}
+        // or by animation {@link #drawGestureTrail(Canvas,Paint,Rect,Params)} below.
+        final int lastInterpolatedIndex = (strokeId == mCurrentStrokeId)
+                ? mLastInterpolatedDrawIndex : trailSize;
+        mLastInterpolatedDrawIndex = stroke.interpolateStrokeAndReturnStartIndexOfLastSegment(
+                lastInterpolatedIndex, mEventTimes, mXCoordinates, mYCoordinates);
         if (strokeId != mCurrentStrokeId) {
             final int elapsedTime = (int)(downTime - mCurrentTimeBase);
             for (int i = mTrailStartIndex; i < trailSize; i++) {
@@ -216,6 +228,10 @@
                 System.arraycopy(eventTimes, startIndex, eventTimes, 0, newSize);
                 System.arraycopy(xCoords, startIndex, xCoords, 0, newSize);
                 System.arraycopy(yCoords, startIndex, yCoords, 0, newSize);
+                // The start index of the last segment of the stroke
+                // {@link mLastInterpolatedDrawIndex} should also be updated because all array
+                // elements have just been shifted for compaction.
+                mLastInterpolatedDrawIndex = Math.max(mLastInterpolatedDrawIndex - startIndex, 0);
             }
             mEventTimes.setLength(newSize);
             mXCoordinates.setLength(newSize);
diff --git a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java
index fc81410..3315954 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/GestureStrokeWithPreviewPoints.java
@@ -21,19 +21,32 @@
 public final class GestureStrokeWithPreviewPoints extends GestureStroke {
     public static final int PREVIEW_CAPACITY = 256;
 
+    private static final boolean ENABLE_INTERPOLATION = true;
+
     private final ResizableIntArray mPreviewEventTimes = new ResizableIntArray(PREVIEW_CAPACITY);
     private final ResizableIntArray mPreviewXCoordinates = new ResizableIntArray(PREVIEW_CAPACITY);
     private final ResizableIntArray mPreviewYCoordinates = new ResizableIntArray(PREVIEW_CAPACITY);
 
     private int mStrokeId;
     private int mLastPreviewSize;
+    private final HermiteInterpolator mInterpolator = new HermiteInterpolator();
+    private int mLastInterpolatedPreviewIndex;
 
-    private int mMinPreviewSampleLengthSquare;
+    private int mMinPreviewSamplingDistanceSquared;
     private int mLastX;
     private int mLastY;
+    private double mMinPreviewSamplingDistance;
+    private double mDistanceFromLastSample;
 
-    // TODO: Move this to resource.
-    private static final float MIN_PREVIEW_SAMPLE_LENGTH_RATIO_TO_KEY_WIDTH = 0.1f;
+    // TODO: Move these constants to resource.
+    // The minimum linear distance between sample points for preview in keyWidth unit.
+    private static final float MIN_PREVIEW_SAMPLING_RATIO_TO_KEY_WIDTH = 0.1f;
+    // The minimum trail distance between sample points for preview in keyWidth unit when using
+    // interpolation.
+    private static final float MIN_PREVIEW_SAMPLING_RATIO_TO_KEY_WIDTH_WITH_INTERPOLATION = 0.2f;
+    // The angular threshold to use interpolation in radian. PI/12 is 15 degree.
+    private static final double INTERPOLATION_ANGULAR_THRESHOLD = Math.PI / 12.0d;
+    private static final int MAX_INTERPOLATION_PARTITION = 4;
 
     public GestureStrokeWithPreviewPoints(final int pointerId, final GestureStrokeParams params) {
         super(pointerId, params);
@@ -44,6 +57,7 @@
         super.reset();
         mStrokeId++;
         mLastPreviewSize = 0;
+        mLastInterpolatedPreviewIndex = 0;
         mPreviewEventTimes.setLength(0);
         mPreviewXCoordinates.setLength(0);
         mPreviewYCoordinates.setLength(0);
@@ -53,35 +67,49 @@
         return mStrokeId;
     }
 
-    public int getGestureStrokePreviewSize() {
-        return mPreviewEventTimes.getLength();
-    }
-
     @Override
     public void setKeyboardGeometry(final int keyWidth, final int keyboardHeight) {
         super.setKeyboardGeometry(keyWidth, keyboardHeight);
-        final float sampleLength = keyWidth * MIN_PREVIEW_SAMPLE_LENGTH_RATIO_TO_KEY_WIDTH;
-        mMinPreviewSampleLengthSquare = (int)(sampleLength * sampleLength);
+        final float samplingRatioToKeyWidth = ENABLE_INTERPOLATION
+                ? MIN_PREVIEW_SAMPLING_RATIO_TO_KEY_WIDTH_WITH_INTERPOLATION
+                : MIN_PREVIEW_SAMPLING_RATIO_TO_KEY_WIDTH;
+        mMinPreviewSamplingDistance = keyWidth * samplingRatioToKeyWidth;
+        mMinPreviewSamplingDistanceSquared = (int)(
+                mMinPreviewSamplingDistance * mMinPreviewSamplingDistance);
     }
 
-    private boolean needsSampling(final int x, final int y) {
+    private boolean needsSampling(final int x, final int y, final boolean isMajorEvent) {
+        if (ENABLE_INTERPOLATION) {
+            mDistanceFromLastSample += Math.hypot(x - mLastX, y - mLastY);
+            mLastX = x;
+            mLastY = y;
+            if (mDistanceFromLastSample >= mMinPreviewSamplingDistance) {
+                mDistanceFromLastSample = 0.0d;
+                return true;
+            }
+            return false;
+        }
+
         final int dx = x - mLastX;
         final int dy = y - mLastY;
-        return dx * dx + dy * dy >= mMinPreviewSampleLengthSquare;
+        if (isMajorEvent || dx * dx + dy * dy >= mMinPreviewSamplingDistanceSquared) {
+            mLastX = x;
+            mLastY = y;
+            return true;
+        }
+        return false;
     }
 
     @Override
     public boolean addPointOnKeyboard(final int x, final int y, final int time,
             final boolean isMajorEvent) {
-        final boolean onValidArea = super.addPointOnKeyboard(x, y, time, isMajorEvent);
-        if (isMajorEvent || needsSampling(x, y)) {
+        if (needsSampling(x, y, isMajorEvent)) {
             mPreviewEventTimes.add(time);
             mPreviewXCoordinates.add(x);
             mPreviewYCoordinates.add(y);
-            mLastX = x;
-            mLastY = y;
         }
-        return onValidArea;
+        return super.addPointOnKeyboard(x, y, time, isMajorEvent);
+
     }
 
     public void appendPreviewStroke(final ResizableIntArray eventTimes,
@@ -95,4 +123,82 @@
         yCoords.append(mPreviewYCoordinates, mLastPreviewSize, length);
         mLastPreviewSize = mPreviewEventTimes.getLength();
     }
+
+    /**
+     * Calculate interpolated points between the last interpolated point and the end of the trail.
+     * And return the start index of the last interpolated segment of input arrays because it
+     * may need to recalculate the interpolated points in the segment if further segments are
+     * added to this stroke.
+     *
+     * @param lastInterpolatedIndex the start index of the last interpolated segment of
+     *        <code>eventTimes</code>, <code>xCoords</code>, and <code>yCoords</code>.
+     * @param eventTimes the event time array of gesture preview trail to be drawn.
+     * @param xCoords the x-coordinates array of gesture preview trail to be drawn.
+     * @param yCoords the y-coordinates array of gesture preview trail to be drawn.
+     * @return the start index of the last interpolated segment of input arrays.
+     */
+    public int interpolateStrokeAndReturnStartIndexOfLastSegment(final int lastInterpolatedIndex,
+            final ResizableIntArray eventTimes, final ResizableIntArray xCoords,
+            final ResizableIntArray yCoords) {
+        if (!ENABLE_INTERPOLATION) {
+            return lastInterpolatedIndex;
+        }
+        final int size = mPreviewEventTimes.getLength();
+        final int[] pt = mPreviewEventTimes.getPrimitiveArray();
+        final int[] px = mPreviewXCoordinates.getPrimitiveArray();
+        final int[] py = mPreviewYCoordinates.getPrimitiveArray();
+        mInterpolator.reset(px, py, 0, size);
+        // The last segment of gesture stroke needs to be interpolated again because the slope of
+        // the tangent at the last point isn't determined.
+        int lastInterpolatedDrawIndex = lastInterpolatedIndex;
+        int d1 = lastInterpolatedIndex;
+        for (int p2 = mLastInterpolatedPreviewIndex + 1; p2 < size; p2++) {
+            final int p1 = p2 - 1;
+            final int p0 = p1 - 1;
+            final int p3 = p2 + 1;
+            mLastInterpolatedPreviewIndex = p1;
+            lastInterpolatedDrawIndex = d1;
+            mInterpolator.setInterval(p0, p1, p2, p3);
+            final double m1 = Math.atan2(mInterpolator.mSlope1Y, mInterpolator.mSlope1X);
+            final double m2 = Math.atan2(mInterpolator.mSlope2Y, mInterpolator.mSlope2X);
+            final double dm = Math.abs(angularDiff(m2, m1));
+            final int partition = Math.min((int)Math.ceil(dm / INTERPOLATION_ANGULAR_THRESHOLD),
+                    MAX_INTERPOLATION_PARTITION);
+            final int t1 = eventTimes.get(d1);
+            final int dt = pt[p2] - pt[p1];
+            d1++;
+            for (int i = 1; i < partition; i++) {
+                final float t = i / (float)partition;
+                mInterpolator.interpolate(t);
+                eventTimes.add(d1, (int)(dt * t) + t1);
+                xCoords.add(d1, (int)mInterpolator.mInterpolatedX);
+                yCoords.add(d1, (int)mInterpolator.mInterpolatedY);
+                d1++;
+            }
+            eventTimes.add(d1, pt[p2]);
+            xCoords.add(d1, px[p2]);
+            yCoords.add(d1, py[p2]);
+        }
+        return lastInterpolatedDrawIndex;
+    }
+
+    private static final double TWO_PI = Math.PI * 2.0d;
+
+    /**
+     * Calculate the angular of rotation from <code>a0</code> to <code>a1</code>.
+     *
+     * @param a1 the angular to which the rotation ends.
+     * @param a0 the angular from which the rotation starts.
+     * @return the angular rotation value from a0 to a1, normalized to [-PI, +PI].
+     */
+    private static double angularDiff(final double a1, final double a0) {
+        double deltaAngle = a1 - a0;
+        while (deltaAngle > Math.PI) {
+            deltaAngle -= TWO_PI;
+        }
+        while (deltaAngle < -Math.PI) {
+            deltaAngle += TWO_PI;
+        }
+        return deltaAngle;
+    }
 }
diff --git a/java/src/com/android/inputmethod/keyboard/internal/HermiteInterpolator.java b/java/src/com/android/inputmethod/keyboard/internal/HermiteInterpolator.java
new file mode 100644
index 0000000..0ec8153
--- /dev/null
+++ b/java/src/com/android/inputmethod/keyboard/internal/HermiteInterpolator.java
@@ -0,0 +1,166 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+package com.android.inputmethod.keyboard.internal;
+
+import com.android.inputmethod.annotations.UsedForTesting;
+
+/**
+ * Interpolates XY-coordinates using Cubic Hermite Curve.
+ */
+public final class HermiteInterpolator {
+    private int[] mXCoords;
+    private int[] mYCoords;
+    private int mMinPos;
+    private int mMaxPos;
+
+    // Working variable to calculate interpolated value.
+    /** The coordinates of the start point of the interval. */
+    public int mP1X, mP1Y;
+    /** The coordinates of the end point of the interval. */
+    public int mP2X, mP2Y;
+    /** The slope of the tangent at the start point. */
+    public float mSlope1X, mSlope1Y;
+    /** The slope of the tangent at the end point. */
+    public float mSlope2X, mSlope2Y;
+    /** The interpolated coordinates.
+     * The return variables of {@link #interpolate(float)} to avoid instantiations.
+     */
+    public float mInterpolatedX, mInterpolatedY;
+
+    public HermiteInterpolator() {
+        // Nothing to do with here.
+    }
+
+    /**
+     * Reset this interpolator to point XY-coordinates data.
+     * @param xCoords the array of x-coordinates. Valid data are in left-open interval
+     *                <code>[minPos, maxPos)</code>.
+     * @param yCoords the array of y-coordinates. Valid data are in left-open interval
+     *                <code>[minPos, maxPos)</code>.
+     * @param minPos the minimum index of left-open interval of valid data.
+     * @param maxPos the maximum index of left-open interval of valid data.
+     */
+    @UsedForTesting
+    public void reset(final int[] xCoords, final int[] yCoords, final int minPos,
+            final int maxPos) {
+        mXCoords = xCoords;
+        mYCoords = yCoords;
+        mMinPos = minPos;
+        mMaxPos = maxPos;
+    }
+
+    /**
+     * Set interpolation interval.
+     * <p>
+     * The start and end coordinates of the interval will be set in {@link #mP1X}, {@link #mP1Y},
+     * {@link #mP2X}, and {@link #mP2Y}. The slope of the tangents at start and end points will be
+     * set in {@link #mSlope1X}, {@link #mSlope1Y}, {@link #mSlope2X}, and {@link #mSlope2Y}.
+     *
+     * @param p0 the index just before interpolation interval. If <code>p1</code> points the start
+     *           of valid points, <code>p0</code> must be less than <code>minPos</code> of
+     *           {@link #reset(int[],int[],int,int)}.
+     * @param p1 the start index of interpolation interval.
+     * @param p2 the end index of interpolation interval.
+     * @param p3 the index just after interpolation interval. If <code>p2</code> points the end of
+     *           valid points, <code>p3</code> must be equal or greater than <code>maxPos</code> of
+     *           {@link #reset(int[],int[],int,int)}.
+     */
+    @UsedForTesting
+    public void setInterval(final int p0, final int p1, final int p2, final int p3) {
+        mP1X = mXCoords[p1];
+        mP1Y = mYCoords[p1];
+        mP2X = mXCoords[p2];
+        mP2Y = mYCoords[p2];
+        // A(ax,ay) is the vector p1->p2.
+        final int ax = mP2X - mP1X;
+        final int ay = mP2Y - mP1Y;
+
+        // Calculate the slope of the tangent at p1.
+        if (p0 >= mMinPos) {
+            // p1 has previous valid point p0.
+            // The slope of the tangent is half of the vector p0->p2.
+            mSlope1X = (mP2X - mXCoords[p0]) / 2.0f;
+            mSlope1Y = (mP2Y - mYCoords[p0]) / 2.0f;
+        } else if (p3 < mMaxPos) {
+            // p1 has no previous valid point, but p2 has next valid point p3.
+            // B(bx,by) is the slope vector of the tangent at p2.
+            final float bx = (mXCoords[p3] - mP1X) / 2.0f;
+            final float by = (mYCoords[p3] - mP1Y) / 2.0f;
+            final float crossProdAB = ax * by - ay * bx;
+            final float dotProdAB = ax * bx + ay * by;
+            final float normASquare = ax * ax + ay * ay;
+            final float invHalfNormASquare = 1.0f / normASquare / 2.0f;
+            // The slope of the tangent is the mirror image of vector B to vector A.
+            mSlope1X = invHalfNormASquare * (dotProdAB * ax + crossProdAB * ay);
+            mSlope1Y = invHalfNormASquare * (dotProdAB * ay - crossProdAB * ax);
+        } else {
+            // p1 and p2 have no previous valid point. (Interval has only point p1 and p2)
+            mSlope1X = ax;
+            mSlope1Y = ay;
+        }
+
+        // Calculate the slope of the tangent at p2.
+        if (p3 < mMaxPos) {
+            // p2 has next valid point p3.
+            // The slope of the tangent is half of the vector p1->p3.
+            mSlope2X = (mXCoords[p3] - mP1X) / 2.0f;
+            mSlope2Y = (mYCoords[p3] - mP1Y) / 2.0f;
+        } else if (p0 >= mMinPos) {
+            // p2 has no next valid point, but p1 has previous valid point p0.
+            // B(bx,by) is the slope vector of the tangent at p1.
+            final float bx = (mP2X - mXCoords[p0]) / 2.0f;
+            final float by = (mP2Y - mYCoords[p0]) / 2.0f;
+            final float crossProdAB = ax * by - ay * bx;
+            final float dotProdAB = ax * bx + ay * by;
+            final float normASquare = ax * ax + ay * ay;
+            final float invHalfNormASquare = 1.0f / normASquare / 2.0f;
+            // The slope of the tangent is the mirror image of vector B to vector A.
+            mSlope2X = invHalfNormASquare * (dotProdAB * ax + crossProdAB * ay);
+            mSlope2Y = invHalfNormASquare * (dotProdAB * ay - crossProdAB * ax);
+        } else {
+            // p1 and p2 has no previous valid point. (Interval has only point p1 and p2)
+            mSlope2X = ax;
+            mSlope2Y = ay;
+        }
+    }
+
+    /**
+     * Calculate interpolation value at <code>t</code> in unit interval <code>[0,1]</code>.
+     * <p>
+     * On the unit interval [0,1], given a starting point p1 at t=0 and an ending point p2 at t=1
+     * with the slope of the tangent m1 at p1 and m2 at p2, the polynomial of cubic Hermite curve
+     * can be defined by
+     *   p(t) = (1+2t)(1-t)(1-t)*p1 + t(1-t)(1-t)*m1 + (3-2t)t^2*p2 + (t-1)t^2*m2
+     * where t is an element of [0,1].
+     * <p>
+     * The interpolated XY-coordinates will be set in {@link #mInterpolatedX} and
+     * {@link #mInterpolatedY}.
+     *
+     * @param t the interpolation parameter. The value must be in close interval <code>[0,1]</code>.
+     */
+    @UsedForTesting
+    public void interpolate(final float t) {
+        final float omt = 1.0f - t;
+        final float tm2 = 2.0f * t;
+        final float k1 = 1.0f + tm2;
+        final float k2 = 3.0f - tm2;
+        final float omt2 = omt * omt;
+        final float t2 = t * t;
+        mInterpolatedX = (k1 * mP1X + t * mSlope1X) * omt2 + (k2 * mP2X - omt * mSlope2X) * t2;
+        mInterpolatedY = (k1 * mP1Y + t * mSlope1Y) * omt2 + (k2 * mP2Y - omt * mSlope2Y) * t2;
+    }
+}
diff --git a/tests/src/com/android/inputmethod/keyboard/internal/HermiteInterpolatorTests.java b/tests/src/com/android/inputmethod/keyboard/internal/HermiteInterpolatorTests.java
new file mode 100644
index 0000000..3ff5aa4
--- /dev/null
+++ b/tests/src/com/android/inputmethod/keyboard/internal/HermiteInterpolatorTests.java
@@ -0,0 +1,203 @@
+/*
+ * Copyright (C) 2013 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.
+ */
+
+package com.android.inputmethod.keyboard.internal;
+
+import android.test.AndroidTestCase;
+import android.test.suitebuilder.annotation.SmallTest;
+
+@SmallTest
+public class HermiteInterpolatorTests extends AndroidTestCase {
+    private final HermiteInterpolator mInterpolator = new HermiteInterpolator();
+
+    @Override
+    protected void setUp() throws Exception {
+        super.setUp();
+    }
+
+    private static final float EPSLION = 0.0000005f;
+
+    private static void assertFloatEquals(final String message, float expected, float actual) {
+        if (Math.abs(expected - actual) >= EPSLION) {
+            fail(String.format("%s expected:<%s> but was:<%s>", message, expected, actual));
+        }
+    }
+
+    // t=0 p0=(0,1)
+    // t=1 p1=(1,0)
+    // t=2 p2=(3,2)
+    // t=3 p3=(2,3)
+    //   y
+    //   |
+    // 3 +       o p3
+    //   |
+    // 2 +           o p2
+    //   |
+    // 1 o p0
+    //   |    p1
+    // 0 +---o---+---+-- x
+    //   0   1   2   3
+    private final int[] mXCoords = { 0, 1, 3, 2 };
+    private final int[] mYCoords = { 1, 0, 2, 3 };
+    private static final int p0 = 0;
+    private static final int p1 = 1;
+    private static final int p2 = 2;
+    private static final int p3 = 3;
+
+    public void testP0P1() {
+        // [(p0 p1) p2 p3]
+        mInterpolator.reset(mXCoords, mYCoords, p0, p3 + 1);
+        mInterpolator.setInterval(p0 - 1, p0, p1, p1 + 1);
+        assertEquals("p0x", mXCoords[p0], mInterpolator.mP1X);
+        assertEquals("p0y", mYCoords[p0], mInterpolator.mP1Y);
+        assertEquals("p1x", mXCoords[p1], mInterpolator.mP2X);
+        assertEquals("p1y", mYCoords[p1], mInterpolator.mP2Y);
+        // XY-slope at p0=3.0 (-0.75/-0.25)
+        assertFloatEquals("slope x p0", -0.25f, mInterpolator.mSlope1X);
+        assertFloatEquals("slope y p0", -0.75f, mInterpolator.mSlope1Y);
+        // XY-slope at p1=1/3.0 (0.50/1.50)
+        assertFloatEquals("slope x p1",  1.50f, mInterpolator.mSlope2X);
+        assertFloatEquals("slope y p1",  0.50f, mInterpolator.mSlope2Y);
+        // t=0.0 (p0)
+        mInterpolator.interpolate(0.0f);
+        assertFloatEquals("t=0.0 x", 0.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.0 y", 1.0f, mInterpolator.mInterpolatedY);
+        // t=0.2
+        mInterpolator.interpolate(0.2f);
+        assertFloatEquals("t=0.2 x", 0.02400f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.2 y", 0.78400f, mInterpolator.mInterpolatedY);
+        // t=0.5
+        mInterpolator.interpolate(0.5f);
+        assertFloatEquals("t=0.5 x", 0.28125f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.5 y", 0.34375f, mInterpolator.mInterpolatedY);
+        // t=0.8
+        mInterpolator.interpolate(0.8f);
+        assertFloatEquals("t=0.8 x", 0.69600f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.8 y", 0.01600f, mInterpolator.mInterpolatedY);
+        // t=1.0 (p1)
+        mInterpolator.interpolate(1.0f);
+        assertFloatEquals("t=1.0 x", 1.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=1.0 y", 0.0f, mInterpolator.mInterpolatedY);
+    }
+
+    public void testP1P2() {
+        // [p0 (p1 p2) p3]
+        mInterpolator.reset(mXCoords, mYCoords, p0, p3 + 1);
+        mInterpolator.setInterval(p1 - 1, p1, p2, p2 + 1);
+        assertEquals("p1x", mXCoords[p1], mInterpolator.mP1X);
+        assertEquals("p1y", mYCoords[p1], mInterpolator.mP1Y);
+        assertEquals("p2x", mXCoords[p2], mInterpolator.mP2X);
+        assertEquals("p2y", mYCoords[p2], mInterpolator.mP2Y);
+        // XY-slope at p1=1/3.0 (0.50/1.50)
+        assertFloatEquals("slope x p1",  1.50f, mInterpolator.mSlope1X);
+        assertFloatEquals("slope y p1",  0.50f, mInterpolator.mSlope1Y);
+        // XY-slope at p2=3.0 (1.50/0.50)
+        assertFloatEquals("slope x p2",  0.50f, mInterpolator.mSlope2X);
+        assertFloatEquals("slope y p2",  1.50f, mInterpolator.mSlope2Y);
+        // t=0.0 (p1)
+        mInterpolator.interpolate(0.0f);
+        assertFloatEquals("t=0.0 x", 1.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.0 y", 0.0f, mInterpolator.mInterpolatedY);
+        // t=0.2
+        mInterpolator.interpolate(0.2f);
+        assertFloatEquals("t=0.2 x", 1.384f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.2 y", 0.224f, mInterpolator.mInterpolatedY);
+        // t=0.5
+        mInterpolator.interpolate(0.5f);
+        assertFloatEquals("t=0.5 x", 2.125f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.5 y", 0.875f, mInterpolator.mInterpolatedY);
+        // t=0.8
+        mInterpolator.interpolate(0.8f);
+        assertFloatEquals("t=0.8 x", 2.776f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.8 y", 1.616f, mInterpolator.mInterpolatedY);
+        // t=1.0 (p2)
+        mInterpolator.interpolate(1.0f);
+        assertFloatEquals("t=1.0 x", 3.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=1.0 y", 2.0f, mInterpolator.mInterpolatedY);
+    }
+
+    public void testP2P3() {
+        // [p0 p1 (p2 p3)]
+        mInterpolator.reset(mXCoords, mYCoords, p0, p3 + 1);
+        mInterpolator.setInterval(p2 - 1, p2, p3, p3 + 1);
+        assertEquals("p2x", mXCoords[p2], mInterpolator.mP1X);
+        assertEquals("p2y", mYCoords[p2], mInterpolator.mP1Y);
+        assertEquals("p3x", mXCoords[p3], mInterpolator.mP2X);
+        assertEquals("p3y", mYCoords[p3], mInterpolator.mP2Y);
+        // XY-slope at p2=3.0 (1.50/0.50)
+        assertFloatEquals("slope x p2",  0.50f, mInterpolator.mSlope1X);
+        assertFloatEquals("slope y p2",  1.50f, mInterpolator.mSlope1Y);
+        // XY-slope at p3=1/3.0 (-0.25/-0.75)
+        assertFloatEquals("slope x p3", -0.75f, mInterpolator.mSlope2X);
+        assertFloatEquals("slope y p3", -0.25f, mInterpolator.mSlope2Y);
+        // t=0.0 (p2)
+        mInterpolator.interpolate(0.0f);
+        assertFloatEquals("t=0.0 x", 3.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.0 y", 2.0f, mInterpolator.mInterpolatedY);
+        // t=0.2
+        mInterpolator.interpolate(0.2f);
+        assertFloatEquals("t=0.2 x", 2.98400f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.2 y", 2.30400f, mInterpolator.mInterpolatedY);
+        // t=0.5
+        mInterpolator.interpolate(0.5f);
+        assertFloatEquals("t=0.5 x", 2.65625f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.5 y", 2.71875f, mInterpolator.mInterpolatedY);
+        // t=0.8
+        mInterpolator.interpolate(0.8f);
+        assertFloatEquals("t=0.8 x", 2.21600f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.8 y", 2.97600f, mInterpolator.mInterpolatedY);
+        // t=1.0 (p3)
+        mInterpolator.interpolate(1.0f);
+        assertFloatEquals("t=1.0 x", 2.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=1.0 y", 3.0f, mInterpolator.mInterpolatedY);
+    }
+
+    public void testJustP1P2() {
+        // [(p1 p2)]
+        mInterpolator.reset(mXCoords, mYCoords, p1, p2 + 1);
+        mInterpolator.setInterval(p1 - 1, p1, p2, p2 + 1);
+        assertEquals("p1x", mXCoords[p1], mInterpolator.mP1X);
+        assertEquals("p1y", mYCoords[p1], mInterpolator.mP1Y);
+        assertEquals("p2x", mXCoords[p2], mInterpolator.mP2X);
+        assertEquals("p2y", mYCoords[p2], mInterpolator.mP2Y);
+        // XY-slope at p1=1.0 (2.0/2.0)
+        assertFloatEquals("slope x p1", 2.00f, mInterpolator.mSlope1X);
+        assertFloatEquals("slope y p1", 2.00f, mInterpolator.mSlope1Y);
+        // XY-slope at p2=1.0 (2.0/2.0)
+        assertFloatEquals("slope x p2", 2.00f, mInterpolator.mSlope2X);
+        assertFloatEquals("slope y p2", 2.00f, mInterpolator.mSlope2Y);
+        // t=0.0 (p1)
+        mInterpolator.interpolate(0.0f);
+        assertFloatEquals("t=0.0 x", 1.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.0 y", 0.0f, mInterpolator.mInterpolatedY);
+        // t=0.2
+        mInterpolator.interpolate(0.2f);
+        assertFloatEquals("t=0.2 x", 1.4f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.2 y", 0.4f, mInterpolator.mInterpolatedY);
+        // t=0.5
+        mInterpolator.interpolate(0.5f);
+        assertFloatEquals("t=0.5 x", 2.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.5 y", 1.0f, mInterpolator.mInterpolatedY);
+        // t=0.8
+        mInterpolator.interpolate(0.8f);
+        assertFloatEquals("t=0.8 x", 2.6f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=0.8 y", 1.6f, mInterpolator.mInterpolatedY);
+        // t=1.0 (p2)
+        mInterpolator.interpolate(1.0f);
+        assertFloatEquals("t=1.0 x", 3.0f, mInterpolator.mInterpolatedX);
+        assertFloatEquals("t=1.0 y", 2.0f, mInterpolator.mInterpolatedY);
+    }
+}